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March 2011 / BULLETIN 10-

Thermostatic Expansion ValvesTheory o Operation, Application, and Selection

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Page 2 / BULLETIN 10-9

THERMOSTATIC EXPANSION VALVES

Outstanding Features & Benefitsof Sporlan Thermostatic Expansion Valves

Refer to Bulletin 10-10 for complete specifications ofThermostatic Expansion Valves, with Selective Thermostatic Charges.

Refer to Bulletin 10-11 for a complete discussion on Installing and Servicing Thermostatic Expansion Valves.

10

The Refrigeration System .................................................3Types of Expansion Devices .............................................3How the Thermostatic Expansion Valve Works .............3

Basic Operation ............................................................3Effect of Pressure Drop Across the Valve Port ..........4Balanced Port TEVs ......................................................5Equalization Method ....................................................5Thermostatic Charges ..................................................6

Sporlan Thermostatic Expansion Valves .............................7

Alternative Refrigerants .................................................7Sporlan Selective Charges ..........................................7

Air Conditioning & Heat Pump Applications ...............7Refrigeration Applications ...........................................8Special Selective Thermostatic Charges and

Elements ......................................................................9Thermostatic Expansion Valve Applications ..................9

System Design Factors ................................................9Balanced Port TEVs ....................................................10

System Design For Part-Load Conditions .....................11Two or more evaporators sections

handling the same load .......................................11Single evaporator controlled by two TEVs ...................11Hot gas bypass and desuperheating TEVs ..............12Off-Cycle Pressure Equalization ................................12R-717 (Ammonia) Applications .................................13Thermostatic Charges for Ammonia Valves............14

Factors Affecting TEV Operation and Performance ........14

Superheat....................................................................14Valve Setting ..............................................................15Evaporator Temperature ...........................................15Subcooling ..................................................................15Refrigerant Liquid Temperature and Pressure

Drop Across TEV ...................................................16Thermostatic Charge .................................................16

Selection Procedure ........................................................16Recommended Thermostatic Charges ..........................18

TABLE OF CONTENTS

SELECTIVE THERMOSTATIC CHARGESDesigned to provide optimum performance for all appli-cationsair conditioning and heat pump, medium andlow temperature refrigeration.

THERMOSTATIC ELEMENT DESIGNLong lasting and field proven stainless steel diaphragmand welded element construction.

DIAPHRAGM DESIGN Large flat diaphragm permits precise valve control.

REPLACEABLE THERMOSTATIC ELEMENTSField replaceable elements on all standard valves.

BALANCED PORT DESIGNTYPES (E)BF, EBS & OProvides perfect pin and port alignment, and preventschanges in pressure drop across the valve from influ-encing valve operation. Provides excellent control on

applications having widely varying operating conditions.

PIN CARRIER DESIGN(CONVENTIONAL VALVES)Provides precise pin and port alignment, and betterseating.

ACCESSIBLE INTERNAL PARTSDurable, leakproof body joint construction allows the valveto be disassembled, and the internal parts cleaned andinspected.

MATERIALS OF CONSTRUCTIONPin and port materials offer maximum protection againstcorrosion and erosion.

SILVER SOLDERED CONNECTIONSFor leakproof, high strength connection-to-body joints.

ADJUSTABLE SUPERHEAT DESIGNAll standard valves are externally adjustable except theType Nl, which is internally adjustable through its outlet

connection.

WARNING USER RESPONSIBILITYFailure or improper selection or improper use of the products described herein or related items can cause death, personal injury and property damage.

This document and other information from Parker Hannifin Corporation, its subsidiaries and authorized distributors provide product or system options for furtherinvestigation by users having technical expertise.

The user, through its own analysis and testing, is solely responsible for making the final selection of the system and components and assuring that all performance,endurance, maintenance, safety and warning requirements of the application are met. The user must analyze all aspects of the application, follow applicable industrystandards, and follow the information concerning the product in the current product catalog and in any other materials provided from Parker or its subsidiaries orauthorized distributors.

To the extent that Parker or its subsidiaries or authorized distributors provide component or system options based upon data or specifications provided by the user,the user is responsible for determining that such data and specifications are suitable and sufficient for all applications and reasonably foreseeable uses of the compo-nents or systems.

OFFER OF SALE

The items described in this document are hereby offered for sale by Parker Hannifin Corporation, its subsidiaries or its authorized distributors. This offer and its accep-tance are governed by the provisions stated in the detailed Offer of Sale available at www.parker.com.

FOR USE ON REFRIGERATION and/or AIR CONDITIONING SYSTEMS ONLY

Bulletin 10-9, March 2011 supersedes Bulletin 10-9 dated August 2005 and all prior publications.

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BULLETIN 10-9 /Page

THE REFRIGERATION SYSTEM

To understand the function of the thermostatic expansionvalve, a short discussion of the refrigeration system is nec-essary. The refrigeration system can be defined as a closedsystem in which the process of absorbing and rejecting heatis performed by flowing a refrigerant in a vapor compressioncycle. In its simplest form, the refrigeration system consistsof five components: the compressor, condenser, evaporator,expansion device, and interconnecting piping.

The heart of the system is the compressor since it causes therefrigerant flow. Its function is simply to receive low pres-sure (and temperature) refrigerant vapor from the evapora-tor and compress it into high pressure (and temperature)refrigerant vapor. The high pressure vapor is then convertedto a liquid phase in the condenser. The condenser performsthis function by removing heat from the vapor and rejectingthe heat to the air, or to water in the case of a water cooledcondenser. The liquid, which remains at a high pressure,passes through the expansion device and becomes a lowpressure two phase (liquid and vapor) mixture. This refriger-ant mixture returns to its vapor phase in the evaporator byabsorbing heat from the medium being cooled.

The selection of the expansion device is of particular impor-tance to the operation of the refrigeration system because it

regulates refrigerant flow into the evaporator. An expansiondevice which is misapplied or incorrectly sized will ordinar-ily result in operational difficulties and poor system perfor-mance. For example, an undersized expansion device willprevent sufficient refrigerant from flowing into the evapora-tor causing a reduction in the design cooling capability of thesystem. An oversized expansion device may allow too muchrefrigerant into the evaporator causing liquid refrigerant toflow back to the compressor. The latter condition is referredto as floodback. Both conditions will invariably resultin compressor damage if not quickly remedied. Therefore,the expansion device requires attention to its selection andapplication.

TYPES OF EXPANSION DEVICES

Expansion devices can be divided into four general categories:the fixed area restrictor, the automatic (constant pressure)expansion valve, the thermostatic expansion valve, and the elec-tric expansion valve. The fixed area restrictor expansion deviceis simply a precisely formed restriction through which liquidrefrigerant flows. Two common examples of this type of deviceare the capillary tube, or cap tube, and the short tube restrictor,or plug orifice. These devices are typically used on certain smallair conditioning and refrigeration systems where operating con-ditions permit moderately constant evaporator loading and con-stant condenser pressures. The drawback associated with thesedevices is their limited ability to efficiently regulate refrigerantflow in response to changes in system operating conditions,

since they are sized based on one set of conditions.

Like the fixed area restrictor, the automatic expansion va(AEV) is best suited for applications having moderateconstant evaporator loading. The AEV regulates refrigeraflow by simply maintaining a constant evaporator or valoutlet pressure. As the heat load on the evaporator rises, t

AEV decreases refrigerant flow to maintain evaporator prsure at the valves setting. Conversely, the AEV increasrefrigerant flow when the evaporator heat load decreasto maintain evaporator pressure at the valves setting. Aresult, the AEV starves the evaporator at high load contions, and overfeeds it at low load conditions.

The thermostatic expansion valve provides an exclent solution to regulating refrigerant flow into a direexpansion type evaporator. The TEV regulates refrigeraflow by maintaining a nearly constant superheat at tevaporator outlet. As superheat at the evaporator outrises due to increased heat load on the evaporator, tTEV increases refrigerant flow until superheat returto the valves setting. Conversely, the TEV will decrearefrigerant flow when superheat lowers as a result odecreased heat load on the evaporator. The effect of thtype of regulation is it allows the evaporator to remain nearly fully active as possible under all load conditionThe concept of superheat, and the proper method of mesuring it is further explained on Page 14, TEV Operatiand Performance.

The thermostatic expansion valve provides an additionbenefit when charging the system with refrigerant. Wha TEV is used, the system refrigerant charge is usually nas critical as with the other expansion devices. The propoperation of a fixed restriction and, to a lesser extent, automatic expansion valve depends on having an exaamount of refrigerant in the system.

The electric expansion valve (EEV) provides a means which applications can be designed with sophisticatsystem control functions. This type of valve is controllby an electronic circuit which is often designed to allothe valve to control some aspect of system operation addition to superheat at the outlet of the evaporator. F

example, evaporator discharge air temperature or wattemperature from a chiller could be monitored by the EEVcontroller. See Bulletin 100-9 for details on electric valvfor refrigerant control or contact the Sporlan Division Parker for additional information.

HOW THE THERMOSTATIC EXPANSIONVALVE WORKS

Basic Operation

In order to understand the principles of thermostatic expansivalve operation, a review of its major components is necessa

Asensing bulb is connected to the TEV by a length of cap

lary tubing which transmits bulb pressure to the top of t

The thermostatic expansion valve (TEV) controls the flow

of liquid refrigerant entering the direct expansion (DX)

evaporator by maintaining a constant superheat of the

refrigerant vapor at the outlet of the evaporator. Superheat

is the difference between the refrigerant vapor temperature

and its saturation temperature. To measure the superheat

the TEV controls, the difference between the actual tem-perature at the sensing bulb and the saturation temperature

corresponding to the suction pressure at the sensing bulb

location is determined. By controlling superheat, the TEV

keeps nearly the entire evaporator surface active while no

permitting liquid refrigerant to return to the compressor

The ability of the TEV to match refrigerant flow to the rate a

which refrigerant can be vaporized in the evaporator make

the TEV the ideal expansion device for most air conditioningand refrigeration applications.

SPORLAN THERMOSTATIC EXPANSION VALVES

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valves diaphragm. The sensing bulb, capillary tubing, anddiaphragm assembly is referred to as the thermostaticelement. The thermostatic element on all standard SporlanTEVs is replaceable.

The diaphragm is the actuating member of the valve. Itsmotion is transmitted to the pin and pin carrier assem-bly by means of one or two pushrods, allowing the pin tomove in and out of the valve port. The superheat springis located under the pin carrier, and a spring guide sets it

in place. On externally adjustable valves, an external valveadjustment permits the spring pressure to be altered.

There are three fundamental pressures acting on the valvesdiaphragm which affect its operation: sensing bulb pressureP1, equalizer pressure P2, and equivalent spring pressureP3 (see Figure 1). The sensing bulb pressure is a function ofthe temperature of the thermostatic charge, i.e., the sub-stance within the bulb. This pressure acts on the top of thevalve diaphragm causing the valve to move to a more openposition. The equalizer and spring pressures act togetherunderneath the diaphragm causing the valve to move to amore closed position. During normal valve operation, thesensing bulb pressure must equal the equalizer pressureplus the spring pressure, i.e.:

P1 = P2 + P3

Equivalent spring pressure is defined as the spring force dividedby the effective area of the diaphragm. The effective area of thediaphragm is simply the portion of the total diaphragm areawhich is effectively used by the bulb and equalizer pressures toprovide their respective opening and closing forces. Equivalentspring pressure is essentially constant once the valve has beenadjusted to the desired superheat. As a result, the TEV functionsby controlling the difference between bulb and equalizer pres-sures by the amount of the spring pressure.

The function of the sensing bulb is to sense the temperatureof the refrigerant vapor as it leaves the evaporator. Ideally,the bulb temperature will exactly match the refrigerantvapor temperature. As the bulb temperature increases, bulbpressure also increases causing the valve pin to move awayfrom the valve port, allowing more refrigerant to flow intothe evaporator. The valve continues in this opening direc-tion until the equalizer pressure increases sufficiently thatthe sum of the equalizer and spring pressures balance withthe bulb pressure. Conversely, as the bulb temperature

decreases, the bulb pressure decreases causing the valve pinto move toward the valve port, allowing less refrigerant toflow into the evaporator. The valve continues to close untilthe equalizer pressure decreases sufficiently that the sumof the equalizer and spring pressures balance with the bulbpressure.

A change in refrigerant vapor temperature at the outlet ofthe evaporator is caused by one of two events: (1) the springpressure is altered by means of the valve adjustment, and(2) the heat load on the evaporator changes. When springpressure is increased by turning the valve adjustmentclockwise, refrigerant flow into the evaporator is decreased.

Vapor temperature at the evaporator outlet increases sincethe point where the refrigerant completely vaporizes moves

further back within the evaporator, leaving more evapora-tor surface area to heat the refrigerant in its vapor form.The actual refrigerant vapor and bulb temperature will becontrolled at the point where bulb pressure balances withthe sum of the equalizer and spring pressures. Conversely,decreasing spring pressure by turning the valve adjustmentcounterclockwise increases refrigerant flow into the evapora-tor and decreases refrigerant vapor and bulb temperature.Spring pressure determines the superheat at which thevalve controls. Increasing spring pressure increases super-heat, decreasing spring pressure decreases superheat.

An increase in the heat load on the evaporator causes refrig-erant to evaporate at a faster rate. As a result, the point ofcomplete vaporization of the refrigerant flow is moved fur-

ther back within the evaporator. Refrigerant vapor and bulbtemperature increase, causing bulb pressure to rise and thevalve to move in the opening direction until the three pres-sures are in balance. Conversely, a reduction in the heat loadon the evaporator will cause the vapor and bulb temperatureto fall and the valve to move in a closed direction until thethree pressures are in balance. Unlike a change in the springpressure due to valve adjustment, a change in the heat loadon the evaporator does not appreciably affect the superheatat which the thermostatic expansion valve controls. Thisis due to the fact that the TEV is designed to maintain anessentially constant difference between bulb and equalizerpressures, thus controlling superheat regardless of the heatload.

Effect of Pressure Drop Across the Valve Port

An additional pressure affecting valve operation, which isnot considered fundamental, arises from the actual pressuredrop across the valve port. This pressure P4 can be related tothe three fundamental pressures as the product of pressuredrop across the valve port and the ratio of the port area tothe effective area of the diaphragm, i.e.:

P4= Pressure Drop x (Port Area / Effective Diaphragm Area)

With Sporlans conventional TEV design, this pressure is anopening influence since refrigerant flow tends to move thevalve in an opening direction. As a result, our original equa-tion is modified as follows:

P1 + P4 = P2 + P3


Superheat

Evaporator Temperature

Bulb Temperature

Closing

Force

23

2

Clo

sing

Force

2+32

1BulbPressure

SpringPressure

EvaporatorPressure

Refrig.Curve

1

Ope

ning

For

ce

Figure 1

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P4 becomes more significant to TEV operation the greaterthe port area to effective diaphragm area ratio, and thegreater the pressure drop varies across the valve port.

Balanced Port TEVs

Sporlan introduced the concept of the balanced port thermo-static expansion valve in 1946 on large tonnage Types T andW valves. This concept provided the means to either largelyreduce or eliminate the effect of pressure drop across the valve

port. This design utilized a double seating piston operated bya single pushrod. The two port construction divided the refrig-erant flow in opposite directions, thereby providing a semi-balanced pressure differential across the piston.

Improved balanced port designs resulted in a fully balancedType O valve, and then the Types (E)BF, SBF, and EBSvalves for smaller capacity applications. For additional infor-mation on the types and applications of balanced port TEVs,refer to Page 9, Thermostatic Expansion Valve Applications.

Equalization Method

As previously discussed on Pages 3 and 4, the operation ofthe thermostatic expansion valve is determined by the rela-

tionship between three fundamental pressures: bulb pres-sure, equalizer pressure, and equivalent spring pressure.These pressures are illustrated in Figure 1. The equalizerpressure is the evaporator pressure the valve senses. Themeans used to transmit this pressure from the refrigerationsystem to the underside of the valve diaphragm is referredto as the equalization method.

Evaporator pressure is transmitted to the underside ofthe valve diaphragm by one of two methods. If the valve isinternally equalized, the evaporator pressure at the valveoutlet is transmitted to the diaphragm via a passagewaywithin the valve body or through a clearance around thepushrods. If the valve is externally equalized, the under-side of the valve diaphragm is isolated from the valve outlet

pressure by the use of packing material around the pushrodsor with pushrods which are closely fitted. Evaporator pres-sure is transmitted to the diaphragm by a tube connectingthe suction line near the evaporator outlet to an externalfitting on the valve. The external fitting is connected to apassageway which leads to the underside of the valve dia-phragm. See Figure 2.

Internally equalized TEVs should be limited to single circuitevaporator coils having a pressure drop no greater than theequivalent of a 2F saturated temperature change. Refer toTable 1 for recommended maximum allowable pressure dropvalues for internally equalized valves.

Externally equalized TEVs, however, are not affected by pres-sure drop across the evaporator, including pressure drop from

refrigerant distributors employed by multi-circuited evaporator

IMPORTANT: The External Equalizer must be used on evaporators wh

employ a refrigerant distributor.

coils. An externally equalized TEV may be used for refrigeration applications. It provides no operational dadvantages with respect to an internally equalized valother than requiring an external equalizer line be connectFigures 3, 4, and 5 illustrate the effects of evaporator presure drop on an internally and externally equalized TEV.

When an externally equalized TEV is used, the equalizconnection on the TEV must be connected to the suction linear the outlet of the evaporator, and not capped!

Figure 3 shows an internally equalized valve feedingsingle circuit evaporator which has no pressure drop. Tsystem refrigerant is R-22 and, for the purpose of illusttion, R-22 is also used as the thermostatic charge. Tevaporator pressure at the valve outlet and at the sensibulb location is 52 psig. The sum of this pressure and t12 psi spring pressure produces a 64 psig pressure in tclosing direction. For the valve to properly operate, a psig opening bulb pressure is required to balance pressuSince the sensing bulb consists of liquid R-22, its pressurtemperature characteristic is identical to the saturaticurve of R-22, and a 37F bulb temperature is required. Tsuperheat at which the valve is controlling is calculated subtracting the saturation temperature of the evaporat

pressure at the sensing bulb location by the bulb tempeture. In this case, the superheat is 9F.

BULLETIN 10-9 /Page

Valve with INTERNAL

Equalizer

CloseTolerance

FitInternalEqualizer

ExternalEqualizerFitting

PushRods

ValveOutlet

Pressure

EvaporatorOutlet

Pressure

PushRods

Valve with EXTERNAL

Equalizer

Figure 2

tnaregirfeR

erutarepmeTgnitaropaEv F

04 02 0 02 04

porDerusserP is p

431,21 a 00.2 05.1 00.1 57.0

22 00.3 00.2 05.1 00.1 7.0

705,205,A404 00.3 05.2 57.1 52.1 0.1

A(717 ainomm ) 00.3 00.2 05.1 00.1

Table 1

3752

52

52

64

Bulb Pressure64 psig

Evaporator

Inlet Pressure

52 psig

Evaporator

Outlet Pressure

52 psig

Diaphragm

Spring Pressure

12 psi

Closing Pressure............................................................................= 52 + 12 = 64 psig(Evaporator Inlet Pressure Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve..........................................................64 psig

Bulb Pressure Equivalent to 64 psig.....................................................................37F

Saturated Temperature Equivalent to Evaporator Outlet Pressure.........................28F

SUPERHEAT......................................................................................................9 F Bulb Temperature Minus Saturated Evaporator Temperature

12

Converted to Temperature = 37F

Figure 3

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Figure 4 shows the same internally equalized valve on asystem having the same evaporator pressure at the sens-ing bulb location. The evaporator coil, however, now has apressure drop of 6 psi. Since an internally equalized valvesenses evaporator pressure at the valve outlet, the totalpressure in the closing direction becomes 58 psig plus the 12psi spring pressure, or 70 psig. A bulb pressure of 70 psig isnow required for proper valve regulation, which translatesto a 41F bulb temperature. The superheat becomes 13F, or4F higher than the superheat calculated in Figure 3. This

rise in superheat is due to the pressure drop in the evapora-tor. Consequently, pressure drop between the valve outletand the sensing bulb location causes an internally equalizedTEV to operate at a higher than desired superheat.


Figure 5 shows the same system as in Figure 4, but withan externally equalized TEV installed. Since an externallyequalized TEV senses evaporator pressure at the evapora-tor outlet, it is not influenced by pressure drop through theevaporator. As a result, the TEV senses the correct pressure,and controls at the desired superheat.

These diagrams can be used to show the influence evapo-rator pressure drop has on internally equalized TEVs asevaporating temperatures fall. Table 1 provides general

recommendations for maximum pressure drops that can besafely tolerated by internally equalized valves. These recom-mendations are suitable for most field installed systems.Use externally equalized TEVs when pressure drops exceedvalues shown in Table 1, or when pressure drops cannot bedetermined. An externally equalized TEV should beused whenever a refrigerant distributor is used withthe evaporator.

Refer to Bulletin 10-11, TEV Installation, Field Service andAssembly, regarding recommendations for the location ofthe sensing bulb and external equalizer connection to thesuction line.

Thermostatic Charges

As previously mentioned, the TEVs sensing bulb transmitspressure to the top of the diaphragm by a length of capillarytubing. The thermostatic charge is the substance in theTEVs sensing bulb which responds to suction line tempera-ture to create the bulb pressure, and it is designed to allowthe TEV to operate at a satisfactory level of superheat overa specific range of evaporating temperatures. The subject ofthermostatic charges is best approached by describing thecategories into which charges are classified. These catego-ries are the following:

1. Liquid Charge2. Gas Charge3. Liquid-Cross Charge4. Gas-Cross Charge5. Adsorption Charge

The conventional liquid charge consists of the same refriger-ant in the thermostatic element that is used in the refrig-eration system, while the liquid-cross charge consists of arefrigerant mixture. The term cross charge arises fromthe fact that the pressure-temperature characteristic of therefrigerant mixture used within the sensing bulb will crossthe saturation curve of the system refrigerant at some point.

Both the liquid and liquid-cross charges contain sufficientliquid such that the bulb, capillary tubing, and diaphragmchamber will contain some liquid under all temperature condi-tions. This characteristic prevents charge migration of thethermostatic charge away from the sensing bulb if the sensing

bulb temperature becomes warmer than other parts of thethermostatic element. Charge migration will result in loss ofvalve control. An additional characteristic of these charges istheir lack of a maximum operating pressure (MOP) fea-ture. A thermostatic charge with an MOP feature causes theTEV to modulate in the closed direction above a predeterminedevaporator pressure, thereby restricting flow to the evaporatorand limiting the maximum evaporator pressure at which thesystem can operate.

Similarly, the gas charge consists of the same refrigerant inthe thermostatic element that is used in the refrigerationsystem, while the gas-cross charge consists of a refrigerantmixture. Unlike the liquid type charges, both gas charges aredistinguished by having a vapor charge in the thermostatic

element which condenses to a minute quantity of liquid when

4152

58

58


Evaporator

Inlet Pressure

58 psig

Evaporator

Outlet Pressure

52 psig

Diaphragm

Spring Pressure

12 psi

Closing Pressure............................................................................= 58 + 12 = 70 psig(Evaporator Inlet Pressure Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve.........................................................70 psig

Bulb Temperature Equivalent to 70 psig................................................................41F

Saturated Temperature Equivalent to Evaporator Outlet Pressure................ ..........28F

SUPERHEAT....................................................................................................13F Bulb Temperature Minus Saturated Evaporator Temperature

12

70


3752

58


Evaporator

Inlet Pressure

58 psig

Evaporator

Outlet Pressure

52 psig

Diaphragm

Spring Pressure12 psi

Closing Pressure.............................................................................= 52 + 12 = 64 psig(Suction Pressure at Bulb Plus Spring Pressure)

Bulb Pressure Necessary to Open Valve..........................................................64 psig

Bulb Temperature Equivalent to 64 psig.................................................................37F

Saturated Temperature Equivalent to Evaporator Outlet Pressure...........................28F

SUPERHEAT............. ......................................................................................... 9FBulb Temperature Minus Saturated Evaporator Temperature

52

Suction Pressureat Bulb 52 psig

12

64


Figure 5

Figure 4

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Table 2 lists some of the major HFC and HCFC replacemerefrigerants for R-11, R-12, R-114, and R-502.

Sporlan Selective Charges

Sporlan introduced Selective Charges for TEVs over years ago, recognizing that a single thermostatic charcannot work effectively over the useful range of evaporing temperatures of many standard refrigerants. The prent universal acceptance of Selective Charges is eviden

of their many operational advantages. An explanation their applications, design features, and advantages of eaSelective Charge follows. Recommended Sporlan thermstatic charges for various applications are listed on Page

The thermostatic expansion valves static superheat vsus evaporator temperature is referred to as the superhecharacteristic curve. This curve is helpful in understaning TEV operation since its shape describes the valvoperation at a given setting over a range of evaporatitemperatures. Figure 6 illustrates the superheat charactistic curves of standard Sporlan thermostatic charges. Tconcept of static superheat is described on Page 14, Facto

Affecting TEV Operation and Performance.

Air Conditioning and Heat Pump Applications

These applications usually require a pressure limiti(MOP type) thermostatic charge to limit compressor loaing during system pulldown. The pressure limiting charcauses the TEV to open only slightly until the system evaprator pressure is reduced below the MOP of the charpermitting rapid pulldown.

The Sporlan thermostatic charges listed on Page 18 und

the air conditioning and heat pump section are gas-crocharges.

Figure 6 illustrates the superheat characteristic curvesthe Sporlan VCP100 and VG charges, a gas-cross charge aa gas charge respectively for R-22 applications. The VCP1charge has a flatter operating range which allows the TEVmaintain a more constant superheat with changes in evaprating temperature. This characteristic is generally desirsince many air conditioning and heat pump systems operaover a significant range of evaporating temperatures. T

VG charge has limited application except for our WVE-1valve. The vertical portion of the curves is the MOP regiof both charges.

Sporlan pressure limiting charges also help reduce t

problem of the TEV alternately overfeeding and underfee

BULLETIN 10-9 /Page

the TEV is in its normal operating range. This characteristicprovides an MOP for the valve at the bulb temperature atwhich the liquid component of the charge becomes vapor.

Above this bulb temperature, a temperature increase doesnot significantly increase thermostatic charge pressure, lim-iting the maximum evaporator pressure at which the systemcan operate. A disadvantage of this type of thermostaticcharge is the possibility of charge migration.

The adsorption charge consists of a noncondensable gas and

an adsorbent material located in the sensing bulb. As thetemperature of the bulb increases, gas is expelled (desorbed)from the adsorbent material increasing bulb pressure.Conversely, as the temperature of the bulb decreases, gas isadsorbed thus decreasing bulb pressure. Like the liquid andliquid-cross charges, the adsorption charge does not providean MOP, and it will not migrate.

SPORLAN THERMOSTATIC EXPANSION VALVES

Sporlan manufactures thermostatic expansion valves for allair conditioning and refrigeration applications. For applica-tions using refrigerants R-12, R-22, R-134a, R-404A, R-502,and R-507, Sporlans standard line of TEVs are availablewith SAE flare, ODF solder, ODF solder flange, and FPT

flange connections. Specifications for the TEVs are providedin Bulletin 10-10. Materials and details of construction arealso provided in Bulletin 10-10.

For refrigerant R-717 (ammonia) applications, TEVs areavailable with FPT and socket weld flange connections.These valves are manufactured and marketed throughParker Refrigerating Specialties (R/S) Division.

Valve capacity ratings for refrigerants R-12, R-22, R-134a,R-401A, R-402A, R-404A, R-407A, R-407C, R-408A, R-409A,R-502, R-507, and R-717 are listed in Bulletin 10-10. Thecapacity tables on these pages specify valve ratings atselected evaporator temperatures. Contact Sporlan for appli-cations not specifically listed in Bulletin 10-10.

In addition to the standard line of TEVs listed in this bul-letin, Sporlan also manufactures special valve types to fillspecific requirements for OEM customers. These OEM valvetypes include the Type BI, I, FB, and X TEVs. Special fea-tures such as bleed ports, nonadjustable construction, andextra length capillary tubing are available for many stan-dard and OEM valves. Automatic expansion valves are alsoavailable on special order. If you have a special refrigerantflow control application, contact Sporlan for assistance.

Alternative Refrigerants

Sporlan has an ongoing program to evaluate alternative refrig-erants and, when applicable, their associated refrigerant lubri-

cants to assess compatibility with our materials of construction.For additional information on this subject, contact Sporlan.

CFC )CFCH(sevitanretlAetaidemretnImreTgnoL

sevitanretlA (HFC)

11-R 321-R

21-R

)93PM(A104-R

)66PM(B104-R

)65-XF(A904-R

a431-R

411-R 421-R

205-R)08PH(A204-R

)01-XF(A804-R

)26PH(A404-R

)06*AELK(A704-R

)05-ZA(705-R

(*VGA)

Evaporator Temperature F

SuperheatRange

* Ballasted

-20-40 0 20 40 60

SuperheatF

0

5

10

15

20 * Gas-CrossCharge (ZP)

Sporlan SelectiveThermostatic Charges

Liquid

Cross Charge (Z)

*GasCharge(VG)

LiquidCharge(L)

* Gas-CrossCharge(VCP100)

Liquid

CrossCh

arge(C)

Figure

Table 2

*

KLEA is a trade name of ICI FLUOROCHEMICALS.

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ing the evaporator, which is usually termed hunting orcycling. The amount of hunting in a system is influenced bythe design of the evaporator coil, suction line piping at thevalves sensing bulb location, and the variability of the heatload on the evaporator. Hunting may cause a reduction intotal system capacity, and a noticeable variation of evapora-tor pressure on systems having one evaporator. If hunting issevere, occasional floodback may result.

To help reduce or eliminate valve hunting, many Sporlan

pressure limiting thermostatic charges feature theFLOWMASTER design introduced by Sporlan in 1948.This design incorporates a thermal ballast with the chargeto help stabilize valve control.

Originally, it was felt that a highly temperature sensitiveTEV would best be able to reduce hunting. This concepthas proved to be incorrect for the majority of air condition-ing and heat pump applications and, in fact, it was foundto often aggravate hunting problems. A less temperaturesensitive TEV using specifically designed pressure limitingthermostatic charges has proven to be the best solution forthese applications.

Type VGA Thermostatic Charge The VGA charge isa specially designed pressure limiting charge for R-22 air

conditioning and heat pump applications. The constituentsand thermal ballast used with this thermostatic chargeprovide exceptional anti-hunt characteristics, which makesit the recommended charge for the majority of these applica-tions. Due to its design, the MOP of the VGA charge is notas defined as the VCP100 charge, our alternate standardthermostatic charge for R-22 air conditioning and heatpump applications. Therefore, if a defined MOP is notrequired, the VGA charge may be used in place of theVCP100 charge.

Maximum operating pressures for standard Sporlan pres-sure limiting charges are listed in Table 3. The factory airtest pressure represents the valve MOP determined by aSporlan air test fixture. The nominal system pressure is theactual system MOP. If an application requires a pressurelimiting charge with an MOP not shown, contact Sporlan forassistance.

Due to the design of pressure limiting charges, the valve dia-phragm and capillary tubing must be kept at a temperaturewarmer than the bulb during system operation. Otherwise,migration of the charge away from the bulb will occur, and

cause loss of valve control.

A properly selected and applied pressure drop type dis-tributor is effective in preventing charge migration. Figure 7illustrates how the pressure drop across this type of distribu-tor keeps the TEV outlet pressure and temperature higherthan the suction gas temperature.

Pressure drop at the refrigerant distributor does not affectsystem capacity. The refrigerant distributor simply lowersthe pressure drop across the TEV by a small amount. If theTEV is properly sized, it will maintain desired superheat

(and system capacity) with the remaining pressure dropavailable to the valve.

When applying a TEV and distributor, the two compo-nents perform together to provide stable system operation.

Application of these components is much more critical onsystems that operate at part-load conditions much of theiroperating time, e.g., variable air volume (VAV) systemsand refrigeration systems with compressor unloading. SeeBulletin 20-10 for complete information on refrigerantdistributors.

Refrigeration Applications

Ordinary refrigeration applications may be divided into thefollowing three categories: commercial refrigeration, lowtemperature refrigeration, and extremely low temperaturerefrigeration. For each of these categories, Sporlan hasdeveloped a Selective Charge to provide optimum valve per-formance. These charges are described below.

Type C Charges The charges listed under the commer-cial refrigeration section in the Recommended ThermostaticCharges table on Page 18 are collectively known as CCharges. These charges are liquid-cross charges and havean operating range from an evaporating temperature of50F to 10F. Figure 6 illustrates a typical superheatcharacteristic curve of the C Charge. For comparisonpurposes, the superheat characteristic curve of a straightliquid charge is also shown. The flatter curve of the C

Charge allows the valve to respond in a more stable man-ner to changes in evaporator pressure. Depending on thestatic superheat requirements, the Type C Charge has beenapplied by some manufacturers to display cases operatingat both medium and low temperature.

Types Z and ZP Charges The charges listed underthe low temperature refrigeration section are the Types Zand ZP Charges. The Z Charges (FZ, VZ, SZ, RZ, and PZ)are liquid-cross charges having an operating range from anevaporating temperature of 0F to 40F. A typical super-heat characteristic curve of the Z Charge is illustrated inFigure 6. Since the curve slopes upward to the right, thevalve will control at lower superheat values as evaporatortemperature decreases, providing operational advantages for

low temperature refrigeration. This characteristic prevents


R-22

196 psig(100F)

P1= 94 psig

(56F)

P2

= 69 psig(40F) 66 psig (Superheat to 50F)

66 psig(38F)

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06PCF 60 50

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22

001PCV 100 90

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PCV 65 55

04PZV 40 30

a43106PCJ 60 50

PCJ 40 30

A404

511PCS 115 105

PCS 75 65

PZS 45 35

205

511PCR 115 105

PCR 75 65

PZR 45 35705 PZP 45 35

* s.noitidnocgnitarepolamronevobA

Figure 7

Table 3

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BULLETIN 10-9 /Page

floodback during compressor startup, reduces the load on thecompressor after startup, and permits rapid pulldown. Sincethe majority of low temperature systems operate at or neara specific evaporating temperature, the TEV can be set foroptimum superheat at the design temperature permittingthe system to operate as efficiently as possible.

The Types ZP Charges (FZP, VZP, SZP, RZP, and PZP) aregas-cross charges having the same operating range as the

Type Z Charges. A typical superheat characteristic curveof the ZP Charge is illustrated in Figure 6. The Z and ZPCharges are essentially the same with the exception of theZP Charge providing an MOP. Type ZP Charges are notintended as replacements for Z Charges. Each shouldbe selected for its unique purpose. A ZP Chargeshould only be used for low temperature refrigera-tion systems where it is necessary to limit evaporatorpressure during pulldown.

During and after a hot gas defrost cycle or after a shutdownperiod, evaporator pressure may rise to a level the compres-sor motor cannot handle. In such cases, a pressure limitingcharge is often effective in limiting suction pressure at thecompressor. For systems employing long suction lines, acrankcase pressure regulating (Sporlan CRO type) valve

may be required to limit suction pressure at the compressorquickly. While a pressure limiting charge can be used witha CRO valve, pulldown time may be adversely affected ifthe charge MOP and the CRO valve setting are close to oneanother. Therefore, Sporlan does not recommend a CROvalve and a pressure limiting TEV be used on the samesystem.

Type X Charge The charges listed under the extremelylow temperature refrigeration are known as the X Charges.The X Charges are liquid-cross charges having an operatingrange from an evaporating temperature of 40F to 100F.This curve is similar to the Z Charge curve since the perfor-mance characteristics of the Z Charges previously discussedapply very well to extremely low temperature refrigeration.

Contact Sporlan for assistance in selecting TEVs for applica-tions requiring the X Charge.

Special Selective Thermostatic Charges andElementsSporlan manufactures a number of special thermostaticcharges and elements designed for specific applications. Afew of these are described below:

Type N Charge This charge is an adsorption type chargewhich has a superheat characteristic curve similar to theC Charge but tends to be less responsive. The N Charge isa noncondensable charge, and it has no MOP feature. TheN Charge is used on special medium and high temperature

applications such as chillers which are located outdoors andmust operate while exposed to cold temperatures.

Hydraulic Elements These thermostatic elements arespecially designed double diaphragm elements which pro-vide a pressure limiting feature without the problems associ-ated with charge migration from the bulb when the elementbecomes cooler than the bulb. The hydraulic element isoften used on chillers which require a TEV with an MOPtype charge, but experience problems with charge migra-tion caused by cold ambient temperatures. For additionalinformation on the hydraulic element, contact the SporlanDivision of Parker.

Mechanical Pressure Limit Elements These thermo-

static elements may use either liquid or liquid-cross charges,

and they employ a mechanical means to limit suction prsure (PL-type). A collapsible member is used to limit evapotor pressure when it exceeds a specified value. This methof limiting evaporator pressure is considered obsolete, areplacement valves and thermostatic elements are no longavailable. A cross reference is available from the obsolete Pelement to the thermostatic element with the MOP charplease refer to Bulletin 210-10-17.

Special Refrigerants Thermostatic charges for uwith special refrigerants are available. These refrigeraninclude: R-13, R-23, R-13B1, R-124, and R-503. Contact tSporlan Division of Parker for assistance in valve selectifor special refrigerant applications.

Desuperheating Charges Special thermostatic charghave been developed for applications requiring suction gdesuperheating. The subject of hot gas bypass and desupheating TEVs is discussed on Page 12.

THERMOSTATIC EXPANSION VALVEAPPLICATIONS

Due to its superior operating characteristics, the TEVcurrently used on a wide variety of applications. Theapplications include both large and small capacity air coditioning and heat pump systems; commercial refrigeratisystems including refrigerated display cases, ice cubers, asoft drink dispensers; and low temperature refrigeratisystems.

Most air conditioning and refrigeration systems use sommethod of capacity reduction to match the capacity of tsystem to a reduced heat load condition, commonly referrto as partload operation. The simplest method of capacreduction is cycling the compressor, usually in responto a thermostat. Other methods of capacity reductiinclude using compressors equipped with cylinder unloaers, bypassing hot gas, or some combination of the abo

A discussion on these capacity reduction methods and theffect on TEV operation is presented later in this section.

The thermostatic expansion valve is a modulating type flcontrol device with the capability to adjust to low load contions and maintain reasonable refrigerant flow control. Trange of effective TEV control, however, has limits and mnot be capable of operating properly on a system requirinhigh degree of capacity reduction. As a result, systems usicapacity reduction methods require the use of proper desiand installation practices.

System Design Factors

Predicting TEV performance at reduced system capacities

difficult due to the many influencing design factors presein any system. These factors include: TEV sizing, refrigeradistribution, TEV setting, evaporator coil design, suctiline piping, and bulb location. General recommendatiowhich address these factors are provided below. By obseing these recommendations, a conventional TEV can expected to operate satisfactorily down to approximately percent of its rated capacity. The Types (E)BF, SBF, EBand O valves, featuring the balanced port design, can expected to operate satisfactorily down to approximately percent of its rated capacity.

Valve Size The TEV should be sized as close as possiblethe systems maximum designed heat load condition. A valwith a capacity rating up to 10 percent below the full load co

ditions may be selected if the system is to operate at reduc

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loads for long periods of time, and if slightly higher than nor-mal superheats can be tolerated at full load conditions.

Distributor Sizing The proper sizing of the distributoris extremely important for systems using methods of capac-ity reduction. The function of the refrigerant distributor is toevenly distribute refrigerant to a multi-circuited evaporator.If the distributor cannot perform its function at all load condi-tions erratic TEV operation can be expected. For the pressuredrop type distributor, the distributor nozzle and tubes must be

checked for proper sizing at both minimum and maximum loadconditions. See Bulletin 20-10 for further information.

Superheat Adjustment The superheat setting of theTEV should be set at the highest possible superheat that canbe tolerated at full load conditions. A high superheat settingwill reduce problems associated with mild TEV hunting atlow load conditions. High superheats are more acceptable onair conditioning systems where the wide temperature differ-ence between the refrigerant and the air allows the TEV tooperate at higher superheats without a significant loss incoil capacity.

Evaporator Coil Design When the evaporator is cir-cuited to provide counterflow of the refrigerant relative to

the direction of the air flow, superheat will normally havethe least effect on evaporator capacity and suction pressurefluctuations will be minimized.

Refrigerant velocity inside the evaporator should be highenough to prevent excessive trapping of liquid refrigerant andoil, which may cause TEV hunting. Multi-circuited coils shouldbe designed in such a manner that each circuit is exposed tothe same heat load. Air flow across the coil must be evenlydistributed.

Large capacity air conditioning evaporator coils are often splitinto multiple sections so that one or more of these sectionscan be shut off for capacity control during part-load operation.Therefore, a TEV is required to feed each of these sections. Themethods used to split these coils are referred to as: row split,

face split, and interlaced. Generally, TEVs will operate beston interlaced coils.

Suction Line Piping Approved methods of suction linepiping including recommended bulb locations and use of trapsare covered in Bulletin 10-11. Where system designers andmanufacturers have tested and approved other methods ofpiping, these methods should be used when installing or ser-vicing their systems.

Sensing Bulb Location The TEVs sensing bulb should belocated on a horizontal section of suction line near the evapo-rator outlet and, in the case of an externally equalized valve,upstream of the equalizer connection on the suction line. Referto Bulletin 10-11 for additional information on bulb location

and installation.

Vapor Free Liquid Refrigerant Another importantaspect in assuring proper TEV operation is providingvapor free liquid refrigerant to the inlet of the TEV. Vaporin the liquid line may severely reduce the capacity of theTEV hindering proper refrigerant flow to the evaporator.

An adequately sized liquid-to-suction heat exchanger willhelp assure vapor free liquid by providing some amount ofsubcooling to the liquid. In addition, the heat exchanger pro-vides an added advantage to the system by vaporizing smallquantities of liquid refrigerant in the suction line before theliquid reaches the compressor. A Sporlan SeeAll Moisture-Liquid Indicator installed near the TEV inlet offers a visualcheck for vapor free refrigerant.

Balanced Port TEVs

One of the factors limiting a TEVs ability to operate atpart-load conditions is a variation in pressure drop acrossthe TEV during normal system operation due to changes inhead pressure. As previously discussed on Page 3, How TheThermostatic Expansion Valve Works, pressure drop acrossthe TEV influences valve operation, particularly with thelarger capacity valves which possess larger port areas. Tocounteract the effects of this force Sporlan has incorporatedbalanced port design features into selected valve types.

Sporlan introduced this feature in 1946 using a double portconstruction on two large capacity valves: the Types T andW. The Type T valve later became our Type V valve whenthe valve design was modified. This double port constructionfeatures a piston which seats against two ports, and signifi-cantly reduces the effects of pressure drop across the valve.

The refrigerant flow entering these valve types is dividedbetween the two ports, the force of the refrigerant flow beingtransmitted to the midsection of the piston. The force of theflow heading to the lower port is largely canceled out by theforce of the flow heading to the upper port due to the designof the piston. Asemi-balanced valve is achieved, allowing

the valve to operate at a lower percentage of its rated capac-ity than a conventionally designed valve.

Sporlan introduced a discharge bypass valve with a fullybalanced design in 1965, the Type ADRHE-6. This designwas later used with the Type O TEV, which was introducedin 1971.

The Type O valve is designed to eliminate the effects ofpressure drop across the valve. The Type O valve features apiston which seats against the valves single port. See Figure8. A passageway drilled through the piston allows liquid linepressure to be transmitted to the bottom side of the piston.

A synthetic cup seal encircling the piston traps this pres-sure underneath the piston, which causes the force due to

the liquid line pressure on top of the piston to be canceled.Satisfactory operation down to 25% or lower of rated capac-ity can be expected with the Type O valve provided that theaforementioned design recommendations are followed.

Recent efforts by system manufacturers to reduce operatingcosts of refrigeration systems by allowing condenser pres-sures to fall or float with lower ambient temperatures hascreated a need for a small capacity TEV with a balanced portdesign and superior modulating characteristics. This effortis particularly apparent with supermarket applications.Sporlan introduced the Types (E)BF and EBS valves in 1984to meet this need.

Pin Guide

Seal Cartridge

Pushrod

Pushrod Seal

Piston Assembly

Types (E)BF,SBF, and EBF

Type O

Figure 8

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This technique may be carried further by using additionevaporator sections, each controlled by a separate TEV arefrigerant distributor. Using multiple evaporator sectiowill let highly reduced loads to be properly controlled.

Single Evaporator Controlled by Two TEVs

For evaporator coils which are not split by design, i.e., rosplit, face split, or interlaced, the following techniques mbe employed to improve part-load operation.

Figure 10 illustrates the use of two TEVs and two distribtors feeding a single evaporator. Each evaporator circuitfed by two distributor circuits, one from each distributThe solenoid valves are connected to the compressor capaity modulating system as mentioned before. Using this cofiguration, TEV and distributor capacities can be reducedthree stages. As an example, assume that TEV and distribtor combination Aare sized to handle 67% of the load acombination B 33% of the load. The three stages of valve adistributor capacity reduction result from opening or closithe solenoid valves according to the following table:

Another variation of this technique is to have each evarator circuit fed by a single distributor circuit and size tTEVs and distributors on the expected load of the tonumber of circuits fed by each TEV. Reducing evaporatcapacity is accomplished by closing a solenoid valve whideactivates the circuits being fed by the TEV and distribudownstream of the solenoid valve. This method of capaccontrol, however, requires a degree of care since the heload on the evaporator circuits will be affected in the mannin which circuits are deactivated.

The Types (E)BF and EBS valves feature a single pushrodwhich extends through the port of the valve. See Figure 8.The port and pushrod cross sectional areas are identical sothat the opening force created by pressure drop across theport is canceled by the pressure drop across the pushrod.Furthermore, excellent pin and port alignment is providedby this design. Refer to the section, Effect of Pressure Drop

Across the Valve Port, on Page 4 for additional information.

The Type (E)BF valve with the AA port was developed by

Sporlan in 1988. Its original design used a two pushrod con-struction similar to the conventional Type F valve, and thebalanced design was achieved by the use of a third floatingrod located above the valve port. As with the single rod bal-anced port construction, thefloating rod causes the pressuredrop across it to offset the opening force created by the pres-sure drop across the port.

The AA port Type (E)BF valve was later redesigned in 1993to a single pushrod construction like the other Type (E)BFvalve sizes. All AA port valves carrying a 3393 date code orlater will have the single pushrod construction.

System Design For Part-Load Conditions

On systems where the compressor can unload to 50 percentof its rated capacity, care must be exercised when selectingexpansion valves and refrigerant distributors. If the com-pressor can unload below 33 percent of its rated capacity,special design considerations may be necessary to assureproper TEV operation. Figures 9, 10, and 11 are piping sche-matics illustrating three possible methods of balancing thecapacity of the TEV and distributor with the compressor dur-ing low load operation. Recognized piping references such asthe equipment manufacturers literature and the ASHRAEHandbooks should be consulted for further information onthis subject. Sporlan cannot be responsible for dam-ages arising from improper piping practices or theimproper use of its products.

Two or More Evaporator Sections Handling theSame Load

Figure 9 illustrates two parallel evaporators each controlledby a separate TEV and refrigerant distributor. Each evapo-rator shares half of the total common load. The liquid linesolenoid valve ahead of each TEV is electrically connectedto the compressor capacity modulating system. When thecompressor capacity is reduced to 50%, one of the two sole-noid valves closes stopping refrigerant flow to one TEV. TheTEV remaining in operation will then have a rated capacityapproximately equal to the compressor capacity operating

50% unloaded.

BULLETIN 10-9 /Page

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SolenoidValve

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handling same load.

TEV and Distributor

Figure 9

Solenoid

Valve

"A" TEV and Distributor

"A"

TEV and Distributor

"B"

Solenoid

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"B"

Capacity Reduction Single evaporator controlled with2 TEVs and 2 Solenoid Valves.

Figure 10

Table

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Hot Gas Bypass and Desuperheating TEVs

Systems which are required to operate at load conditionsbelow the unloading capabilities of their compressors pres-ent an additional design problem. To balance the systemunder these conditions, bypassing a controlled amount ofhot gas to the suction side of the system provides a practicalsolution. Bypassing hot gas is accomplished with a modu-lating control valve known as a discharge bypass valve.Sporlan manufactures a complete line of these valves. For

details, refer to Bulletin 90-40.

For close coupled systems, the preferred method of hot gasbypass is bypassing to the inlet of the evaporator. Thismethod has three advantages: (1) the TEV will respond tothe increased superheat of the vapor leaving the evapora-tor and will provide the liquid required for desuperheating;(2) the evaporator serves as an excellent mixing chamberfor the bypassed hot gas and the liquid vapor mixture fromthe TEV; and (3) oil return from the evaporator is improvedsince the refrigerant velocity in the evaporator is kept highby the hot gas.

For multi-evaporator or remote systems, bypassing hot gasdirectly into the suction line in the manner illustrated in

Figure 11 may be necessary. In addition to the dischargebypass valve, an auxiliary TEV known as a desuperheatingTEVis required to supply the necessary liquid refrigerant tocool the discharge gas entering the suction line. Compressormanufacturers generally rate their air conditioning compres-sors for a 65F return gas temperature, and this temperatureis usually appropriate for selecting desuperheating TEVs.Many refrigeration and low temperature compressors, how-ever, require lower suction gas temperatures to prevent dis-charge gas temperatures from rising too high and damagingcompressor parts and carbonizing oil. Consult the compressormanufacturer if the maximum permissible suction gas tem-perature for a compressor is not known.

Sporlan has developed special desuperheating thermostaticcharges. See Table 5 below. Each charge will allow the desu-perheating TEV to control the listed suction gas superheat.For suction gas temperatures that require superheats otherthan those listed, contact the Sporlan Division of Parker orthe compressor manufacturer for assistance.

Sizing a desuperheating valve involves determining theamount of refrigerant liquid necessary to reduce the suc-tion gas temperature to the proper level. For hot gas bypassapplications, a desuperheating valve can be properly sized

from the selection procedure provided in Bulletin 90-40.

An externally equalized TEV is recommended for most desu-perheating applications. If the piping of the desuperheatingTEV is close coupled, an internally equalized valve may beused. Figure 11 illustrates the use of an externally equal-ized desuperheating TEV. Refer to the section, EqualizationMethod on Page 5 for further information on this subject.

When piping the discharge bypass valve and the desuper-heating TEV, remember that good mixing of the dischargegas and liquid must be obtained before the mixture reaches

the sensing bulb of the desuperheating TEV. Improper mix-ing may produce unstable system operation causing thedesuperheating TEV to hunt. Proper mixing can be accom-plished in two ways: (1) install a suction line accumulatordownstream of both valve outlet connections with the desu-perheating TEV bulb downstream of the accumulator; or (2)mix the liquid vapor mixture from the desuperheating TEVand the hot gas from the bypass valve together before con-necting a common line to the suction line. The latter methodis illustrated in Figure 11.

Off-Cycle Pressure Equalization

Certain applications utilizing low starting torque singlephase compressor motors (e.g., a permanent split capacitormotor) require some means of pressure equalization duringsystem offcycle. Pressure equalization is necessary since lowstarting torque compressors are not capable of restartingagainst a large pressure differential. Typical applicationsrequiring pressure equalization are small air conditioningand heat pump systems which frequently cycle on and off inresponse to a thermostat.

Permanent Bleed Port Any Sporlan thermostaticexpansion valve may be ordered with a bleed port. Standardbleed port sizes are: 5%, 10%, 15%, 20%, 30%, and 40%.

Bleed ports are designated by the percentage they increasenominal valve capacity at 40F evaporator temperature.For example, a 2 ton TEV with a 30% bleed will have thecapacity of: 2 x 1.3 = 2.6 tons. Refer to Page 17 for Orderinginstructions. Please contact Sporlan for assistance in select-ing appropriate bleed port sizes.

The subject of pressure equalization during system off-cycle should not be confused with the external equalizer ofthe TEV. System pressure equalization is accomplished byallowing a certain amount of refrigerant to leak through amachined notch or hole in the valve seat during system off-cycle. The external equalizer of the TEV, however, simplyallows the valve to sense evaporator pressure. The externalequalizer does not provide pressure equalization during

system off-cycle.


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* For suction gas temperatures that require superheats other than those listed

above, contact the Sporlan Division of Parker or the compressor manufacturer

for assistance.

External Equalizer

Evaporator

Compressor

SeeAll

SolenoidValve

TEV

Catch-All

Condenser

ReceiverExternal Equalizer

DesuperheatingTEV

Hot Gas

Solenoid Valve

DischargeBypassValve

Figure 11

Table 5

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BULLETIN 10-9 /Page

The Rapid Pressure Balancer (RPB) Feature Thethermostatic expansion valve with the Rapid PressureBalancer (RPB) feature was developed by Sporlan in responseto an industry demand for a TEV which would equalize sys-tem pressures during off-cycle more rapidly than a TEVwith a permanent bleed port. In some cases, the bleed porthas proved somewhat slow at equalizing system pressurescreating restart problems for low starting torque compres-sor motors. The RPB feature, however, has been proven toreduce equalization times, normally to within two minutes

after system off-cycle.

The RPB feature is actuated following system off-cycle.Immediately after compressor shutdown, the evaporatorpressure rises forcing the valves pin carrier to a more closedposition. When the RPB feature is used, the pin carrier con-tinues its motion and opens a secondary spring loaded bleedport allowing rapid pressure equalization to occur. Uponcompressor restart, evaporator pressure falls closing thespring loaded bleed port. The bleed position and the normaloperating position of the RPB are illustrated in Figure 12.

The RPB feature has a specific application. The featureshould only be used on small air conditioning and heat pumpsystems which use a low starting torque single phase com-pressor motor. On heat pump applications, the RPB featureshould only be used on the indoor coil. Since the outdoor coilmay be exposed to cold ambient temperatures, there exists apossibility the evaporator pressure may fall too slowly uponcompressor restart to reset the RPB feature. In addition, theRPB feature is not recommended nor is it required for anysystem employing electrical hard start components.

The RPB feature is available with the Type RI TEV, and itcan be specified on a special order basis for Types C and S

TEVs up to and including 4 tons R-22 nominal capacity.

Refer to the valve specification sheets for further informatioFor OEM type TEVs, contact the Sporlan Division of Parkregarding the availability of the RPB feature. ACatch-AFilter-Drier should be installed near the inlet of a TEV haing the RPB feature to assure proper valve operation.

The normal capacity of the valve is increased by 15% whthe rapid pressure balancer is used. A cross drilling is partthe internal construction of the RPB feature and this drilliprovides the additional refrigerant flow.

R-717 (Ammonia) Applications

The traditional Sporlan ammonia product line is curently manufactured and marketed by Parker RefrigeratiSpecialties (R/S) Division. The following information hbeen included in Bulletin 10-9 for reference only.

Thermostatic expansion valves for ammonia applicatiorequire special design considerations due to the erosieffects of ammonia vapor. TEVs Type D and A have bedeveloped for this type of application. Like other compnents of any ammonia system, the Types D and A valves amade from steel and steel alloys. The materials used in tmanufacture of these valves are listed in Catalog R/S 7

Refrigerant 717 Ammonia Products, a transitional referenguide from Sporlan to R/S valves.

With ammonia systems, the formation of flash vapor at texpansion valve port causes valve seat erosion or wire draing to occur. This effect is further aggravated by high velocammonia mixed with dirt or scale passing through the portthe expansion valve. Fortunately, seat erosion can be mimized and valve life extended if the following steps are take

1. Maintain vapor-free liquid at the TEV inlet at all times2. Maintain clean ammonia through effective filtration.3. Reduce the velocity of the ammonia through the TE

port by reducing the pressure drop across the port.

Step 1 can be accomplished through proper system desig

Liquid line vapor is prevented by adequately sizing liqulines and providing sufficient subcooling. Step 2 can assured with the use of a Sporlan Catch-All Filter-DrieThis filter-drier is an effective scale trap when used ammonia systems. For further information on the use of tCatch-All Filter-Drier with ammonia systems, contParker Refrigerating Specialties.

Step 3 is accomplished through the use of a removable dcharge tube located in the outlet of all Type D valves athe nominal 20, 30, and 50 ton Type A valves. This dischartube represents the principal difference between ammonTEVs compared to TEVs used with other refrigerants. Tdischarge tube functions by removing a portion of the topressure drop across the valve resulting in a lower pressu

drop across the valve port. Liquid velocities and the formatiof flash vapor at the valve port are reduced, extending the lof the valve. Discharge tube sizes are listed in the Typesand A valve specifications located in Catalog R/S 717.

The discharge tube should be removed and discarded whenrefrigerant distributor is used with the ammonia TEV sinthe function of the discharge tube is accomplished by the dtributor nozzle. If the discharge tube is not removed from tvalve, the combination of the discharge tube and distribunozzle may create an excessive pressure drop resulting insubstantial loss of TEV capacity. Refer to Catalog R/S 7for further information on ammonia distributors.

The nominal 75 and 100 ton Type A valves do not emp

a discharge tube since their valve outlets are designed

Typical Valve Cross Section

Bleed or EqualizingPosition

Normal Operating

Position

RIVE

With

RPB

Figure 12

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and subtracting the saturation temperature from the vaportemperature measured at the sensing bulb location. Forexample, the superheat of R-22 vapor at 50F and 68.5 psigat the sensing bulb location is calculated as follows:

saturation temperature of R-22 vapor at 68.5 psig = 40Fsuperheat = 50F - 40F = 10F

Another method of measuring superheat the TEV is control-ling is the two temperature method. With this method,

saturation temperature is measured directly by placing atemperature probe on the evaporator surface, normally ata location one-half to two-thirds the distance through theevaporator coil. Since this method can only approximate truesaturation temperature, it is not as reliable as the pressure-temperature method, and it should be avoided wheneverpossible.

The TEV is designed to control superheat at a constantvalue at the location of its sensing bulb. The level of super-heat determines to what extent the valve is open. A TEVcontrolling at a high superheat will be further open thana TEV controlling at a low superheat. Refer to the section,How the Thermostatic Expansion Valve Works, on Page 3for additional information. Figure 13 shows a plot of valve

capacity versus superheat for a typical TEV, illustratingthe effect superheat has on valve capacity. For the purposeof understanding the relationship between superheat andvalve capacity, superheat may be described as follows:

Static Superheat static superheat is the amount ofsuperheat necessary to overcome the spring and equalizerpressures so that any additional superheat will cause thevalve to open.

Opening Superheat opening superheat is the amount ofsuperheat required to move the valve pin away from the seatafter the spring and equalizer pressures have been overcometo permit refrigerant flow.

Operating Superheat operating superheat is the super-heat at which the TEV operates on a refrigeration system.Operating superheat is the sum of static and opening super-heats. The valve capacity versus operating superheat curveis referred to as the valve gradient.

The most desirable operating superheat for a particular sys-tem largely depends on the temperature difference (TD)between the refrigerant and the medium being cooled. Thebasic definition of TD is the difference between evaporatortemperature and the entering temperature of the mediumbeing cooled, i.e., air or water. Systems with a high TD, suchas air conditioning and heat pump systems, can toleratehigher superheats without appreciable loss in system capac-ity. Refrigeration and low temperature systems require lowsuperheats due to their lower TDs. The table below provides

general recommendations for superheat settings for differ-ent evaporator temperature ranges. These settings areonly estimates for typical system designs and shouldonly be used if setting guidelines are unavailablefrom the system manufacturer:


serve as a secondary orifice to reduce pressure drop acrossthe valve port.

Thermostatic Charges for Ammonia Valves

Thermostatic charges C, Z, and L are available for the TypeD thermostatic expansion valve. The Type L thermostaticcharge is the only charge available for the Type A valve.

The Types C and Z thermostatic charges provide operating

advantages for systems that cycle in response to a suctionpressure switch or thermostat. These charges are also rec-ommended for systems using a small capacity compressor.The table below lists the recommended temperature rangefor each charge.

Cold storage plants will often have large centralized ammo-

nia systems. These systems will consist of many evaporatorsconnected to one or more large compressors. With manythermostatic expansion valves operating at a common evapo-rator pressure, a change in flow rate made by one valve willnot have a significant effect on the evaporator pressure.This operating characteristic makes it more desirable forthe thermostatic expansion valve to be more responsive tochanges in bulb temperature. This is the feature of the TypeL charge. Therefore, for large ammonia systems consistingof multiple evaporators, the Type L charge is recommended.

FACTORS AFFECTING TEV OPERATION ANDPERFORMANCE

Many factors exist which influence TEV operation and per-

formance. The following discussion lists the major factors:

Superheat

Superheat is defined as the difference between the refrig-erant vapor temperature and its saturation temperature.To properly measure the superheat the TEV is controlling,the pressure-temperature method is used. This methodconsists of measuring the suction pressure at the sensingbulb location, converting this pressure to its saturationtemperature by using a pressure temperature (P-T) chart,

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50 to 40 40 to 0 0 to 40

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Z 0 to 30

For applications at evaporator temperatures below minus 30F, consult Parker

Refrigerating Specialties Division.

RatedCapacity

Full OpenCapacity

Reserve

Capacity

Superheat

ValveCapacity

0A B

C

A = Static Superheat

B = Operating Superheat

C = Operating Superheat

Figure 13

Table 6

Table 7

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BULLETIN 10-9 /Page

When a Sporlan TEV is properly selected and applied, thefactory superheat setting will usually provide an operatingsuperheat in the range of 8 to 12F. A precise determinationof the valves operating superheat from a factory setting isnot possible since factory settings are determined on thebasis of static superheat, and opening superheat of the valveis influenced by several design factors within the system.Once the TEV has been placed on the system and set tothe desired operating superheat, however, the valves staticsuperheat can be measured on a test fixture permitting the

desired setting to be duplicated for production runs.

All Sporlan TEVs have reserve capacity in addition to thecapacity shown in the rating tables in Bulletin 10-10. Thisreserve capacity should not be considered when selecting avalve and, in most cases, will not be utilized if the valve isproperly selected and applied. Reserve capacity, however,is an important and necessary characteristic of any welldesigned TEV. Reserve capacity enables the valve to adjustfor a temporary increase in load, periods of low condensingpressure, and moderate amounts of flash gas in the liquid line.

Valve Setting

All Sporlan TEVs will produce rated capacity at the stan-dard factory setting. If the valve adjusting stem is turned

clockwise, the additional spring pressure created wincrease static superheat and decrease the valves capacto a limited degree. Turning the adjusting stem countclockwise will decrease static superheat and increase tvalves capacity to a limited degree. Figure 14 illustrates teffect setting has on valve capacity.

Referring to Gradient CurveAin Figure 14, Capacity C2achieved with a static superheat setting ofAand an opering superheat ofC. Turning the adjusting stem clockw

will increase the static superheat and shift the curve the right. This new curve, identified as Gradient Curveshows that valve capacity will decrease to capacity C1the same operating superheat C. Capacity C2 can only achieved at the expense of a higher operating superhedesignated as D.

On an operating system where a given valve capacityrequired, any valve adjustment will merely change tsuperheat at which the valve is operating.

Evaporator Temperature

The pressure-temperature curves for all refrigerants haa flatter slope at lower temperatures. Figure 15 illustrat

a P-T curve using R-22 as an example. The P-T curve forthermostatic charge will also be flatter at lower tempertures. As a result, a given bulb temperature change causa smaller bulb pressure change at lower evaporator teperatures. A given change in superheat will result in lepressure difference across the valve diaphragm at lowevaporating temperature causing a reduction in valve opeing and valve capacity.

Subcooling

Subcooling is defined as the difference between the refrigant liquid temperature and its saturation temperature. Fexample, the amount of subcooling of R-22 liquid at 85F a196 psig is calculated as follows:

saturation temperature of R-22 liquid at 196 psig =100F subcooling = 100F - 85F = 15F

Adequate subcooling of the refrigerant liquid is necessato prevent the formation of liquid line vapor due to presure losses in the liquid line. Vapor in the liquid line, evin small quantities, will measurably reduce valve capaciSeveral methods by which liquid line vapor can be preventin spite of relatively high liquid line pressure losses aexplained in Bulletin 10-11.

Pressure

-

psig

Temperature - F

Refrigerant - 22

Pressure - Temperature

70

10 20 40

30

50

P = 7.1 psi

P = 5.0 psi

5F

5F

30

tnaregirfeR

a431,21 25 psi

705,205,A404,22 35 psi

A014 45 psi

)ainommA(717 40 psi

*Average Pressure Drop Across Distributo

Superheat

ValveCapacity

0

B A & B Static SuperheatC & D Operating Superheat

Capacity C2

Full OpenCapacity

Capacity C1

A

CD

Gradient Curve - A

Gradient Curve - B

Figure 14

Figure 15

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Table

Table

*See Sporlan Bulletin 20-10 for pressure drop data as related to percent load

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R-408A, R-409A, R-502 and R-507. R-717 (ammonia) capaci-ties listed in Catalog R/S 717 are based on 86F. For otherliquid temperatures, apply the correction factor given in thetables for each refrigerant.

3. Select valve from the capacity tables Select a valvebased on the design evaporating temperature and the availablepressure drop across the valve. If possible, the valve capacityshould equal or slightly exceed the design rating of the system.Be sure to apply the appropriate liquid temperature and pres-

sure drop correction factors to the valve ratings shown in thetables. Once the desired valve capacity has been located, deter-mine the nominal capacity of the valve from the second columnof the tables. On multiple evaporator systems, select each valveon the basis of individual evaporator capacity.

4. Determine if an external equalizer is required Theamount of pressure drop between the valve outlet and bulblocation will determine if an external equalizer is required.Refer to the section, Equalization Method, on Page 5 for fur-ther information on this subject.

5. Select body type Select the body type from Table 10according to the style connections desired. For completespecifications on each TEV type including nominal ratings,refer to Bulletin 10-10 for valves specifications.

6. Select the Sporlan Selective Thermostatic Charge Selectthe charge according to the design evaporating temperature fromthe Table on Page 18. Refer to Pages 7 thru 9 for a complete dis-cussion of the Sporlan Selective Thermostatic Charges available.

Selection Example

Refrigerant 22Application: air conditioning

Design evaporator temperature ....................40FDesign condenser temperature ..................105FRefrigerant liquid temperature .....................90FDesign system capacity ..............................2 tons

Available pressure drop across TEV:Condensing pressure (psig) ..................211Evaporating pressure (psig) ....................69

____142

Liquid line and accessories loss (psi) ......7Distributor and tubes loss (psi) 1 ......... 35

____100

Refrigerant liquid correction factor .............. 1.06

Pressure losses in the liquid line result from friction and staticpressure losses. Minimizing these pressure losses as much aspossible is necessary for proper system design. Friction lossesmay be minimized by properly sizing the liquid line and liq-uid line accessories such as a solenoid valve and filter-drier.Static pressure losses, however, are solely the result of theweight of the vertical height of refrigerant liquid. As a result,static pressure losses can only be minimized by reducing theupward vertical height refrigerant liquid must travel. Table 8may be used to determine the static pressure loss of a liquid

line. When the sum of the static pressure and friction lossesare known, the amount of subcooling necessary to preventvapor from forming in the liquid line can be determined. Forexample, if the sum of the static and friction losses is 14 psifor an R-22 system, and the condensing temperature is 100F,the subcooling necessary is as follows:

saturation pressure of R-22 at 100F condensing = 196psig pressure at TEV inlet = 196 -14 = 182 psigsaturation temperature of R-22 liquid at 182 psig = 95Fsubcooling required = 100 - 95 = 5F

Refrigerant Liquid Temperature and Pressure DropAcross TEV

The refrigerant liquid temperature entering the TEV and thepressure drop available across the TEV influence valve capac-ity. The valve capacity ratings displayed in Bulletin 10-10,are based on 100F vapor free liquid entering the valve forR-12, R-22, R-134a, R-401A, R-402A, R-404A, R-407A, R-407C,R-408A, R-409A, R-502, and R-507. R-717 (ammonia) valvecapacity ratings listed in Catalog R/S 717 are based on 86Fvapor free liquid entering the valve. Liquid correction factors forother liquid temperatures are included in Bulletin 10-10 alongwith the ratings tables for each of the refrigerants listed above.The tables also provide valve capacities for typical pressuredrops across the TEV.

Thermostatic Charge

The pressure-temperature curves of the various Sporlan Selective

Charges have different characteristics. The same amount ofsuperheat will not produce equal valve openings for each type ofcharge. The valve capacity ratings shown in this bulletin specifythe thermostatic charges which they are based on.

SELECTION PROCEDURE

The following procedure should be used when selecting aSporlan TEV:

1. Determine pressure drop across valve Subtract theevaporating pressure from the condensing pressure. Thecondensing pressure used in this calculation should be theminimum operating condensing pressure of the system.From this value, subtract all other pressure losses to obtain

the net pressure drop across the valve. Be sure to considerall of the following possible sources of pressure drop: (1)friction losses through refrigeration lines including theevaporator and condenser; (2) pressure drop across liquidline accessories such as a solenoid valve and filter drier; (3)static pressure loss (gain) due to the vertical lift (drop) ofthe liquid line; and (4) pressure drop across a refrigerantdistributor if used. Table 9 specifies typical pressure dropsacross Sporlan type refrigerant distributors at design loadconditions. Refer to Bulletin 20-10 for further informationon refrigerant distributors.

2. Determine the liquid temperature of the refrigerantentering the valve The TEV capacity tables in Bulletin10-10, are based on a liquid temperature of 100F for R-12,

R-22, R-134a, R-401A, R-402A, R-404A, R-407A, R-407C,


RECOMM

ENDED

VCP100,

VGAVZ,

VZ

EVAPOR

ATOR

20

0-10

0.22

0.19

0.17

0.27

0.25

0.22

0.38 0.

330.27

0.49

0.43 0

.35

CAPACITY(tons)EVAPORATINGTEMPCondensingTemp.(F)

80 0.41 0.56 0.6990 0.37 0.53 0.66

100 0.33 0.49 0.62

0 5 10

The valve capacityshould equal or slightly exceedthe tonnage rating of the system

Designevaporatingtemperature

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BULLETIN 10-9 /Page

The SVE-2 has valve capacity of: 2.00 x 1.06 = 2.12 tons at40F evaporating temperature, 100 psi pressure drop, and90F liquid temperature.

Thermostatic charge (from Table on Page 18): VGA2

Selection:

SVE-2-GA 1/2 x 5/8 ODF 5, 1/4 ODF equalizer

1 An externally equalized valve must be used on evapora-tors employing a refrigerant distributor due to the pressuredrop created by the distributor.

2 Refer to the section, Sporlan Selective Charges, on Page7 for information regarding the differences between the

VGA and VCP100 charges. Please note that the refrigerantcharge designation in the thermostatic

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