Download pdf - Hydro Tanks

PRESENTATION

ON

HYDROPNEUMATIC TANKSBY

JAMES E. PANDOLPH, P.E.

TEAM

ANKNGINEERING

NDANAGEMENT

CONSULTANTS, INC.

WATER STORAGE TANKS

ARE CRITICAL TO THE EFFICIENT OPERATION OF ANY WATER DISTRIBUTION SYSTEM

PURPOSE OF STORAGE

VOLUME

PRESSURE

TYPES OF STORAGE

PROVIDE LARGE VOLUMES OF WATER, USUALLY FOR LARGER WATER SYSTEMS

GROUND STORAGE TANKS OR RESERVOIRS

DO NOT PROVIDE PRESSURE TO THE SYSTEM UNLESS:

1. BUILT ON A HILL

2. PUMPED TO AN ELEVATED TANK.3. USE OF HIGH SERVICE PUMPS TO PROVIDE

PRESSURE TO THE SYSTEM

INSERT A GROUND STORAGE TANK HERE ST. PETE OBERLY

TYPES OF STORAGE

ESSENTIALLY A GROUND STORAGE TANK WHOSE HEIGHT WILL PROVIDE ADEQUATE SYSTEM PRESSURE.

STAND PIPES

ONLY UPPER VOLUMES ARE AVAILABLE TO PROVIDE ADEQUATE PRESSURE

1. CAREFULL CIRCULATION IS REQUIRED TO PREVENT STAGNATION, STRATIFICATION & OTHER PROBLEMS.

2. PROPER SOIL BEARING IS MANDATORY.

ELEVATED STORAGE TANKS

HEAD RANGE (HR)

HT. TO LCL

HT. TO HCL

HCL ESTABLISHES MAX PRESSURE

HR CONTROLS Pressure variation

LCL ESTABLISHES MIN PRESSURE

ELEVATED STORAGE TANKS

HYDROPNEUMATIC TANKS

Hydropneumatic tanks (or pressure tanks) are very common in small water systems that use wells to supply drinking water. The hydropneumatic system combines the energy from a pump (usually the well pump) with the principle of air pressure to force water into the distribution system. These tanks are installed between the well pump and distribution system and are intended to:

Maintain an adequate and relatively even pressure in the distribution system

Reduce the number of times the well pump turns on and off

Hydropneumatic tanks are usually not large enough to provide sufficient water storage for fire fighting. Availability of alternate water sources must be considered when selecting a hydropneumatic system for a municipal supply.

Because the volume of stored water is minimal, operational failures that occur with hydropneumatic tank systems can result in the water system customers being completely out of water within a matter of minutes. It is therefore important for all operators of these systems to be familiar with basic troubleshooting steps to identify andcorrect problems with the water system.

Types of Hydropneumatic Tanks While the number and size of hydropneumatic tanks

may vary widely from system to system, there are four basic styles of tanks. Depending on the type and size, these tanks can be installed vertically or horizontally. The general differences between the four styles (shown below) involve the method of separating the air and the water inside the tank. Operators should be familiar with the type of tank(s) in their system.

TYPICAL HYDROPNEUMATIC TANKConventional tank WITH AIR COMPRESSOR

The air cushion is in direct contact with the water. Because air can dissolve in the water, an air volume controller is necessary as well as an air compressor system

WATER

AIR

MAJOR COMPONENTS OF A HYDROPNEUMATIC TANK SYSTEM

PURPOSECOMPONENTThe Well and pump. Includes Check Valve, Air relief & Meter.

Water Source1

Supports the tank and insures that the tank will not tip over and break a main water supply line.

Tank Foundation

3

Regulates air volume in tank (controls compressor)

Air Volume Controller

4

Stores water and air. Pressurized vessel. Florida requires periodic cleaning & Inspection.

Steel Tank2


PURPOSECOMPONENTSupplies air to the tank to maintain air cushion. Unit should be oil free type or be fitted with filters to prevent oil from entering the water.

Air Compressor5

Prevents excessively high pressure in the tank. Generally 100 psi maximum.

Pressure Relief Valve

6

Allows flow of water in and out of tank. Both should be fitted with gate valves and inlet pipe should be fitted with a check valve.

Inlet/Outlet Piping

7


PURPOSECOMPONENTAllows direct observation of air-to-water ratio. Generally the ratio should be 1 to 2, i.e.: 1/3 air to 2/3 water.

Sight Glass (Tube)

8

For monitoring pressure inside the tank and on the distribution system.

Pressure Gauges

9

Controls cut-in (start) and cut-out (stop) cycles of the well pump.

Pump/Motor Controls

10


PURPOSECOMPONENTRegulates the pump/motor controls based on pre-set cut-in and cut-out points. These are adjustable but adjustments should be performed only by qualified personnel. The settings should generally provide a minimum of 40 psi and a maximum of 70 psi throughout the distribution system. The pressure should never be allowed to drop to below 20 psi. Alarms should be provided to notify the operator in the event of a system failure (low water pressure)

High/Low Pressure Controls

11


PURPOSECOMPONENTRegulates water level in the tank.High/Low Water

Level Controls12

Measures quantity of water pumped.

Master Water Flow Meter

13

Records total hours of water supply pump operation.

Elapsed Time Meter

15

Records number of pump cycles. Should be limited to a maximum of 10-15 cycles per hour. Cycles can adjusted by high/low pressure controls.

Cycle Counter14

2/3 water

1/3 air

Foundations

TYPICAL HYDROPNEUMATIC TANKWITH AIR COMPRESSOR

Air Compressor

Well Pump

Pressure ReleaseWater Level Site Gage

Check Valve

Air ReliefMaster Meter

HYDROPNEUMATIC TANK

WellOutletInlet

Types of Hydropneumatic TanksFLOATING WAFER TYPE

There is a floating wafer (usually constructed of a ridged material, flexible rubber, or plastic) that separates the air and water. This wafer, however, does not completely separate the air and water, and therefore some dissolving of air is expected. These tanks require occasional recharging with air

wafer

Types of Hydropneumatic Tanks

Tanks with Flexible Separator: These tanks provide a complete separation of the air and water. A separator is fastened around the inside of the tank (diaphragm type) or a bag is provided for containing the air (air bladder). These units may be charged with air at the factory, however most are fitted with an air valve (similar to a tire), which the operatorcan use to adjust the pressure inside the tank. Care must be taken when adding air to these tanks in order to avoid over-pressurization and a possible rupture of the separator. Manufacturers literature must be consulted before adding air to these tanks and the procedure should be performed only by qualified personnel

WATER

AIR

BLADDER TYPE

WATER

AIR

DIAPHRAM TYPE

Types of Hydropneumatic Tanks

DIAPHRAMBLADDER

DESIGN CODE ASME SECTION VIII

CODE STAMPED VS. NON CODE STAMPED PRESSURE VESSELS

XXAuthorized Inspection

NOYESNOYES

ASMENo Stamp

CODE STAMPED

XXWeld Map XXHeat No. Transfer

XXReceiving ReportXXTraveler

XXDrawings XXDesign


XXHydro Test

NOYESNOYES

ASMENo Stamp

CODE STAMPED

XXStamping XXData Report

XXNDT XXWeld Visual Inspection XXWelder Qualifications XXWeld Procedures


XXP.O. Review by Q.C

NOYESNOYES

ASMENo Stamp

CODE STAMPED

XXOPTIONAL

National Board Registration

XXTraceability XXWeld Wire Certs XXMTR's XXFinal Inspection

HYDROPNEUMATIC TANKCONSTRUCTION

WELDING

JOINT EFFECIENCYTYPES OF JOINTS

BUTT WELDS

TYPES OF WELD JOINTS

LAP WELDS

E = 100% IF FULL X-RAY

E = 45% IF SINGLE LAP

E = 85% IF SPOT X-RAYE = 70% IF NO X-RAY

E = 55% IF DOUBLE LAP

Lap Welded Construction

Lap Welds

HYDRO PNEUMATIC TANK CONSTRUCTION

FOUNDATIONS

Tank saddles

Steel Concrete

GROUND SUPPORT

Water weighs 8.33 lbs/gallon a 30,000 gallon tank will weigh about 250,000 lbs or 125 Ton.

Soil bearing must allow for this load.

HYDROPNEUMATIC TANK CONSTRUCTION

HEAD TYPES

HEMISPHERICALELLIPSOIDALTORISPHERICAL

Tank Diameter (D)

ELLIPSOIDALr1 + R2 = K

HEMISPHERICALR= 1/2D

TORISPHERICAL

R usually =D

r r

ACCEPTBLE TANK HEAD TYPES

FLAT HEAD

DOME

SHELL SHELL

SHELL SHELL

UNACCEPTABLE HEAD TYPES

PRESSURE VESSEL INSPECTION CODE:MAINTENANCE INSPECTION, RATING,

REPAIR, AND ALTERATION

API 510

NO SADDLE

Unsealed saddle

Concrete pier

Note saddle overhang

SUPPORT PIER AND SADDLE

Improper head Radius

Poor Weld

Code Stamp

Sight Glass

Factory Installed Pressure MW

Air from Compressor

All Butt WeldedJoints

This aftermarket 24 MH does not meet ASME Code and can be very dangerous

Severe dent may affect tank integrity

This tank blew its lid

Lap welded HeadNot welded inside

Patch Plate

Severe corrosion

No saddle

CONCLUSIONHydropneumatic tanks are pressure vessels.

As such they should:

2. Be pressure rated on the stamp

3. Be Inspected by qualified Inspectors who know the pressure vessel code

4. Upgrades and repairs must be designed by engineers and work performed by qualified welders.

1. Be ASME Code Stamped Vessels.

CONCLUSIONWater Storage tanks are necessary for every water

system.Although relatively smaller, hydropneumatic tanks must

be treated respectfully. They can cause considerable damage if improperly operated.

A system failure of a hydropneumatic tank could result in being completely out of water within a matter of minutes.

Proper maintenance is necessary for continued safe operation.

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