Civil Engineering Reference
In-Depth Information
typical hydropneumatic tank requirements have been developed based upon operating
experience:
The tank should be located above the normal ground surface. In areas where
freezing occurs, the tank should be completely housed, or earth-mounded with
one end projecting into a piping / operations building.
•
The tank should have bypass piping or a duplicate unit to permit operation of the
system while the tank or the tank accessories are being repaired or painted.
•
Each tank should have an access manhole, a drain, and control equipment con-
sisting of pressure gauge, water sight glass, automatic or manual air blow-off,
mechanical means for adding air, and pressure-operated start-stop controls for
the pumps.
•
The total capacity of the wells and pumps in a hydropneumatic system should be
at least six to 10 times the average daily consumption rate of the community. A
minimum of two wells or pumps should be provided.
•
For the supply of water from a pressure tank system to be adequate, the storage
and water mains must be sized to meet peak demands. In small service areas, peak
flow rates may be as much as 10 times greater than the average annual flow rate.
Where available, meter readings should be used to determine average and peak flow
rates. Pump systems should be capable of delivering 125 percent of the peak flow.
Hydropneumatic tanks typically are sized to have a capacity equal to 30 times the
pump capacity. Another rule of thumb is to provide 10 gallons (40 L) of storage per
person served. In general, only about 10 to 20 percent of the total volume of the
pressure tank is available storage.
A simple and direct method for determining the recommended pump size and pres-
sure for conventional horizontal tank capacity was given by J. A. Salvato, Jr.
24
It is
based on the following formula:
V
m
V
P
1
1
P
2
where:
V
pressure tank volume, gallons (m
3
)
V
m
15 minutes storage at the peak hourly demand rate, gallons (m
3
)
P
1
minimum absolute operating pressure, psi (kPa)
gauge pressure plus 14.7 (101.3 kPa)
P
2
maximum absolute pressure, psi (kPa)
gauge pressure plus 14.7 (101.3 kPa)
The design of bladder-type pressure tanks must also consider the number and size of
tanks to provide pump protection and the precharged air pressure of the tank.
Aquifer Storage and Recovery (ASR)
The applicability of ASR is generally evaluated using three principal cri-
General
teria:
