What is a Hydrotank
Hydropneumatics tanks (hydrotanks) use compressed air to maintain the pressure in a distribution system as opposed to overhead storage tanks, which rely solely on water elevation. They are commonly smaller and less expensive than overhead storage tanks and are used to control pump cycles in raw water, potable water, and sewer systems.
Modeling hydrotanks within a hydraulic computer model allows the system designer to evaluate the efficiency, pressure, pump cycles and flows by performing an extended period simulation.
Hydrotank Schematic
The schematic above shows how hydrotanks work. Hydrotanks are controlled by pressure settings. The pump starts when the pressure in the tank reaches its minimum level. With the pump on, the tank is refilled to its maximum level, and the air within the tank is compressed until the maximum pressure setting is attained. During this period while the tank is filling, the system demand is provided by the pump. When the maximum pressure is reached, the pump turns off and the demand is met by the pressurized water stored in the tank. As the tank drains the water level drops and the pressure decreases until it reaches the minimum setting. The pump then restarts and the cycle repeats.
The Hydro-Pneumatic Pump Cycles Tool (Pump Cycles Program)
This tool assists the user in selecting the appropriate size for a hydrotank. It iteratively completes a set of calculations which account for the following:
1) The pump’s head/flow curve over a range of pressures.
2) Required tank outlet pressure.
3) Variations in system demand.
The analysis requires performing many repeated calculations at small intervals of time for each size of tank considered. The Pump Cycles tool performs these calculations for two configurations. These are:
1) Hydrotank located just downstream from the pump station.
2) Hydrotank located a significant distance downstream from the pump station.
For a tank just downstream from the pump station, the following information is required:
1) Maximum pressure (psi).
2) Minimum pressure (psi).
3) 3 points of pressure/flow data for the pump (or pumps) (psi and gpm).
4) The tank volume (gallons).
5) The available suction head at the pump (psi).
If the hydrotank is not located just downstream from the pump station, the following additional information is required:
6) Tank and pump elevation.
7) Pipeline length between the pump and the tank, along with the pipe’s diameter and Hazen-Williams roughness coefficient.
The calculations are carried out over a range of demands, typically equal to the average demand +/- 50%. If the demand is too large and the pump/hydrotank system is incapable of meeting this demand, the Pump Cycles program alerts the user.
The Pump Cycles tool is a KYPipe Premium Package feature.
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