A hydro pneumatic storage tank that cycles the pump on and off is usually caused by which condition?

• A. A high pressure limit that is too high
• B. Not enough air in tank
• C. A low pressure limit that is too low
• D. Too much air in tank

Answer: (B)

Short cycling happens because the air cushion inside a hydro-pneumatic storage tank provides the space that allows water to be stored and pressure to change gradually as demand varies. If there isn’t enough air in the tank, the cushion is too small to absorb the incoming water. The tank fills with water quickly, causing the pressure to rise rapidly to the cut-off point and stop the pump. As water is used and pressure falls, the pump starts again, leading to a rapid on/off cycling pattern. Recharging the tank with the proper air pre-charge (matching the system’s cut-in pressure) restores the cushion and stops the short cycling. The other conditions would alter when the pump starts or stops but don’t produce this rapid cycling pattern.