- Accumular Tank
On a fire hydrant, hose reel or automatic fire sprinkler system, an accumulator tank is a pressure chamber with an integrated bladder that forms part of the pressure maintenance pump (jacking pump) arrangement to store a volume of pressurised air. In fire safety, an accumulator tank is installed in the discharge side of a jacking pump to dampen water pressure 'spikes' to help reduce pump cycling and prolong the pump's life.
How an accumulator tank works
An accumulator tank with a bladder stores energy by compressing a gas (usually air) when water is pumped into the system. Here’s how it works with a pressure maintenance pump:
- Normal Operation:
The pump maintains system pressure by circulating water until the pressure reaches a set level. As water enters the accumulator tank, it compresses the pre-charged air inside the bladder. This stored energy is proportional to the pressure difference between the system and the pre-charge. - Response to Transient Pressure Drop:
When a sudden demand or minor leak causes a brief drop in pressure, the compressed gas in the accumulator expands. This forces water out of the tank rapidly, compensating for the loss and smoothing the pressure dip. Because the accumulator quickly discharges water to maintain the pressure, the pressure switch—set to trigger a larger fire pump if the pressure falls too low—does not see a sustained low-pressure condition. - Preventing Unnecessary Pump Activation:
Pressure switches often include a delay to avoid nuisance tripping. The accumulator’s rapid response covers short-term pressure dips, keeping the pressure above the trigger threshold long enough that the larger (electric or diesel fire) pump does not start. Essentially, the accumulator acts as a buffer, using stored energy to stabilise pressure during transient events.
This design ensures that only sustained low-pressure conditions (beyond the accumulator’s capacity or duration) will activate the larger pump, optimising system performance and preventing unnecessary cycling.