An accumulator is a small tank which is fitted on a narrowboat as close to the pump outlet as possible. The pressurised water supply partially fills the tank, which is itself charged with pressurised air. The water and pressurised air in the tank are separated by a rubber membrane, which allows energy generated by the pump to be stored and released by the compression and expansion of the air behind the membrane. This compression and expansion damps out fluctuations in supply pressure permits the pump to be switched off for short periods with no loss of water supply.

The benefits are less cycling of the pump, prolonging life and the ability to flush the loo or fill a glass of water in the night without the pump running.

Some accumulators are supplied for narrowboats pre-charged. Sometimes this charge pressure is way too high to even allow water flow so the accumulator has to be matched with your system.

You will need a tyre pressure gauge and a bicycle pump and possibly a helper to turn the pump on and off at the fuse panel.

Firstly locate the air valve on the accumulator. This may be under a cap but will be of the standard car tyre or bicycle inner tube type. If you know the cut-in pressure of your pump, turn the pump off at the fuse panel and open a tap until the water stops flowing. Now measure the air pressure in the accumulator with the tyre pressure gauge. The pressure in the accumulator should be the same as the cut-in pressure of the pump. Adjust accordingly either by depressing the valve to let air out or pumping air in with the bicycle pump. Then close the tap turn the pump back on at the board and test the flow. The pump should run smoothly with no spitting or cycling. If you are not sure of the cut-in pressure of the your pump, either check with the manufacturer or pump the accumulator up to around 25psi and fiddle with the pressure gradually using the method above until the pump runs smoothly.