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Home » Product & Planning Guide » Plumbing » Accumulators on
Narrowboats & Canal Boats


Accumulators in marine fresh water systems smooth water flow and prolong pump life.

Here we discuss how they work and how to set them up correctly

An accumulator reduces pump cycling time and is designed to smooth the flow of water through the taps and shower head.

The electrically operated pumps we commonly use for distributing water around canal boats work by using pressure switches. Open a tap or outlet, the pressure switch senses a drop in line pressure and activates the pump. The pump will keep running until the outlet is closed which allows pressure to build up in the line to a pre-set value at which the switch turns the pump off.

An accumulator is a small tank which is fitted 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 to loo or fill a glass of water in the night without the pump running.
Some accumulators are supplied 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.
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