Accumulator

A component of the water system, this smooths out the pressure fluctuations that can occur with a pressure-switched pump.

The pump is fed from the fresh-water tanks through a manifold and the pump provides the pressure required to supply the taps / hot water system / showers / etc. The pump has a pressure limiting switch that turns off the pump once it has reached a preset pressure - in this case; 3.4 Bar. However, the downstream environment, when all taps are closed, is a relatively small, rigid pipe system containing only water - which is non-compressible. When a tap is opened, the pressure drops and the pump turns on to maintain flow.

The problem with this is that the pump creates pressure faster than the open tap removes it. The pump detects a rise in pressure and switches off. The pressure drops and it turns on. The current draw each time the pump turns on is enough to make the lights flicker and this happens more that once per second. It doesn't do the pump much good to be cycling that quickly either.

There are a number of things that can be done to alleviate this problem; some electrical, some mechanical. It is quite likely that more than one of these needs to be applied but the accumulator should address one aspect of the problem.

The Accumulator stores pressure. It is a pressure vessel with an outlet at the bottom connected to the outlet pipe of the pump. When the pump comes on, water is forced in through this outlet and into the accumulator. As water enters, the air in the upper part starts to compress. When this reaches 3.4 Bar, the pump switches off but the pipe system now has a reserve of pressure that will drive water to the outlets. Only when the pressure drops to the pump's turn-on value will the pump restart.

The overall effect of this is that the pump cycles less ofter but stays on longer for each cycle.

Overview of the operation at stages of the cycle.
The accumulator is an empty vessel made out of waste pipe and various fittings. There is a hose connector at the bottom and a bicycle valve at the top. The top valve anticipates a time when air may leak or be otherwise removed from the vessel. This can be replaced without dismounting the unit.

Made from a few waste pipe and plumbing fittings.

Final assembly and mounting will be done on the boat (so that I can make it as long as possible to fit into the available space).

In situ under the galley sink.