How I designed and fitted a better shower sump pump

John Edwards suggests a more efficient way to empty your shower tray

A sump box fitted with a float switch allows the shower to drain without the pump having to run continuously while showering

TAGS: In the workshop Practical Projects

When our existing electric heads shower pump came up for its fourth expensive overhaul, I decided to redesign the system to try to make a cheaper and more reliable alternative, writes PBO reader John Edwards.

First, I measured the outflow from a showerhead and estimated I would need a pump with a flow of 40-50lt/min.

I then constructed two 200 x 225 x 150mm sump boxes, one each for the forward and aft bilges.

The boxes were made in WBP ply, filleted and saturated with epoxy laminating resin. A visit to the marina chandlery with my boxes showed that pumps with 20mm hose stubs fitted neatly inside.

A sump box fitted with a float switch allows the shower to drain without the pump having to run continuously while showering

The output of the pumps was less than ideal, especially as they needed to lift the water 1.5m and their efficiency falls off rapidly when the head is above one metre, but they fitted the existing pipework so the decision was made.

I equipped each box with a float switch to control the pump, and placed fine strainers in the drains of the washbasin and shower trays to prevent hair entering the system.

A restrictor valve stops the pump being overwhelmed by the shower

In case the pumps were overwhelmed by the inflow from the heads, I fitted a restrictor in the outfall pipe to slow down the flow, effectively storing the water in the wash basin/shower tray and pipework until the pump had time to complete the job.

I also added a non-return valve 300mm up the outlet pipe to prevent a pipeful of water flowing back into the box, setting the pump off again ad infinitum. The system works well, quietly and efficiently, without the need for the restrictor, and the total cost equalled two overhauls of the previous displacement pump, which after eight years was definitely feeling its age.

COSTS
Pumps and float switches x 2 …….. £52
Non-return valves ……….. £18
Ancillary connectors, hose clips …. £10
WBP ply …………………… £8.40
Epoxy was already on board
TOTAL: £88.40