Do I need an in-line check valve?

[Hoolie]

I'm planning to fit a Whale diaphragm shower pump with a connection rising high up on the sink waste. Will I need an in-line check valve to prevent back-flow to the shower tray or does the pump when not running prevent reverse flow? Thanks!

 

[vyv_cox]

A diaphragm pump has non return valves of its own, so no further check valve should be needed. Whether there will be sufficient head to activate the valves remains to be seen! My shower pump is centrifugal, I added a NRV to prevent backflow but it has never been effective.

 

[jwilson]

For bilge or shower drain pumps NRVs generally soon start to leak backwards: any grit or hair defeats the seal

 

[Hoolie]

I did wonder about the long-term effectiveness of a NRV; it's not very clear what mechanism they use, but there are some described as "flap" valves that might be better.

The effective head back to the pump won't be much - 50cm at most - as the connection will have to be as far as I can get above the waterline but limited by the worktop height

 

[Plum]

I'm planning to fit a Whale diaphragm shower pump with a connection rising high up on the sink waste. Will I need an in-line check valve to prevent back-flow to the shower tray or does the pump when not running prevent reverse flow? Thanks!

With a diaphragm pump any water in the hose between pump and skin fitting will not flow back but any between pump and showertray will. In reality, diaphragm pumps do a reasonable job of pumping a mixture of air and water so if you keep the pump running for a few seconds after it stops sucking just water the amount that runs back is less than the volume of the hose. I live with this as either the trapped water will eventually/slowly run back into the shower tray or it will stay in the hose and may freeze in the winter or the valve suffers from trapped hair!

Www.solocoastalsailing.co.uk

 

[Moodysailor]

A Whale gulper pump has a check valve on the pump body, however this is only to stop a bit of back-flow. If you are concerned with syphoning, and anti-syphon valve is needed, if it's just a bit of back-flow, the joker valve on the pump should be OK provided there isn't too much head.

 

[LadyInBed]

A mesh strainer in the shower tray drain will help to stop the hair.

 

[Donald M]

In my knowledge the diaphragm pump has non return valves so the reverse flow doesn't work in this situation

 

[Hoolie]

Thanks to all for your useful comments! I'll buy a pump while I'm in the UK and fit it early next season, initially without a check-valve. When I get to the boat I'll see how easy it is to fit a hair strainer.