My one way valve swings both ways!

[Cardo]

I redid a large part of our fresh water plumbing over the winter, including adding a second tap to the galley sink that is supplied by both a foot pump and the watermaker. The pipes are joined by a simple "Y" connector with one way valves in them to stop the water going the wrong way.
The one way valves look like these, though I don't think they came from Force4:
http://www.force4.co.uk/6611/Force-4-Non-Return-Valve-for-1-2---3-4----1--hose.html

I have today discovered that at least one of these valves is allowing water to flow back down.

Is the valve broken?
Is the pressure I'm dealing with not high enough to correctly shut off the valves?
Should I be using a different type of valve? If so, what?

Cheers!

 

[Salty John]

I've always managed to avoid using these valves by bringing the two flow pipes together into a downward pointing Y junction. Gravity helps to make it more arduous for one stream to turn back up the other leg of the Y.

 

[macd]

Sorry, Cardo, can't help with your question, although I recognise the part, sold here in Greece by hardware stores as a distinctly non-boaty item. I bought one for the spares locker for it's potential as a hose size step-down/step-up, just in case. A fraction of of the silly price of a Vetus item.

On second thought I suspect the simple flap valve isn't as dependable as the tricuspid arrangement usual in most boaty one-way valves.