Clonking check valve

[tuppence]

I've replaced a diaphragm type check valve on the inlet side of my water softener with a swing type check valve. I did so because of the continuous buzzing noise made by the old valve. The new check valve is silent except when the kitchen tap is turned off and then it clonks. Arghhh! I've now discovered that rubber seated swing valves are also made. Is silent operation the purpose of the rubber seat and if so would it still be silent at mains pressure?

 

[JayJay1978]

I bet the check valve is mounted horizontally am I right? you will find that the noise stops if you can mount if vertically.

 

[muggles]

Alternatively go back to the old-style valve, the old one was probably buzzing because it was worn

 

[tuppence]

I bet the check valve is mounted horizontally am I right? you will find that the noise stops if you can mount if vertically.

You win your bet! The plate swings and clonks to and fro 2 or 3 times whenever the kitchen tap is turned off. Vertical mounting (upward flow) is possible but tricky to do. I can see that vertical mounting would be silent in a low pressure system such as a CH circuit but from experience, is that also generally true at mains pressure? Just after some idea of what to expect before ripping it all apart again.

 

[tuppence]

Alternatively go back to the old-style valve, the old one was probably buzzing because it was worn

No, this isn't the reason for the problem. I have tried 3 diaphragm type check valves - one double and two singles, all of different makes, all new and all buzzed.

Why did they buzz? Well, I have a theory for what it's worth (not much probably). The output of the water softener goes directly to the cold water tank in the loft, there are no other branches. The buzzing doesn't happen when water is rushing into the tank or when it is just dribbling in (or stopped of course). It happens when water runs into the tank at a moderate rate. If there was a binary float valve, one that is either fully on or fully off, that would solve the problem but I don't know of any. Of course the tank fills in at the "noisy speed" most of the time.

What I think is happening is that the float valve and check valve are interacting by pulsing each other on and off at these intermediate flow rates and that causes the diaphragm to vibrate. That's my theory anyway. Replacing the float valve would be a possibility but it's a bit hit and miss too (just like changing check valves has become).

 

[tuppence]

Just to tidy this thread up in case anyone stumbles across it in the future with a similar problem. I replaced the check valve with a rubber seated one, mounted vertically as advised. It is much quieter - there's still the occasional noise but now it's an isolated dull thud that's in no way annoying.

Thanks for the advice JayJay!