Double check valve vibrating / noisy

[Anak]

Can anyone offer up suggestions on how to resolve a check valve vibrating and making a noise when water is moving through it at a low flow rate?

While not directly relevant to the question I will offer up that it is for a bidet before people start questioning if it should be there and the purpose of it etc.

 

[CBW]

I presume you have the correct setup, but here’s advice in case you weren’t aware: https://www.wras.co.uk/approvals/re.../fittings/installation_requirements/irn_r070/ anyhow providing that your double check valve is suitable, I’d be checking if it’s installed in correct orientation, and it could be damaged internally.

 

[Madrab]

I was going to say, I don't think your (double?) check valve is suitable if your bidet has any type of water outlet/flexi hose or an ascending spray type attached to it.

All water in a bidet is classed as CAT5 and they should not be served by the mains as the link from @The Novice explains. It should be supplied by a tanked water supply with a suitable air gap or another suitable CAT5 backflow protection. It certainly shouldn't have a problem with a check valve, as there really shouldn't be one there to start with.

 

[Madrab]

Your vibrating check valve will be pressure related and it's sticking a little at low flow, the pressure is making one of the valves jump ..... they can't be serviced.

 

[Anak]

It's over rim type, installation guide recommended check valves. Admittedly I probably don't need double but seeing as they were the same price I thought at the time why not...
I assume as you have said it is sticking at low flow or oscillating open and closed.
Any suggestions of fixes?
I understand there are also gravity versions, would they be better in the situation? If so can anyone recommend a supplier in 15mm.

 

[Madrab]

It's over rim type

So it has a tap on the end like a basin with an air gap to the max water level and you fill the bidet up and then use a cloth etc?

As suggested there is no fix for a chattering valve, these valves are not serviceable. I would suggest it may be the make of valve, if you spend a little more on better quality valves it may correct the issue. Either that or the sustained pressure of your supply at very low flow isn't uniform causing the valve to bounce, is there a PRV on the system?

Gravity versions? Nope, can't say I've ever seen them. If it's a gravity fed system from a Cold water cistern/hot water cylinder then the cistern has an incorporated air gap that itself supplies CAT3 protection, therefore as check valves provide the same level of protection they would be redundant and there would be no need to make them.

Check valves, by their very nature, are a killer on gravity systems.

 

[Anak]

So it has a tap on the end like a basin with an air gap to the max water level and you fill the bidet up and then use a cloth etc?

Yes, much like in the the top section of the guide that "the novice" posted.

I think it might be bounce as you have said. The ones I got were just from screwfix.

By "gravity version" I mean the check valve, I'm not sure what they are called, I've heard that some have flaps rather than springs, so these might not chatter, but I'm not sure such a thing exists readily for purchase.

The bidet is fed from mains hot and cold (I have combi). No PRV that I know of, but I guess the tails are narrow compared to a 15mm pipe (but then I guess that's the same for most sinks). Unless you have the tap open quite wide (which can cause a bit of splash-back) there is this vibration which I would assume it the springs opening and closing.

If you think it is a cheap valve and can suggest a good brand of valve, or point me at something decent I am all ears.

 

[Madrab]

You do get to get gravity non return valves that stop gravity flow in non pumped hw heating systems but they're not really check valves and wouldn't be used in a mains water situation.

I wouldn't usually have an issue with screwfix's check valves, never had a problem with them which may point to your supply being the issue but Reliance and pegler are good names for valves.