Non-return valves for mixer tap

[LlMikeybll]

Hi all, I'm planning on fitting my new sink which has a mixer tap. I'm using an unvented system, will this still require non-return valves fitted to the taps connections?

 

[Stigster]

Edited -

Sorry, for some reason I read "vented" instead of "unvented" first time I looked and answered. With cold mains feeding the tap and also the unvented cylinder you should not need non-return valves. Unless you have very high pressure on the cold feed it should be fine.

 

[LlMikeybll]

Sorry, for some reason I read "vented" instead of "unvented" first time I looked and answered. With cold mains feeding the tap and also the unvented cylinder you should not need non-return valves.

I'm using an unvented

Edited -

Sorry, for some reason I read "vented" instead of "unvented" first time I looked and answered. With cold mains feeding the tap and also the unvented cylinder you should not need non-return valves. Unless you have very high pressure on the cold feed it should be fine.

The cold comes straight from the mains and the hot from the cylinder, the cold mains is at high pressure though. Would the pressure from the cold not cause backflow to the cylinder or is there usually a non return valve at the cylinder to prevent that?

 

[ShaunCorbs]

Nope non needed providing the tap is suitable for the uk

 

[Stigster]

I'm using an unvented

The cold comes straight from the mains and the hot from the cylinder, the cold mains is at high pressure though. Would the pressure from the cold not cause backflow to the cylinder or is there usually a non return valve at the cylinder to prevent that?

Yes, there's a non-return in the combination valve (aka "Group Inlet") which will not allow water to feed back to the cylinder no matter how unbalanced the pressures are in the hot and cold feeds.

The issue occurs when you have cold mains and gravity (tank fed) hot, the cold can overpower the flow of hot water inside the mixer tap (even then that depends upon the tap design and how the waterways are made) and feed back up to the header tank and cause it to overflow.

 

[Plumb Tidy]

Yes, there's a non-return in the combination valve (aka "Group Inlet") which will not allow water to feed back to the cylinder no matter how unbalanced the pressures are in the hot and cold feeds.

The issue occurs when you have cold mains and gravity (tank fed) hot, the cold can overpower the flow of hot water inside the mixer tap (even then that depends upon the tap design and how the waterways are made) and feed back up to the header tank and cause it to overflow.

What if the tap was a single flow mixer tap would the high pressure cold not force its way back through the hot and back to the cylinder? Its normally what happens in bar mixer showers that's all if the cold is not taken off the balanced feed from the combination valve. I came across a domestic property in south wales where the mains was over 12 bar it almost broke my gauge!

 

[Stigster]

I don't see how any pressure of cold mains could push water back to the cylinder because of the non-return in the group inlet. That would need to let by for that to happen and given the design of the non-return I cannot see how water could backfeed through that provided it was in good working condition.

The harder the water pushes against the non-return, the harder it pushes it shut and keeps it shut so under normal conditions, even 12 bar cold mains, I can't see that happening.

It would set off the expansion relief port though I suppose. If the pressure were that unbalanced then a check valve is not the answer, pressure reducing valve on the mains would be the thing to do if you had 12 bar coming in.

 

[LlMikeybll]

I don't see how any pressure of cold mains could push water back to the cylinder because of the non-return in the group inlet. That would need to let by for that to happen and given the design of the non-return I cannot see how water could backfeed through that provided it was in good working condition.

The harder the water pushes against the non-return, the harder it pushes it shut and keeps it shut so under normal conditions, even 12 bar cold mains, I can't see that happening.

It would set off the expansion relief port though I suppose. If the pressure were that unbalanced then a check valve is not the answer, pressure reducing valve on the mains would be the thing to do if you had 12 bar coming in.

From my understanding, I wouldn't need a non return fitted at the sink source if the hot and cold pressure was balanced, however the cold is being fed from the CWM directly at a much higher pressure than the hot, so if i put a non return on the hot pipe will this stop the expansion relief port from activating? Apologies I'm really not an expert on all this haha

 

[Plumb Tidy]

From my understanding, I wouldn't need a non return fitted at the sink source if the hot and cold pressure was balanced, however the cold is being fed from the CWM directly at a much higher pressure than the hot, so if i put a non return on the hot pipe will this stop the expansion relief port from activating? Apologies I'm really not an expert on all this haha

I have not seen this happen but i was thinking it would be a possibility after thinking back to this 12 bar house it may be more my gauge only goes up to 12 bar. I said to the bloke we could fit a pressure reducing valve but he wouldn't have it as the pressure has been like it for years and caused no problems. The tap i was fitting was not designed for 12 bar not many taps are!
I believe a check valve would stop the back feed to the cylinder and stop the expansion relief from sounding off but ideally you should not rely on a check valve.A pressure reducing valve should be fitted if the pressures are different to an extreme as the amount of check valves on showers, basins, and sinks would add up to the cost of a reducing valve and time and effort would be saved.

 

[LlMikeybll]

I have not seen this happen but i was thinking it would be a possibility after thinking back to this 12 bar house it may be more my gauge only goes up to 12 bar. I said to the bloke we could fit a pressure reducing valve but he wouldn't have it as the pressure has been like it for years and caused no problems. The tap i was fitting was not designed for 12 bar not many taps are!
I believe a check valve would stop the back feed to the cylinder and stop the expansion relief from sounding off but ideally you should not rely on a check valve.A pressure reducing valve should be fitted if the pressures are different to an extreme as the amount of check valves on showers, basins, and sinks would add up to the cost of a reducing valve and time and effort would be saved.

Ah that makes sense, I'm going to put a pressure reducing valve on the cold mains in to the mixer tap, that way I can balance the hot and cold both to same Bar. Will install a couple of check valves anyway as well to both feeds, good practice to I guess. Thanks for your feedback

 

[Stigster]

From my understanding, I wouldn't need a non return fitted at the sink source if the hot and cold pressure was balanced, however the cold is being fed from the CWM directly at a much higher pressure than the hot, so if i put a non return on the hot pipe will this stop the expansion relief port from activating? Apologies I'm really not an expert on all this haha

Yes a check valve at on the hot feed under the tap would prevent that. I still stand by the fact that a pressure reducing valve on the cold mains is the proper thing to do if the pressures are ridiculously out of balance. Put in a PRV and set it to the same pressure as the group inlet on the hot water cylinder, usually 3 bar but I have seen them half a bar either side of that.