Check Valves - where needed?

[MortarThePoint]

As I understand it you need a single acting check valves wherever hot and cold are mixed and a double acting one where it could be more serious like for an outside tap, washing machine or dishwasher. You also need one before a water softener, though it is debatable whether you need a double or single check valve. I think mixer taps are the most likely to be overlooked. Are most people fitting check valves there?

 

Unvented Cylinder:

I have a Caleffi 533201 PRV with integrated check valve to protect the upstream mains supply, but interestingly nothing between the outlet for cold and the outlet to the cylinder. When cylinder fills with cold water and is then heated up, could the water not expand back up the cylinder feed and through the Caleffi manifold into the expansion vessel (or cold) branch? If the next tap to be turned on is a cold one that water would get pushed into the cold branch.

 

Shower Mixers:

 

 

Not sure why (particularly with an unvented cylinder system like mine), you're supposed to have a check valve on both the hot and cold connections of a shower mixer or mixer tap. I understand the cold side as the hot water is a high category than the cold.

 

One of our shower mixers' instruction manual clearly labels two check valves, whereas the other one talks of a check valve and how to maintain it but doesn't use the plural. The diagram for maintenance shows a position next to the hot feed. There is a similar position next to the cold feed, but that may be empty.

 

Another shower has a cheap eBay mixer bar which may not include check valve(s) so will need to check that.

 

Bath Thermostatic Mixing Valve (TMV):
 

Likely include check valves but confirm. Example Pegler PEG402 "Each tail piece comprises: a housing with union nut and an internally fitted, WRAS approved non-return valve."

 

Basin mixer taps:

 

Don't normally integrate check valve(s), but should people be adding them?

 

NOT ACTUAL ONE - 533112-CST-UV3-PRV-Monobloc-Manifold_DS_06-15.pdf Same as Family Bath Valve - WP1500RC.pdf Master_Shower_Cambridge Manual.pdf