Is 22mm pipe worth it when using a 15mm pressure equalising valve?

[Oxbow16]

Hi all

 

Making some final decisions on the plumbing for our bathroom refit.  Background:  we'll be having a shower mixer tap on the bath, hot water is gravity fed, and cold is mains.  So I'll be having a pressure equalising valve (PEV) before the shower mixer to balance the hot and cold.  I know the shower power will be pitiful, and am happy with that.  

 

But I don't want it to be any more pitiful than it has to be!  So...

 

If the pipework from the cylinder to the PEV, and from the PEV to the tap, were all 22mm - would that perform better than 15mm pipes?  I ask because the connectionson the PEV are all 15mm, and I don't know if it's a case of "the weakest link in the chain, as it is with so many of these things.  Logic suggests to me that 22mm pipework would still be helpful.  But I'm an armchair plumber, so it's over to you guys.

 

Cheers   

[Conor]

Water doesn't quite work like that. You can have a "restriction" point like a smaller valve that will have a pressure loss effect, but may not be significant if you have long pipe runs either side of it and they are greater diameter. Basically, when diameter narrows, velocity increases along that distance and leads to an increase in friction and pressure loss. At the far end, velocity will return to "normal" and you have no further additional loss (apart from some turbulent flow).

 

There are other factors, namely the length of the pipework, size of the outlets, number of bends etc etc... But yes, larger diameter will mean better flow rates.... But how much of a difference is unknown.

 

[Oxbow16]

Thanks @Conor - that's really helpful. 

 

The length of pipework will be around 5.5m, with a fair few twists and turns along the way.  The outlet is 22mm.  

 

I think based on what I've learnt that 22mm might be useful, so think I'll go with that. 

 

One thing I didn't consider though is the shower hose itself, so will be looking for a wide bore hose....

 

Cheers