Pressure Difference

[LeeJC]

Hello All.

Only a small problem really, but i have a huge pressure difference at the taps on my bath, which wasn't a problem until a mechanical mixer type shower was fitted.

Now with hot water only its scorching as soon as the cold is turned on it's freezing.

I know this to be caused by the fact that the cold is at mains pressure through a 15mm pipe and the hot is feeding the bath from what looks like 22mm pipe (but could be 18) All copper.

Is there any way without replacing or changing pipework of equalising the pressure at the minute i have a large tap washer in there which is increasing the pressure enough to just about manage a warm shower but it's not very scientific.

Any help greatly recieved.
Lee

 

[Slugbabydotcom]

Mains cold pressure = 3 bar
tank fed pressure = 0.1 -0.4 bar and thats being optimistic

If you can relate better to this in PSI [car tyre pressues] there are 14.5 PSI to the bar.

Answer is to get hot and cold at the same pressure.
Fit a combi
Get an unvented cylinder or heatstore.
If your hot water is tank fed your cold water to the mixer should be tank fed also. Then you could perhaps fit a shower pump.

Did you read the instructions for your mixer?

 

[ricarbo]

If you cut in a gate valve to the 15mm cold supply, you could limit the flow rate of the cold, to match the hot when both taps are fully open. You'd also be able to isolate the cold locally for servicing. If you added another isolating valve to the hot - even better!
I'd use a gate valve, not a stop valve or quarter turn 'ballofix' style isolater on the cold, because I think you will find that will be quieter in use.
Some mixer taps can be technically unsuited to use with mains and tank fed supplies, because of cross contamination fears (are the hot and cold waterways on your tap maintained entirely separate to the outlet, for a clue on that?). I suppose adding a non return valve before the gate valve would get you over that.

 

[LeeJC]

Thanks for the advice, no instructions to read to be honest.

Not sure if you are confusing a "Mixer Shower" with what i'm referring to which is a tap set with shower attachment.

Anyway i could try cutting in a gate valve to reduce the cold pressure, huge pain that would be with the pipes situated as they are.

Am i right in thinking that attempting to fit a power shower to the current plumbing install would be a nightmare due to the pressure difference as well??

Cross contamination i think could happen because the cold is at such a higher pressure than the hot so if both taps are open then i imagine it would be possible to force the hot back into the tank.

I'm going to go into the loft and investigate, but i think the best possible although costliest and most inconvenient is to put a cold storage tank into the loft space and use this to feed the bathroom rather than mains cold throughout the house.

What does anyone else think???

 

[Gasman1015]

Pressure equalising valve on bath supply.

http://www.rwc.co.uk/product.aspx?page=CAT9

 

[ChrisR]

Minimum pressure for those is 0.3bar = 3 metres head, which you may not have, in which case it won't work.

 

[chrishutt]

You want a Venturi shower.

 

[Gasman1015]

You want a Venturi shower.

Ever fitted one chris, do they produce results.

 

[chrishutt]

Only fitted one, some years ago . Performance depends on how well the design parameters are met - pressure of cold and hot, but if you look at New Team Jetstream (screwfix) for example its performance looks good on paper (although the shower itself looks a bit weird). There's also the Treviboost.

 

[Softus]

In case it's of interest, I've fitted two Trevi Boosts this year - they're marvellous.

As Chris says though, you need to ensure that you operate within the design limits.