Testing Water Pressure


Postby chewy69 » Fri Jun 11, 2010 6:10 pm

I need to check the water pressures of the hot and cold tap in the bathroom prior to installing a mixer shower.

The water pressure test gauge I've bought only has a connector suitable for washing machine taps.

Can anyone suggest a pressure tester or adapter I can use that isn't gonna cost a fortune when I'm only likely to use it once!!

Regards...
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Postby plumbbob » Fri Jun 11, 2010 9:52 pm

chewy69 wrote:Can anyone suggest a pressure tester ......


How about your thumb?? It's free, and you can use that over and over again.

Seriously though, why do you need to test the pressure in the bathroom pipes anyway? If your system is low pressure, it probably won't even register on the gauge you've got. I guess what you are really after is the expected flow rate of a shower you want to fit?

Remember though, pressure alone isn't always the sole factor in deciding which shower to fit. You have to consider flow rate too. As the flow increases, the pressure will fall. Flow rate depends on the head of water (pressure), diameter of pipe and length of run.

What exactly are you trying to find out?

Oh, and I was serious about the thumb!
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Postby chewy69 » Sat Jun 12, 2010 9:59 am

We have an unvented high pressure system - Hot water tank only -

I wanted to see if the pressures coming out of the hot and cold are the same before I install a thermostatic mixer shower - the instructions on most thermo mixer showers I've seen state that the pressures must be equal for it to operate effectively.

I also need to check flow rate but I can do that with a timer and a bucket !!

I was going to tee off a feed from the hot and cold going to the bath; my reasoning being that you tend not to run the bath and the shower at the same time and I don't want to start pulling floors up in a new build house to get to other pipes.

Cheers..........
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Postby htg engineer » Sat Jun 12, 2010 5:02 pm

Take taps off, or disconnect at service valve, fit washing machine valve (only 15mm compression) and connect pressure gauge. Or better - if you have hot a cold washing machine valves at the washing machine check it there - the pressure will be the similar throughout the house - only the flow rate will change.

If the tap says minimum 1 bar pressure, and you have 3 bar at washing machine - it'll be ok.

Some taps and showers will specify a minimum pressure - I take it this is why you want to know.

Using your thumb wont tell you the pressure, unless you've been doing it for years it may be a good guestimate but I doubt it'll be accurate.

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Postby plumbbob » Sat Jun 12, 2010 8:35 pm

chewy69 wrote:
I wanted to see if the pressures coming out of the hot and cold are the same before I install a thermostatic mixer shower - the instructions on most thermo mixer showers I've seen state that the pressures must be equal for it to operate effectively.



Pretty much all mixer showers these days are designed to work with combi boilers or high pressure systems like yours where the hot side will almost certainly be at a lower pressure than the cold. Some shower valves are a bit picky about the difference, so the manufacturer supplies them with yellow or green flow restrictors that you can fit to help maintain equal flow.

When the manufacturer refers to "equal pressure" they are often referring to the vast difference between high and low pressure supplies and not to the small differences found in high pressure feeds.

I would suggest examining the instructions to see what variation can be tolerated and if this is not mentioned either as a figure or as a list of suitable installations, give the manufacturer a ring and ask them.
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