What is a Pressure Limiter Supposed to Do, Exactly?

[Geflugenmitt]

Hello,

We had major plumbing work carried out last year. Mains pressure is very high here (10 Bar I think) so the contractor fitted a 3 Bar limiter after the stopcock. I would have expected (possibly incorrectly) that this would 'regulate' rather than 'limit' the pressure to 3 Bar. I come from an electronics background, so anyone who understands what a constant current source does will understand what I mean - it will keep the flow the same under a changing load.

So, when I open a tap, I would have expected the limiter to ramp the flow up to compensate. What actually happens is that I get an initial gush from the tap, but it then tails off to a relatively pathetic flow. This means filling a bath takes 20 minutes. Worse, it means that whilst that bath is filling, other taps in the house become next to useless.

Is it really to be expected that my wife can't wash her hands upstairs whilst a bath is running, or that I can't fill a kettle whilst someone else is using a hosepipe? I have never lived in a house before where this is the case. Is the limiter faulty, or is this normal behaviour?

NB: All our water is off the mains, there is no cold tank. The hot water cylinder is unvented, so again is using mains pressure to feed the taps.

Thanks.

 

[bernardgreen]

Quite common

The pressure limiter / regulator can only function properly when there is a flow of water through it. With no flow the pressure after the regulator builds up to be the same as the supply pressure. ( in electronics the same effect as a voltage regulator with no drain / connection to 0 volts, the voltage on the output will be the same as the voltage on the input when there is no current flowing through the device ).

Hence the water in the pipe work is at the supply pressure until a tap is opened and water flows.

Just one more adverse effect of removing cold water storage tanks from plumbing designers list of options

 

[picasso]

If your contractor has put the pressure reducing valve just after the stopcock (which is probably part of the unvented cylinder setup) he may have put the filter (again part of the unvented cylinder setup) there as well, the filter can be cleaned out, can you post a picture of the valve and pipework around it ?

 

[simond]

The gush you are getting is from the expansion vessel in your unvented setup, in electronics parlance you would describe this as a capacitor.

You can have a high pressure but a poor flow rate, this is what you have described.

If this effect you described is ever since the unvented went in, then it won't be dirt in the filter(s); but if it has since occurred, then the dirt is a prime contender.

 

[Dan Robinson]

Just one more adverse effect of removing cold water storage tanks from plumbing designers list of options

Yeah, because crap pressures/noisy pumps, leaking cisterns, stagnant water, dead squirrels rotting in the bottom of the cistern, frozen pipes and all that extra pipe work are sky high on my list of design options.

 

[Servotech]

Is there a gauge fitted on the pressure reducing valve so that you can check if the valve as been set properly? I've been to quite a few that have been reduced far too much or not enough in some instances.

 

[stardanny]

It is nothing to do with pressure, as long as the pressure is stable at 3bars. It is do with flow rate. Something is affecting, reducing it.
Did you check the stopcock is fully open?
Is there a filter, if yes, check that it is clean.
Or worse, there is a leak on water main underground.

Daniel.