Tap pressure OK then decreases

[tomfromfife]

Hi.
Before I start taking things to pieces I thought I would check with the experts.

I have a renovated cottage with all new plumbing from the cold water mains. The system is mains pressure. There is a stopcock, filter, check valve and pressure reducing valve with a gauge. The mains pressure into the property is around 5 bar. The PRV is set to 3.5 bar with no taps on.

When a hot or cold tap is turned on the pressure is good at the tap then reduces after a short time (about 5 seconds). The gauge on the PRV reduces to around 1 bar when a tap is on. On turning the tap off I can hear what sounds like the pipes repressurising for a few seconds.

2 questions...

Could this be the filter partially blocked or a PRV problem?

Normally, would the gauge on the PRV show set pressure of 3.5 bar when a tap is on or would it normally show less than the set pressure?

Thanks

 

[DeltaT2]

Hi Tom, I hope the weather in Fife is better than Glasga today!!
Tom, the only advice I'll give you is call in a Plumber that has an Un-vented cylinder ticket G3. As those of us with that qualification are the only people that can repair your fault. If you can't get a recommendation from friends or family, look on the SNIPEF web site for someone in your local area.
HTH

 

[tomfromfife]

So that's the answer - call a plumber!

OK, let's say, out of interest, it's a vented system with a kitchen tap directly on the cold water mains and the kitchen tap is ok when turned on but the flow reduces after 5 seconds. Where would you say the problem is, assuming the same setup on the mains - stopcock, filter, check valve and pressure reducing valve.

 

[simond]

Tom

You already have an unvented system so there is little chance of you creating a dangerous situation unless you substitute incorrect parts.

The pressure boost is caused by the expansion vessel air gap returning to atmospheric pressure.

Your loss of flow will be, as you say, a blocked strainer or a diminished water supply (eg: leak down the road or flattened pipe).

 

[DeltaT2]

Tom

You already have an unvented system so there is little chance of you creating a dangerous situation unless you substitute incorrect parts.

The pressure boost is caused by the expansion vessel air gap returning to atmospheric pressure.

Your loss of flow will be, as you say, a blocked strainer or a diminished water supply (eg: leak down the road or flattened pipe).

But he still can't touch his UVC without a G3, sorry Tom but you need a Plumber with an un-vented ticket.

 

[DeltaT2]

You already have an unvented system so there is little chance of you creating a dangerous situation unless you substitute incorrect parts.

You don't know what Tom intends to do, so you can't say it's safe for him to touch anything!!

 

[tomfromfife]

I checked the inline filter and it was as clean as when new. There is also a filter in the Comap PRV I believe. Maybe that's causing the problem although I don't see how anything muck will get through the inline filter to block the PRV filter.

Anyway, I'll probably get a plumber in but can you answer 1 question... I the PRV is set to 3 bar, should the gauge drop to 1 bar when a bathroom sink tap is turned on? I have 2 houses at the moment and the house I am staying in shows only a small reduction of about .5 bar on the gauge when a tap is turned on.

Thanks for your advice guys.

 

[tomfromfife]

Anyone got an answer to my last question...
If the PRV is set to 3 bar, should the gauge drop to 1 bar when a bathroom sink tap is turned on? I have 2 houses at the moment and the house I am staying in shows only a small reduction of about .5 bar on the gauge when a tap is turned on.

Thanks

 

[ianblue]

Tom, your pressure gauge is showing 3bar. That is static pessure. If for example you had an almost complete blockage before the PRV . the gauge would still build up to 3bar . However if you the turned the tap on the pressure would fall dramatically because of the partial blockage the water could not get through fast enough.
Ergo you simply have a restriction somewhere before the gauge.
I do hope this explains it clearly.
Good luck
Ian

 

[tomfromfife]

Hi again,
The filter was removed from the PRV to clean it. It was clean.
It was reassembled and the problem has gone away! It was definitely clean when the filter was removed.

Here's my theory...
The filter is circular with a 'weld' where it joins and the filter is flatter where the join is. If the join is lined up with the outlet hole inside the valve it restricts the flow, hence the problems I was having and the problem going away when the filter was removed and refitted. I didn't notice where this join in the filter was when I removed it but it sounds feasible.

What do think?

 

[ianblue]

Hi Tom well it sounds as though you have cleared the restriction. Great!
Always nice to hear someone's problem has been resolved.

 

[tomfromfife]

If the PRV is set to 3 bar, should it drop to 1 bar when a basin tap is turned on?

 

[Weedrip]

If by 'a basin tap' you mean one 1/2" std basin tap then no.

hope that helps.

regards