Is this a flow or pressure problem ?

[DiyNutJob]

Thank you all for your help and comments. I have now fixed the problem.

It turned out there was considerable amount of debris in the double check valve. There was a piece of gravel that was blocking at least half of the flow, and a chip of wood that was blocking the other half. Added into the mix was sand, and some black material resembling the stuff found in water filter cartridges, except these black particles were bigger like sand grains. After I replaced the double check valve, and ran the taps, there was quite a bit of the black particles coming out of all of the taps. Then it was cleared after a while.

I am pretty there are a lot more debris in the mains supply. But I didn't have the right equipment and parts to run the mains clear. So after a bit I imagine my new valve will also get blocked. That's something I will deal with next time.

For now I have more or less the full water flow back. But I have a few more questions I am not sure about:

1. The old double check valve had one of its valves physically removed by the original flat builder/plumber. I can guess that was done to reduce restriction. Now that I have put in a normal double check valve, would I have introduced more restriction ? What is the restriction difference between a single and double check valve anyway ?

2. I didn't have any tools to remove the old pipe olives. So I just reused the old olives and check valve nuts. The original valve was chrome with chrome nuts. My new valve was brass. Are the old chrome nuts chemically compatible with the new brass valve or will I get a bad chemical reaction at some point ?

3. Although the water flow is now great, at least for one tap. While the large bath tap is open, the flow on other taps are weak, but better than nothing anyway. What is the normal expected flow rate for a straightforward 15mm pipe-work ? I still haven't measured my flow rate yet. But I am interested to see how that compares to the expected rate in an ideal circumstance.

 

[Madrab]

Glad it's sorted DIY but lol the plot did thicken there, you never mentioned anything about a check valve on your mains inlet prior to this.
Wondering why there's a checkvalve on your mains inlet if it's only 2 sinks and a bath connected to the mains? Both the sinks and the bath have AUK2 air gap backflow prevention by design so there's really no need for a check valve to be on your mains supply as it enters your premises IMO. If a check valve should be anywhere it should be just before the isolation valve of the outlet it is to protect.
Check valves reduce flow by their very construction (sprung valves) as can isolation valves unless they are full bore types, just look down the end of a 15mm isolation valve, it narrows to about 8 mm at the centre.

The chrome is only plate, the actual valve and nuts are brass no issue with sacrificial corrosion.

Flow rates vary hugely around the country, time of day, type of taps etc. E.g my sink tap, pillar mixer type, ceramic cartridge/aerator, 15mm pipe/ iso valve, flows at 12 ltrs/min but my bath tap, 3/4 mixer tap flows at 15ltrs/min, this is all at 2.5bar. If you really want to know contact your supplier, they may be able to advise.

 

[DiyNutJob]

I didn't know how a check valve worked until the day before when I went to B&Q and looked at an opened sample. Then things started to make sense. Prior to that I kept thinking it must an air lock and so didn't mention it in my first post. I did mention it in a later post though "Mon Aug 12, 2013 11:42 pm". But it doesn't matter we all miss some details.

My bathroom toilet cistern is also mains fed. I presume this could be the reason for the check valve, unless it has its own check valve. But from what is visible it just has an isolating ball valve.

The check valve is immediately connected to the mains stop cock and on the outlet side (towards my taps) of the stop cock. I imagine each of the flats has one to prevent contamination of the shared mains source. It also make sense now the builders deliberately removed one of the valves in the check valve to not hinder the flow too much. Clearly it must have been a known problem for them. So they cheated by putting the check valve in to pass a regulation of some sort and then modified the valve to allow water to flow more freely.

Thanks for your flow figures. At least now I have something to compare against. Although my flow will probably match yours on a single tap. The flow is just not so great when two taps are open and that I can attribute to the check valve having too great a restriction. When I first looked at a check valve at B&Q, I was quite shocked how small the hole was.

 

[Madrab]

Yep, I did miss that but again your toilet will have an air gap to avoid back-siphonage/pressure. This was probably incorporated as best practice for whole site protection or the water supplier had stated zone protection was required. Usually more likely in commercial rather than domestic situations unless there is a real risk of contamination from category 2 fluid or higher.

 

[DiyNutJob]

It's easy to miss. I never thought anything of it all along. I did wonder what that thing was on the pipe and did think maybe there was something wrong with it. I tried to turn that screw/bolt in the middle of the valve, found it extremely tight, gave up, and never considered it again.

I think flats are commercial in nature. The managing agent certainly makes a huge meal from us. They send their plumbers around every year to check stuff and often create leaks from flats above to generate insurance claims where the agent takes a percentage. Last time they played dumb about my flow. They'd take an arm and leg off me if I get them to fix it.

I am glad this episode is over, and feel I have a slightly more control over my fate. But I have plenty more plumbing niggles in another house I live in. Mayhaps you will have more insights for me. Thanks again for your help. It was the fastest help I ever received in my life long use of forums of all kinds.

 

[DiyNutJob]

Happy ending.

I decided to redo the job. Having removed the new double check valve, I looked inside and found another piece of gravel jamming open one of the valves. So I rigged up a temporary pipe work to allow the mains feed to flow unhindered. The water pushed out more gravel. I ran the mains quite a bit until I was convinced no more debris was coming out.

Then I decided to put the old check valve back in having cleaned it up and noted it was still functional, although I had no way to tell the condition of the valve seal rubber. It looked ok.

I measured the flow rate at the bath tap since it gave the maximum flow:

With the new double check valve plus a small piece of gravel: 17.65 litres/minute
With the old builder tampered check valve: 18.3 litres/minute

If anyone ever wants to know the flow rate difference between a single and double check valve, in my case, going from double to single increased the flow rate by 3.6%. I found this difference to be perceptible at the tap.

Now, when fully opened individually, the flow and pressure at the bathroom sink and kitchen taps are so strong, the water is splashing out of the sink. With all of the taps open and the toilet cistern running a refill, the kitchen tap, being at the highest level, is still producing a passable water supply.

 

[Madrab]

Happy Days...Job's a guddun