water flow rate to cold supply

[suluki]

What is the best way to test if the water flow rate from the cold mains is correct.

I know it should be set at 3bar mains cold supply and if it is higher, a pressure reducing valve can be fitted and adjusted to 3 bar.

My way of thinking is that if the cold water tap when turned on is splashing out of the sink then it is over pressurised at a ruff guess,(which i have been told this way should not be used as this way, even if water is splashing out of the sink means the mains is over pressurised. but how can i find out the exact flow rate, (in bar) when the cold mains is turned on at the tap.

OOps and one more question, what is cp3 used for regarding gas certs


Many thanks

 

[kevplumb]

flow is measured in litres per minute

pressure is in bar

see how long it takes to fill a 10 litre bucket

CP3 is a warning notice

 

[suluki]

thanks agian kev

 

[Agile]

Whilst Kevin has defined the units, he has not mentioned that the water supply pressure is set by the water supply Co and will vary over the day inversely in proportion to the demand.

If the pressure is over about 2-3 Bar then a pressure reducing valve could be considered.

Alternatively, an isolating valve on the supply to each outlet is good practice and this can easily be partially closed to restrict flow. I do this as a matter of course to ensure the flow is not excessive but particularly to ensure that sensitive showers are not affected when another demand occurs.

There are also automatic flow restrictors with different flow rates.

Tony Glazier

 

[chrishutt]

Tony, don't you find that using isolating ballvalves, partially closed, to restrict supply to individual outlets results in excessive noise generation? I know that there are special isolating valves available that take flow restricting inserts, but these are at least 10 times the price of normal iso. valves.

 

[Agile]

Yes, I agree in theory but in practice the sound of a splashing kitchen tap overides the slight sound of the water flowing through an isolating valve underneath the unit.

If the local supply pressure really is high then other solutions may be needed. I mostly work in London where 1.5 bar is pretty lucky!

Tony

 

[chrishutt]

In my area of Bristol pressures of between 2 and 3 bar are normal, so noise generation can be quite a problem, as well as splashing from taps, particularly into wash basins. But the high pressures are good for showers of course, so using pressure reducing valves has a down side.

Ideally I would like to find a source for those little flow restrictors that are fitted in combi boilers and shower valve inlets, usually colour coded according to the flow rate, and fit them into tap connectors.

 

[traineegasman]

how can i find out the exact flow rate, (in bar) when the cold mains is turned on at the tap.
Many thanks

Ego`s aside fellahs, could anyone give an answer

 

[chrishutt]

Suluki seams to be confusing flow rate with pressure.
the flow rate is easily determined, as has already been said, by seeing how long it takes to fill a bowl or bucket of a known capacity. So if a 5 litre bucket fills in 15 seconds, the flow rate is 5 x 4 litres/minute.

The pressure measurement requires a pressure gauge, and the distinction must be made between static pressure, when no flow takes place, and operating pressure when a certain flow occurs. So a high static pressure does not necessarily mean high flow rates.

 

[traineegasman]

Or if all else fails....ask your local authority/ water supplier.....they may have an inkling..

 

[Slugbabydotcom]

how can i find out the exact flow rate, (in bar) when the cold mains is turned on at the tap.
Many thanks

Ego`s aside fellahs, could anyone give an answer

I find it quite pleasantly strange to find TGM focusing on a question but here is the answer that suluki was looking for. Apart from the 'flow rate isnt measured in bar' thing of course.
When you have finished with it just flog it on ebay.

 

[traineegasman]

Very kind of you to answer...next time.... just answer the question directly to the person posting... no need to get personal...I never asked the question & didn`t invite you to answer me personally...saves problems in the future

 

[Agile]

Chris Hutt, the flow restrictors are available, I am not sure where but someone else can probably tell us.

I think they are about £6 each and come in a 15 mm compression format in a small range of flow rates, 6 and 10 li/min seems to ring a bell.

If your inlet pressure is 2-3 Bar then I would have thought a pressure reducing valve to 1.5 Bar would have been useful and still give a very good shower.

A lot of people seem to forget that its the pressure at the shower head that matters and 1.5 Bar would be very good.

The problem is London is that most houses have a pressure of about 1.3 Bar static and an open pipe flow rate of about 12 li/min. As a shower needs about 0.5 bar working pressure to give good jets then this is never achieved.

I always advise people to measure the flow rate whilst retaining 0.5 Bar working pressure. In London this is often as low as 5 li/min due to the resistance of the old lead pipe and stopcocks.

As part of the installation of a combi boiler I always replace stopcocks with full flow lever valves to reduce the resistance. I also remove flow restrictors in the boilers too. This gives a very significant improvement in DHW performance.

Tony Glazier

 

[chrishutt]

Tony, I know about the valves with restrictors that you mention, made by www.cottampreedy.co.uk/, but at around £6 each (compared to 40p for normal isolating valves) I don't think I can just carry a handful around with me. All I require is the restrictor insert, which could be inserted into the tap connector joint.

 

[Agile]

Many combi manufacturers have the insert within the boiler.

The vaillant 242 has one behind the funny nut from the plate HE to the diverter valve. Brown or yellow depending on boiler output perhaps. the Puma has one in the CW inlet too.

Unfortunately buying it as a Vaillant spare will probably still be a few pounds and may not conveniently fit anywhere in your pipework.

They are however a failure point as I have encountered some in boilers where the rubber "O" ring goes spongy and reduces the flow.

Tony Glazier