Water pressure out of kitchen tap - calculation

[John]

Can anyone show me how to convert static head of water pressure into delivery of water at the tap - or even better, please do it for me because I never was any good at maths :-(

First the numbers, then the explanation - it was taking 58 seconds to fill a 1-litre jug, so how many metres static head is that?

Explanation - United Utilities have fixed a problem on their "communication pipe" (whatever that is) that was causing us to have very low water pressure. According to their 'standards of service' (as pointed out to me by their own inspector), we may be eligible for 50 quid compensation and, given these tough economic times I thought "great", whereas in the past I may not have bothered. Anyway, I digress...

There wasn't enough pressure to open the solenoid valve of the shower and because there's always a slug of cold water in the pipes that has to come through first, it was taking seven minutes to get enough hot water from the combi boiler in the loft to fill the bathroom wash basin. We then had to stand in the bath and scoop the hot water out of the basin with a jug and pour that over ourselves every morning for 10 days.

So their 'standards of service' wording is:

"If the water pressure in our communication pipe falls below 7 metres static head twice within a four week period (each time for longer than one hour) we will automatically pay you £50 once per annum"

From first reporting low water pressure to UU, it took 5 days for an inspector to come out and have a look, and then another 5 days before the guys arrived to dig the hole and fix the problem - a total of around

240 hours.

Having just rung UU to see about this compensation, they first tried to weasel out of it by saying that we'd only had one period of low pressure within four weeks but to qualify for compensation we need two periods of more than one hour each - seems that one continuous period of 240 hours doesn't qualify, or so they are trying to say!!!

[Scott M]

Flow and pressure are two different things. You can't tell one from the other (tho I presume some rules of thumb might be used to take average uses of pipework, stopcocks & taps in a domestic environ and calculate an average flow restriction. From that you could have a stab at working a pressure from a flow rate.)

Anyway, the most useful thing you need to know is 1 bar (14 psi) pressure = 10m head. So their 7m head is 0.7bar which is Not Very Much.

Also, one litre / minute is Very Poor.

IIWY I wouldn't bother with numbers and just fight your corner that the water supply was unusable for long periods.

[John]

Thanks Scott, that's just what I'll do.

[michael adams]

What they seem to be saying there, is that if there's a problem, and their first attempt at fixing it doesn't work, to the extent that you can report two separate incidents of pressure loss or whatever then and only then do you qualify for compenation.

As worded there there is no compensation payable for any delay in their rectifying a problem.

Although that may be covered in a separate clause.

michael adams

...

[John]

Darn newsreader keeps cutting at strange places, sorry. Anyway, thanks for that Michael, I hadn't thought of it that way - think I'll post it in one of the legal groups and see what they think.

Cheers.

[Tim Downie]

While you're at it, shoot the bozo who fitted a combi in a house with such poor supply pressure. If ever there was a case for a storage tank system, you've got it!

Thinking about it, it's hard to believe that any plumber would have fitted a combi in those circumstances so have circumstances changed? Did your house ever receive a better supply pressure? Are your neighbours affected?

If they're not, you may have a problem with you plumbing. Have you checked that the mains water c*ck is fully open? Do you have a stopcock in the street that you can check?

Another simple test you could do is to hold your thumb over the cold tap. If the pressure builds to the point of forcing past your thumb then it's a flow restriction you've got rather than a lack of supply pressure.

Tim

Tim

[John]

You've got the wrong end of the stick Tim :-)

This was a recent problem (first water problem in 28 years) at our house and the neighbours at either side of us were unaffected. Now that the problem is fixed, it's taking about two seconds to fill that 1-litre jug instead of 58 seconds. What had happened (apparently) is that it's a (cast?) iron main running along the street and some sediment had dislodged and was blocking the point where our feed pipe joins the main.