Pressure and water main upgrade

[Martin Pentreath]

Dear all,

I'm thinking of having an unvented cylinder installed to improve my hot water supply. I really need to get the water main upgraded though. The current pressure/flow rate (and I've never fully understood the difference) is pretty poor. I can stop the flow of water at my kitchen tap with my thumb.

Thames Water say that the minimum which they are obliged to supply is

1 bar, but they've said on the phone that if I can do the thumb-on-the-tap trick then my pressure is probably too low. The only means I have of measuring pressure any more accurately is using the presure guage on my boiler when I fill the radiators from the mains. This registers a pressure within the system of a about 1.5 bar. Is this a remotely accurate way of measuring mains pressure? I understand that this is measuring (if anything) static pressure. Is that what Thames Water's 1 bar minimum refers to I wonder. Maybe I just have very strong thumb muscles.

What I would really like is for the old 1880 0.5" lead communication pipe from the main in the street to the stop valve at the boundary of my property to be replaced at their expense. The main runs on the other side of the street, meaning quite a lot of digging or moling, and for me to pay for the work would run into four figures I think. I've also tried the lead-pipe-complaint technique, but they say that the pipe will be sufficiently scaled by now not to be a problem (in fact I guess that's why the flow is so bad, it's probably got an internal diameter of about 3mm!).

Any hints or tips on this? Anyone who can save me £1,000+ is entitled to the resale value of all the reclaimed lead ;-)

[Christian McArdle]

Pressure is not really as important as the flow rate. Anything over 1 bar is easily sufficient for a nice shower. However, low pressure can be indicative of a problem that will also lead to poor flow, which really is a problem.

Have you measured the flow rate from your kitchen/garden tap? Ensure that all stopcocks are wide open before the test. Modern kitchen taps may have narrow passages that lead to artificially low readings.

Flow is easily measured by timing the filling of a bucket of known size.

< 20lpm - don't bother 20-40lpm - OK, but you won't get the full benefit at the lower end

Sometimes they do special offers where they'll replace the lead up to the street stop c*ck if you replace the lead up to the house stop c*ck. It may be worth asking.

It is certainly worth replacing an old 0.5" supply, lead or not. It won't affect the static pressure on your supply, but it could vastly improve the flow rate, if the street main itself has enough capacity to supply it.

If you do replace, ensure it is done in no less than 25mm MDPE. 20mm MDPE is not acceptable. >=30mm MDPE would be nice, but not really necessary.

Christian.

[Andy]

I guess the following assumes a little understanding of electricity.

I was once told, and it makes sense to me, that pressure is like voltage. The higher the voltage (pressure) the more current (water) will flow through a given circuit (pipes and taps).

So given the same network of pipes and taps a higher pressure will result in a higher flow rate, flow rate being the amount of water that comes out of the tap over a given time.

If you close a tap a few turns you increase the resistance but the pressure remains the same so the flow rate will reduce. So the tap is like the equivalent of a variable resistor. If your were to then increase the pressure then the flow rate would go up again.

With electricity a given bit of wire can only carry so much current before it melts. I assume that there is an equivalent maximum in water pipes but the pipes probably burst rather than melt ;-)

[Martin Pentreath]

"Christian McArdle" wrote in news:41dd6b61$0$16586$ [e-mail]:

Hmmmmm, just done it, 11 litres per minute at the kitchen tap (and it's not a modern one), well within the "don't bother" band. I've got the Thames Water man coming round to check out the pressure sometime soon. Is there any way that this sort of flow rate could be regarded as acceptable?

[Christian McArdle]

If your flow really is 11lpm and there were no restrictions, like modern taps or half closed stopcocks, then you simply won't be able to use a mains pressure hot water system of any description. It is, however, within the specs of what they are allowed to supply.

The way to fix this is to replace your connection to the mains with modern

25mm MDPE pipe. This won't be cheap and depends on the street main being reasonable, too.

If you think the water supply will be upgraded in the future, you can still fit the unvented cylinder, but run it off a pumped tank in the loft. It's a waste of money to do so, though, unless the supply really will be upgraded in the future.

Christian.

[Lee]

Having high water pressure doesn't guarantee a high flow rate, for example the static pressure here is over 7 bar but there is a significant amount of air in the water and the flow rate is only around

40 lpm. 'Tis noisy too, but the 15mm pipework probably contributes to that...

Lee

[Christian McArdle]

Well, 40lpm is plenty, really. Enough to fill a bath in 3 minutes. The 15mm is probably limiting it, though.

A good static pressure usually (but not always) indicates that the street main is well stocked with water if your house's plumbing is man enough to take it.

Christian.

[Lee]

With cold anyway... ;)

Ah, well there is a fire hydrant about 100m away that might have something to do with it ;)

Lee

[Christian McArdle]

Or hot.

40lpm per minute is a bath full in 3 minutes. Whether you choose to heat it or not is up to you!

Christian.

[ARWadsworth]

What are Water Companies allowed to supply?

I have recently had Yorkshire Water round to test my supply. It turns out I have 6 bar pressure and 4 (four) lpm flow. The stoptap on the street controls 4 houses. Within 24 hours of the test in my house YW have dug the pavement up and replaced the street stoptap to allow them to measure the flow on the street. Well over 50 lpm at the street stoptap was the somewhat imprecise result. It is now down to me to change my supply and so I now have to start digging.

On the plus side YW have agreed to connect the new supply up for free.

Adam

[Martin Pentreath]

"Christian McArdle" wrote in news:41de53c6$0$16585$ [e-mail]:

Thanks Christian. You're right, I spoke to a not-very-helpful woman at Thames Water today who said that so long as the flow was above 9 lpm then it's not their problem. They'll upgrade the communication pipe, but only if I fork out.

I've just posted an application form to get a quote for the work (in 32mm MDPE), but it looks like it will cost a lot, because as I said in an earlier post, it seems that the main in the street runs along the opposite side from my house, and they charge by the meter. The charges are £452 connection charge, £400 to disconnect the existing supply (seems like daylight robbery) and then £117 per meter to lay the pipe. Total bill will be well over a grand.

I'm planning on being in this house indefinitely, could be a forty years, so as I'm doing work I'm doing it properly. My front garden is all dug up at the moment, so this is the obvious time to be replacing the pipework. Although it will hurt, I don't mind coughing up the money if it means my baths will fill in less than twenty mins and I can use more than one tap at once. But I certainly don't want to do it only to find that the pressure in the street main is crap anyway, and I only get 15 lpm after it's all done. Any suggestions for predicting the likely success of the job?

Thanks,

Martin

[Christian McArdle]

Well, the static pressure gives a good indication of the potential supply, provided two conditions are met. Firstly, the static pressure should not vary excessively during the day, especially during peak shower hours in the morning. Secondly, the street main should be serving quite a number of houses, i.e. a surburban street.

If these conditions are met, then your supply is unlikely to affect the pressure at the main, and it will pump through as much water as your supply is capable of swallowing. 32mm MDPE can swallow a lot, even at only 1.5 bar.

I would buy a cheap water pressure gauge and attach to the rising main. Then log the pressure over the course of a few days, especially between 7am and

10am on weekdays (when you are not drawing water, as the pressure will fall dramatically). If it stays at or above 1.5 bar during this, then I would say the supply is probably worth a punt, as the street main is keeping up with demand.

Christian.