Rising Main Water Pressure

[Vortex]

I'm looking to replace the section of water pipe within my house which is at mains pressure. I want to use Hep2O.

Out of curiosity I took a 10bar pressure gauge purchased from BES ages ago to measure the static pressure. I measured 9 Bar, approximately 90 metres of head!!!

Is this plausible??? Hep2O's only rated to approx 12 bar at room temperature. Could this be true? Could I have a dodgy pressure gauge? What pressure should I expect the mains water to be at?

Any ideas? I'm reluctant to use plastic at these pressures.

David

[Ian Stirling]

As a check. Connect a hosepipe to the end. Now, if the interior diameter of the hosepipe is 1/2", the area of this is (0.5^2 *3.14 )/4, or about 0.2 square inches. It will require a force of 90PSI*0.2 square inches = 18 pounds to keep your finger pressed against the flow, so that it cuts it off.

[Ed Sirett]

I have seen pressures over 7 bar but not often. If your house/road is somewhat lower than some of the surrounding area you may have quite high pressure.

When presures get over 6 bar you start to find that 'contract' quality taps will become apt to jam and wear quickly. Also the taps tend to have too high a flow rate, difficult to control and 'spit' at you.

It would be a sensible move to fit a pressure reducing valve to the incoming supply.

I take it the pressure guage reads zero when disconnected?!? 8-)

[Lee]

Ours, Thames Water, is around 9 Bar. It is quite aerated though, which means the plumbing is fairly noisy. As Ed said, we have had problems with "cheap" taps, although the ceramic mixers we have now have been fine. We have had to fit a pressure reducing valve on part of the pipework to help with the noise, and because the plastic valve in the loo cistern didn't take kindly to 9 Bar :)

Lee

[Vortex]

Thanks Ed (and others) for the feedback.

In no particular order:

• The pressure gauge seems fine and starts at zero. I could improvise some kind of "dead weight tester" with an old hydraulic bottle jack I have....but frankly life's too short!

• Our home is about 20-25 vertical metres below the highest in the area. OK that accounts for 2 to 2.5 extra bar!

• I *cannot* stem the flow from the end of a standard Hozelock connector (ID about 8mm) with my thumb.

• I have often wondered why hozelock connectors won't stay attached to my hose as they should.

CONCLUSION Purchase a pressure reducer and keep using Hep2O.

David

[G&M]

Or if you aren't on a meter consider driving a turbine with the excess head and cancel your electricity supply contract.

[Vortex]

G&M.......You got me thinking - here are the numbers and assumptions:

• Water pressure P (static head) is 90 metres

• Max flow rate is 60litres/minute = 1 litre/second. Call this R.

• Fudge Factor "F" = 0.25 (this is because in a dynamic situation I reckon I'd be lucky to get 0.5 litres/sec at 45 metres head)

• mechanical efficiency "M" = 0.5 (Efficiency of turning water energy into rotating mechanical energy)

• 1 litre of water has mass 1kg, g = 10 (gravitation acceleration)

• "E" = 0.5 (power conversion efficiency mechanical > electrical energy:

240V/50Hz)

So electrical output O of my imaginary machine:

O = P * R * F * g * M * E = 56 (in Nm/Sec = Watts)

...and I would use 0.5 x 60 x 60 = 1800 litres/hour of water ...1kWh would therefore use 1800/56*1000 = 32000 litres ...as it happens I am metered and water costs me about £1/1000 litres

So £32 per kWh versus £0.06 per kWh with my current supplier.

I think I'll keep the electricity supply contract for the time being...

David

[IMM]

Hep2O should be fine on the cold mains. Good quality plastic pipe (not Speedfit) is usually OK on a cold water pipe. using it on 9 bar with a 12 bar maximumm maybe pushing it too close. Polyplumb is only 7 bar max. Plastic tends to be more troublesome on hot pipes as they expand and flex. Having 9 bar mains pressure on the hot using plastic is something I would not be easy with. Best fit a pressure reducer down to a pressure you are comfortable with (a bit of trial and error here), without it being a nuisance. The only outlet you need high pressure is the shower, all the rest can be just above zero (the most desirable) as long as the flow is there.

[Andy Hall]

... remembering to read the instructions and use a pipe cutter rather than hacking with a hacksaw of course........ :-)

.andy

To email, substitute .nospam with .gl

[IMM]

Or remembering not to use it at all.

[Vortex]

Best fit a pressure reducer down to a pressure you are

Actually I did not tell the whole story in my original post.

I'm almost certain to be installing a heatbank later in the year, in which case the Hot Water will also be at high pressure.

I'm certainly not comfortable with the combination of this at 9 Bar and Hep2O.

In the wee hours this morning I ordered a pressure reducer from BES. I guess later in the year I'll see if this also impacts flow rate....and therefore heatbank efficacy for decent shower performance....that's for worrying about later.

Ho hum.

[IMM]

You could get a heat bank with two separate plate heat exchangers that operate independently of each other. One does showers only at full mains pressure, the other all the other outlets under a pressure reducer. Make sure thenplateb heat exchanger can take 9 bar. Most can do 10 bar at least.

Where the mains enters the house run a 22mm pipe to the shower plate heat excahnger. Before the plate tee off for the shower cold supplies. Take the hot pipe from the plate and the cold for the showers and install a pressure balancing valve. This will keep both hot and cold pressures balanced up atthe showers. All this can be around the heat bank.

Where the mains enters the house tee off and insert a pressure reducer. This does all the other oulets. Keep the pressure reducer as low as pssible to achieve a good flow.

The shower supplies will then take priority in a pressure/flow conflict.

Sorted.

[Fash]

OR.... why not fit 2 combi boilers, one to do the shower and one for the rest - also gives natural zoning to the CH and keeps certain group members happy, I hear 2x Worcester Bosch Juniors is an excellent solution to almost any problem!

Fash

[IMM]

Good choice and a worthwhile solution.

[Fash]

Thanks, good to know I'm still learning!! > >

[IMM]

And that you are. Keep it up. 6/10.

[Hepworth Plumbing Products Tea]

Hep2O is perfectly suitable in this mains cold water application even at pressures in excess of 9 bar. Hep2O is rated at 12 bar at 20 deg C, however there is a factor of safety built in to the pressure rating of

1.5 times, i.e. 18 bar, which is also the recommended test pressure for Hep2O systems.

Mains water service pipes to modern properties (and any refurbishments that take place) are invariable in blue MDPE pipe which is normally also rated at 12 bar.

For further information see

Hepworth Plumbing Products Team

-- Tel: [phone] |Hepworth Plumbing Products Fax: [phone] |Edlington Lane, Edlington Email: [e-mail] |Doncaster, UK

|DN12 1BY