Water pressure and accumulators

[Martin Pentreath]

I'm still looking for a way of improving my water pressure and rate of flow (barely over 1 bar and 11 litres per minute).

Thames water have given me a price of £1400 to replace the furred-up

0.5" lead communication pipe from the main in the street to the boundary of my land with 32mm MDPE. This could be the ideal lasting solution, although there is no guarantee that the pressure in the main in the street is that great, so I can't be sure that the rate of flow would be increased all that dramatically.

My plumber has suggested putting an accumulator in the cellar as an alternative. I've googled for information on these things, but I don't seem to be able to find anything very useful. My understanding is that an accumulator is a large cylindrical tank fed from the main with a pump which pressurises it so that everything fed from the accumulator is at decent pressure, is that right? Does anyone have any experience of these things? The plumber reckons that it would cost about £500 to install. I'm tempted to go ahead with this, but I'm a bit put off by the idea of a noisy pump whirring away underneath the living room floor every time anyone opens a tap.

[Christian McArdle]

Measure the static pressure of your system over time when you aren't drawing water. This will give you some idea of how the main is responding to demands of other nearby users. If it stays consistent and at a reasonable value (over 1 bar), then provided there are plenty of other users on the same main to make it a good test, it suggests that plenty of water is available, if you can install a large enough pipe to tap it. If the pressure often drops below 1 bar (especially during morning shower rush), it suggests that the main really isn't up to the job. When taking measurements, ensure that no water is being drawn, such as by a loft tank or toilet cistern.

Christian.

[Set Square]

If there's plenty or static pressure, but a poor flow due to a restricted supply pipe, I wonder whether you would need a pump if you were to use an accumulator. I admit that I don't have any experience of these things, but if you had a large sealed (pressure capable) tank fed from the mains through a non-return valve, and connected to a pressure vessel similar to the type used on sealed heating systems, but much larger, you should be able to satisfy short duration high flow demands from this - and it would re-charge itself at its leisure. Depending on the actual static pressure in the mains, you may need some device to cut the mains feed off when the accumulator pressure reaches a specified value - but that doesn't sound to me like rocket science!

Anyone know whether such systems exist?

[Andrew Mawson]

furred-up

lasting

accumulator

experience

restricted

things, but

accumulator

Pumps and accumulators sound complicated and liable to fail in the future.

I don't know how long your 1/2" lead pipe is, but if we are talking of a normal front garden senario, digging a trench and laying the blue MDPE is a fairly straightforwards job. The pipe is dead cheap and easy to terminate. A navvy for a day (perhaps £100) and maybe another £100 for the pipe and fittings. When I had to do this at my last house I dug the trench myself before going to work and left a plumber to do the connection. Now (a few years later !) I'd do it the other way round. I had to pay the local council a 'disturbance fee' to make good the pavement but it wasn't very much.

You may well be able to 'mole' the pipe without digging a trench (a pit is dug at both ends and a special air operated device rams it's way from one to the other dragging the pipe behind it). Specialist conntractors and Hire Shops have them

AWEM

[Aidan]

I believe that, if you have replaced the lead water pipe on your property, then the water supplier 'can be required' to replace their lead service pipe. I got this from the OFWAT website. I think this was a government initiative from a few years back. I was unable to find any details about how one would 'require' the supplier to replace their lead pipes, or who would do the requiring. Even if they did replace the lead service pipe, they may still want a wad of cash to upgrade it from say 20mm to 32mm. If anyone's got more info, I'd be grateful to have it.

I'd also check your neighbours' water pressures, it may be a damaged pipe or fitting on your supply.

My understanding is that accumulators will remedy low flow rate (i.e., restricted pipe ) but not low static pressure. An accumulator is the big brother of the bladder expansion vessels, most commonly seen on sealed heating systems. They have a volume of 100, 150+ litres, as against 6 or 12 on most domestic heating systems. The water accumulates in the bottom of the vessel, at a low flow rate but over a long time, compressing the gas charge in the top. On opening a tap, you get the benefit of the additional flow rate propelled by the accumulator's gas charge until the accumulator pressure has dropped to equal the mains pressure (which will have dropped, because of the draw off). The flow rate diminishes as the gas expands.

A pumped system can remedy both low pressure and low flow rates, but you have to have a storage cistern or break tank on the mains, upstream of the pump. Do a Google for pressurisation units (or pressurization units for those who are Yanks, pedantic and/or correct). The pump draws water from the tank and is switched by a pressure switch. There's usually an accumulator/ bladder vessel downstream of the pump, to reduce the number of on/off cycles caused by small volume draw-offs.

[Ed Sirett]

Accumulators solve the problem when the pressure is OK sometimes and bad at others (like at 7am when everyone is running a shower). They do not have pumps. AFAIK

If the pressure in the main is over 1 bar 32MDPE will be a very good flow.