gravity Hot Water & mains Cold Water mixer tap problem

[MarkB]

Hello,

I've got a problem with a mixer tap that has been recently installed.

It's a twin lever monoblock basin mixer that is fed by gravity for the HW and mains for the CW. As a result it is very dificult (imposible!) to balance the temperature of the HW. When the CW tap is opened it even seems to force CW back up the HW feed.

Has anyone used a pressure equalising valve in these circumstances?

I've never used one but it would seem to be ideal for solving this problem.

Thanks

Mark

 

[uug197h]

The supply of water and energy is one of our most critical National problems. If we cannot increase our supply, then it's imperative to reduce our consumption. Fortunately it has been proven that we can conserve dramatically and in a manner, which will not seriously affect the lifestyles we have become used to.

Water and energy conservation are so intimately intertwined that they are practically synonymous. Any reduction in the usage of water will automatically result in a reduction of the use of energy. What this means, therefore, is that our whole philosophy on the use of water is changing and we are finally recognizing that we have been water rich over the years and it is now time to get back to reality by adjusting to our actual needs and to practice good conservation principles.

In the UK mains water pressure varies considerably; older properties that have, not had, their mains supply upgraded may have less than 1bar of pressure. This is insufficient for most modern appliances such as the combination central heating boiler, which requires water pressures of above 1 bar to operate and receive an acceptable flow rate of water.

At the other extreme, where for example a new water main has been laid to service a new development such as a new Hospital or commercial estate, water pressures could rise to above 10 bar, this may cause damage to older existing installations due to the stress caused by increased water pressure on pipework and joints.

The average mains water pressure tends to be around 3 bar during the day and slightly lower at peak usage times. However as usage drops during the late evening and early hours the pressure rises, and has been known to exceed 10 bar.


What is a water pressure regulator?

A pressure-reducing valve acts as a buffer between the high water pressure supply and the system or appliance. The mains water pressure is reduced to the safe required level during flow or non flow conditions.

Also called water pressure reducing valves they are compact, inexpensive regulators that perform two functions: (1) they automatically reduce the high incoming water pressure from the water mains to provide a lower, more functional pressure for distribution in the home; (2) they "regulate" by maintaining a set pressure in the home usually 50 Ibs. thereby insuring that the home piping and appliances operate under a safe, more moderate, but satisfactory pressure.


The Watts DRV15E is a compact pressure reducing valve for domestic plumbing systems. 15mm compression fitting. Brass body. Nbr diaphragm. High impact plastic bonnet.

* Max. supply pressure: 375psi (25bars).
* Max. outlet pressure: 90psi (6bars)*
* Min. outlet pressure: 23psi (1.5bars)
* Operating temperature range: min. 1°C - max. 80°C
* Suitable for water, air, neutral gases and non corrosive liquids.F1/4" pressure gauge connection point.

* adjustable.


What is water pressure?

When a fixture i.e. a tap, shower etc in a home is opened and water flows from it, it is because the water is "pushed." This "push" is pressure. The speed at which water flows from the opened outlet depends on the amount of "push" or pressure which exists at that time in the system. In short, the higher the pressure, the stronger the "push" behind the water.


What is wrong with high water pressure?

High water pressure, which is generally considered anything above 60 Ibs., has some advantage, such as in firefighting systems. However, in the home plumbing system, it can be damaging because water, with a strong "push" behind it, can erode or wear away many materials and cause leaking water heaters, banging water pipes, dripping taps, dishwasher and washing machine noise and breakdown, and leaking water pipes.

Therefore, water flowing at a rate in excess of that necessary to satisfy normal fixture or appliance demands becomes damaging, wasteful and reduces the life expectancy of equipment in the system. But, probably most important to the average homeowner is that it can add to the cost of water, energy and waste water bills.

you may want to put a check valve in the HW side to prevent cold water feeding back up the hot water pipes

 

[MarkB]

Thanks for the promt reply uug.

I'd already thought about the check valve on the HW. The CW already has one.

I guess I could use a PRV but as the HW is at a relatively low pressure (approx 0.5 bar) I was wondering if an equalising valve would be more suitable.

Mark

 

[uug197h]

pressure reducer is about £45 and you would need to balance the supply manualy, the equaliser is around £70 and it will balance the pressure its self there both easy to fit but with the equliser you can get heat transfer so you may get warm water from the cold supply if you have had both running and then you just want cold

 

[MarkB]

Thanks uug.

BES do an equaliser for £35.00 so I may give that a go first

Mark.

 

[Bernie2]

Is the tap a bi-flow? They where designed to stop the problems you seem to be having. In the past with stored water systems the problem was very common.
It may be quicker to change the tap if its new and can be sent back.

 

[MarkB]

Is the tap a bi-flow? They where designed to stop the problems you seem to be having. In the past with stored water systems the problem was very common.
It may be quicker to change the tap if its new and can be sent back.

Bernie2,

By bi-flow do you mean like a kitchen tap? - ie. the outlet is split for H & C.

It's a monoblock basin mixer with in-body mixing - hence the problem. An isolating valve has been fitted to restrict the flow from the cold and it has helped somewhat but has not completely solved the problem.

Mark

 

[Bernie2]

Mark

Yes! A split flow if you like. As you know there have been many revisions to the water regs over the years. The old water Regs did not ask for none return valves on the cold main. So it was easy to get cross flow problems. The regs asked you to fit a Bi-flow mixer, some time in the sixties or seventies, but usually only on the sink unit as this was usually the only tap in a house that had a direct potable water supply.

Most of the bathroom cold water was off stored water, but not always, it depended on local by laws. In some areas you may well have been required to fit NRV's on the main.
The mono-blocs had just come out and even if fitted both the hot and cold water where equal pressure off a shared stored storage cistern, usually about 60 gallon actual, 70 gallon nominal, the difference in capacity being the space over the actual water level in the cistern required for ball valves and overflows. (some call it a tank, but its officially a cistern).
You can get bi-flow mono blocs by the way, I did a web search just to check.

Now it's universal regs, so nrv's are fitted, to stop what is happening in your mixer. I think we sometimes forget mains water is a food stuff. It was a far simpler system and perhaps more repair proof than nrv's. But it had problems. Some washing machines where fed through a hose that fitted over the mixer nozzle and combined flows and so cross flow could occur.