Fresh Water Plumbing Issue?!

Dougal

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Had to replace our fresh water pump, and in doing so, now have some issues… The hot and cold systems are not separate – there was always just a ‘Y’ connector supplying a cold feed to the hot tank. I’ve never really needed an accumulator tank, as the hot water tank is on its side, and thus has a large airspace at the top, making for a really smooth pressure system.

However, to remove the possibility of water on electrics, I moved the new pump to another (lower) location. The pump is still above the main tank as it was, but now slightly lower than the hot tank. I then noticed that a substantial amount of hot water was finding its way to the cold taps, so placed a non-return valve in the hot tank supply. That stopped the problem, only now I’m going to need an accumulator in the cold system to stop that from pulsing. Until then, the mixer tap is now pretty useless, due to the pulsing cold pressure.

The biggest problem though, seems to be that the pressure switch/sensor in the new pump (Jabsco Par-Max) is obviously very different to the old one, as the hot side now has very large, and very slow pressure fluctuations. The hot tap can now run for around 5 seconds before the pump starts, staying on for the same after closing it

I’d be very grateful for any advice as to how best plumb this system?

As always here, many thanks.
 

RichardS

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The biggest problem though, seems to be that the pressure switch/sensor in the new pump (Jabsco Par-Max) is obviously very different to the old one, as the hot side now has very large, and very slow pressure fluctuations. The hot tap can now run for around 5 seconds before the pump starts, staying on for the same after closing it

Unless I've misunderstood something, I'm not sure why that is a problem? :confused:

Richard
 

RichardS

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Because the hot water flowing through the mixer tap varies enormously, making for 'shrieks and shouts' coming from the heads/shower;-)

OK. I thought it was the 5 second thing that was the problem. If the pump is in the cold feed close to the water tank before the hot water system is t'eed off then when the pump runs it must surely pressurise both the hot and cold systems equally unless there are different sized pipes or a restriction somewhere in one side or the other. I believe that this is the way all these systems work.

When the hold and cold water arrive at the mixer tap they should therefore be pressure balanced. I don't therefore understand where the hot water is feeding into the cold water system which means you need a non-return valve which seems to be causing the temperature variations.

Sorry I can't be of more help but I find it difficult to visualise what is going wrong.

Richard
 

Norman_E

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Put an accumulator between the pump and the Y connector. You also need to get rid of any air in the hot water tank (calorifier) because it will cause fluctuations in flow from the hot tank as pressure varies in the system as a whole, leading to variations in temperature at the mixer tap and shower head.
 

VicS

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13 Jul 2002
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Had to replace our fresh water pump, and in doing so, now have some issues… The hot and cold systems are not separate – there was always just a ‘Y’ connector supplying a cold feed to the hot tank. I’ve never really needed an accumulator tank, as the hot water tank is on its side, and thus has a large airspace at the top, making for a really smooth pressure system.

However, to remove the possibility of water on electrics, I moved the new pump to another (lower) location. The pump is still above the main tank as it was, but now slightly lower than the hot tank. I then noticed that a substantial amount of hot water was finding its way to the cold taps, so placed a non-return valve in the hot tank supply. That stopped the problem, only now I’m going to need an accumulator in the cold system to stop that from pulsing. Until then, the mixer tap is now pretty useless, due to the pulsing cold pressure.

The biggest problem though, seems to be that the pressure switch/sensor in the new pump (Jabsco Par-Max) is obviously very different to the old one, as the hot side now has very large, and very slow pressure fluctuations. The hot tap can now run for around 5 seconds before the pump starts, staying on for the same after closing it

I’d be very grateful for any advice as to how best plumb this system?

As always here, many thanks.

Ideally your system should have an accumulator tank in the cold water system, although some pumps are claimed to operate satisfactorily without one.

The hot water system should be fed via a non return valve ..... which you have fitted .

The hot water system should have an expansion tank to absorb the expansion of the water as it is heated, rather than releasing it via the PRV.
If the calorifier has an air space this may be adequate to do this , but not being sealed off by a diaphragm as it would be in a expansion tank may mean that it becomes ineffective if the air is lost, or result in air spurting from the hot taps if the air volume increases.

The pressure on the whole system will cycle between the pump cut in and cut out pressure whatever you you do short of having some form of pressure control valve/system. The bigger the accumulator the slower this will be.


If you fit your calorifier with a thermostatic blend valve you may be able to do away with the mixer tap , or at least use it almost entirely as a hot water tap. Some calorifiers have a blend valve fitted as standard while they are accessories for other makes.


You will find advice on line to correctly size accumulator and expansion tanks.
 

Dougal

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Some useful stuff there - thanks. I cannot do as Norman suggests though, and remove the trapped air, as the tank fittings are at the end of the tank - not the top. There is no physical way to achieve this without unbolting the tank each time it happens! Before changing pumps, this air space in the tank has worked quite well (as Vic mentions) as the accumulator tank, for both the hot AND cold, as previously there was no non return valve in the hot tank feed. I can only guess, that the lowering of the pump, is what causes the hot water to bleed into the cold?

It seems like the 'range' of the pressure switch in the new pump is much greater than the old one. Guess I'll have to try a proper accumulator with a membrane in the cold circuit and see what happens. VERY limited for space though.

If I fit a thermostatic blend valve at the tank, then presumeably, I won't have very hot water going to the galley sink? Or can they have multiple outlets?
 

VicS

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Maybe a separate blend valve on the supply to the wash room and shower , rather than one integral with the calorifier will allow the galley to be supplied with very hot water directly from the calorifier.

If the mixer is just on your shower perhaps a thermostatic one is the answer?


Grinding the little grey cells a little more:

If the size of the accumulator is sufficient you should be able to get to a point where it controls the pressure in both hot and cold water systems simultaneously and allows a mixer tap to function normally while if it is small compared to the reserve held by the expansion tank the latter will tend to maintain a more steady hot water flow while the cold water flow fluctuates ........... not good news for a manual mixer valve or tap.
 

Dougal

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If the size of the accumulator is sufficient you should be able to get to a point where it controls the pressure in both hot and cold water systems simultaneously and allows a mixer tap to function normally.

Which is exactly how it worked before I fitted the new pump, when using just the air pressure in the hot tank as the accumulator.

PS If you ever find an extra abundance of those "little grey cells", please put some in the mail;-)
 

duncan99210

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We have what was referred to by someone as an accumulator but it doesn't have a membrane in it. It's a simple inverted bottle, about one litre volume with a t piece on the bottom. The original was translucent and you could see was about one third full of water when the pump was off. It split. The replacement (which is how we found its an accumulator, as I took it in to the Italian chandler to help explain what we needed) took a few days to find, so I bypassed it. The pump hunted as the op,described, both hot and cold water. Since the replacement was fitted, the system works fine. The thing is fitted just after the pump in the cold line before it tees off to the hot system. The whole thing is no bigger than a bottle of pop and was only about €40 so not expensive.
 
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