Separate accumulators for hot and cold water circuits?

[nwj2000]

Hi There,

 

I'm new to plumbing, so bear with me!

 

I have one 5L accumulator right next to the water tank after the water pump. The water feed then goes to the galley where there is another 5L accumulator off the same cold water pipe. From there a feed goes to the marco water heater and there is a valve that allows you to switch between the water heater and calorifier which is at the other end of the boat.

 

Now, take it as said that whoever plumbed the boat was a total monkey. He's not done a great job trust me. But my question is this;

 

Should I have two accumulators coming off the same pipe within four metres of each other? Shouldn't I have one on each the hot and cold circuits? The pressure on the hot is pretty poor.

 

Also I only have a 20psi water pump, is it worth upgrading to 30psi or is my pressure valve going to keep blowing then?

 

Cheers,

 

Nick

[by'eck]

Can't see the need to have two accumulators on the cold circuit at least. Some fit a second one in the hot water circuit to provide pressure release, thus save water leaking to wherever if the calorifier PRV opens.

 

In any case this can't increase the hot water pressure long term, which is provided by the cold water pump.

Edited May 4, 2012 by richardhula

[DeanS]

 

Also I only have a 20psi water pump, is it worth upgrading to 30psi or is my pressure valve going to keep blowing then?

 

 

Hi Nick.

I have a new Jabsco 20psi water pump on our boat. (10.8 l/min .......i think you get lesser ones....7l/min etc)

The pipes are 15mm black hard plastic.

we have a gas water heater. It has quite small piping (3/8 perhaps).

 

We get a brilliant spray out of the shower, because we replaced the shower head with one that has very fine holes. I think before that it was less impressive by far. We have a single accumulator tank a metre or so after the water pump, which then feeds the kithen cold water, the water heater supply, and the shower/basin cold water.

 

Hope that helps.

[alan_fincher]

There is no reason why two suitably pressurised accumulators on the cold water side should not be OK, although it is clearly unusual. Effectively they should perform about the same as one with the combined capacity of the two.

 

Accuumaltors, (and eually hot water expnasion vessels), do nothing to improve an overall rate of flow, so this has no bearing on your sluggish hot water. That will be to do with pump cut-out pressure, and pipe sizes and runs. Also, if the flow is slower when going through the Morco, than drawing off the calorifier, don't be surprised - they do restrict flow a lot, even if the adjustable restrictor valve on them is in its most open position.

 

Most PRVs on calorifiers have an operating pressure of 3 bar, although some are higher (e.g. 4 bar). Even a 30 psi pump is only 2 bar, so increasing to that would not normally overcome the setting of a PRV. If you try a 45 psi pump, with a 3 bar PRV, then it can well leak, though.

 

PRVs are often marked with their rating, I think.

[nicknorman]

Just echoing what Alan said, having 2 cold water accumulators is slightly unusual but not a problem - it is the same as having one larger one. Adding an accumulator in the hot circuit will not improve the hot flow rate, and of course if it were after the source of hot water, it would represent a reservoir of cold water that would be discharged into the hot circuit causing an issue with water temperature fluctuation at least when the tap was first turned on.

 

Some people fit what might be called an accumulator but should be called an expansion vessel in the hot circuit - it must be pressurised much higher than the cold accumulator to do it's job - normally set around the pump cut-out pressure - so that it remains empty until the water trapped in the calorifier heats up and expands, thus increasing the pressure towards that which might operate the PRV. I can't see any point in having such a device in a Morco circuit since the volume of stored water is very small and the heat source should only be present when there is a tap open.

 

Also as has been said, check the pressure rating of the PRV before upgrading the pump. You should leave a significant margin between pump cut-out pressure and PRV pressure. And don't forget that the limiting factor might be the pump flow rate, not the max pressure. If the pump remains on constantly whilst the tap is open, it is not meeting the flow demand at the max pressure and so a larger pump with higher flow rate would help.

 

If there is a big difference between the cold flow, and the hot flow from the calorifier, it would be worth checking the pipework for any restrictions. If a non-return valve has been installed in the inlet to the calorifier, those of poor quality can restrict flow quite a bit and either removing it or improving it might help. (remove it if the distance from the calorifier inlet to the previous nearest cold tap is quite a long way, and you have no hot water expansion vessel).

Edited May 4, 2012 by nicknorman

[ChrisPy]

for the hot water accumulator or expansion vessel to work you need to fit a non-return valve after the tee where the cold water supply is directed to the calorifier. Then the expanding hot water will not be forced back into the cold feed pipe.