Accumulator/Expansion Tank

[purplerobbie]

I fitted a calorifier to my boat over the winter and just need to finish it off now.

I was reading that its a good idea to have one on the cold side to even out the cycle effect on the pump.

I was going to fit one on the hot wter side anyway but can i get away with fitting one? or should i fit 2?

If i can get away with just fitting one where should i put it?

Rob

 

[NormanS]

Normally, one is sufficient, fitted soon after the pump.

 

[purplerobbie]

If i do that will it take up the expansion from the hot water?

Rob

 

[dje67]

Many calorifiers are fitted with a non-return valve between the cold inlet to the tank and the pump. This means that when the tank heats up, the expansion of the contents has nowhere to go and will either lift the relief valve or cause a rupture/leak on the hot water side. So, you should have an expansion tank on the hot circuit to protect your hot pipework.

If you don't have a non-return valve, then you could probably get away with having an expansion tank on the cold circuit only, but you do risk getting a small amount of heated water being back-fed from the calorifier into the cold circuit (probably not a major issue). My previous boat had exactly that setup and it worked fine.

My new boat has an accumulator on the cold circuit, which is great for giving some protection againt the pump cycling on and off, and another tank on the hot circuit. Initially there was no non-return valve between the calorifier and the cold circuit, so when I turned the cold tap on, the hot accumulator back-fed into the cold circuit until he pump cut in. So, I now have a valve fitted to prevent this.

The only slight downside of my current setup (and it is only a minor niggle) is that when the shower is turned on, it takes a fair bit of time before all the pressures in the various parts of the circuits equalise. The advantage is that I've got so much expansion tank space in use that turning a tap on at night doesn't waken the whole boat up when the pump kicks-in.

So, on balance, I would be inclined to fit a tank on the hot side as a minimum. If the 2 circuits are kept separate by a non-return valve then I would fit a cold and a hot expansion tank.

Too many options....!

 

[sailorman]

If i do that will it take up the expansion from the hot water?

Rob

it is there to stop the pump repeatedly cycling in use & nothing at all to do with expansion of the hot water in the pipes / calorifier.
connect pipe work thus --supply> pump>accumulator tank> split pipe work to cold taps & Calorifier supply

 

[vyv_cox]

Many calorifiers are fitted with a non-return valve between the cold inlet to the tank and the pump.

I can't say I have ever seen one but you may be right. However, it is a completely pointless arrangement because the pump itself is a non-return valve. So, discounting the very slight elasticity of the hoses, adding a NRV will not have the slightest effect.

So answering the OP, adding an accumulator immediately after the pump is sufficient, any expansion of the hot water will be taken up by it. A second accumulator, although I have read several times in these pages that they are sometimes installed, seems to have little purpose. My boat was built without an accumulator at all but the calorifier never blew off its relief valve. This would have been obvious as it has its own bilge. The boat had been like that for 10 years before I bought it.

 

[PCUK]

Vyv has it right. An accumulator tank in the normal position just after the pump will perform both functions - smooth pump flow and contain the expansion of the heated water. I'll have to contradict sailorman as it has everything to do with expansion in systems with heated water.

 

[bendyone]

I fitted a cold one just after the pump and a hot one after the tank. Works very smoothly.

 

[sailorman]

Vyv has it right. An accumulator tank in the normal position just after the pump will perform both functions - smooth pump flow and contain the expansion of the heated water. I'll have to contradict sailorman as it has everything to do with expansion in systems with heated water.

if the pressure in the system exceeds the safety valve ( in the Accu tank ) settings the valve will open

 

[NormanS]

The accumulator is primarily to prevent the pump cycling.
The hot tank, (calorifier) is protected by the relief valve. It's not rocket science.

 

[stuhaynes]

I fitted a calorifier to my boat over the winter and just need to finish it off now.

I was reading that its a good idea to have one on the cold side to even out the cycle effect on the pump.

I was going to fit one on the hot wter side anyway but can i get away with fitting one? or should i fit 2?

If i can get away with just fitting one where should i put it?

Rob

I recently fitted an expansion tank of .65 litres which I think was maybe too small. Although it does work the pump does cut in very quickly and remains running until the tap is closed. Mine is straight after the pump.

 

[nedmin]

As suggested you need a pressure release valve (4 bars) .Important to fit one.If you have an immersion heater and the thermostat fails you will blow up the system ! If you are getting hot water from engine dont forget to put U-bends in the hot pipes from engine,ie just let the pipes drop below calorifier,otherwise you will lose the hot water due to thermal syphoning thro. engine.

 

[nedmin]

Re: My last post, I shouldnt have used "blow up the system" as thats a bit dramatic,but it could pressurise the system too much,also if the pump pressure switch failed.A pressure release valve is a must.

 

[vyv_cox]

As suggested you need a pressure release valve (4 bars) .Important to fit one.If you have an immersion heater and the thermostat fails you will blow up the system !

All calorifiers come with a relief valve fitted

If you are getting hot water from engine dont forget to put U-bends in the hot pipes from engine,ie just let the pipes drop below calorifier,otherwise you will lose the hot water due to thermal syphoning thro. engine.

Nonsense.
Firstly, it doesn't happen.
Secondly, if it did, how would a U-bend prevent it?

 

[nedmin]

Thermo syphoning is a fact if the pipes have a rise from the calorifier you will lose hot water thro. the engine when the engine is stopped ie overnight. If you put a drop in the pipes it stops thermo syphoning,