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Accumulators for calorifiers


Strettonman

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The last work done on my boat before I bought it was to replace the split calorifier at a cost of £700 (2013 prices).

 

The boat was not fitted with an EV, and the repetitive pressurisation work hardened and then split the calorifier, this was despite the PRV constantly dribbling once the water was up to temperature.

 

Once I owned the boat I fitted an EV to avoid a repetition.

Edited by cuthound
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On 12/04/2021 at 00:46, nicknorman said:

The only thing with relying on the cold water accumulator, is that when the pump cuts out, it is already mostly full

If there is an accumulator on the calorifier, won't the pump fill that one too?

 

Or is the idea that there are two accumulators at different pressures?

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Yes, different pressures, the accumulator on the pump has a set pressures at the pump start pressure so this fills and empties over the pump operating pressure range. The EV on the calorifier is set to the pump stop pressure or very slightly above so it does not fill during the pump operating cycle, it only starts to fill once the calorifier is heated and the water expands. The pressure still increases when the water heats up but much less than without the EV.

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Alright, thanks, I'm convinced. Also means that I can fit a NRV to the cauliflower, may as well add an isolation to it as well for maintenance, so something like https://www.screwfix.com/p/pegler-8028-isolating-check-valve-15mm/2059v

 

So what pressures should the two EVs ideally be set to? And what size EV is appropriate for a calorifier - according to this link water expands 2.5% every 100 degrees F, so 5% perhaps over the normal operating temperature of a calorifier - so 12 litres should be plenty (https://www.screwfix.com/p/flomasta-potable-expansion-vessel-12ltr/714kk )?

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4 minutes ago, jetzi said:

Alright, thanks, I'm convinced. Also means that I can fit a NRV to the cauliflower, may as well add an isolation to it as well for maintenance, so something like https://www.screwfix.com/p/pegler-8028-isolating-check-valve-15mm/2059v

 

So what pressures should the two EVs ideally be set to? And what size EV is appropriate for a calorifier - according to this link water expands 2.5% every 100 degrees F, so 5% perhaps over the normal operating temperature of a calorifier - so 12 litres should be plenty (https://www.screwfix.com/p/flomasta-potable-expansion-vessel-12ltr/714kk )?


The accumulator should be set to a few psi below pump cut-in pressure. The EV should be set to pump cut-out pressure. There is no “right answer” for the size of the EV, the bigger it is, the less stress on the calorifier. But the downside of having a huge one is that after you heat the water and then turn on the hot tap for the first time, the flow out of the tap will all be from the EV until it’s empty, and that water is likely to be cold.

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2 minutes ago, nicknorman said:

The accumulator should be set to a few psi below pump cut-in pressure. The EV should be set to pump cut-out pressure.

 

Thanks this is really helpful.

 

I don't know what my fresh water accumulator is set to, I can't get to the valve unless I cut away some of the wall (which I'm willing to do but only if really necessary - and I'm not sure how accurate my bike pump is at measuring pressure anyway). My freshwater pump is marked at 2.1 bars (30 PSI) operating pressure. So I expect my current accumulator must be set around 26 PSI / 1.8 bar?

So the EV I get for my calorifier should be set to 30 PSI / 2.1 bar?

 

6 minutes ago, nicknorman said:

There is no “right answer” for the size of the EV, the bigger it is, the less stress on the calorifier. But the downside of having a huge one is that after you heat the water and then turn on the hot tap for the first time, the flow out of the tap will all be from the EV until it’s empty, and that water is likely to be cold.

 

What size is a "huge one"? My current accumulator is probably about 2-3 litres (judging from the external size), so 12 litres sounds a bit on the large side.

 

Can I insulate the EV to try to keep the water that expands into it warm, or is that pointless because of how long the majority of the water in it will be in there for?

 

 

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34 minutes ago, nicknorman said:

But the downside of having a huge one is that after you heat the water and then turn on the hot tap for the first time, the flow out of the tap will all be from the EV until it’s empty, and that water is likely to be cold.

Not if you fit the EV between the non return valve and the calorifier inlet. When you turn a hot tap on that will just release cold water into the bottom of the calorifier.

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27 minutes ago, David Mack said:

Not if you fit the EV between the non return valve and the calorifier inlet. When you turn a hot tap on that will just release cold water into the bottom of the calorifier.

Oh yes that’s a very good point which I hadn’t thought of! I’m glad you said that because fitting an EV is on my list of things to do.

56 minutes ago, jetzi said:

 

Thanks this is really helpful.

 

I don't know what my fresh water accumulator is set to, I can't get to the valve unless I cut away some of the wall (which I'm willing to do but only if really necessary - and I'm not sure how accurate my bike pump is at measuring pressure anyway). My freshwater pump is marked at 2.1 bars (30 PSI) operating pressure. So I expect my current accumulator must be set around 26 PSI / 1.8 bar?

So the EV I get for my calorifier should be set to 30 PSI / 2.1 bar?

 

 

What size is a "huge one"? My current accumulator is probably about 2-3 litres (judging from the external size), so 12 litres sounds a bit on the large side.

 

Can I insulate the EV to try to keep the water that expands into it warm, or is that pointless because of how long the majority of the water in it will be in there for?

 

 

2.1bar/30 psi is the pump cut-out pressure. The accumulator should be set to just below cut in pressure, which is likely to be around 15-20psi. So around 15psi is about right for the accumulator, 30psi for the EV.

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If you go on the surecal website it gives recommended size for an expansion vessel, from memory 55l litre calorifier is at the upper limit for a 5l EV and lower limit for 8litre EV so you are looking for something in the  range of 10-15% of the calorifier volume. The EV needs to be bigger than the water expansion as the air behind the diaphragm will compress.

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