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Accumulators for calorifiers


Strettonman

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1 hour ago, Strettonman said:

Thanks everyone - sorry for radio silence but phone threw a woddler and only just got it back. 

 

I will I’ll go for a EV downstream of the calorifier. 

 

It doesn't really matter if it's upstream or downstream of the calorifier as long as it's downstream of the NRV. 

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  • 1 month later...

I'm about to fit a EV to my calorifier but due to the positioning of the NRV and supply shut-off valve on the inlet, do not have space to install a Tee for the EV. I figured on replacing the drain cock with a Tee piece, screwing the drain into one side of that and having the EV connected to the other. Same difference right?? (Water in a pressurized cylinder etc..)

 

Stephen 

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5 minutes ago, Stephen Jeavons said:

I'm about to fit a EV to my calorifier but due to the positioning of the NRV and supply shut-off valve on the inlet, do not have space to install a Tee for the EV. I figured on replacing the drain cock with a Tee piece, screwing the drain into one side of that and having the EV connected to the other. Same difference right?? (Water in a pressurized cylinder etc..)

 

Stephen 

Yes I guess so. But also remember that the EV can be anywhere in the pipework from calorifier to hot taps etc. There might be a more convenient place to fit it.

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5 minutes ago, Stephen Jeavons said:

I'm about to fit a EV to my calorifier but due to the positioning of the NRV and supply shut-off valve on the inlet, do not have space to install a Tee for the EV. I figured on replacing the drain cock with a Tee piece, screwing the drain into one side of that and having the EV connected to the other. Same difference right?? (Water in a pressurized cylinder etc..)

 

Stephen 

 

A hot water expansion vessel can be fitted on either side of the calorifier

On ‎19‎/‎06‎/‎2019 at 21:27, blackrose said:

 

It doesn't really matter if it's upstream or downstream of the calorifier as long as it's downstream of the NRV. 

 

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11 hours ago, Tony Brooks said:

But not if there is a NRV on the calorifier cold inlet.

Understood Tony.

My NRV is very close to the inlet of the calorifier hence my reason for fitting the EV off of the original drain plug point rather than on the inlet or outlet of the calorifier. The reason I asked the question was... In an open vented system, pressure is higher at the bottom due to the head of water. However, I figured that in a pressurized vessel the EV can be fitted anywhere. (so long as it's downstream of the NRV) 

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2 hours ago, Stephen Jeavons said:

Understood Tony.

My NRV is very close to the inlet of the calorifier hence my reason for fitting the EV off of the original drain plug point rather than on the inlet or outlet of the calorifier. The reason I asked the question was... In an open vented system, pressure is higher at the bottom due to the head of water. However, I figured that in a pressurized vessel the EV can be fitted anywhere. (so long as it's downstream of the NRV) 

You are right, the pressure does vary with height. But on a narrowboat, the vertical variation isn’t much. The difference over 4’ (which is surely the absolute max one is likely to encounter) is 1.75 psi, not really significant. If you wanted to be perfectionist, you’d just adjust the EV air pressure slightly, to compensate.

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On a slightly different topic. Can someone recommend a thermostatic valve that I can use on the engine-heating coil of the calorifier to prevent the latter from getting too hot when cruising?

I assume it would be an electrical device (12V) to shut off when a desired water temp is reached in the calorifier?

Stephen

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49 minutes ago, Stephen Jeavons said:

On a slightly different topic. Can someone recommend a thermostatic valve that I can use on the engine-heating coil of the calorifier to prevent the latter from getting too hot when cruising?

I assume it would be an electrical device (12V) to shut off when a desired water temp is reached in the calorifier?

Stephen

 .. Or a thermostatic mixing valve on the supply to the hot taps.  For examle,   https://www.screwfix.com/p/pegler-peg402-tmv-15mm/96288

  • Greenie 1
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10 minutes ago, Stephen Jeavons said:

Hmm! I was thinking more of something to stop the engine heating the calorifier once the latter reaches a temp of say 50C

It’s free heat, why waste it? A thermostatic mixing valve will use less hot water thereby extending the free tankful. 

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This is the sort of thing I was thinking of controlled from say a domestic style cylinder-stat?

 

https://www.solidrop.net/product/12v-motorised-ball-valve-brass-2-way-3-4-dn20-electric-shut-off-valve-3-wires-cr03-wiring-for-water-control.html

 

Anyone done this or is there an easier way? Thoughts?

Stephen

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2 minutes ago, WotEver said:

It’s free heat, why waste it? A thermostatic mixing valve will use less hot water thereby extending the free tankful. 

I hear you, I just wasn't keen on the cylinder getting scorchingly hot and then reheating the engine once moored up. How do you stop that from happening?

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1 hour ago, Stephen Jeavons said:

I hear you, I just wasn't keen on the cylinder getting scorchingly hot and then reheating the engine once moored up. How do you stop that from happening?

Well at a pinch you could fit a gate valve into the engine - calorifier circuit. But with an anti-syphon loop in the piping, it shouldn’t happen.

 

As to you original idea, a calorifier tends to heat from the top down so you wouldn’t end up with a cylinder all at 50C. It would be very hot at the top and warm at the bottom. A thermostatic mixer on the output is best if you want to avoid scalding hot water coming out of the taps.

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  • 1 year later...

My old calorifier split after several years of good service (and after a "temporary" repair continues to give me service a year later!).

I have one accumulator at the fresh water pump and the calorifier is 55 feet away at the other end of the boat. I'm installing a new calorifier and I hadn't planned to put in an EV. Changing my mind after reading this thread though, given that the cost of an EV is about 10% of the cylinder,


Unfortunately I don't know what the pressure rating of my new calorifier is, the data sheet doesn't specify. I had planned to just re-use my 3 bar PRV from my old calorifier. I have pasted the data sheet the vendor gave me in case anyone can advise on the working pressure of that calorifier.
https://heatmyboat.co.uk/product/twin-coil-marine-calorifier-hot-water-tank/?attribute_size=600+x+450+(24"+x+18")

So, if I assume that the maximum pressure of the calorifier is 3 bar, would I want an EV that was slightly less?

 

There's an affordable 2.7bar 12 litre EV at screwfix for 37 gbp.
https://www.screwfix.com/p/flomasta-potable-expansion-vessel-12ltr/714kk

 

 

 

 

 

image.png.36604c38d845f5cfb8b8aac6d3d21560.png

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I wouldn't know what the pump cut out pressure is, but it must be less than 3 bar because otherwise my calorifier PRV would be leaking water into the canal. If the hot water EV had an equal or higher pressure than the cold feed EV, then that should protect it, right?

 

Actually, I'm struggling to accept that a second EV can be beneficial, unless you have a NRV on the cold feed into the calorifier.

 

Pascal's law states that the pressure change anywhere in a closed system is transmitted instantaneously everywhere else in the system. So it shouldn't matter whether you have an EV at the cold pump feed or at the calorifier, either way your system is protected. And then you have an extra layer of protection in the calorifier PRV.

 

I think I've convinced myself off the second EV ?

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I thought you said that you did have a NRV on the calorifier inlet.

 

If you put a tyre pressure gauge on the accumulator valve as soon as the pump cuts off that will be the cut-out pressure.

 

If you don't have an NRV in the calorifier inlet then a decent sized accumulator will act as an expansion vessel but it will allow hot/warm water to flow back into the cold system to some degree. It is said this may lead to legionella in the pipe and under certain conditions and pipework designs you can get warm/hot water out of a cold tap.

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Grade 1 cylinders are tested to 3.65 bar, working pressure 2.5 bar (25m head), grade 2 - 2.2 bar test 1.5 working, grade 3 - standard domestic - 1.45 test 1.0 working.

IIRC the one I purchased some years ago from a chandlery was 4.5 bar test, 3.5 bar working (still functioning perfectly). Apparently for cylinders over grade 1 pressures both ends of the cylinder have to be convex, with a foot ring on the bottom, whereas domestic graded cylinders normally have a concave bottom.

 

springy

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1 hour ago, Tony Brooks said:

If you don't have an NRV in the calorifier inlet then a decent sized accumulator will act as an expansion vessel but it will allow hot/warm water to flow back into the cold system to some degree. It is said this may lead to legionella in the pipe and under certain conditions and pipework designs you can get warm/hot water out of a cold tap.

 

Calorifier doesn't have a NRV at the moment. I could fit one but I don't really see the benefit. There's about 5m of cold feed pipe between the calorifier and the nearest cold tap, and over 10m between the calorifier and the tap we use for drinking water. So I judge the risk to be rather minor.

 

 

32 minutes ago, springy said:

Grade 1 cylinders are tested to 3.65 bar, working pressure 2.5 bar (25m head), grade 2 - 2.2 bar test 1.5 working, grade 3 - standard domestic - 1.45 test 1.0 working.

IIRC the one I purchased some years ago from a chandlery was 4.5 bar test, 3.5 bar working (still functioning perfectly). Apparently for cylinders over grade 1 pressures both ends of the cylinder have to be convex, with a foot ring on the bottom, whereas domestic graded cylinders normally have a concave bottom.

 

springy

 

Thanks for that! My cylinder has convex top and bottom and is marked Grade 1. So that suggests that my 3 bar PRV is appropriate then.

 

 

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The only thing with relying on the cold water accumulator, is that when the pump cuts out, it is already mostly full. So when the calorifier heats up and water expands, there isn’t much room for the additional volume in the accumulator and so the pressure rises relatively easily/quickly. Whereas with an EV, it is still empty when the pump cuts out and only starts to fill when the water heats and expands. So even if an EV is a similar nominal volume to the accumulator, its effective volume is much greater.

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6 hours ago, jetzi said:

 

Calorifier doesn't have a NRV at the moment. I could fit one but I don't really see the benefit. There's about 5m of cold feed pipe between the calorifier and the nearest cold tap, and over 10m between the calorifier and the tap we use for drinking water. So I judge the risk to be rather minor.

 

 

It's more of a long term compound risk. The calorifier can be gradually weakened with repeated expansion and contraction until it eventually cracks. It doesn't always happen if you don't have an EV bit it happens often enough to be a well known risk.

 

To me the benefit of fitting an EV seems to outweigh the benefit of not fitting one, but everyone's free to make their own decisions and do what they want on their own boats of course.

Edited by blackrose
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