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NewCanalBoy

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I was looking inside a cupboard following a few pipes around as you do. Just trying to understand where everything is going. I came across this white bottle like a gas bottle, I thought it wasn't connected to anything so was tugging at it to get it out - doh !!

Realised it had a pipe coming out from underneath it. Haven't traced it yet so unsure where it comes/goes.

It sits next to my hot water tank 

Your starter for 10 -

 

 

IMG_20190805_194400533.jpg

Edited by NewCanalBoy
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It is called an accumulator, and provides a back up pressure to keep your water flowing when the water pump pressure sensor sometimes doesn't keep up. Under the black cap is an air valve. You will generally have the pressure at 1/2 to 2/3 of the kick in pressure of your water pump.

Some boats have just one, some have two, one by the calorifier(as you have), and one for the cold supply nearer the water tank

 

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An accumulater. A device for smoothing out water flow spurts from water pump.

So, what is my prize ?

 

Damn, beaten to it

Edited by Slim

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This is probably an expansion bottle to limit pressure rises in the calorifier as the water heats and expands.  The pump up pressure is just above the pump cut-off pressure so higher pressure than an accumulator.  The accumulator (if you have one) is probably close to the pump which is set to just above the pump cut in pressure.

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25 minutes ago, matty40s said:

It is called an accumulator

 

24 minutes ago, Slim said:

An accumulater

 

21 minutes ago, Chewbacka said:

This is probably an expansion bottle

I’m with Chewy. An expansion tank. 

Not an accumulator. 

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13 minutes ago, matty40s said:

You are right

 

.

www.bes.co.uk/expansion-vessel-for-unvented-hot-water-18-litres-21195

 

...and its pre-pressured to 3.bar......

 

so basically, exactly the same as an accumulator

..

 

 

Structurally the same, but has a very different function, hence pre-set pressure is set higher than the pump pressure.

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The only sure way to tell if it is an expansion vessel, or an accumulator is to follow the pipe coming out the bottom. If the pipe goes in to one of the hot water pipes coming out of the top of the calorifier, then it is an expansion vessel and its job is to stop the cauliflower and hot water system from getting over pressurised. If it is connected to the cold water pipes somewhere downstream from the water pump, then it is an accumulator and is there to smooth out the pressure and make the pump cut in and out less often. Different pressures set inside, depending on the function, but otherwise they can look identical.

 

Jen

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I simple terms, what's the difference between an expansion vessel and an accumulator?  I have two of these things that look very similar.  One is next to my calorifier, one is next to my clean water pump.

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19 minutes ago, doratheexplorer said:

I simple terms, what's the difference between an expansion vessel and an accumulator?  I have two of these things that look very similar.  One is next to my calorifier, one is next to my clean water pump.

They are doing different things, they are essentially the same though - a lump of air in a rubber bag inside a metal cylinder

Richard

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41 minutes ago, doratheexplorer said:

I simple terms, what's the difference between an expansion vessel and an accumulator?  I have two of these things that look very similar.  One is next to my calorifier, one is next to my clean water pump.

Presumably you mean function as they are built the same.

An accumulator stores a (say) a litre of water at pump pressure, so when you turn on the tap the accumulator will supply until the pressure drops and the pump starts, whilst the pump is running the accumulator tends to hold the pressure fairly steady.  Without an accumulator, if you only take a very small flow the pump will turn on/off every few seconds, with an accumulator it will turn on/off a lot less often.  Result is less pressure/flow fluctuations at the tap, and less contact wear on the pump pressure switch.

 

Expansion vessel - most calorifiers have a non return valve to stop hot water going back into the cold pipe.  When water heats up it expands and if it can not push the water into the cold pipe, then it increases pressure in the calorifier, if someone uses some hot water this will release the excess pressure, but if they don’t the pressure will rise, possibly to the point the ‘emergency’ pressure release valve opens.  The other worry, is that if this happens frequently then it will stress the copper walls of your calorifier which will eventually cause it to crack and leak.  At least one calorifier manufacturer will not give warranty for this type of failure.  The expansion vessel will take the ‘expanded’ water so preventing excessive pressure increase.

 

For these ‘bottles’ to work correctly they must be at the correct pressure to do their job (see posts above), there is a tire valve at the opposite end to the pipe which is where you pump air in if it needs adjusting.

Edited by Chewbacka
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Thank you all.

 

I have just found one similar looking at the bow next to the water pump as suggested, so all seems ship shape !

 

I assume that if either of these were to fail/or incorrect pressure, the pump would come on sooner or more of an iratic pressure would occur ?

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2 minutes ago, NewCanalBoy said:

Thank you all.

 

I have just found one similar looking at the bow next to the water pump as suggested, so all seems ship shape !

 

I assume that if either of these were to fail/or incorrect pressure, the pump would come on sooner or more of an iratic pressure would occur ?

Yes.  I use a bicycle pump and pressure gauge every six months or so.  I can't remember what pressure mine should be though, it says on the side.  Something like 1.7bar?

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41 minutes ago, doratheexplorer said:

Yes.  I use a bicycle pump and pressure gauge every six months or so.  I can't remember what pressure mine should be though, it says on the side.  Something like 1.7bar?

When you buy an accumulator/expansion tank there is a sticker on the side to indicate the pressure it has been filled to.  This is simply their best guess as to what you need.  The actual pressure you need is (contrary to what I said in #4 above) is 

 

Accumulator - about 3psi below pump cut-in pressure

Expansion - about 3psi above pump cut-out pressure

 

added - when checking/adjusting the pressure you must depressurise the water system by turning off the pump and turning on both a hot and cold tap.

Edited by Chewbacka

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7 minutes ago, Chewbacka said:

When you buy an accumulator/expansion tank there is a sticker on the side to indicate the pressure it has been filled to.  This is simply their best guess as to what you need.  The actual pressure you need is (contrary to what I said in #4 above) is 

 

Accumulator - about 3psi below pump cut-in pressure

Expansion - about 3psi above pump cut-out pressure

How do I find out the pump cut-in/cut-out pressure?

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5 minutes ago, doratheexplorer said:

How do I find out the pump cut-in/cut-out pressure?

Either with a pressure gauge or look at the spec sheet for the pump.

 

added if not sure what pump you have, I would try

accumulator at 15psi

expansion at 33psi 

Edited by Chewbacka

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Just now, Chewbacka said:

Either with a pressure gauge or look at the spec sheet for the pump.

I don't have the spec sheet.  What do you mean by a pressure gauge?  Like the thing on the bike pump?  Where would that go?

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14 minutes ago, doratheexplorer said:

I don't have the spec sheet.  What do you mean by a pressure gauge?  Like the thing on the bike pump?  Where would that go?

You can get them on eBay and it would need connecting to the cold water pipe, doesn’t need to be close to the pump.  But it is a bit of work.

 

I would see what model pump you have and ask on here to see if anyone knows the pressures, or try google.

 

added -  you can get a pressure gauge that screws onto a washing machine cold supply tap, but it is really intended for mains water pressure so goes up to 11bar, whereas your boat pump is probably about 2 bar.  But it would do the job, assuming you have a tap you can screw it on to.

toolstation sell one

https://www.toolstation.com/mains-water-pressure-test-gauge/p75711

 

Added some more - a link if you would like a better explanation than mine https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

 

Edited by Chewbacka

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41 minutes ago, doratheexplorer said:

I don't have the spec sheet.  What do you mean by a pressure gauge?  Like the thing on the bike pump?  Where would that go?

With the pump off and tap ipen sich a car tyre pressure gauge on the valve you use to blow the tank up. That will be the air pressure in the "tank".

 

Close tap and turn pump on. When the pump stops running measure the pressure again. that is the pump cut out pressure.

 

Get someone to turn a tap on a little and keep measuring the pressure. When the pump starts its the cut in pressure.

 

Anyway the cut in pressure is as near to make little difference to the operation about half the cut out pressure.

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I've found it: PRESSURE SWITCH - cuts in at 1.0bar (15psi) - cuts out at 1.7bar (25psi)

So my accumulator should be at 12psi and my expansion vessel at 28psi

Edited by doratheexplorer
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44 minutes ago, doratheexplorer said:

I've found it: PRESSURE SWITCH - cuts in at 1.0bar (15psi) - cuts out at 1.7bar (25psi)

So my accumulator should be at 12psi and my expansion vessel at 28psi

Sounds good to me?

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12 hours ago, RLWP said:

They are doing different things, they are essentially the same though - a lump of air in a rubber bag inside a metal cylinder

Richard

Actually a rubber bag of water in a pressurised metal cylinder.

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I didn't measure the pressure when I fitted my accumulator.  I experimented and set the pressure so that I got the maximum amount of water from the cold tap before the pump switched on.

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On 06/08/2019 at 00:02, matty40s said:

You are right

 

.

www.bes.co.uk/expansion-vessel-for-unvented-hot-water-18-litres-21195

 

...and its pre-pressured to 3.bar......

 

so basically, exactly the same as an accumulator

..

 

 

Yes, physically the same, but needing a different pressure, as others have already said here.

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