Calorifier evacuation

[Chris Pink]

Never having had a clorrifier before I am struggling with this modern technology.

 

I assume by the fact that there are 2 heating cols at each end means it is a horizontal calorifier installed properly.

 

A recent thread alerted me to the probability that it's operating as an accumulator. I have emptied the (standard) accumulator completely but the water pump still takes a lot longer than it should to get the system up to pressure. So I conclude there is substantial air in the calorifier.

 

Question: how do I bleed the air out of it?

 

is there any way of fitting a bleed screw to the top?

 

[RobinJ]

Never having had a clorrifier before I am struggling with this modern technology.

 

I assume by the fact that there are 2 heating cols at each end means it is a horizontal calorifier installed properly.

 

A recent thread alerted me to the probability that it's operating as an accumulator. I have emptied the (standard) accumulator completely but the water pump still takes a lot longer than it should to get the system up to pressure. So I conclude there is substantial air in the calorifier.

 

Question: how do I bleed the air out of it?

 

is there any way of fitting a bleed screw to the top?

Looking at the first picture, the two grey plastic pipes are presumably the cold feed and hot outlet (with the tee).

There is no obvious pressure relief valve?

The thickness of the insulation may be deceptive, but as the calorifier is at a slight angle, there is presumably an air gap above the hot outlet?

Where does the pipe from the tee go, which is visible is the second picture?

Fitting a bleed valve at some point in the pipe may allow some air to be vented!

The 22mm pipes in the second picture are one coil (from the engine or central heating)?

The second coil in the first picture seems to be fitted with 15mm pipes.

[Ryeland]

It looks to me as though it should be rotated slightly so that the hot outlet is right at the top (immersion heater horizontal). That is anti clockwise in the first picture. This will allow the minimum amount of air in the top of the cylinder.

 

Whether its worth changing the pipework.......!

 

Richard

[nicknorman]

It looks to me as though it should be rotated slightly so that the hot outlet is right at the top (immersion heater horizontal). That is anti clockwise in the first picture. This will allow the minimum amount of air in the top of the cylinder.

 

Whether its worth changing the pipework.......!

 

Richard

My thoughts too. With the outlet not at the top it is pretty inevitable that a fair bit of air will be trapped at the top.

 

It may have been installed like that because there is insufficient room for the immersion heater cover if it was in the correct orientation - can't quite make that out from the photos.

Edited January 18, 2012 by nicknorman

[Mac of Cygnet]

Congratulations! You have a combined calorifier and accumulator, and therefore don't need the latter. Seriously, if the system works and you have enough hot water, why change it? If you put a bleed valve at the highest point, then you need a PRV - you could put that there, but you'd need somewhere for the expanded water to go, and it looks like your calorifier is somewhere that may make it difficult. Without a PRV, and a completely full calorifier the whole system will be put under extra stress as the water heats, and may burst.

 

As you may guess, I'm in the 'if it ain't broke, why fix it?' camp.

Edited January 18, 2012 by Mac of Cygnet

[MikeV]

....the water pump still takes a lot longer than it should to get the system up to pressure.

I have a similar problem although my hot water take off is only about an inch below the top of the tank which is mounted on its side like yours. I just live with it. It may take longer for the cut-off switch to activate on the pump, but equally you can run the hot tap for longer before the pump cuts in.

 

I have a PRV so if the tank is heated from cold any excess pressure from the trapped air should be alleviated. I also have a non-return valve on the cold feed into the tank so it doesn't affect the cold water system.

 

I'd thought about fitting some kind of bleed valve into the side of the tank at the top, but I'm not confident of doing it without risking a leak.

[alan_fincher]

I agree with Ryeland and NickNorman.

 

Looking at first picture, if grey pipe at somewhere just after "one o'clock" with Tee on is hot outlet, then the whole thing should be rotated anti-clockwise, (as viewed in first picture), so that pipe is at "12 o'clock" and immersion is at "9 o'clock".

 

Also agree with Nick Norman that maybe it has been put in "on the twist", because that's the only way the immersion will not foul what it is close to.

 

You would undoubtedly get less trapped air, (and hence at least some more hot water), if it could be installed with the outlet at the top.

 

Also, (but less serious, perhaps), because it also results in cold feed not being at the true bottom, as you draw water off, new cold coming in will not be at the coldest point, and likely to mix with already part hot water, resulting in perhaps water coming out at the top being maybe not quite as hot as it could have been. Not sure if that will be enough to be significant though ?

 

I also can't se a PRV, so hope there is one added on a bit that's not in your pictures!

Edited January 18, 2012 by alan_fincher

[Proper Job]

Just to clarify -

 

The posters above are refering to a PRV - Pressure Relief Valve, not a PRV - Pressure Regulating/Reducing Valve

 

The two are not the same

[LesR]

Could someone explain what pressure the pressure relief valve should be for safety?

 

Les

[Mac of Cygnet]

 

I also can't se a PRV, so hope there is one added on a bit that's not in your pictures!

 

If the system has been deliberately set up with an air space in the calorifier, then a Pressure Relief Valve would not be necessary - the heating, expanding water would only compress the air (a bit), with little increase in pressure - probably no more than in an accumulator. Only if the calorifier is full, and the expanding water has nowhere to go, would damage result. So even if there really is no PRV fitted, the system is OK as it is (but a little less hot water).

[Chalky]

Could someone explain what pressure the pressure relief valve should be for safety?

 

Les

 

Because the system works by the pump pressurising the water in the tank. The PRV is the safety valve to release excess pressure and stop it bursting.

 

Most domestic hot water cylinders are gravity fed and have an open vent to let the excess pressure out. Boat ones are usually sealed and need the PRV.

Edited January 18, 2012 by Chalky

[RobinJ]

Could someone explain what pressure the pressure relief valve should be for safety?

They do vary, depending on the rated pressure of the calorifier, but normally not above about 3 bar!

[alan_fincher]

They do vary, depending on the rated pressure of the calorifier, but normally not above about 3 bar!

What though if you have a water pump that is of a type that can pump up to 45 psi before it cuts out ?

 

Surely if that 45 psi cut-out and the 3 bar (i.e. about 43.5 psi) rating of the PRV were both accurate, your water pump could just keep pumping water straight though it ?

[RobinJ]

What though if you have a water pump that is of a type that can pump up to 45 psi before it cuts out ?

 

Surely if that 45 psi cut-out and the 3 bar (i.e. about 43.5 psi) rating of the PRV were both accurate, your water pump could just keep pumping water straight though it ?

Presumably it costs more for a calorifier that can work at a higher pressure, but water pumps should have an adjustable cut-out pressure (are the separate pressure switches adjustable?).

Thats why you need to have a supply pressure less than the PRV!

Most sytems are designed to run between 30 and 45 psi.

[alan_fincher]

Presumably it costs more for a calorifier that can work at a higher pressure, but water pumps should have an adjustable cut-out pressure (are the separate pressure switches adjustable?).

Thats why you need to have a supply pressure less than the PRV!

Most sytems are designed to run between 30 and 45 psi.

Robin,

 

I was surprised when a similar topic came up recently to find that the Surecal range from Surejust now is documented as coming with a 4 bar PRV.

 

Surecal comes complete with thermostatic mixer valve, 4 bar pressure release valve, 1kw immersion heater, non return valve, 15mm barbed connections for coil and ready for push fit plastic plumbing in 15mm. Also supplied st/steel mounting feet

 

I keep meaning to check the one I installed on "Chalice", (and forgetting!), but my memory is it may have come pre-fitted with a 3 bar one. Despite having a large expansion vessel fitted, I have noted leakage at the PRV, so if mine proves to be 3 bar, I was going to ask Surejust if they have since uprated the Calorifiers, or whether a 4 bar PRV on an older one would still offer enough protection.

[RobinJ]

I was surprised when a similar topic came up recently to find that the Surecal range from Surejust now is documented as coming with a 4 bar PRV.

They look nice!

Perhaps the increased rating helps them to hold more water too?

I need to measure and check if I can fit one of those in my corner 'ole!

[Chris Pink]

Looking at the first picture, the two grey plastic pipes are presumably the cold feed and hot outlet (with the tee).

There is no obvious pressure relief valve?

The thickness of the insulation may be deceptive, but as the calorifier is at a slight angle, there is presumably an air gap above the hot outlet?

Where does the pipe from the tee go, which is visible is the second picture?

Fitting a bleed valve at some point in the pipe may allow some air to be vented!

The 22mm pipes in the second picture are one coil (from the engine or central heating)?

The second coil in the first picture seems to be fitted with 15mm pipes.

 

i nearly ran away from this because my brain is hurting. But I will try.

 

There is no PRV (release valve) in the grey plumbing (other than the speedfit (?) T which would pop (?) in the hot water system (picture 1))

 

Yes, there is a gap (presumably) and I would like to sort this as the time pumping is much larger than the apparent water availability, ie there would be much less pumping = power with no (less) air.

 

Looking again after your answers it looks like there is not enough space to rotate the cylinder because of the 240V boss (maybe why it was installed like this and yes, there would be a lot of copper plumbing to rotate it vertical (I could probably make space to rotate the boss but it would be unremovable after.

 

The T in picture two goes to the header tank for engine cooling (the 22mm in picture 2 is the engine cooling system)

 

The 2nd coil is a t from the back boiler and the lower goes straight to the 28mm return for the back boiler through a gate valve (presumably) to prioritise the radiator

 

The amount of 'presumably's reflects the pain in my brain

 

I guess it would be easiest (if possible) to fit a PRV and a Shrader valve on the top of the tank - any idea how I could fit this? Could I get a spanner in through the immersion boss to fit a tank connector?

[smileypete]

Question: how do I bleed the air out of it?

 

is there any way of fitting a bleed screw to the top?

I take it the heated water outlet is the top grey one, so it should be self bleeding to some extent. Why is it a problem if air is trapped above that in the top?

 

If you really want to use the extra capacity for hot water (instead of air ), you could fit an 'essex flange' in the top side of the cylinder and take the heated water outlet from that instead.

 

cheers,

Pete.

Edited January 18, 2012 by smileypete

[by'eck]

Presumably it costs more for a calorifier that can work at a higher pressure, but water pumps should have an adjustable cut-out pressure (are the separate pressure switches adjustable?).

Thats why you need to have a supply pressure less than the PRV!

Most sytems are designed to run between 30 and 45 psi.

 

I think 25 or less psi water pump pressure is closer to the norm. This will work well with the above mentioned calorifier PRV pressures.

 

I can't see the point of fitting a higher pressure water pump. Its pump throughput that gives a good flow, extra pressure just leads to leaks & incompatibility with accumulator, EV, PRV etc.

 

Looking at the Flojet range, nearly all cut in at 10 psi & out at 20 psi. Even the expensive constant pressure ones run at 25 psi.

[Chris Pink]

I take it the hot outlet pipe to the taps etc is the top grey one, so it should be self bleeding to some extent. Why is it a problem if air is trapped above that in the top?

 

cheers,

Pete.

 

I don't think the air is trapped there, as the water must be coming that way.

 

The amount of time the pump goes is fairly extreme

[RobinJ]

I don't think the air is trapped there, as the water must be coming that way.

 

The amount of time the pump goes is fairly extreme

If the system works!

Only reason to remove air would be to hold more water, do you need it?

Doing that would mean fitting an expansion vessel etc.

 

Just make sure you understand it, so when it does go wrong!

[Yellowback]

Question: how do I bleed the air out of it?

 

 

 

Initial thought is obviously too easy and will get corrected by those more knowledgeable.

 

Shift ballast, by moving or adding additional until outlets are at top, bleed cylinder and both coils, adjust ballast back to normal.

 

I don't need to mention sealing hull outlets that may get submerged, so I won't.

[Mac of Cygnet]

I don't think the air is trapped there, as the water must be coming that way.

 

The amount of time the pump goes is fairly extreme

 

There is no reason air cannot be trapped above the outlet - in fact every reason for it to be, as when the calorifier was first filled on installation, there would be no way of getting rid of it. As soon as the water level reached the outlet, it would run out, leaving air above it, if a tap was on. If a tap was off, it would continue to enter, compressing the air above it until the pump cut out. I don't see anything wrong with this except you have a little less hot water.

 

The pump is running for a long time because in effect it is having to pressurise two accumulators instead of one. As someone has already said, it should also take a long time to cut in when running water.

[nicknorman]

I guess it would be easiest (if possible) to fit a PRV and a Shrader valve on the top of the tank - any idea how I could fit this? Could I get a spanner in through the immersion boss to fit a tank connector?

I would strongly recommend against trying to make a new hole in the top of the tank. The copper is as thin as it can be, and the strength it needs is gained by spreading the load uniformly. A break in the skin, even a smooth one, will increase the local stress and could lead to failure, especially when aggravated by being clamped between 2 nuts etc. That is even assuming you could get it to seal! Remember that force = pressure x surface area (of the tank skin) so even a modest pressure such as 30 psi translates to a large force trying to tear the tank skin apart. When you perforate the skin, tearing becomes much easier (think of old fashioned stamps etc). Where there are existing fittings for pipe connections etc, you will find the copper is much thicker.

 

You could leave it alone, though I think you should fit a PRV if there is a non-return valve in the cold feed to the calorifier (if not, expansion will probably be catered for by the existing accumulator, though you can possibly get hot water in the cold supply). If there is a PRV, you are relying on the air gap to absorb the overpressure. Over time, the air might start to dissolve in the water, reducing its volume and risking an over-pressure failure of the calorifier or plumbing. Of course if you run out of water the air will be replenished! (in other words, the capability of the tank to act as an EV is variable and unknown).

 

If you are desperate to get rid of the air, fit a PRV then make up a bleeding device, something like a wine brewers cork (large cork with hole in the middle) through which you push some stiff (eg microbore copper) piping. With the system depressurised, remove the hot water outlet, push in the pipe, bent upwards, and seal the calorifier exit with the cork. Now start the pump - the air will get pumped out through the inserted pipe which is hopefully near the top of the calorifier.

 

OK not sure how easy it would be to get the pipe to the top of the calorifier (having never seen what the outlet at the top of the calorifier looks like inside) but you could at least have hours of endless fun with water play!

Edited January 18, 2012 by nicknorman

[bizzard]

And of course all this is not unlike bowel evacuation. ''Get it to hold its breath and strain''