Calorifier evacuation

[alan_fincher]

 

Not relevant to Chris, but.......

 

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.

 

I'm not familiar with Flojet, but looking quickly at the popular Shurflo range most of them are at least 30 psi cut out pressure, and some are 40 psi.

 

If the pump itself can get the pressure in there up to 40 psi, (and not withstanding the switches are inaccurate anyway), then a 3 bar PRV really offers little extra overhead before it may start to open, if there is no other way for expanded water to find a space.

 

Back to Chris......

 

I was trying to envisage an immersion heater hole without it's immersion fitted, and whether I could get a hand through, to aid fitting something inside the cylinder, as he suggests. They seem to be 2 1/4" BSP, which I guess means maybe a bit more than that in terms of actual hole size. But nothing like the 3.5" or so that my hand looks like it might need, I think. My guess is maybe possible if done by someone with "petite" hands, but I doubt possible if they are as big as mine ?

 

I also had the same thoughts as NickNorman. Relying on the trapped air to act as expansion space I agree is dodgy. If over time the air gets absorbed in the water and flushed through, you can't rely on any "known" volume being present.

[bizzard]

Also the calorifiers relief valve is best as high up on the calorifier as pos as there's usually some trapped air up there which cushions the valve from sudden hydraulic shocks which can jolt the valve open. Personally i'm not keen on the horazontal

calorifiers in my experience they are far more prone to evacuating water from the valve than the vertical type with the valve on its summit..

[Ryeland]

I can't see any point in trying to remove the air as the hot water which replaces it can never be used. It won't flow down to the outlet as it is the hottest water in the cyclinder. So the same volume of water below the outlet will still be available.

 

Richard

[smileypete]

Plan B:

 

Remove the heated water outlet at the top and make some sort of 'pipe in pipe' fitting that allows you to have a pipe continuing inside the tank that curves up the top.

 

But have a fish around with some mild steel wire to find where the coils are.

 

cheers,

Pete.

[RobinJ]

I can't see any point in trying to remove the air as the hot water which replaces it can never be used. It won't flow down to the outlet as it is the hottest water in the cyclinder. So the same volume of water below the outlet will still be available.

I thought thats where these feed through fittings with the upturned end came in?

Don't they allow the water (or air) above the outlet to be let out (provided they are fitted right)!

[Chris Pink]

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!

 

 

More playing this morning; from empty the pump ran for 34 seconds to full pressure (the proper accumulator is empty of air) and then I ran off a little water and it cut in again almost immediately. So doing nothing is not really an option. Abandoning the pressurised system to hot water only is the position of last resort and put a Galley Gusher for cold . I need to get some air out of the system. The option above seems feasible.

 

I am not quite sure why cutting a hole in the tank would be so catastrophic, surely the pressure is not so great as to compromise the entire hot water tank? I thought also of cutting a hole in the top of the tank and putting the brewers bung in with a PRV that doubles as a bleed valve.

 

Latest question is. If the air is in the hot water system why does the pump run when cold water is drawn?

 

I am struggling, I think,mainly as a result of living, happily, the last 10 years with a Galley gusher and little else.

[RobinJ]

More playing this morning; from empty the pump ran for 34 seconds to full pressure (the proper accumulator is empty of air) and then I ran off a little water and it cut in again almost immediately. So doing nothing is not really an option. Abandoning the pressurised system to hot water only is the position of last resort and put a Galley Gusher for cold . I need to get some air out of the system. The option above seems feasible.

 

I am not quite sure why cutting a hole in the tank would be so catastrophic, surely the pressure is not so great as to compromise the entire hot water tank? I thought also of cutting a hole in the top of the tank and putting the brewers bung in with a PRV that doubles as a bleed valve.

 

Latest question is. If the air is in the hot water system why does the pump run when cold water is drawn?

 

I am struggling, I think,mainly as a result of living, happily, the last 10 years with a Galley gusher and little else.

One of the problems with cylinders and tapping the side, is that the curve is what holds the pressure, so fitting a flat flange will create a weak point!

 

If the accumulator is empty of air then it will not be helping the flow, any water drawn off will have to be replaced by the pump. Is the accumulator mounted with the air valve at the top or bottom or horizontally?

 

It is also possible there is an air lock in the cold pipework?

 

Make sure you have a sketch of the plumbing, especially where any valves are etc. (you can then figure out where water should be going!)

If the accumulator is immediately after the pump in the cold system, this will need pumping up (with the system unpressurised) to 10 - 15 psi. With the system pressurised, running the cold (probably around 5l) should cause the pump to cut in until the system pressurises again.

Then test what happens with the hot, does it behave differently?

[smileypete]

More playing this morning; from empty the pump ran for 34 seconds to full pressure (the proper accumulator is empty of air) and then I ran off a little water and it cut in again almost immediately. So doing nothing is not really an option. Abandoning the pressurised system to hot water only is the position of last resort and put a Galley Gusher for cold . I need to get some air out of the system. The option above seems feasible.

 

...

 

Latest question is. If the air is in the hot water system why does the pump run when cold water is drawn?

Maybe there's a problem with the pressure switch bleed hole in the pump, or there's a non return valve in the plumbing somewhere.

 

What happens if you draw water from the tap downstream of the calorifier? If you fit a guage along with the safety relief valve (aka PRV) that'll help tell what's going on, BES do a combined on, part # 11348,11349.

 

But I hope there's a safety relief valve (PRV) fitted already!!!

 

I am not quite sure why cutting a hole in the tank would be so catastrophic, surely the pressure is not so great as to compromise the entire hot water tank? I thought also of cutting a hole in the top of the tank and putting the brewers bung in with a PRV that doubles as a bleed valve.

I'd only use a proper flange and an accurately cut hole.

 

I am struggling, I think,mainly as a result of living, happily, the last 10 years with a Galley gusher and little else.

I think the top priority is something that's safe and avoids expensive or disastrous problems, whether the pump or immersion thermostat fails.

 

cheers,

Pete.

[nicknorman]

More playing this morning; from empty the pump ran for 34 seconds to full pressure (the proper accumulator is empty of air) and then I ran off a little water and it cut in again almost immediately.

Do you mean you ran off water from the hot, or the cold system? If from the cold, and you have no air in the accumulator, and an NRV at the inlet to the calorifier, the pump is bound to run immediately (you need to pressurise the accumulator, with pump off and taps open, to just below pump cut-in pressure). If you ran off a bit of hot water and it cut in again immediately and ran for another 30+ seconds, that is a bit strange and I would wonder if the pump was OK.

 

I can't remember if you have said, but do you have a non-return valve at the inlet to the calorifier (it doesn't seem to be visible in the photos)

 

 

I am not quite sure why cutting a hole in the tank would be so catastrophic, surely the pressure is not so great as to compromise the entire hot water tank? I thought also of cutting a hole in the top of the tank and putting the brewers bung in with a PRV that doubles as a bleed valve.

Remember it is not the pressure so much as the force, which is pressure x area. You only put 30 psi into your car tyres but they manage to hold up you car weighing over a ton. Copper is expensive, so they make it as thin as possible with little over-engineering and compromising its structure might just work, but then again a ruptured calorifier with the entire contents of the water tank lost into the bilges is not a nice prospect.

 

ETA for fault-finding, you might consider adding a shutoff valve at the inlet to the calorifier (dead easy with plastic plumbing). If you isolate the calorifier inlet, pressurise the accumulator and the pump is still misbehaving, your problems lie elsewhere. The shutoff valve would also be useful if you decide to disregard the advice not to cut a hole in the calorifier!

Edited January 19, 2012 by nicknorman