Calorifier

[Troll]

The calorifier on one of my boats sprang a pin hole type leak, god knows how, the makers replaced it free no questions. (what a company) next day new one arrives by courier but when fitted it swelled up a little like a balloon , any ideas why?

 

Funny thing is a week or so before my water pump played up (stopped working) and they (Boothestown Marina on bridgewater) sorted it and reduced the pressure so why did my new calorifier blow out a little like a balloon?

 

I`m confused.

[alan_fincher]

Faulty PRV ?

[Smelly]

Faulty PRV ?

 

Either that or it was made of rubber.

 

A Cruel Fate that you gets your new tank and the valve's stuck, 'less of course the supplier provided the PRV as well...

 

We are, of course, assuming that you'd heated the tank up to provide the pressure for the tank to blow up... If not it was definitely option number two.

[Guest TerryL]

Either that or it was made of rubber.

 

A Cruel Fate that you gets your new tank and the valve's stuck, 'less of course the supplier provided the PRV as well...

 

We are, of course, assuming that you'd heated the tank up to provide the pressure for the tank to blow up... If not it was definitely option number two.

 

What is the pressure rating of the calorifier, the pump output, the expansion vessel air pressure and the PRV? They should all be lower pressure than the calorifier, in order, the PRV, then the pump, then the expansion vessel air.

[John Orentas]

Could well be the pressure switch on the water supply pump, as has been said many times on the this forum the built in pressure switches can be very poor, a search will give some ideas for suitable replacements..

 

A small leak in a copper calorifier is quite repairable.. An invaluable tool on a boat is an old fashioned soldering iron, the type you simply heat up an a gas ring, mine has come in useful many times.

[Guest TerryL]

Could well be the pressure switch on the water supply pump, as has been said many times on the this forum the built in pressure switches can be very poor, a search will give some ideas for suitable replacements..

 

A small leak in a copper calorifier is quite repairable.. An invaluable tool on a boat is an old fashioned soldering iron, the type you simply heat up an a gas ring, mine has come in useful many times.

A blow lamp is easier, too much heat loss with all that copper for a soldering iron.

[John Orentas]

A blow lamp is easier, too much heat loss with all that copper for a soldering iron.

 

 

I did say "an old fashioned soldering iron" perhaps I should have included 'a big one'.

[chris w]

What is the pressure rating of the calorifier, the pump output, the expansion vessel air pressure and the PRV? They should all be lower pressure than the calorifier, in order, the PRV, then the pump, then the expansion vessel air.

 

If by the "expansion vessel", you mean the expansion vessel on the calorifier (if fitted) rather than the accumulator on the water pump, then your list is in the wrong order.

 

The PRV will be the highest pressure setting (typically around 3 bar/42psi), the expansion vessel on the calorifier must be set between this figure and the cut-OFF figure for the pump. The latter is typically around 30psi so the expansion vessel needs to be set at around 35psi. If one set them in the order you advocate, the expansion vessel wouldn't do its job if you go through the sequence logically.

 

It's the accumulator on the water pump that is set lower than the pump's cut-IN pressure, the latter being typically 20psi so the accumulator can be set almost anywhere from say 10-15psi (it's not critical).

[Guest TerryL]

If by the "expansion vessel", you mean the expansion vessel on the calorifier (if fitted) rather than the accumulator on the water pump, then your list is in the wrong order.

 

The PRV will be the highest pressure setting (typically around 3 bar/42psi), the expansion vessel on the calorifier must be set between this figure and the cut-OFF figure for the pump. The latter is typically around 30psi so the expansion vessel needs to be set at around 35psi. If one set them in the order you advocate, the expansion vessel wouldn't do its job if you go through the sequence logically.

 

It's the accumulator on the water pump that is set lower than the pump's cut-IN pressure, the latter being typically 20psi so the accumulator can be set almost anywhere from say 10-15psi (it's not critical).

 

So you're a heating engineer as well are you? Well not a good one because you would know there is no setting for any expansion vessel on the water side! I said the air side! The side that gives the initial pressure, typically set on an empty system at 0.5 - 1 bar air pressure to inflate the diaphram! If it were higher than the water pressure there would be no expansion would there? The water pressure is the same throughout the system and the calorifier expansion vessel is in the calorifier cold feed to give additional expansion capacity for hot water and local protection rather than as an accumulator at the pump. If people follow your advice it's no wonder the PRV or calorifier would blow. Don't you get fed up with getting things wrong?

[Chris J W]

If you two are going to start having another spat, would you mind doing it via PM? You never know, it's entirely possible that you're looking to resolve the issue but from entirely different angles with, possibly, different usages of terminology.

[Guest TerryL]

If you two are going to start having another spat, would you mind doing it via PM? You never know, it's entirely possible that you're looking to resolve the issue but from entirely different angles with, possibly, different usages of terminology.

He started it! I don't think excessive and unusable pressure in an expansion vessel can be looked at any differently and it's these blatantly wrong and ingrained ideas that ChrisW continues to perpetuate as gospel that cause confusion and problems unnecessarily for other people. I don't usually comment on things I haven't good experience and some in depth knowledge of and I wish he would be fair to people and do the same.

 

You probably don't realise that because he doesn't have all the information or experience he tries to blind you with science and maths which are often wrong, rubbish or unrelated. He doesn't fool me and hopefully other people and that's why he will never answer my questions or agree with me (well he did once!) and insults me instead. I can often catch him out and so I can't take him seriously.

Edited November 1, 2008 by TerryL

[ChrisPy]

So you're a heating engineer as well are you? Well not a good one because you would know there is no setting for any expansion vessel on the water side! I said the air side! The side that gives the initial pressure, typically set on an empty system at 0.5 - 1 bar air pressure to inflate the diaphram! If it were higher than the water pressure there would be no expansion would there? The water pressure is the same throughout the system and the calorifier expansion vessel is in the calorifier cold feed to give additional expansion capacity for hot water and local protection rather than as an accumulator at the pump. If people follow your advice it's no wonder the PRV or calorifier would blow. Don't you get fed up with getting things wrong?

Terry:

No wonder you manage to get into silly arguments. You seem to have a habit of misquoting CW. For example:

- Where did CW refer to setting 'the expansion vessel on the water side'?

- Where did you say 'the air side'?

 

I will present my own conclusive advice on expansion tanks and diaphragms later ..............................

[koukouvagia]

The calorifier on one of my boats sprang a pin hole type leak, god knows how, the makers replaced it free no questions. (what a company) next day new one arrives by courier but when fitted it swelled up a little like a balloon , any ideas why?

 

I`m confused.

 

I’m intrigued by your description “swelled up a little like a balloon.” This may sound daft, but are you absolutely sure that it’s not the insulation that’s swollen, rather than the copper? I replaced a calorifier recently with exactly the same symptoms only to find it was perfectly OK once I’d removed the foam.

[chris w]

So you're a heating engineer as well are you? Well not a good one because you would know there is no setting for any expansion vessel on the water side! I said the air side! The side that gives the initial pressure, typically set on an empty system at 0.5 - 1 bar air pressure to inflate the diaphram! If it were higher than the water pressure there would be no expansion would there? The water pressure is the same throughout the system and the calorifier expansion vessel is in the calorifier cold feed to give additional expansion capacity for hot water and local protection rather than as an accumulator at the pump. If people follow your advice it's no wonder the PRV or calorifier would blow. Don't you get fed up with getting things wrong?

I am afraid that you are espousing nonsense again. I have an expenasion vessel on my calorifier on the hot water outlet and it is set at about 35psi (ie: between the water pump's cut-OUT pressure and the PRV setting). This is exactly what the supplier of the expansion vessel stated should be done and is entirely logical if you follow the sequence of events. If the expansion vessel pressure were lower than the pump's cut-OUT pressure then there would be no expansion space available. It would get "expanded into" everytime the pump came on.

 

"Surecal", the manufacturer from whom I obtained my expansion vessel (and one of the largerst manufacturers of calorifiers and expansion vessels etc) agree with my thinking if you care to check out their website.

Edited November 1, 2008 by chris w

[Batavia]

I am afraid that you are espousing nonsense again. I have an expenasion vessel on my calorifier on the hot water outlet and it is set at about 35psi (ie: between the water pump's cut-OUT pressure and the PRV setting). This is exactly what the supplier of the expansion vessel stated should be done and is entirely logical if you follow the sequence of events. If the expansion vessel pressure were lower than the pump's cut-OUT pressure then there would be no expansion space available. It would get "expanded into" everytime the pump came on.

 

"Surecal", the manufacturer from whom I obtained my expansion vessel (and one of the largerst manufacturers of calorifiers and expansion vessels etc) agree with my thinking if you care to check out their website.

 

You are more or less correct, apart from the bit in bold. There will still be space available, but less than if the pre-charge pressure is higher.

 

With an accumulator, you are trying to maximise dV/dP (should be partial derivatives, but can't find the right symbol), which you get by setting the set pressure at a point where tere is no liquid in the vessel at the normal operating pressure. In your example, it could be be set at 10 psi, but when the pump cuts out at 30 psi, nearly half of the vessle is full of liquid and dV/dP will be much lower than had the precharge pressure been 30-35 psi. This assumes isothermal compression - if you think it is part-adiabatic, then add in a bit of gamma.

 

Chris G

Edited November 1, 2008 by Batavia

[chris w]

You are more or less correct, apart from the bit in bold. There will still be space available, but less than if the pre-charge pressure is higher.

 

With an accumulator, you are trying to maximise dV/dP (should be partial derivatives, but can't find the right symbol), which you get by setting the set pressure at a point where tere is no liquid in the vessel at the normal operating pressure. In your example, it could be be set at 10 psi, but when the pump cuts out at 30 psi, 2/3rds of the vessle is full of liquid and dV/dP will be much lower than had the precharge pressure been 30-35 psi. This assumes isothermal compression - if you think it is part-adiabatic, then add in a bit of gamma.

 

Chris G

 

I would agree that it's primarily isothermal rather than adiabatic due to the relatively long system times involved.

 

The calculations on sizing the expansion tank assume that half the volume is available for expansion, so a calorifier whose contents will expand by around 4% when very hot will require an 8% expansion tank. In round numbers, the rule of thumb is therefore to use an expansion vessel nominally 10% of the volume of the calorifier. This assumes of course that, as you correctly point out, the expansion vessel is pressurised to above the pump's cut-out pressure.

 

Chris

[david and julie]

I also have a Surecal calorifier and a second expansion vessel, indeed it sounds like I may have the same set up as Chris.

 

The way mine works is the cold supply comes from the pump to under the bed(next to the calorifier) it then has a tee piece to an expansion tank, then a second tee for the cold supply. The cold supply then continues to the calorifier via a non return valve.

 

The hotwater supply out of the calorifier then has the second expansion tank along with a prv.

 

Hot water expansion and any pulsating in the hot water supply is taken care of by the second expansion vessel and cold water pulsating has its own.

 

I'm assuming we all mean the same thing by expansion tank and accumulator?

[ChrisPy]

I did promise ... so here goes:

 

Expansion and accumulator vessels.

 

Assume

o the accumulator/expansion tanks each have a diaphragm that can move between 100% full of air to 100% full of water.

o The pump cut-in/cut-out pressures are 15psi and 30psi (gauge pressures)

o the calorifier is OK for 60psi and has a pressure relief valve set at 35psi

o there is a check valve between the pump and the calorifier.

o The accumulator is upstream of the check valve and the expansion tank is downstream.

o Calorifier volume is 50 litres

o Accumulator volume is 5 litres.

 

Accumulator vessels are normally supplied with some pre-set internal pressure, so that the diaphragm is in the ‘full of air’ position.

I use a 12 volt car tyre inflator that has a pressure gauge – easy to check.

 

The volume of air is inversely proportional to the absolute pressure – this is the gauge pressure plus atmospheric pressure.

Atmospheric pressure is 14.7psi.

(Add 15psi to all gauge pressures to get absolute pressure).

 

Check the cold water accumulator, and set at 7.5psi (22.5psia). Start the pump.

When the pump cuts out at 30psi (45psia) the volume of air in the accumulator is 5x22.5/45 = 2.5 litres.

The water stored in the accumulator will provide flow until the pressure drops to the pump cut-in pressure of 15psi (30psia). At this point the volume of air in the accumulator is 2.5x45/30 = 3.75 litres.

So the effective volume of a 5litre accumulator is only 1.25litres.

 

The calorifier may be pressurized to the pump cut-out pressure of 30psi (45psia) before it heats up.

The expansion of water in a 50litre calorifier when the temperature is raised from 40F to 160F is about 2 litres.

If the expansion vessel is pre-set at 15psi (30psia) then in order to accommodate 2 litres of expanding water the volume will reduce from 5litres to 3litres and the pressure will rise to 30x5/3 = 50psia or 35psi

[Batavia]

I would agree that it's primarily isothermal rather than adiabatic due to the relatively long system times involved.

 

 

Chris

 

The only thing I have just thought of is that, unless the connection between the calorifier and the vessel is very long and uninsulated, you are actually putting hot water into the vessel, so it is definitly not isothermal - but the flow should be slow.......!

 

But who cares (apart from a few pendants), if it doesn't make much difference?

 

Chris G

[Guest TerryL]

I am afraid that you are espousing nonsense again. I have an expenasion vessel on my calorifier on the hot water outlet and it is set at about 35psi (ie: between the water pump's cut-OUT pressure and the PRV setting). This is exactly what the supplier of the expansion vessel stated should be done and is entirely logical if you follow the sequence of events. If the expansion vessel pressure were lower than the pump's cut-OUT pressure then there would be no expansion space available. It would get "expanded into" everytime the pump came on.

 

"Surecal", the manufacturer from whom I obtained my expansion vessel (and one of the largerst manufacturers of calorifiers and expansion vessels etc) agree with my thinking if you care to check out their website.

You have only one expansion vessel where as in my business I have fitted hundreds in domestic and marine installations. You have to remember that marine calorifiers do not have the same safety features as domestic calorifiers and standards are lower. The expansion vessel is normally required to be fitted at the cold inlet to the calorifier or the coolest part of a heating system. It must be pre-charged with air which as I stated will be the lowest pressure in the system.

 

A common mistake that you have made is to adjust this pressure and assume the volume when the system is pressurised, it means nothing, you can still have pressure but no volume especially if the pressure is lost as it will do over time and then if it is only re-pressurised to the same as before with or without relieving the system pressure. It is the wrong way to do it and will result in under or over pre-charge pressure and no volume, the reason why PRV's and calorifiers can blow.

 

I also have a Surecal calorifier and a second expansion vessel, indeed it sounds like I may have the same set up as Chris.

 

The way mine works is the cold supply comes from the pump to under the bed(next to the calorifier) it then has a tee piece to an expansion tank, then a second tee for the cold supply. The cold supply then continues to the calorifier via a non return valve.

 

The hotwater supply out of the calorifier then has the second expansion tank along with a prv.

 

Hot water expansion and any pulsating in the hot water supply is taken care of by the second expansion vessel and cold water pulsating has its own.

 

I'm assuming we all mean the same thing by expansion tank and accumulator?

 

The expansion vessel and accumulator do the same thing but some accumulators have no barrier or pre-charge and simply trap air as the cushion. They must be drained often to replenish the volume of air trapped.

[ChrisPy]

I did promise ... so here goes:

 

Expansion and accumulator vessels.

 

Assume

o the accumulator/expansion tanks each have a diaphragm that can move between 100% full of air to 100% full of water.

o The pump cut-in/cut-out pressures are 15psi and 30psi (gauge pressures)

o the calorifier is OK for 60psi and has a pressure relief valve set at 55psi

o there is a check valve between the pump and the calorifier.

o The accumulator is upstream of the check valve and the expansion tank is downstream.

o Calorifier volume is 50 litres

o Accumulator volume is 5 litres.

 

Accumulator vessels are normally supplied with some pre-set internal pressure, so that the diaphragm is in the ‘full of air’ position.

I use a 12 volt car tyre inflator that has a pressure gauge – easy to check.

 

The volume of air is inversely proportional to the absolute pressure – this is the gauge pressure plus atmospheric pressure.

Atmospheric pressure is 14.7psi.

(Add 15psi to all gauge pressures to get absolute pressure).

 

Check the cold water accumulator, and set at 7.5psi (22.5psia). Start the pump.

When the pump cuts out at 30psi (45psia) the volume of air in the accumulator is 5x22.5/45 = 2.5 litres.

The water stored in the accumulator will provide flow until the pressure drops to the pump cut-in pressure of 15psi (30psia). At this point the volume of air in the accumulator is 2.5x45/30 = 3.75 litres.

So the effective volume of a 5litre accumulator is only 1.25litres.

 

The calorifier may be pressurized to the pump cut-out pressure of 30psi (45psia) before it heats up.

The expansion of water in a 50litre calorifier when the temperature is raised from 40F to 160F is about 2litres.

If the expansion vessel is pre-set at 15psi (30psia) then this will rise to 45psia to match the calorifier pressure, reducing the available space to 5x30/45 = 3.3litres. In order to accommodate 2 litres of expanding water the volume will reduce from 3.3litres to 1.3litres and the pressure will rise to 45x3.3/1.3 > 100psia. This is unworkable. So the expansion vessel is too small.

 

Using a 10litre vessel set at 10psi (25psia), there is 10x25/45 = 5.5litres of space, reducing to 3.5. This corresponds to a pressure of 45x5.5/3.5 = 70psia or 55psi. So the PRV setting needs to be 55psi to avoid dumping water.

as (very politely) pointed out by Chris G, there is a flaw in the last paragraph, corrected above.

P.S. have I got it right this time ?

[Troll]

Yes I googled all this as well

 

Simple fact is Mine sprang a leak factory sent me a new one complete with all the other valves and stuff, and it kind of swelled either side of the straps, it`s fine but dont understand why since my water pressure had been turned down?

[Batavia]

as (very politely) pointed out by Chris G, there is a flaw in the last paragraph, corrected above.

P.S. have I got it right this time ?

 

Yes - looks sensible to me!

 

This means that either:

• People's TRVs are lifting more than one would wish
  
• Calorifiers are quite elastic
  
• Any NRVs on the inlet to calorifiers pass enough in the reverse direction to keep the pressure down
  

 

Any thoughts?

 

Chris G

[smileypete]

This means that either:

• People's TRVs are lifting more than one would wish
  
• Calorifiers are quite elastic
  
• Any NRVs on the inlet to calorifiers pass enough in the reverse direction to keep the pressure down
  

Any thoughts?

 

Copper expands when heated, so a copper calorifier will a get a bigger as it heats up!

 

Haha!!! 'The experts' hadn't thought of that, had they?

 

cheers,

Pete.

[Guest TerryL]

Yes - looks sensible to me!

 

This means that either:

• People's TRVs are lifting more than one would wish
  
• Calorifiers are quite elastic
  
• Any NRVs on the inlet to calorifiers pass enough in the reverse direction to keep the pressure down
  

 

Any thoughts?

 

Chris G

Why does it look sensible?

 

The TRV is a safety device pre-set to 3 Bar and should never open in normal use, if it blows it means the calorifier is over pressured!

Calorifiers will get damage if over pressured!

NRV's cannot be relied on to pass in the reverse direction and should not be needed anyway!

 

The expansion vessel is still too small by half if the mixed metric/imperial sums are right and which should also have a reserve for overheating to boiling if an immersion is fitted. But why mess about with this when manufacturers of expansion vessels will simply quote the size needed according to water capacity? Is that too simple or am I too used to cutting through the crap and getting solutions quickly?

 

What might have happen here is the PRV has stuck and or the expansion vessel diaphram has stuck/rusted to the casing, it does happen when stored or it is not pre-charged properly or some other installation problem. What about a picture?