Calorifier backflow

[Narrowjack]

Something I've been meaning to address for years, but never got around to, is the cooling effect of return convection from the domestic hot water tank to the engine (& thus the hull panel), resulting in a reduction of hot water in the mornings, particularly in winter . All it needs is a check valve in the flow from the engine to the bottom of the calorifier, but as it's only the pressure of the engine water pump pushing the flow I'm a bit unsure of the suitability of a normal domestic water system valve. Anyone any recommendations as to type of valve?  

[Tony Brooks]

22 minutes ago, Narrowjack said:

Something I've been meaning to address for years, but never got around to, is the cooling effect of return convection from the domestic hot water tank to the engine (& thus the hull panel), resulting in a reduction of hot water in the mornings, particularly in winter . All it needs is a check valve in the flow from the engine to the bottom of the calorifier, but as it's only the pressure of the engine water pump pushing the flow I'm a bit unsure of the suitability of a normal domestic water system valve. Anyone any recommendations as to type of valve?  

 

I think you may have that wrong, it will probably still work but the water in the coil being heated will rise so the valve needs to go into the top connection. I found a correctly orientated and mounted flap valve did the job.

 

Despite what some on here say try putting your figure partially over the open hose and revving the engine. I think that you will find more pressure than people often think but the impellor will cavitate easily i you stop the compete flow.

 

PS sometimes swapping the top and bottom calorifier connections over stops the thermo-syphoning.

 

Edited July 27, 2020 by Tony Brooks

[Tracy D'arth]

36 minutes ago, Tony Brooks said:

 

I think you may have that wrong, it will probably still work but the water in the coil being heated will rise so the valve needs to go into the top connection. I found a correctly orientated and mounted flap valve did the job.

 

Despite what some on here say try putting your figure partially over the open hose and revving the engine. I think that you will find more pressure than people often think but the impellor will cavitate easily i you stop the compete flow.

 

PS sometimes swapping the top and bottom calorifier connections over stops the thermo-syphoning.

 

Horizontal cylinder? Take the flow into the lower connection of the coil in the calorimeter after you have taken the pipe all the way down to the floor, as low as you can get.

This will stop the hot water rising due to thermosyphon action. And it makes getting the air out of the coil easier.

TD'

[Narrowjack]

Hi, thanks for the quick response.

Perhaps you are correct, but I refer to a normal calorifier set up where the flow comes in from the bottom and the heat will sink out of the coil as the tank cools. However, I guess either will work to stop the flow. Thanks for the experience on cooling pump flow, I guess that sounds like a good bit more that the 0.3 bar min pressure for a normal domestic check valve. Cheers.

[PeterF]

I put one in mine as I also have a towel radiator after the calorifier and that caused back flow. I used an unsprung flap valve as Tony recommends and it works fine. Just get the orientation right, if it is horizontal pipe the hinge is at the top so it closes by gravity. If it is in vertical pipe it will only work if the flap opens upwards, reverse thermosyphon will not generate enough flow to close a valve that opens downwards. I never had any issues with water circulation from the engine through the calorifier and towel radiator.

Edited July 27, 2020 by PeterF

[JonesBoy]

I used one of these and it cured the problem, as per Tony Brooks post

 

https://www.bes.co.uk/water-swing-check-valve-brass-1-2-bsp-7462/

[dor]

As mentioned, a flap valve is the answer.  Very little restircion to flow.

[Narrowjack]

Thanks all, it's a vertical calorifier, normal household size, I'm not clear from your responses which side you're saying to fit, though probably doesnt make much difference I guess...?

[nicknorman]

I can’t see that it would make any difference whether you fitted it to flow or return side - the point is just to stop reverse circulation.

[Ryeland]

3 hours ago, Narrowjack said:

Thanks all, it's a vertical calorifier, normal household size, I'm not clear from your responses which side you're saying to fit, though probably doesnt make much difference I guess...?

But you have to find a suitable bit of pipe for the valve with the flow in the upward direction, so the flap valve closes by gravity and stops the reverse flow. A flap valve is not the same as a (spring loaded) check valve.

 

Richard

[Tony Brooks]

13 minutes ago, Ryeland said:

But you have to find a suitable bit of pipe for the valve with the flow in the upward direction, so the flap valve closes by gravity and stops the reverse flow. A flap valve is not the same as a (spring loaded) check valve.

 

Richard

 

I would suggest a horizontal run, not a vertical one. Especially as the OP seemed to be concerned about the ability of the water pump to open it.

[Narrowjack]

Thanks folks