Calorifier back siphoning to engine

[Top cat]

Over night hot water from the calorifier back siphons through the engine so in the morning we have a warm engine and a cold shower. The calorifier is lower than the engine. Whats the best way of stopping this ? will and ordinary non return valve do the job or do I have to be careful about the forward pressure drop I see midland chandlers have them for £0 and domestic ones are less than half that

. I've seen check valves in the plumbers merchants, is that just another way of describing a non - return valve ? Would I be better re routing the pipe work to take it above engine hieght ? or will it still siphon ?

 

Regards

 

TC

Edited July 6, 2009 by Top cat

[alan_fincher]

I see midland chandlers have them for £0 and domestic ones are less than half that

 

How much is less than half of £0 ?

 

We went for the approach suggested by Catweasel of putting a downward loop in both feed and return. (A search of old threads should yield a diagram he supplied).

 

The tank still heats well, and we still have quite a bit of hot water the next day.

 

It's hard to say how much we might still be loosing through reheating the engine, and how much through the calorifier insulation, though.

 

I've no experience of putting a valve in, but found the calorifier circuit hard enough to bleed of air, without adding extra hurdles.

 

Whether a valve will impede flow probably depends on how strong your engine water pump is.

[Ray]

We have a non-retrun valve (from MC) but we're not convinced it does much for our 55 litre vertical calorifier.

 

Different people reckon that we can and can't expect enough water for a shower in the morning, even after more than eight hour's cruising the day before.

 

I do wonder if the problem is all to do with the amount of water you run off in the evening for dish washing and the like.

 

I plan to fit a further insulation jacket over the cylinder at some stage and see what impact that has.

 

I've also heard it said that there is a possibility that the water isn't gettting hot enough during the day and wonder whether the working temperature of different engines accounts for different results from their owner's calorifiers. We have a Beta 43 and don't believe that the coolant water gets much above 65 degrees when cruising. As we also have a cylinder thermostat for use when we use the gas boiler to heat the cylinder, and that is set to 55 degrees and is only just hot enough for a shower, maybe expecting a cylinder not to drop 10 degrees overnight is a bit too much.

[alan_fincher]

Yes,

 

Ray has a very valid point.

 

Before I installed our calorifier, I upped the engine thermostat from a 74 degree to an 82 degree one.

 

I have no reason to doubt that the water in the calorifier is not getting heated somewhere near that 82 degree number, a lot higher than Ray's 65 degrees, (and which I still think sounds low for a modern engine).

 

A thermostatic mixer valve on the outlet to the calorifier avoids water out of the taps actually being at skin stripping temperatures over 80 degrees, (hopefully!) - I'm just waiting for the really safety concious types to tell me I need another valve that cuts off the water supply if the TMV fails.

[Top cat]

How much is less than half of £0 ?

Sorry that should be £30

 

I see that Catwheasel had a Rise in the pipes not a dip would either work ?

 

TC

[alan_fincher]

I see that Catwheasel had a Rise in the pipes not a dip would either work ?

Not sure,

 

Our pipes don't rise from the engine, but have been dipped down in both the feed and return, to be lower than both the engine take offs, and the calorifier.

 

Seems to work, but our situation is somewhat different as our calorifier is horizontal.

 

We left some slack in the radiator hose used to feed it, so we could raise or lower bits to get it right - in practice it was left where we first put it, as it's good enough.

 

As an aside.......

 

I have never understood why people seem to think back syphoning is more likely if the calorifier is higher than the engine.

 

It always seems intuitive to me that it would be more likely where the calorifier is lower than the engine. Hot waster rises by convection, not falls, after all.

 

Where's Chris W when you need a scientific explanation ?

[Smelly]

An NRV costing 30 quid? Ours cost about a fiver.

 

It's probably an easier job than putting loops in pipes and can't do any harm... Can it?

 

A loop will probably help but why not stop the syphon in the first place?

[alan_fincher]

It's probably an easier job than putting loops in pipes and can't do any harm... Can it?

Rightly or wrongly, some people on here have reported they slowed the flow, delaying, or even preventing the calorifier filling completely.

 

I can neither confirm, nor deny, but my pipe loops seem to be working, represent two less joins that could leak, and the extra pipe almost certainly cost less than your five quid valve.

 

If I had found my hot water gone by the morning, my next move would have been to try it, though.

[RobinJ]

I have never understood why people seem to think back syphoning is more likely if the calorifier is higher than the engine.

 

It always seems intuitive to me that it would be more likely where the calorifier is lower than the engine. Hot waster rises by convection, not falls, after all.

It should not matter whether one is higher than the other!

Any hot water which is in a position to cool (outside the calorifier) will fall to a lower point (engine or calorfier), in doing so, it will :-

1) go to a point which is warmer and get hotter (convection)

This could mean that one calorifier pipe is simply radiating the heat away.

2) cause warmer water to rise to a higher point (circulation)

This is the case where the reverse of normal heating is taking place.

If either event heat will be lost!

The convection effect will be reduced if plastic pipes have been used or they are well insulated.

The circulation effect can be reduced by inserting loops (air lock - heat lock), but that can result in forcing a convection effect to take place.

 

Inserting an NRV will prevent reverse circulation; it may create a convection effect as with loops if not put in the right place; or could prevent heating taking place (due to opening pressure).

Inserting a flap valve can resolve the problem too (provided in can handle the tamperatures), but it may need gravity to help it operate, so it can be important to get the correct orientation and location (i.e. the top inlet on the calorifier).

[Top cat]

An NRV costing 30 quid? Ours cost about a fiver.

 

Well thats what Midland chandlers want and they are not renowned for low prices so I was wondering if there was something special about it or would an ordinary £5 one do ?

 

I think in our boat fitting a valve will be marginally easier than putting in extra pipe loops

 

Are flap valves gernally available at plumbers merchants ?

 

Regards

 

TC

[nb Innisfree]

Why not stop back syphon with NRV and if probs with circulation stick a pump in which will accellerate calorifier warm up, plus you could leave pump off to speed engine warm up if you so desired

[buggsy]

Over night hot water from the calorifier back siphons through the engine so in the morning we have a warm engine and a cold shower. The calorifier is lower than the engine. Whats the best way of stopping this ? will and ordinary non return valve do the job or do I have to be careful about the forward pressure drop I see midland chandlers have them for £0 and domestic ones are less than half that

. I've seen check valves in the plumbers merchants, is that just another way of describing a non - return valve ? Would I be better re routing the pipe work to take it above engine hieght ? or will it still siphon ?

 

Regards

 

TC

Hi TC,

 

i had the same problem but i have posted about adding a "flap" valve fitted in the pipe from the engine to the calorifier not the return and all works ok and our hot water is back too remaining hot. I think you can get these from Aquafax, i got mine given to me.

 

cheers,

 

Steve

[Ray]

Measured the temperature of the coolant today ten minutes after turning the engine off after cruising for 3.5 hours. Water temperature was just 70.5 degrees.