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Hot water cylinder to hot


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#1 Womble

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Posted 15 January 2018 - 10:24 PM

Is there supposed to be something in the engine hot water circuit that stops the temperature in the cylinder from reaching explosion levels?

 

I started using our hot water cylinder the other day for the first time in two years and since we have had the boat and the freshwater outlet blew off after motoring for a couple of hours.  The engine temperature was sitting around it's normal 90degC.  The boat became a bit of a steam room for he next half an hour while the remaining water boiled off.

 

I haven't tried exploring the water pipes to see if there is something in the circuit, like a temperature regulator that isn't working, but given this has happened I would kind of expect something to exist?

 

Thanks


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#2 BNG

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Posted 16 January 2018 - 05:52 AM

Was it actually full of water and not air-locked up? I always run the hot tap prior to a good motor to flush any air out. 

 

It takes roughly 10 x as much energy to heat the same volume of water as air so if its partially empty its likely to get way hotter than

it should as its not transferring the energy (heat) to water.


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#3 wheels

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Posted 16 January 2018 - 06:30 AM

Womble, normally the water cylinder has a heat exchanger internally. The engine cooling water flows through this, and transfer the Engine heat to the Cylinders fresh water. The pressure relief for the engine water is the Radiator cap at the engines own heat exchanger.
The fresh water should have it's own pressure relief mounted on the tank.
The fact that the fresh water is getting too hot is indeed a problem and the only way to solve this is with a temperature regulator mixing valve. Something that is now compulsory on Home installations.


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#4 Neil

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Posted 16 January 2018 - 10:51 AM

On our boat, if the engine is run for an extended period not only do you get hot water from the hot tap but also for a short time out of the cold tap too. I've been putting this down to some sort of backflow from the hot water tank into the feeding cold water pipes due to pressure or expansion. The previous boat didn't have the luxury of hot water so have not been sure if this normal. Should I be worried that the hot water tank is not venting pressure elsewhere? 


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#5 Jon

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Posted 16 January 2018 - 11:15 AM

We have a ball valve in the hose between the engine and the hot water cylinder
Up in the tropics I would just crack it open to reduce the flow as it took no time to heat
Down here I leave it open but close it if I’m motoring a long way after about an hour otherwise we have 90deg water at the hot tap
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#6 Womble

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Posted 12 February 2018 - 03:33 PM

Thanks all. I don't have a radiator. The water from the ocean is just pumped through the engine. That same water is pumped through the heat exchanger in the hot water cylinder.

I have followed the hoses and there is no pressure release valve anywhere. So it's not surprising that the cylinder blew its outlet hose off.

I am guessing that I need to fit a pressure release valve in the circuit, but I am not sure where to release the pressure too...

Thanks for the responses all.

Rowan
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#7 wheels

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Posted 12 February 2018 - 04:20 PM

This is what you need to do.
Diagram-7-Marine.png


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