Pressurised Hot Water

Out of curiosity, how long must you run the engine to get enough hot water for a shower say?

I have actually considered dumping my airtonic and fitting one the hydro types with a radiator circuit around the boat too. Trouble is, this means a lot of pipework and serious changes to the fresh water system, including a long run from the tank to the heater and back to the heads. But this would be a similar problem for engine heated water... How much water do you need to run off before hot starts coming through..

See, water is precious on a small boat, and really, we all sail small boats.

I am also guessing you need copper pipe to deal with the heat, this would all add to weight on board our tonka sized cat, thus it will probably remain a 'pipe dream' <pun intended> So I should stick to the 'DogWatch KISS hot water system™' I think.
 
All my hotwater pipework is plastic.....

I reckon that 20mins of running should have plenty of hotwater available....

It probably only needs to run for 10 secs in order to get hot water through....

It is however, as you have recognised, a lot easier to chew through water when you start using hot water for washing up, showers, cleaning your hands etc etc...

Its for this reason that i've bought a watermaker!... although yet to install it.
 
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I reckon that 20mins of running should have plenty of hotwater available....

[/ QUOTE ] I have to say, that is a great deal quicker than I thought it would be.
 
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I reckon that 20mins of running should have plenty of hotwater available....

[/ QUOTE ] I have to say, that is a great deal quicker than I thought it would be.

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axshully, my Yanmor 3YM30 produces usable hot water in less than 10 minutes enough for a shower and a half...... full heat achieved in just over 20 minutes which is 30 litres.
 
I prefer the idea of a calorifier rather than a gas geyser, because with the calorifier you get the benefit of using the waste heat from the engine, instead of using (and paying for, gas). But then, I'm a Fifer.
Seriously, calorifiers are excellent, and, provided you can find a suitable space for it, are easy to instal.
 
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Heres another system schematic.

It's important to fit a pressure relief valve to the HW cyclinder to vent if over pressure (select location of discharge carefully it could be very hot if a fault occurs) and if your fitting an electric immersion heater too, fit a high temp cut out thermostat in addition to the normal HW control thermostat (often in the same casing)!

BOATHWSYSTEM.jpg


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There does not appear to be a non return valve in this diagram, before the pressure pump, which I believe is necessary? Or is the non return valve incorporated in one side of the pump.

It certainly was not incorporated on the Whale pressure pump I bought, and I had to insert a new non return valve, just before it at per the first diagram in this post. I don't know how the system worked before with the old pump (same design) and I have never found a failed non return valve in the system!
 
I agree, depending on pump type a non-return valve should be fitted between the tank and pump to prevent backflow into the tank and pump cycling.

I have a SHURflo Aqua King on my boat, that utilises diaphram type valve assemblies - I have not seen a NRV in the system, I expect the valves themselves and/or the filter prevents backflow.
 
A non-return valve is unnecessary for two reasons.

1. In a typical installation using a reciprocating pump, the pump's own suction valves are non-return, i.e. they allow water to move forwards by the pump's action but do not let it return.
2. For water to drain back into the tank it needs to be replaced by air. None can enter the system in the stationary situation. Think mercury barometer!

Different perhaps if you have a centrifugal pump sited above the tank, although even here the column of water should remain intact if you are lucky. Better in this case to have the pump at tank outlet level so that it always primes itself.
 
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A non-return valve is unnecessary for two reasons.

1. In a typical installation using a reciprocating pump, the pump's own suction valves are non-return, i.e. they allow water to move forwards by the pump's action but do not let it return.
2. For water to drain back into the tank it needs to be replaced by air. None can enter the system in the stationary situation. Think mercury barometer!

Different perhaps if you have a centrifugal pump sited above the tank, although even here the column of water should remain intact if you are lucky. Better in this case to have the pump at tank outlet level so that it always primes itself.

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Vyv, I had a problem last year that the pump would not switchoff, and a loud hissing noise would develop from the manual sink pump, which I assume is between the main tank and the pump. I first changed the pressure switch - no change. I then cut in a non return valve into the line after the manual sink pump. Pump cut out OK, BUT manual pump would not pump water. Then the pump gave up, and I replaced with a new Whale pump identical to the old (which is not a reciprocating pump), and thinking that a new pump would have cured the pressure problem, removed the NR valve. - Hissing started again, so put back NR valve. What I dont understand is why the NR valve stopped the manual pump from working.

I will be changing the position of the NR valve to either just before the Pump, or before the Manual pump, though for the life of me I cannot see why it should make any difference. I cannot see where the actual pipes go, as they dissappear under the fridge etc, and then appear 2 meters away again, so the layout may not be as I am thinking. - But definitley a NR valve required!!! - Though I have no idea where the original one was/is!!!!!

I am assuming that the manual pump is in between the water tank and the pressure pump, in that is pumps both hot and cold water. There is no loss of water anywhere into the bilges, so the only plavce the pressure could be going is back to the tank, through the manual pump (as the hissing is clearly coming from it).

Any ideas???
 
I think you need to find out for certain where the take-offs for the manual and pressurised pumps are. Mine are completely separate, with two pipes into the tank. The only explanations I can think of for your problem require the take-offs to be in some unusual locations, so I think you need to be certain before going any further.

Are you certain that when you put the NR valve in that you installed it the correct way around? That would be one possibility for the manual pump not working.
 
VYV agree with your first point which is why I do not have a NRV in my system, pump valves hold the pressure, but with regard to your second point:

You do not need air to enter for water to escape, you just need a difference in pessure. If you have an accumulator or expansion vessel upstream of the pump (and the pump lets-bye) water will pass from the higher pressure side of the system to the lower pressure side i.e. the tank!

If your going to install a NRV I would install it to the suction side on the pump.
 
The pump would have to be completely knackered for that to happen. Not only would the suction valves be passing, the discharge valve would as well. Stretching the imagination too far for me.

I repeat - with a positive displacement pump, which the majority of pressurised water systems will have, there is no need for a NRV.
 
I think it is back to the drawing board and map out where the pipes go - not that easy to see though! I have spoken to whale, and you are right, it should not need a NR valve. (not that I doubted you of course!)
 
VYV I am certainly not disagreeing with you regarding the fitting of a NRV - I dont have one in my system and have no intention of installing one.

I was just out of synch with you regarding your second statement, that air has to enter the system before water can leak out!

Clearly, a faulty valve on a pump would permit water to pass back through the system into the tank, without air having to enter the system, due to the pressure difference.

So:

Would I fit a NRV - no

Is one required - no (unless you have a pump that lets by)

If I were to decide to install one where would I put it - suction side of pump! /forums/images/graemlins/cool.gif
 
Mmmmm: I suppose if the pump was switched-off, the shower hose/valve was fully open, shower head was dropped into the water and remained full, someone turned on a tap inside the boat and left it open, it is theoreticaly possible a siphon could occur, but highly unlikely IMO. The overflow on the sink would have to be blocked too for the boat to flood. Still, an interesting topic to debate.

As far as back contamination is concerned: IMO I would also suggest the riak is low and not improved much by installing a NRV. For the same reason a kitchen tap is not always protected by a NRV, a simple air gap between contaminated water and the mains is deemed adequate.

Mind you, if you do drop a shower head or hose into the sea it will do no harm to well flush it through and/or clean it in a mild bleach solution!
 
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