Diaphragm pump for engine cooling.

[jamie N]

Anyone got experience of this? 10hp engine with a heat exchanger. The diaphragm pump circulates the seawater and is activated by an thermostat switch from the heat exchanger, so will be running intermittently depending on the usage of the engine.

 

[pvb]

Isn't this excessively complicated?

 

[black mercury]

Anyone got experience of this? 10hp engine with a heat exchanger. The diaphragm pump circulates the seawater and is activated by an thermostat switch from the heat exchanger, so will be running intermittently depending on the usage of the engine.

It must be a dry exhaust then?
What pumps the coolant round the engine, a vane type pump or a rubber impeller type pump?

 

[jamie N]

The impeller pump circulates the fresh water around the engine and through the heat exchanger. The thermostat switch is 'off of' the heat exchanger and activates the diaphragm pump which pumps seawater through the heat exchanger and out of the exhaust.

 

[VicS]

The impeller pump circulates the fresh water around the engine and through the heat exchanger. The thermostat switch is 'off of' the heat exchanger and activates the diaphragm pump which pumps seawater through the heat exchanger and out of the exhaust.

You must have a continuous flow of water into the exhaust, right from the time the engine is started, to cool it

 

[jiris]

The impeller pump circulates the fresh water around the engine and through the heat exchanger. The thermostat switch is 'off of' the heat exchanger and activates the diaphragm pump which pumps seawater through the heat exchanger and out of the exhaust.

Judging from the mention of a "heat exchanger", there is a primary fresh water jacket with a circulation pump and - a thermostat. So, the minimum temperature of the engine is being taken care of. As you need a continuous water flow thru the exhaust, why a thermostat for the raw water pump?

 

[gordmac]

You must have a continuous flow of water into the exhaust, right from the time the engine is started, to cool it

Not always the case. Some engines run a dry exhaust, obviously not the normal rubber type exhaust hose though.
I would imagine the system described allows the engine to warm up more quickly, probably a good thing on a sailboat where the engine doesn't run long.

 

[VicS]

Not always the case. Some engines run a dry exhaust, obviously not the normal rubber type exhaust hose though.
I would imagine the system described allows the engine to warm up more quickly, probably a good thing on a sailboat where the engine doesn't run long.

But the op does say it pumps water through the HE and out of the exhaust.

A thermostat in the engine coolant circuit should ensure a quick warm up.

 

[Fr J Hackett]

When I bought my last boat it was fitted with a half arsed add on fresh water cooling that relied on a small electric diaphragm pump to circulate the fresh water with the sea water being circulated through an inadequate heat exchanger via the engines impeller pump. The net result if you ran the engine for more than a few hours it overheated. The first thing I did was to revert to raw water cooling and then fit the standard Yanmar freshwater cooling system sadly the damage had been done and the rear oil seal was the victim.

 

[jamie N]

Thanks for the input.
VicS, you're absolutely right, I was swithering between getting a 'metal' exhaust, but that would've still left heat in the engine bay, so have gone for a 2nd diaphragm pump, that's controlled by the thermostat switch; the pump for the exhaust runs seawater through the exhaust, then when the thermoswitch is up to temp, a relay switches the other pump on, through the heat exchanger and out of the exhaust. The 2 pumps switch on & off between each other ensuring the constant flow through the exhaust, controlled by the relay which is controlled by the thermostat switch.
It sounds far more complicated than it really is.
I hope that answers jiris also.
Fr J, the heat exchanger is rated at 22kW/30hp, and the engine is 7.5kW/10hp, so there's a fair margin in hand.
In a test, the heat exchanger got up to temp, and then was cooled within 10 seconds of the pump running cooling water through it, and didn't require 'cooling' again for a minute or so.

I'm aware that this isn't real life situation, and that the boat isn't generating full heat.
For the downsides, it's putting a little bit of extra stuff in the system, which can always cause problems, however that's also the upside as there's so much redundancy here; the engine requires 1 pump to be able to run, there're 3, each one of which can cool the engine by simply plugging the 'surviving' pump into the seawater side and running it as before, directly through the engine, which is almost 'plug & play'.
The heat exchanger was from a previous 'thing', as was one of the pumps. The 2nd pump was £20, the thermostat switch and relay were about £8 or £9, so this isn't a great investment!
I believe that it'll enable the engine to run much closer to the optimal temperature, and to only be circulating clean and friendly liquids within it, rather than salt water.
One other benefit was that I was bored, and this kept me happy for a little while.

 

[LittleSister]

Be aware that you probably need more (i.e. faster) flow capacity for indirect cooling, to cope with the fact your engine is operating at a higher temperature (part of the point of having indirect cooling - you will also need a different thermostat) and consequently you are having to transfer more heat via the heat exchanger.

As an example, the spec for the pump(s) for my own Bukh DV36 at 3,600 rpm are -
Direct Cooling (50-70 degrees C)
Seawater pump - 24-30 litres per minute
Indirect Cooling (70--95 degrees C)
Seawater pump - 36-42 litres per minute (same pump type as above, but higher cam)
Freshwater pump - 132 litres per minute

Note also that cooling water pumps are normally centrifugal type, I believe, rather than diaphragm. I would have thought the latter would tend to have lower throughput. As the pump doesn't have the need to cope with significant solids, is there any advantage to a diaphragm pump in this service?

I am interested, though, in considerations and kit for converting from direct to indirect cooling, as I'd like to do that to my engine, but the standard Bukh DV36 gear-driven freshwater pump for it is prohibitively expensive (€1,900! ).

Another Bukh I have has both replacement seawater pump and freshwater pump belt driven by means of additional pulleys bolted to the flywheel. It has belt driven Jabsco seawater pump (replacing the direct driven DV10/20 original, which can risk leaking water into the engine if not properly maintained), and a belt-driven Ford automotive freshwater circulation pump (off an ancient Ford Transit, I suspect!).

That arrangement is not really an option on my DV36 as there isn't the same space at the front of the engine in my boat. An electric pump might be an answer, but few, if any, provide the sort of flow specified above, and it would be wasteful to be pumping for maximum flow all the time when I rarely use maximum power, and then only very briefly. I ponder the possibility of two (or more) electric freshwater pumps in parallel, one on all the time the engine is running, and the other(s) triggered by temperature or perhaps engine revs.

ASAP has an interesting variety of cooling pumps available - Engine Pumps for Marine Applications

 

[lw395]

There are loads of electric coolant pumps you could use to circulate the freshwater/coolant.
Often used in rally cars, some motorbikes etc.
That leaves the 'made for the job' impeller to do the seawater.
The heat exchanger pictured looks reminscent of one I've got in the shed, which came out of a central heating boiler. I would have concerns about the seawater side of it getting clogged?

 

[jamie N]

The diaphragm pump that I've fitted does 10l/min, which does (without having the engine at max load) seem ample, as there's a great flow.
I went to a diaphragm because of the PITA of engineering another pump to run from the alternator belt.
A DV36 is producing far more heat than my humble Ruggerini RM90, so I believe that there'll be enough, however, there are ready options only a little bit pricier for a plug in with greater capacity.
I don't believe that clogging will be a problem, but do admit that I've not really considered it? The unit is s/s, and I do have an inline filter, but cheers for the heads up.

 

[gordmac]

But the op does say it pumps water through the HE and out of the exhaust.

A thermostat in the engine coolant circuit should ensure a quick warm up.

It could be out the exhaust at the hull end rather than the manifold though. If the exhaust pipe is metal it doesn't need the water to cool it.
Would agree about the engine stat,I was trying to think of an advantage of doing the cooling in such a complicated way!

 

[Fr J Hackett]

It could be out the exhaust at the hull end rather than the manifold though. If the exhaust pipe is metal it doesn't need the water to cool it.
Would agree about the engine stat,I was trying to think of an advantage of doing the cooling in such a complicated way!

There isn't one other than being cheaper than the engine manufacturers own equipment.

 

[jamie N]

Water will go into the exhaust manifold in the regular way, from whichever pump is activated. The 'raison d'etre' is to have freshwater cooling at a better temperature on the engine, without making it too complicated. All I've added are 2 diaphragm pumps, a relay and a thermostatic switch.
By trade I'm an ROV guy, which includes doing 'Submarine Engineer' (SubEng) stuff on manned and unmanned submersibles, so this isn't really a stretch!

I do like the idea of it being much cheaper than having any of it done by the manufacturer, which with Ruggerini isn't really possible anyway. The exhaust manifold is a stainless item fabricated by Richie Foss in Dochgarroch; below a £100 by quite a way IIRC. How much do Yanmar/Volvo or Bukh charge for an item that corrodes?

 

[Fr J Hackett]

Water will go into the exhaust manifold in the regular way, from whichever pump is activated. The 'raison d'etre' is to have freshwater cooling at a better temperature on the engine, without making it too complicated. All I've added are 2 diaphragm pumps, a relay and a thermostatic switch.
By trade I'm an ROV guy, which includes doing 'Submarine Engineer' (SubEng) stuff on manned and unmanned submersibles, so this isn't really a stretch!

I do like the idea of it being much cheaper than having any of it done by the manufacturer, which with Ruggerini isn't really possible anyway. The exhaust manifold is a stainless item fabricated by Richie Foss in Dochgarroch; below a £100 by quite a way IIRC. How much do Yanmar/Volvo or Bukh charge for an item that corrodes?

From memory one for a Yanmar 3GM30 was north of a grand early 2000s

 

[jamie N]

Ran it all up this afternoon. The engine with fresh water circulating through the heat exchanger, the exhaust cooling pump running water through the exhaust, with the 2nd pump clicking it in at about 65°C and pumping the cooling water through the heat exchanger and up into the exhaust, then disengaging as the temperature was reduced, and the cycle starting again, without any excitement at all.
The heat exchanger was being pumped for maybe 10 secs every couple of minutes, obviously the engine without any significant load.
One thing that I'd not considered was the exhaust cooling water, which is essential I know but also has to be running only when the engine has started, not when the power to the starter is energised from the key, so I've fitted a double switch, one side of it for the alternator exciter which is there already, the other side will activate the exhaust pump. I always start the engine anyway with the alternator off, then once it's running switch it on.

 

[gordmac]

Will your battery cope ok?

 

[jamie N]

Good point.
The pumps are 60W/5A and the alternator's 600W/50A. The 2 batteries are 70Ah , so I'm not too concerned as only one pump can run at any one time, and then
only when the alternator's running,