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Old 08-03-2018, 11:31   #1
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Engine driven watermaker pump

Dear all,

Do you think it is possible to use an engine driven triplex plunger pump for both cooling water">engine cooling water circulation and watermaker operation?

I have some experience in building watermakers (I have a 1/3 hp electric motor driven watermaker that takes about 30 amps to make 6 gpm) and I noticed that most of the time when I use it I run the engine anyways. So, the idea here is to simplify the process and use the engine more efficiently.

I understand that the biggest drawback of engine driven watermaker pumps is alignment of the pump so that it does not eat the belt and keeping the pressure constant as rpms change.

The Yanmar uses a fresh water pump that produces 7.1 gpm at 2,700 rpms (at max engine rpms) and the head is given as 1 ft. I have found a suitable triplex plunger pump that I want to install in place of the Yanmar fresh water pump (easy installation and belt alignment) that has similar specs. It produces 7.8 gpm at 2,700 rpms, suction head is given as up to 3 ft.

My calculations show that if I run the engine at fast idle, the triplex plunger pump will turn at 900 rpms, produce 2 gpm and draw about 1 hp from the engine when I increase the pressure to 800 psi. When I am not producing water the valve will be open and the pump will run like a regular (if somewhat inefficient) transfer pump. The pump when mounted will be approximately 1 ft below the water level, so there will be no head at all.

Do you think this is worth experimenting with? The benefits are clear (just get the pump and attach to the existing bracket, nice and clean installation, no clutch to worry about, no alignment, no motor needed, large fresh water production, around 20 gph when I upgrade to bigger membranes). The pump may need to be serviced every 100 hours (oil change) and I have the impression it will be noisy but the engine is noisy anyway. I believe the belt should have no problem transferring 1 hp to the pump and I can always upgrade it if needed. In this setup the engine is loaded nicely in fast idle, the alternator draws 2-3 hp and charges the batteries, the pump draws 1 hp and produces water and may be another 1 hp goes to internal components.

I am tempted to get the $200 brass version to experiment with before spending $1,000 on the stainless steel version of the pump. Any ideas why this may or may not work?

Thanks,
SV Pizzazz
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Old 08-03-2018, 14:37   #2
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Re: Engine driven watermaker pump

High pressure pumps aren't made to run continuously 24/7. If you've ever used a pressure washer continuously, the pumps last about 3 years. They can be rebuilt to a point. Another issue is filtering the water before the pump. Raw water pumps can take most small debris found in the water. Not so the pressure pump. In most cases they're used on supplied, clean city water. Also, the high pressure pump is more efficient when supplied water at some pressure.
I had a pressure washer I ran on water from my salt water system. Usually in the winter when in fresh river water. The pump went from 3000 psi to about 1800 in 2 years.
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Old 09-03-2018, 04:53   #3
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Re: Engine driven watermaker pump

More of a pain than they are worth. Some engine manufacturers will void their warranty if they find one of these attached. Call any major watermaker company and you'll find none of them will make engine mounted watermakers. As obvious as it seems, it's fraught with problems. I know some will disagree, but I've been doing this for a long time. I started in this business many moons ago by building my own watermakers on mine and others boats and the engine take off was the first ones I built. None of them really did well and were eventually replaced with a stand alone unit.
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Old 09-03-2018, 21:37   #4
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Re: Engine driven watermaker pump

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More of a pain than they are worth. Some engine manufacturers will void their warranty if they find one of these attached. Call any major watermaker company and you'll find none of them will make engine mounted watermakers. As obvious as it seems, it's fraught with problems. I know some will disagree, but I've been doing this for a long time. I started in this business many moons ago by building my own watermakers on mine and others boats and the engine take off was the first ones I built. None of them really did well and were eventually replaced with a stand alone unit.
What were the sort of problems you experienced Tellie?
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Old 10-03-2018, 16:08   #5
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Re: Engine driven watermaker pump

Thats interesting. My Echotec engine driven watermaker produces 50gal/ph just above idle speed and has been doing for 8 years with very little problem. I make most water motoring in and out of anchorages. I have had AC stand alone systems and this is the best by far and no generator required. It is very important though to have a very robust mount for the hp pump.
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Old 11-03-2018, 12:50   #6
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Re: Engine driven watermaker pump

I ran a 20+ gph watermaker off an engine driven pump for 6 years while cruising the Caribbean on a 42' ketch. I designed an aluminum bracket to mount the pump to the engine and bolted another pulley to the front of the engine. The bracket had slots that provided adjustment both fore and aft as well as for in/out for belt tension. This allowed easy belt alignment to avoid belt wear. The pump had an electric clutch just like your car air conditioner so that it only ran when making water. I tee'd it off the engine raw water pump, which acted as a boost pump for the high pressure pump. It worked great, with absolutely no problems at all. I also had engine driven refrigeration, so when running the engine at anchor, it did triple duty for refrigeration (including making ice), making water, and turning a 105 amp alternator to charge batteries. We ran the engine 45 min in the morning and again at nite. Tanks were always full!
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Old 12-03-2018, 08:24   #7
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Re: Engine driven watermaker pump

Thank you for the replies. I have no doubt that an engine driven watermaker could work if done right. If alternators can be made to work well off the belt, then a water pump should be easier. The question was more specifically if it was possible to combine two pumps in one.

@Lepke - I agree that debris will kill the delicate high pressure pump quickly. The solution is to run it with the filters or at least with the 20 micron filter when in normal operation. Then you end up replacing filters every month or so - too much hassle.
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Old 12-03-2018, 16:21   #8
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Re: Engine driven watermaker pump

Rich at CruiseRO does sell them, but says the electric ones are much less troublesome.

A cheap alternator will pump out more than enough 12V to power the DC ones, and with a good VR you get another high-amp power source and battery charger.
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Old 12-03-2018, 16:41   #9
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Re: Engine driven watermaker pump

You mean a 3 piston pump? I made an engine driven watermaker using a Bronze Cat pump. It was easy. I just used a good needle valve to control pressure with a relief valve for "just in case". Added a 12V clutch to the pump. The clutch pulley was big enough that rpms were low and no belt alignment issues.
I had that boat 3 years with no watermaker issues. Made about 25 GPH.
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Old 12-03-2018, 17:48   #10
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Re: Engine driven watermaker pump

The pressures to do these two tasks are at odds with one another, not to mention the flow rates. Water moving too fast will not cool correctly.

Chris

Quote:
Originally Posted by Pizzazz View Post
Dear all,

Do you think it is possible to use an engine driven triplex plunger pump for both engine cooling water circulation and watermaker operation?

I have some experience in building watermakers (I have a 1/3 hp electric motor driven watermaker that takes about 30 amps to make 6 gpm) and I noticed that most of the time when I use it I run the engine anyways. So, the idea here is to simplify the process and use the engine more efficiently.

I understand that the biggest drawback of engine driven watermaker pumps is alignment of the pump so that it does not eat the belt and keeping the pressure constant as rpms change.

The Yanmar uses a fresh water pump that produces 7.1 gpm at 2,700 rpms (at max engine rpms) and the head is given as 1 ft. I have found a suitable triplex plunger pump that I want to install in place of the Yanmar fresh water pump (easy installation and belt alignment) that has similar specs. It produces 7.8 gpm at 2,700 rpms, suction head is given as up to 3 ft.

My calculations show that if I run the engine at fast idle, the triplex plunger pump will turn at 900 rpms, produce 2 gpm and draw about 1 hp from the engine when I increase the pressure to 800 psi. When I am not producing water the valve will be open and the pump will run like a regular (if somewhat inefficient) transfer pump. The pump when mounted will be approximately 1 ft below the water level, so there will be no head at all.

Do you think this is worth experimenting with? The benefits are clear (just get the pump and attach to the existing bracket, nice and clean installation, no clutch to worry about, no alignment, no motor needed, large fresh water production, around 20 gph when I upgrade to bigger membranes). The pump may need to be serviced every 100 hours (oil change) and I have the impression it will be noisy but the engine is noisy anyway. I believe the belt should have no problem transferring 1 hp to the pump and I can always upgrade it if needed. In this setup the engine is loaded nicely in fast idle, the alternator draws 2-3 hp and charges the batteries, the pump draws 1 hp and produces water and may be another 1 hp goes to internal components.

I am tempted to get the $200 brass version to experiment with before spending $1,000 on the stainless steel version of the pump. Any ideas why this may or may not work?

Thanks,
SV Pizzazz
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Old 12-03-2018, 20:19   #11
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Re: Engine driven watermaker pump

We may be beating a dead horse here but just to clarify. The idea is to use a high pressure, 3-piston pump in place of the the raw water cooling pump on the engine. The flow rate is matched, so no issue here. When not making water, the pump is just moving 7 gallons per minute through the system, the pressure valves are open, so it acts as a transfer pump. When in water making mode, the pump output goes through the membrane and makes 800 psi there but after the control valve there is no pressure and the water just circulates around the engine. It is a dead simple setup with the benefit that the pump mounting bracket is already there.

The only downside I have heard so far is that debris in the raw water, if not filtered, will destroy the delicate pistons. If it is filtered, then it is OK but filters may need to be replaced more frequently.

Those of you who make water regularly, how often do you replace filters? I am estimating 300 hours engine run time per year x 20 gph = 6,000 gallons of fresh water. So, whether I make water or not, I would be driving enough raw water through the filter to make the equivalent of 6,000 gallons of fresh water per year. What is your experience?
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Old 12-03-2018, 22:48   #12
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Re: Engine driven watermaker pump

Most of us with watermakers are pretty choosy about where we run them. Oily, dirty harbour water is particularly to be avoided. But that's exactly where you'll be most likely to run an engine.

I think filter life would be very short, you'd need to keep the filters in good shape or risk damaging the pump or cooking the engine.

And there would be a risk of oil or fuel contamination ending up in the membrane, which can wreck them.
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Old 13-03-2018, 04:23   #13
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Re: Engine driven watermaker pump

IMHO, replacing the impeller pump with a piston pump is fixing a problem that doesnít exist with several far more complex problems that will only exist in series.

Are you considering the yanmar belt driven pump mount that is under the engine and attached with two very small and long bolts? The piston pump will eat that mount alive.

Also the consequences of heat exchanger blockage could be catastrophic. The impeller pump might make 15-20 psi if the tubes are blocked. The piston pump is going to move fluid one way or another.....no matter whatís in the way. Sure you can add a relief valve, but thatís another layer of complexity.

I would rather drive the pump with an electric motor, either DC or AC. This allows prime mover feed options, as well as keeping the complexity off of the engine.
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Old 13-03-2018, 12:49   #14
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Re: Engine driven watermaker pump

Thank you all. @sailmonkey, the blockage concern is really scary. Just the thought of forcing 1,000 psi through the engine made me give up this idea. Oh, well, will keep it as it (1/3 hp motor/pump driven by the alternator.

Happy sailings.

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Old 13-03-2018, 22:01   #15
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Re: Engine driven watermaker pump

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Originally Posted by Sailmonkey View Post
IMHO,

I would rather drive the pump with an electric motor, either DC or AC. This allows prime mover feed options, as well as keeping the complexity off of the engine.
I have used a 12V DC electric impeller pump for this purpose. To ensure it would not flood the engine I powered it from the auxiliary terminal on the key switch through the normally closed terminals of a heavy relay. The coil circuit on the relay was provided with power also from the auxiliary terminal and wired to earth via the oil pressure switch.

When the ignition was turned on the NC relay circuit would attempt to start the pump however as concurrently the oil pressure switch would close the coil circuit the relay would shift to the normally open terminals thereby opening the NC terminals. When the oil pressure rose after the engine started the oil pressure switch would go open circuit thereby removing the coil current and allowing the NC terminals to close powering the pump. Reverse happens when you shut the engine down.

I ran the engine with this setup for about eighteen months without problems before I sold the boat and it's not a bad arrangement to have for contingency engine cooling if the engine driven pump is not available for any reason.
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