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Old 20-11-2015, 17:36   #1
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Engine Rpm For Water Maker HP Water Pump


I am in the process of fitting my new open ocean engine driven water maker and I am at the stage of determining what size pulley to fit on the engine. This is determined by what rev range I want to have the engine at when making water i.e. when I am motoring or if anchored up at idle. The obvious issue for gearing up the system to run when the engine is at idle is the engine pulley needs to be huge to be the correct ratio to the 7' pump pulley.

The pump needs to run at between 1320 and 1750rpm and the engine idles at 700 rpm and motors on ave at 2000rpm so where do I pitch it i.e. closer to idle speed as practical or motoring speed?

In peoples experience when offshore and coastal cruising when do you make water.

I already know about the pulley calculators so its just what engine rpms do I decide on?

Thanks Anthony

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Old 21-11-2015, 02:23   #2
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Re: Engine Rpm For Water Maker HP Water Pump

Why not 2 pulleys. It's not hard to change a pulley or adjust a belt. Or if your pump mount was made so it could slide you could mount both pulleys and slide the pump to line up with the pulley you want.
Another option is to drive the pump with an electric motor that can run off an inverter. Then your alternator/solar/wind turbine keeps the batteries up.

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Old 21-11-2015, 07:59   #3
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Re: Engine Rpm For Water Maker HP Water Pump

Most of our clients that go the engine driven approach set the pulley speed up to make water while underway. Most folks try to minimize time running their engine at idle at anchor and typically have plenty of time motoring or motor sailing to make all the water they could need.
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Old 21-11-2015, 09:42   #4
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Re: Engine Rpm For Water Maker HP Water Pump

You might look into variable diameter pulleys. There are manually adjustable and automatic ones available. Choosing the appropriate drive pulley could keep the rpm in the proper range whether at idle or cruise RPM.
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