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Old 01-19-2019, 02:18 AM   #1
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Engine driven pump against closed valve

Is there any damage done to a typical engine driven bilge/washdown/fire pump (like a Jabsco) if it runs against a closed valve? If so, then perhaps a safety release valve can divert the water overboard until the wash down hose is opened or such.
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Old 01-19-2019, 02:44 AM   #2
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It depends.
If it it a positive displacement pump such as a piston type pump or diaphragm pump; it would be immediately be damaged if the discharge valve was closed.
A turbine pump or similar may run hot, but could handle short term pumping against a closed valve.
A pressure relief valve would be a necessity on a positive displacement pump and recommended for a turbine pump.
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Old 01-19-2019, 03:49 AM   #3
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Thanks. Diverting overboard also makes a nice reminder that you forgot to turn the pump off
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Old 01-19-2019, 07:33 AM   #4
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A Jabsco will take it for a while the rubber blades just bend.


More danger from running dry while selecting the water source , bilge compartment or sea water for deck wash or fire duty.
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Old 01-19-2019, 11:09 AM   #5
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A centrifugal pump running with a closed discharge needs flow to cool the internals. It can however run for a short time aginst a closed discharge.
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Old 01-19-2019, 02:18 PM   #6
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Quote:
Originally Posted by makobuilders View Post
Is there any damage done to a typical engine driven bilge/washdown/fire pump (like a Jabsco) if it runs against a closed valve? If so, then perhaps a safety release valve can divert the water overboard until the wash down hose is opened or such.
The motor will add heat to the little bit of water inside of the pump casing. Enough to do damage? Maybe. Never tried it or seen it done. I can't recall seeing that type used where the discharge is closed off completely. Engine S/W pumps, macerator pumps, and oil change pumps are all open ended discharge.
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Old 01-19-2019, 02:38 PM   #7
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Usually a continuous running pump is plumbed with a small overboard discharge to maintain a flow. It's either controlled by a manual valve or a pressure relief valve. The discharge stream doesn't have to be very big, 3/8" or so.
Main engine driven pumps usually have a clutch so they can be taken offline when not needed.
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Old 01-20-2019, 09:06 AM   #8
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I run a 1 HP pool pump as a raw water wash down and used a 1/4" or 3/8" hose to a 1/4 or 3/8" copper tube glued into hull side for a pump relief. I cant recall the exact hose size right now. I used pl premium glue, but any epoxy will work fine. You dont need a specialty thru hull, the hole will be very small.

Pump side I drilled a small hole into a plastic manifold made from PVC and tapped the plastic fitting with a 1/8" or 1/4" pipe thread and connected a hose barb with or without a brass bushing. I used a large PVC check valve so the line does not drain back.

It works very well and you can never forget to turn off the pump due to the water splash it creates. It shoots out a goodly water stream over the side.

Doing this was a lot easier than figuring out a pressure on-off electric switch. Diverting a tiny amount to keep pump cool does not impact the flow from the big pump.
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Old 01-20-2019, 09:24 AM   #9
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I have seen the results of leaving a diesel powered 4 inch pump that was left in gear, with the output valve shut. Got hot, water turned to steam and blew pump apart, motor continued to run.
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Old 01-20-2019, 11:29 AM   #10
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Old 01-20-2019, 11:53 AM   #11
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Put a clutch on it, especially if it is not needed often.
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