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Old 07-11-2020, 12:40 PM   #1
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Troubleshoot Seawater Washdown?

I've got a Johnson pump WD5.2 (5gpm), 12VDC, been acting up lately. runs on its own circuit breaker switch, flow is activated by a flush deck fitting in bow with a push-in and twist hose coupler. water flow seems to start for a few seconds, but soon has no pressure and stops.
this pump is 10 years old so I could swap out the pump, but want to make sure I'm not missing some other problem. It has its own thru-hull which is open, and a small screen filter which seems to be clear.
Maybe 10 years is a good run for this pump.....?
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Old 07-11-2020, 02:21 PM   #2
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Might be water starvation or restricted flow from the source. I assume the source is from a through-hull. Is there a strainer? Have you checked the through-hull and the strainer? 10 years is a good life for a pump and since it starts strong and then fades, I'd suggest looking for a rebuild kit, if the water source checks out to be sufficient.

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Old 07-11-2020, 05:15 PM   #3
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Does the pump have flow if you disconnect the outlet piping? Worth seeing where you have / dont have flow starting at the thru hull and pump.
Sometimes the thru hull itself gets plugged... I've used a shop vac to blow stuff off the hull. Worth a try if other tips dont pan out.
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Old 07-11-2020, 09:05 PM   #4
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Thanks for these thoughts, I agree. I was thinking of disconnecting at the pump input from the seacock and try to back flush with a dock hose out through the seacock.....
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Old 07-11-2020, 09:08 PM   #5
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Bacchus I’m not sure if it has out put otherwise. My next step After a backflush but before I buy a new pump I thought would be to pull the pump out, maybe take it apart and then I could reassemble and see if it works just sucking water out of a bucket or something...
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Old 07-12-2020, 10:27 AM   #6
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I too would check to be sure the pump is getting the water it needs. If there is a restriction it might be emptying the hose leading to it.

T.Hull or screen on outside plugged, failing suction hose, sucking air from poor connections or failing hose or loose clamps, something plugged the hose, kink in hose.

If it the supply then you will still have the problem after the new pump is installed.
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Old 07-12-2020, 10:53 AM   #7
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Quote:
Originally Posted by sledge View Post
I've got a Johnson pump WD5.2 (5gpm), 12VDC, been acting up lately. runs on its own circuit breaker switch, flow is activated by a flush deck fitting in bow with a push-in and twist hose coupler. water flow seems to start for a few seconds, but soon has no pressure and stops.
this pump is 10 years old so I could swap out the pump, but want to make sure I'm not missing some other problem. It has its own thru-hull which is open, and a small screen filter which seems to be clear.
Maybe 10 years is a good run for this pump.....?
An obvious question, is the pump motor stopping when you lose flow? Because if the motor keeps running then I'd wonder about the 'wet end' of the pump. But if the motor stops, check to see if the power is still being supplied to it. Confirm that it's not deck switch, or the wiring in-between.
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Old 07-15-2020, 04:59 PM   #8
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Thanks I did finally have time to backflush from pump out the thru-hull; we saw some bubbles etc but hard to know if it "blew" much out from there... at least we now know it is clear that direction.
I also removed the pump and did a partial disassembly to at least check diaphragm, seemed ok, then re-installed and we attempted to run it out to bow as normal. It ran but a fair amount of air in line.
The PO had a standard sort of 25' garden hose at the bow output; dumb question but shouldn't the output hose be a much smaller diameter? I've seen many with what looks like about a 3/8" coiled hose, maybe it is not designed to push out a standard 5/8" garden hose...?
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Old 07-15-2020, 08:45 PM   #9
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"clear" is relative when it comes to condition of lines. Various growth can accumulate in lines, so while it may pass a simple test, it might be so clogged as to be unable to keep up with the pump. Which could potentially lead to the pump pulling enough suction to collapse the line.

Every boat washdown I've used has had a regular garden hose fitting. Some have fancier features like recessed sockets and such. But a regular garden hose thread size is common. The hose coil systems tend to use a smaller diameter hose because it's easier to coil it for storage.

When you mention 'air in line' what do you mean? That the hose kept sputtering and spitting air, instead of just a steady water stream? That would make me suspect the wet end of the pump. Most pumps of this type have had a way to replace either the entire wet end, or just parts. I've gone the 'whole wet end' approach and reinvigorated several setups over the years. Bearing in mind that some pumps have changed how hoses fit to them, so sometimes it's a bit of a chore getting the right barb sizes or threads, depending on what's already in the boat.
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Old 07-15-2020, 09:04 PM   #10
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Sounds like the pressure switch is corroded or dying. May be replaceable. I think I would order a new pump ( biggest I could find) plumb it back in the boat in a way so I could quickly switch it over to be used an emergency bilge pump or a washdown --- win/win.
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Old 07-15-2020, 09:56 PM   #11
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If the pump is fairly easy to remove from the boat then maybe put it on the dock and hook up a pickup hose and see what happens. If it works then the problem is in the thru hull and or piping. If it doesnít work then you know what is bad, the pump.
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