5kw Norther Lights generator looses raw water prime

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Sykes

Sykes

Veteran Member
Joined
May 29, 2019
Messages
49
Location
United States
Vessel Name
Godspeed
Vessel Make
Bruno Stillman 42
I have blasted fresh water into the intake hose, then attached it to the raw water source and it will prime. It runs for an hour and I shut it off thinking we are good to go. The next day I go out, gen runs all day and when we stop for the evening it looses prime and shuts down. I have scraped the intake screen and it looked good under the water. The main filter looks good.

Do I need to clean out this yellow water divider and what is it called?

CRRfB1xr
 
You likely have a leak between the second and the raw water pump where air is allowing the pump to lose its prime.
 
Perhaps the raw water pump impeller. I have a NL12K which had similar symptoms. Start OK but clearly overheating. Air in the strainer was puzzling. Checked the impeller, found all vanes gone. Spent a day changing the impeller and fishing vanes out of hoses, siphon breaker and heat exchanger.

I think that some air normally enters the intake as it’s not far under the waterline but a well functioning pump pulls the air through with no problems. As the vanes detached, there was less vacuum and air built up in the strainer until prime was lost.
 
Replace the impeller. They often develop cracks in the tips that won't seal perfectly, letting water drain back out. And because they don't pump as well, they can't pull up the prime.

David
 
It can also be the impeller pump housing is worn. How many hours on the pump?
 
DCDC said:
Perhaps the raw water pump impeller. I have a NL12K which had similar symptoms. Start OK but clearly overheating. Air in the strainer was puzzling. Checked the impeller, found all vanes gone. Spent a day changing the impeller and fishing vanes out of hoses, siphon breaker and heat exchanger.

I think that some air normally enters the intake as it’s not far under the waterline but a well functioning pump pulls the air through with no problems. As the vanes detached, there was less vacuum and air built up in the strainer until prime was lost.
Click to expand...

New impeller and I had been through the same..
 
Common if pump body or cover plate is worn. Can check this by taking off the outlet hose and blowing backward through the pump. If air freely goes through (engine off of course!!), there is too much clearance in the pump body. Sometimes can fix it by machining a new flat on cover plate or replacing it.

Also have bought new impellers that were like 0.010" short, and that was enough to do it. That was frustrating!!
 
Thanks I will try that.

20210314-134258.jpg


I was also wondering is this clogged?
 
When you put in the new impeller, grease the cover plate and inside housing. That way the impeller won't get hot on the first use. It also seals the vanes better so the pump has more suction before the grease is gone. When the impeller gets too hot, it gets hard, doesn't seal as well, and is prone to cracking.

But I'd also make sure there isn't an air leak on the suction side.
 
Ski in NC said:
Common if pump body or cover plate is worn. Can check this by taking off the outlet hose and blowing backward through the pump. If air freely goes through (engine off of course!!), there is too much clearance in the pump body. Sometimes can fix it by machining a new flat on cover plate or replacing it.

Also have bought new impellers that were like 0.010" short, and that was enough to do it. That was frustrating!!
Click to expand...

Today I took off the exit side of the water pump, blew air into it and it was too easy, no restrictions. Afterwards I poured some water into it and blew that, the water came out behind the pump near the shaft.

Do I rebuild the pump or just replace it??
 
I think that’s right. Not sure what you can do for a worn housing.
 
Ski in NC said:
Common if pump body or cover plate is worn. Can check this by taking off the outlet hose and blowing backward through the pump. If air freely goes through (engine off of course!!), there is too much clearance in the pump body. Sometimes can fix it by machining a new flat on cover plate or replacing it.

Also have bought new impellers that were like 0.010" short, and that was enough to do it. That was frustrating!!
Click to expand...
Can you just reverse the cover plate so unworn outside replaces worn inside? Seems too simple and easy...there has to be a reason you can`t.
 
BruceK said:
Can you just reverse the cover plate so unworn outside replaces worn inside? Seems too simple and easy...there has to be a reason you can`t.
Click to expand...

My Jabsco pump has info STAMPED into the cover. No way I would put that surface up against a rubber impeller. There is also an inner wear surface that could be bad.
Buy a new complete pump then send out the old for rebuild at your convenience for a spare. That assumes a new pump is not made of marine gold.
 
Last edited:
New raw water pump $440, installed myself and ran for 30 hours without issue. Thanks to all who contributed.
 
Awesome!
 
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