Generator shredding impellors

[john_morris_uk]

Any ideas what I should look for as to why our generator is shredding impellers? It’s only done a couple of hundred hours and it’s lost two impellers in the last three days. I’m about to dive into the cockpit locker again so I’ll take some photos. I’ll check for fit and irregularities in the housing but there was nothing obvious when I replaced the last one two days ago. There was a bit of weed in the strainer but nothing really blocking it.

My only thought is that as we’re at anchor in the lagoon in Sint Maarten, there’s a lot of weed and rubbish in the water. Perhaps it’s totally blocking occasionally and that’s enough to shred the impeller as it runs dry for a few minutes.

 

[geem]

Any ideas what I should look for as to why our generator is shredding impellers? It’s only done a couple of hundred hours and it’s lost two impellers in the last three days. I’m about to dive into the cockpit locker again so I’ll take some photos. I’ll check for fit and irregularities in the housing but there was nothing obvious when I replaced the last one two days ago. There was a bit of weed in the strainer but nothing really blocking it.

My only thought is that as we’re at anchor in the lagoon in Sint Maarten, there’s a lot of weed and rubbish in the water. Perhaps it’s totally blocking occasionally and that’s enough to shred the impeller as it runs dry for a few minutes.

Do you have a strainer before the impeller?

 

[NBs]

I myself had a similar situation with my northenlight genny, I used a prestigious brand of impellers and they broke down in no time after about 10 hours or so, I had 3 of them in stock. Then I bought 3 more but different brands and now I've done about 500 hours on one, can't remember the brand it was something like an ounce cheap.

 

[Clancy Moped]

A quick swim under might reveal sea grass growth over and around the intake.

 

[geem]

I myself had a similar situation with my northenlight genny, I used a prestigious brand of impellers and they broke down in no time after about 10 hours or so, I had 3 of them in stock. Then I bought 3 more but different brands and now I've done about 500 hours on one, can't remember the brand it was something like an ounce cheap.

I have used several brands of impeller. Never had a premature failure issue. We do have a very good strainer prior to the raw water pump. Could it have been a bad batch of impellers?

 

[NBs]

I have used several brands of impeller. Never had a premature failure issue. We do have a very good strainer prior to the raw water pump. Could it have been a bad batch of impellers?

Possibly or maybe for some reason it doesn't get enough raw water. I had a fish sucked into a pipe and clogged it once, another time with algae. I don't have a strainer at the bottom outlet, just seawater in the filter.

 

[john_morris_uk]

Do you have a strainer before the impeller?

Yes we have a strainer. It had a bit of weed in it but it wasn’t blocked significantly.

 

[john_morris_uk]

Possibly or maybe for some reason it doesn't get enough raw water. I had a fish sucked into a pipe and clogged it once, another time with algae. I don't have a strainer at the bottom outlet, just seawater in the filter.

Our aft heads refused to flush just after we arrived back out here. I found a small fish in the pump.

 

[david_bagshaw]

Firstly did you remove the vanes from the last one from the plumbing to and including the heat exchanger, Is the pump above the waterline?, if so small air leak on suction side? Run water from a hose down the inlet plumbing. see it primes well on first start, as a new impeller takes a while to bed in, when fitted to a slightly worn pump.

 

[john_morris_uk]

Firstly did you remove the vanes from the last one from the plumbing to and including the heat exchanger, Is the pump above the waterline?, if so small air leak on suction side? Run water from a hose down the inlet plumbing. see it primes well on first start, as a new impeller takes a while to bed in, when fitted to a slightly worn pump.

Yes I always check for all bits. In fact the last impeller failed by the metal collar inside the impeller becoming detached from the rubber of the impeller vanes and thus the vanes not spinning at all. No bits missing.

The generator was new last year. I don’t believe the pump is significantly worn.

We did have problems with air leaks on the inlet side when the generator was first fitted and yes the pump is above the waterline but I’ve sorted the leak(s) and it primes instantly now. I can see the water coming up the inlet pipe and hitting the clear lid of the strainer as soon as it starts.

I’ll take some photos.

 

[david_bagshaw]

We have a similar above water line genny pump and I fitted a small piece of hose fitted inside the filter to ensure there is a gulp of water for the pump on first start.

not used wd 40 to lubricate the new impeller, as i have found it fatal to its life.

 

[john_morris_uk]

We have a similar above water line genny pump and I fitted a small piece of hose fitted inside the filter to ensure there is a gulp of water for the pump on first start.

not used wd 40 to lubricate the new impeller, as i have found it fatal to its life.

That’s a possibility regarding priming.

However I lubed up the impeller with the little tube of stuff they supplied with it to ensure it didn’t start dry and it primed immediately.

 

[NormanS]

I use washing up liquid on the impeller when I refit it.
Interesting that the rubber detached from the metal bush. I remember years ago that there was a batch of impellers that did that.

 

[john_morris_uk]

Assumption is the mother of many things. Turns out the new impeller fitted a couple of days ago is fine.



General layout of generator in locker. Water level is about at top of step below generator. Strainer on bulkhead to right of generator.


Cover removed.



Inside faces of pump. I cleaned it up with fine wet & dry.

 

[john_morris_uk]

We applied the electric dinghy pump to the inlet inside the strainer. It struggled a moment and then blew the line clear with lots of air bubbles coming from under the boat. I’m assuming weed/jellyfish/plastic was stuck up the skin fitting.

 

[john_morris_uk]

Here’s the start up. The generator has its own battery which only has a small charger on it and I forgot to isolate it when we left the boat for a couple of months. Hence the jump leads.

You can see it primed immediately.

 

[dunedin]

We applied the electric dinghy pump to the inlet inside the strainer. It struggled a moment and then blew the line clear with lots of air bubbles coming from under the boat. I’m assuming weed/jellyfish/plastic was stuck up the skin fitting.

Caught another fish?

 

[rotrax]

A prudent thing to check is that the 'cam' retaining screw is tight.

A couple of years ago in Lymington a fellow club member left the outside of a raft of three, was back before the next guy left with no water exiting the exhaust.

The little screw holding the cam in on his Volvo had fallen out..............................

The replacement - and the dob of loctite - I fixed him up with is still there.

 

[Clancy Moped]

#4 a blockage from below.

 

[john_morris_uk]

A prudent thing to check is that the 'cam' retaining screw is tight.

A couple of years ago in Lymington a fellow club member left the outside of a raft of three, was back before the next guy left with no water exiting the exhaust.

The little screw holding the cam in on his Volvo had fallen out..............................

The replacement - and the dob of loctite - I fixed him up with is still there.

Sorry but you’ve lost me? Unless you mean the ‘cam’ the impeller runs over inside the pump?