Onan generator raw water pump is eating impellers

[f508]

That's pumping a lot of water.

Yes, and that is what it looks like right up until the impeller shreds. We'll see this cycle. I ran it for about 30 minutes today, with 2 starts. If we get a little break between storms I'll try and take her out tomorrow and get an hour or 2 on it.

 

[f508]

Here is a link to rebuilding your tapered cone sea cock:https://www.pbase.com/mainecruising/tapered_cone_seacocks
Please keep us posted on your generator water pump.

Thanks. I'll get some lapping compound and take care of it at the next haul out.

 

[Dcbeach]

I repaired one with the same issue. We dissembled the heat exchanger and cleaned impeller parts out. But the problem remained. With the pump in place the everything seemed clean. This pump had fittings which included an elbow attached to it. After removing the elbow, the impeller bits and pieces were seen to be lodged lodged inside. They were not visible until disassembly. Curiously we still had water flow, but certainly not enough to keep the pump cool.
The moral of the story is to keep searching!

 

[f508]

I repaired one with the same issue. We dissembled the heat exchanger and cleaned impeller parts out. But the problem remained. With the pump in place the everything seemed clean. This pump had fittings which included an elbow attached to it. After removing the elbow, the impeller bits and pieces were seen to be lodged lodged inside. They were not visible until disassembly. Curiously we still had water flow, but certainly not enough to keep the pump cool.
The moral of the story is to keep searching!
View attachment 85486View attachment 85487

Yes, I did the same thing. I took the pump down to my neighbor to ask him to look at it and he pulled out a chunk of rubber like that from what I thought was a clear path. After that I double checked and we are good.

 

[f508]

A quick update.

I ran the generator for just over 2 hours today, and so far so good. It has run up to 4 hours before failure on earlier repairs, so I am a bit past half way.

 

[Alaskan Sea-Duction]

Once fixed or closeout, please provide us a write up on what you did to fix it. Include the specific stuff with part numbers. if any.

Thanks

 

[f508]

I’ve gotten a total of 6 hours of successful operation on the generator and impellor. I’ve tried the following actions since the impellor issue began.

1. Installed a sea strainer in the raw water line – I thought there might be some sort of intermittent blockage in the raw water source. The impellor failures continued.
2. Replaced the exhaust hose from the generator exhaust manifold to the muffler. – The operation with the impellor failure had run uncooled exhaust through the 2” hose and caused it to internally delaminate. . The impellor failures continued.
3. I re-machined the interior of the impellor chamber to smooth out the surface defects that looked like they had existed since manufacture. At this stage I also polished the flattened the wear plate because of some galling and warping created as the impellors failed. I think this was caused by high temperatures as the impellor blade disintegrated inside the impellor chamber. During this machining operation I increase the diameter of the impellor chamber as much as I thought was safe in order to lessen the wear stress on the impellor operation.
4. After the items in 3 above were completed I have had 6 successful hours of impellor/generator operation.

None of the actions I’ve taken seems to me to be a clear solution, but with things working normally I may never know exactly what caused the impellor failures. If it starts happen again I’ll post it here.

The pump that I bought on eBay should be delivered this week. I am hoping an examination of this duplicate pump might shed light on my pump’s failures. Lacking that, I seem to be at a dead end for a clear diagnosis. It is disappointing not to find an obvious culprit, especially with all the kind help you have all provided, but as long as the problem doesn’t reoccur I am at a loss to figure it out any further.

 

[High Wire]

Impellor: One who impels.

 

[f508]

Impellor: One who impels.

Oops! Noted

 

[caltexflanc]

I’ve gotten a total of 6 hours of successful operation on the generator and impellor. I’ve tried the following actions since the impellor issue began.

1. Installed a sea strainer in the raw water line – I thought there might be some sort of intermittent blockage in the raw water source. The impellor failures continued.
2. Replaced the exhaust hose from the generator exhaust manifold to the muffler. – The operation with the impellor failure had run uncooled exhaust through the 2” hose and caused it to internally delaminate. . The impellor failures continued.
3. I re-machined the interior of the impellor chamber to smooth out the surface defects that looked like they had existed since manufacture. At this stage I also polished the flattened the wear plate because of some galling and warping created as the impellors failed. I think this was caused by high temperatures as the impellor blade disintegrated inside the impellor chamber. During this machining operation I increase the diameter of the impellor chamber as much as I thought was safe in order to lessen the wear stress on the impellor operation.
4. After the items in 3 above were completed I have had 6 successful hours of impellor/generator operation.

None of the actions I’ve taken seems to me to be a clear solution, but with things working normally I may never know exactly what caused the impellor failures. If it starts happen again I’ll post it here.

The pump that I bought on eBay should be delivered this week. I am hoping an examination of this duplicate pump might shed light on my pump’s failures. Lacking that, I seem to be at a dead end for a clear diagnosis. It is disappointing not to find an obvious culprit, especially with all the kind help you have all provided, but as long as the problem doesn’t reoccur I am at a loss to figure it out any further.

You've very likely chosen to ignore the correct answers altogether. And boring out the chamber decreases the pumps effectiveness. Do you have a temperature gauge for your generator?

 

[BruceK]

Are you sure that the impeller is mounted correctly and that the length and diameter are correct? Looks like you are getting too much friction on the impeller and it’s overheating and self destructing. Have you tried a slightly smaller impeller? May allow some water bypass but unlikely to overheat and self destruct. May be worth a try.
Also, have you check the interior surface of the pump for burrs etc as well as the end plate for friction and fit?
Good luck. Hope you eventually post the identification of the problem.

Machining out the impeller housing while (presumably) using the same size impeller seems similar to para 1 above. The OP also seems to have followed para 2.
6 hours and counting. Could it be the method "some guy says he`s gotten away with"?

 

[f508]

You've very likely chosen to ignore the correct answers altogether. And boring out the chamber decreases the pumps effectiveness. Do you have a temperature gauge for your generator?

I put a heat gun on the bearing areas of the pump and they aren't warm. While I did enlarge the chamber, it is still pumping a ton of water.

The generator does not have any gauges, but I have one of those heat guns, and the wet side of the exhaust isn't getting warm. In fact the hoses are all about skin temperature, or cool.