New Cummins Genset chewing through impellers

[KiwiClive]

Replies in-line

1) How fine is the mesh in the strainer? -- Standard Vetus style filter probably about 2mm squares
2) How fine is the outside strainer? -- not very fine at all.
3) How hard does the exhaust system work to expel water? -- Hmm, no idea


Lets pull the impeller early one time and look for a wear pattern on the vains.

If no edge wear and a lot of cracks, there is a restriction some where and the vains are floating.
-- No edge wear just cracks in the base of the vanes.

Assuming you operate the boat often;

Are you pulling from a sea chest? Pulling in air from a chine? Strut, prop wash, transducer mounted ahead of it?
-- only operate the genset at anchor and flow is good in the strainer. Strainer doesn't empty when the boat is left either.

there is a restriction some where and the vains are floating.

Floating? can you explain this? Thanks.

 

[Captain Ralph]

-- No edge wear just cracks in the base of the vanes.

Floating? can you explain this? Thanks.

The lack of edge wear may prove the blades are not rubbing on the Pump housing and floating.
When impellers are restricted while flowing water, the vains will move faster than the water flows, The blades (vains) will collapse closer to the center. The blades will float and fail because of the crushing force against them.

A restricted heat exchanger from old impeller pieces or fouling is what we usually find over here in Jax.
Next on the low side would be restricted inlets, strainer, sea-cock, collapse hoses and fouling any where in these items. We have found the lever up and the ball half open on sea-cocks. We have found the inside laminate of a hose sucking in. Barnacles in the sea-cock and crud restricting the inlet at the pump.

Restricted exhaust riser or dump cans can cause this also. Poorly designed exhaust system has been known once with us to cause this.


Poor elbows, 90s or fittings in the hose route.
We once found a bronze hose/pipe fitting that was not drilled thru completely.


Start at the sea cock, pull the hose off and watch the water flow in, yes you and your boat are going to get wet.
If it's not a gizzer coming up, start there.


Keep in mind; Your trying to pump around 6 gallons per minute.

 

[Bensjoy]

Check the CAM inside impeller housing to see if it is flush

 

[Captain Ralph]

Check the CAM inside impeller housing to see if it is flush

If there is no wear on the blade edges, an askew cam would not be an issue.

 

[Senojev]

Clive

Have a similar problem on our Oman genset and rarely get more than 40 hours before the impeller breaks up. It seems a common problem with this pump from friends with the same genset. I don’t know if you are able to buy them easily but Globe Marine makes an excellent replacement that many have had very long life for just a small extra cost - www.gcsmarine.com

 

[Captain Ralph]

Globe impellers may have a place in real world use,, somewhere. Have not found it yet.


I would not want to switch to them now if there is a real issue and just want the issue covered up.

 

[KiwiClive]

Update

Well it's been around 6 months now and around 200 hours and all is good. I have checked the impeller 3 times in this period and it's been fine.
Problem is I changed 2 things so I can't be sure what made the difference.
1. Lowered the inlet strainer
2. Used an impeller from an alternate manufacturer.

I still have an OEM impeller so I will look at using it on the next impeller change to see if it works.

 

[Captain Ralph]

2. Used an impeller from an alternate manufacturer.

Sherwood usually has their impeller market locked up. Unless you went to a Globe design.

 

[KiwiClive]

Sherwood usually has their impeller market locked up. Unless you went to a Globe design.

it's one of these: 08-32-1201 DJ Pump Impeller; Replaces Sherwood 10077K; Onan 1320375, 1320498, 1320379, SW10077k - Filter Discounters

 

[Captain Ralph]

Ah, Just noticed you were down under.
Please fill us in on your results.

Thanks for the site lead.

 

[Comodave]

Ah, Just noticed you were down under.
Please fill us in on your results.

Thanks for the site lead.

Do impellers spin backwards down under...

 

[Captain Ralph]

Do impellers spin backwards down under...

Wondered myself

 

[KiwiClive]

Haha ... of course .. coriolis effect!

 

[Captain Ralph]

Haha ... of course .. coriolis effect!

Yep.

 

[BandB]

Haha ... of course .. coriolis effect!

I can't believe how many people think the Coriolis effect actually does affect toilets.

 

[BruceK]

I can't believe how many people think the Coriolis effect actually does affect toilets.

I can`t believe anyone bothers to make ancient parochial "jokes" Noah might have thought hilarious,about how water drains or circulates in a water pump across the globe.

 

[KiwiClive]

I can't believe how many people think the Coriolis effect actually does affect toilets.

Yes true.
If you follow the thread you can see that I was only kidding.