Premature impeller failure cause - Page 2 - SailNet Community

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  #11  
Old 07-10-2012
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Re: Premature impeller failure cause

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Originally Posted by Cruisingdad View Post
I am beginning to suspect a product failure if you have followed the installation steps I discussed. Replace the impeller with Westerbeke parts. All I use are Yanmar direct parts - no aftermarket. Replace every 12 mos or 100 hours.

Replace your impeller as I described. Give her a good run for some hours. Open is and take a look at the impeller. Also, at 55ish HP, you should put out about 5 gallons of water/minute from the exhaust. Stick a bucket under there and see what you get. THat is what the specs are for Yanmar anyways, IIRC. CHeck out the amount with Westerbeke.

Hope these suggestions help. ALso, make sure your hose is not collapsing under higher rpms (from Thull/strainer to block).

Brian
Called Hansen Marine (where I got the engine) this morning. They were saying the thru hull should be 1". I think I have a 3/4" with a smaller hose fitting attached. (being 450 mi from the boat I cant check right now) I'm goung to check with Westerbeke directly also. Can't find a specification in the installation guide or manual.

Thanks for the help. The Hansen guy thinks that the impeller is having to work too hard to get water causing the delamination.
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Old 07-10-2012
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Re: Premature impeller failure cause

I think something other than the supply line possibly being a bit too small is going on. If the through hull, strainer and hose supplied the 46 OK I don't see why the impellers are falling apart on the new engine. You said the new impeller is smaller than the old one meaning that it's a smaller pump overall than the old pump. That doesn't make sense to me as they are sized according to gpm required and that would mean that the higher HP engine requires less cooling water than the old engine and if that is true then the through hull and hose should be more than adequate. I would talk directly to Westerbeke and confirm that you have the correct pump for that engine.
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Re: Premature impeller failure cause

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Originally Posted by jrd22 View Post
I think something other than the supply line possibly being a bit too small is going on. If the through hull, strainer and hose supplied the 46 OK I don't see why the impellers are falling apart on the new engine. You said the new impeller is smaller than the old one meaning that it's a smaller pump overall than the old pump. That doesn't make sense to me as they are sized according to gpm required and that would mean that the higher HP engine requires less cooling water than the old engine and if that is true then the through hull and hose should be more than adequate. I would talk directly to Westerbeke and confirm that you have the correct pump for that engine.
Thanks for the ideas. The pump I have looks exactly like the standard pump in the manual drawings and the part # for the impeller that fits the pump is part of the standard part list and the spare part kit so I don't think I have the wrong pump. My understanding is that the standard pump turns at a greater speed than the pump on the old 46 hp.

My initial suggestion to my mechanic was to possibly go with a higher volume pump and at the same time configure the mount so that the impeller was more accessable. Right now you need to unbolt the pump to get to the impeller without working blind. The mechanic indicated that upgrading to a larger thru hull would be a cheaper option to try first. I'll see what Westerbeke suggests.
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Re: Premature impeller failure cause

I think you should consider another possibility, that there is blockage down stream of the pump and it is trying to pump against too much pressure. I believe that if the intake were restricted you'd see overheating of the impellor rubber before it would shear from the hub. Whereas high back pressure would likely show up as shearing. Is there a pressure guage, or guage port? If not I'd consider drilling and tapping a pipe thread hole for one.

An old engine, an old muffler, or old piping and hoses could have lots of sediment in them. A new engine might have casting defect, like a core that didn't get properly removed, or a core that was broken during casting and left only a tiny passage. Sometimes they forget to drill out a passage to the proper size.

A pressure gauge will answer lots of questions quickly. I like the test ports from Sisco P/T Plugs - Pressure & Temperature Test Plugs
You use one gauge with multiple ports. The gauge is easily checked and seldom goes bad because you don't leave it connected. When working with centrifugal pumps you measure differential pressure using the same gauge, so gauge error is already accounted for. I buy these things by the dozen!

Gary H. Lucas
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Re: Premature impeller failure cause

Seems like a false economy to use a smaller pump at higher speed, but I'll leave that to the experts. If the smaller pump is turning faster it's entirely possible that the small supply hose is part of the problem but if the pump was starving for water (vacuum) I would expect to see vane problems similar to running dry.
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Old 07-11-2012
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Re: Premature impeller failure cause

Quote:
Originally Posted by GaryHLucas View Post
I think you should consider another possibility, that there is blockage down stream of the pump and it is trying to pump against too much pressure. I believe that if the intake were restricted you'd see overheating of the impellor rubber before it would shear from the hub. Whereas high back pressure would likely show up as shearing. Is there a pressure guage, or guage port? If not I'd consider drilling and tapping a pipe thread hole for one.

An old engine, an old muffler, or old piping and hoses could have lots of sediment in them. A new engine might have casting defect, like a core that didn't get properly removed, or a core that was broken during casting and left only a tiny passage. Sometimes they forget to drill out a passage to the proper size.

A pressure gauge will answer lots of questions quickly. I like the test ports from Sisco P/T Plugs - Pressure & Temperature Test Plugs
You use one gauge with multiple ports. The gauge is easily checked and seldom goes bad because you don't leave it connected. When working with centrifugal pumps you measure differential pressure using the same gauge, so gauge error is already accounted for. I buy these things by the dozen!

Gary H. Lucas
Gary,

I don't know if you are right, but that was the best troubleshooting thoughts I have heard in a long time! Great thoughts!

Brian
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Re: Premature impeller failure cause

Reduced water flow or a failure ( or a long time) to prime fully.
Keep you hand on the water pump cover plate when starting the engine and at full revs ( as long as its away from the belt) it sould remain cool.
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Re: Premature impeller failure cause

Is the hose between the strainer and the pump new? It might be collapsing under the vacuum, and that could be causing the restriction in flow.
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Re: Premature impeller failure cause

Spoke with Westerbeke today confirming the same thing that I was told by Hansen Marine. Every, hose, fitting, etc. needs to have an inside diameter of 1 inch. That includes the pipe ends on the strainer. I'm pretty sure I'm less than that on the thru hull and the strainer.

Going through the installation and operational manuals I was not able to find the Inside diameter requirement. When I spoke with Joe Joyce at Westerbeke he indicated that it is only shown on the installation drawings. The sales info had specs for fuel line size but not water. They didn't make it easy to get info.

Last edited by LinekinBayCD; 07-12-2012 at 06:27 PM.
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Re: Premature impeller failure cause

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Originally Posted by Cruisingdad View Post
Gary,

I don't know if you are right, but that was the best troubleshooting thoughts I have heard in a long time! Great thoughts!

Brian
Brian,
Thanks! My dad started me out troubleshooting electrical when I was just a kid. He'd send me out on jobs with no electrical drawings, only drawings in foreign languages, or where the wires disappeared in holes going who knows where.

My favorite was when I was about 19 and he sent me to a city sewer plant to troubleshoot a boiler. It didn't help that I looked more like 12! I was convinced that the problem had something to to do with two wires that went to the corner of the drawing, which was torn off. The plant manager was giving me a hard time and asking when someone qualified was going to show up. I said I'd be back the next day with my dad. We came back and I went over everything I had found with dad. Suddenly I realized what was on the missing corner of the drawing. I announced that the problem was the thermostat in the office on the other side of the wall. The plant manager said "Yeah right!" I walked over and turned up the thermostat and the boiler immediately misfired and shut down! An unusual set of weather conditions had triggered the problem.

Dad looked at his watch and says to me "Hey you better get going, you have a plane to catch." Then he explains to the plant manager "He has a trouble call to go on for a chemical company in California." The look on his face was priceless. They told me they needed me for a couple of days, I was out there 2 months!

Gary H. Lucas
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