Raw water impeller question

I have a Jabsco that has eaten another impeller after only 20 or so hrs of use. I fear it was an OLD impeller (it came in a bag of spares with the boat). I didn't see any cracks when bending the blades and I did lube it during install. Anyway.....I'm going to put in a Globe impeller (I've ran them in all of my other boats and been happy). My question is 8 or 10 blades on the impeller? Which will move more water at same RPMs. Naturally the 10 blade unit has a larger diameter body and shorter blades than the 6. I have looked for about an hour and typed in every combination of words I could think of to pull up this info. I can't find any information regarding blade count effect on impeller performance. Any of ya'll have 1st hand knowledge about this one?

I think all the spare impellers and belts I got with the boat are going to be relegated to emergency use only and I'll buy new for routine change outs.

Sounds to me like it is just one manufacturer vs another. As long as it moves enough water. I don't really think it matters.

I have been wrong before.

SD

skipperdude said:

Sounds to me like it is just one manufacturer vs another. As long as it moves enough water. I don't really think it matters.

I have been wrong before.

SD

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I agree, you haven't changed the RPM of the pump so volume should not change significantly from one blade configuration to another. Be careful though that the width of the impellers are exactly the same for proper operation.

Globe makes an 8 and a 10 blade impeller that will fit my pump. I've got 6 and 8 rubber ones now. both Jabsco. So its not manufacturer vs manufacturer. There is a design demand difference-just can't find what it is.

Well get to work.

Let us know.

sd

Greetings,
Contact Globe. http://www.globecomposite.com/pages/contact-form

LOL yeah that twas my next step, RT. I was hoping for a quicker response here. I'll post up whatever they say.

Think of it as head vs volume. My guess would be that having more impellor vanes would allow a higher head pressure, with lower volume. More vanes take up the space that water should occupy. Also a factor is the center hub diameter. Larger diameter hub will allow less water volume but higher head.

Well I just got a rather generic reply that they are recommending the 10 over the 8 in any application that there is an option to do so.

Needless to say I've replied with specific questions but not so specific as to require an engineer to answer. We'll see. I want to be able to put my old girl up on plane reliably! I ran it up to 12-13 kts a couple of times before the "new" impeller went. Its nice knowing I can do that if necessary.

If your impellers are going that fast, I think there is more to the problem than just replacing with a more durable impeller. I'd guess that you have wear in the housing, end plates, or shaft. Or perhaps you have an intake or out-flow restriction that is allowing for cavitation or starvation of the impeller. I just think that if you have gone through 3 impellers in under 20 hrs each, the problem is probably not the impellers themselves.

No it has only eaten 1 impeller. I can see how my first post would lead to thinking it was chewing them up everytime I took the boat out. The housing was pretty smooth as was the cam plate and removable cover plate. I further slicked everything up with some sandpaper. The PO owned her for about 15 yrs and I'm thinking a lot of the spares he passed along to me were bought by the orig owner back in '84! My boat came with the "cruising kit" offered by the manufacturer as an option. It has parts to rebuilt most of the engine accessories and even has a complete fuel injector! I think this impeller may be from that kit as it was loose in the bag. I have since read up on the deterioration rate of rubber impellers in storage improperly and all I can say is read up on it yourselves! You may want to go through your spares! I will be putting a lot of my things in a separate baggie marked "EMERGENCY USE ONLY", and replacing my true spares with new things over the next few months.

As far as Globe's response they closed at 2:30 EST today so I'll have to wait until Monday for the engineering dept to reply.

I've personally never used a globe impeller before, but know a bunch of people who swear by them. I have also heard that when they do melt down, watch out! You end up with a blue glob of fused crap that is nearly impossible to clean out, so don't assume you can run them forever without water. Longer than a rubber impeller - yes. How much longer? You don't want to find out.

I heard the Globes last longer when treated properly. Anyone have experience with that? I'm seriously considering going with Globes at my next impeller change out.

FlyWright said:

I heard the Globes last longer when treated properly. Anyone have experience with that? I'm seriously considering going with Globes at my next impeller change out.

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I've met a number of Nordhavn owners who swear by them. That said, in my own experience the hardest thing on an impeller is sitting idle for an extended time. So far my boats have all been winterized, and in the spring when I pull the impellers to change them, it's pretty clear why the manufacturers recommend annual replacement. I'm not sure I could get comfortable leaving a Globe impeller in my boat for multiple years where a long annual layup is involved. I hate changing them, but it still seems like cheap insurance for reliable operation. I'd probably run it for two years, then remove and inspect and take it from there. The part I'm sure of is that I don't want to change an impeller while broken down and drifting out in open water in a hot engine room with a boat rocking and rolling.

Impeller Lube

Sorry folks,

Slightly off topic but, I am having trouble getting a good read on what I should use as an Impeller Lube.(Vaseline? KY gel?) I am probably overdue to change mine, though I check it regularly and looks fine, pumps great.

I am looking for a name brand Lube type, not just something that someone picks up from the local h/w for $3.95.

Can I get good recommendation from some knowledgeable, experienced folk with quite a number of these under their belt?

Appreciate it.

Thanks.

Not sure how about the pumps on your Volvos Jim, but I use lube that comes with the Jabsco impellers or just plain dish washing liquid. Mine fit in and come out pretty easily. Sometimes I do it without any lube...just a twist and a push.

Some folks who have issues find it helps to use a tie wrap to hold the impeller in a compressed position. As the impeller slides into the pump, the cable tie slides off the impeller blades. It might help to try a practice run on the impeller you remove if you need to verify your technique.

FlyWright said:

Some folks who have issues find it helps to use a tie wrap to hold the impeller in a compressed position. As the impeller slides into the pump, the cable tie slides off the impeller blades. It might help to try a practice run on the impeller you remove if you need to verify your technique.

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I did this for a while with modest success. It was better than nothing, but far from satisfactory. Then I finally realized that an automotive piston ring compressor was just what I needed. I picked one up at Napa for $12 and wow, what a difference for installing large impellers. The little ones are easy, but the big ones can be a real bear. The ring compressor made a huge difference.

My previous boat had a pump that used to eat impellers for breakfast. I rebuilt the pump with a new cam and still could only get 20 or 30 hours on an impeller. My marine supplier suggested switching from the black Jabsco impellers to a Globe. It lasted a couple hundred hours and counting. I just bought 2 for my Lehmans. 40 bucks each but worth it IMHO.

Delta_JimS said:

Sorry folks,

Slightly off topic but, I am having trouble getting a good read on what I should use as an Impeller Lube.(Vaseline? KY gel?) I am probably overdue to change mine, though I check it regularly and looks fine, pumps great.

.

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Another plug for the Globe impeller. They come pre lubed and seem to be more flexible so they are easier to install. I have used the dish soap and zip tie method to install impellers. I've found the biggest problem is getting the old ones out. I have used impellers (not Globes) with a threaded end that uses a bolt that forces the impeller out nicely. I haven't seen this feature on the smaller impellers.

Twistedtree: I'd gone to a diesel class and the instructor recommended taking out the impellers in the fall and leave them in a container full of olive oil or mineral oil.

dach side said:

Twistedtree: I'd gone to a diesel class and the instructor recommended taking out the impellers in the fall and leave them in a container full of olive oil or mineral oil.

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Yes, I've seen that too, and I think it makes sense if you plan to reuse them. The main engine impellers on my boat are a huge pain in the ass to service, so I figure if I'm going to do the work, I might as well use new parts. I see it as cheap insurance against a failure which would be an even bigger pain in the ass at sea, especially if it's rough out. I just change them once a year whether they need it or not.

Another trick that many people practice, including me, it to rotate through your spares so they remain new. I carry a set of spares on the boat and when it's time to swap them, I use the spares and replace them with new.

twistedtree said:

Then I finally realized that an automotive piston ring compressor was just what I needed.

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I bought this 10 years ago. I can't remember from who or what it's called. It's so easy to adjust and remove it isn't even funny!

Delta_JimS said:

I am looking for a name brand Lube type, not just something that someone picks up from the local h/w for $3.95.

Can I get good recommendation from some knowledgeable, experienced folk with quite a number of these under their belt?

Click to expand...

Some types of rubber swell up and become unuseable if coated with conventional (pertoleum-based) grease, or the white lithium stuff. This problem is fairly common with O-rings and car window seals; although I doubt that something as relatively massive as a raw-water pump impeller would show much reaction to a smear of such lube. I keep a tube of Sil-Glyde in my workshop and lubricate all rubber items with it before assembly. it is a non-petroleum grease formulated with synthetic and
natural oils. Available from Amazon at around $12 for the brand name stuff or $9 for the Napa equivalent.

I use a combination of silicon grease an silicon spray lube. The grease has a lot of body to it and serves to hold o-rings and other parts in place where they otherwise want to go walkabout. And I use the spray on the impeller itself. Cummins is explicit in their work shop manual that petroleum lubes should not be used.

theran5317 said:

Think of it as head vs volume. My guess would be that having more impellor vanes would allow a higher head pressure, with lower volume. More vanes take up the space that water should occupy. Also a factor is the center hub diameter. Larger diameter hub will allow less water volume but higher head.

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Im not so sure of your theory, except that less vanes might mean more volume. assuming your impellor housing is 'universal' (which it probably is not), if you can find pump curves for each impellor, you will be able to tell the difference at any given rpm.

Delta_JimS said:

Sorry folks, Slightly off topic but, I am having trouble getting a good read on what I should use as an Impeller Lube.(Vaseline? KY gel?)

Click to expand...

I researched this a bit before installing this last impeller. Water based lube was recommended: KY and the like. Vaseline and other petroleum based lubes were a big No-No from all the manufacturers that I looked into.

(Jim-- Sent you a PM with info)

"I am looking for a name brand Lube type, not just something that someone picks up from the local h/w for $3.95.

Can I get good recommendation from some knowledgeable, experienced folk with quite a number of these under their belt?"


I have been using KY gel for 15 years on three engines and have no reason to change. It, unlike Vaseline, is not petroleum based.

Jabsco doesn't care what type of grease you use. The grease is washed off the impeller in the first few minutes of running.

Here is a link to the Jabsco catalog dealing with replacement impellers. If you scroll down to the last couple of pages, there is a good trouble shooting guide that can help you figure out why an impeller failed and how to avoid the problem.

http://www.xylemflowcontrol.com/files/MTC_12_Impeller_Replacement.pdf

Only problem I've ever heard with Globe impellers is when used on the Hino diesels the center will spin out. I had always heard good things about them but the info I got off the Bayliner site indicated that owners that had used them had the same problem, after that I decided to stick with Jabsco.