impellers?

Hi,

There has been a rangof supposedly dry running impellers known as Barco around for years.

Here is one users thoughts on the matter

http://lists.samurai.com/pipermail/sentoa/2005-February/002160.html

and here are a few others

http://www.sailnet.com/forums/gear-maintenance/16983-globe-impellers.html

A while back I was re building a raw water A/C pump and was deciding on what sort of impeller to use (stainless or bronze). The Stainless will last longer and was almost twice as much $ as the bronze. I then learned that the pump seals will fail before the stainless impeller would. In order to change the seals you need to remove the impeller.
I figured that the best impeller was not necessarily the best impeller for that situation.

Hi,

C4ENG- I think the original poster was asking about flexible impellers as he asks if the hi tech one is better than the standard rubber one's.

A Bronze Impeller would be every bit as good as a Stainless one for an AC SW Pump IMO. What was the casing of the pump made of?

With the original poster I was trying to use an example of how the best may not be needed because other parts of a system may ware out causing failure or maintenance regardless.

Just like you said, a bronze impeller is just as good as stainless, but the stainless will last longer being a more durable material. It just boils down to not being cost effective using the stainless when you have to rebuild the pump every year any ways because of the seals wearing out.
As far as the casing, they are almost always bronze that I come across.

Geez, this one really pushed a button.

At a time when owners are demanding quality and performance, and their perception of receiving value for every dollar spent on yacht maintenance is more and more important, we read this inadvertent admission of just how low the quality has dropped in some areas.

It's pushed that button because I have just become involved in trying to clean up a mess that has cost an owner tens of thousands of dollars, as well as costing a contractor a lucrative contract because they had technicians who lacked such fundamental knowledge and training.

Was this some kind of engineering epiphany?

Do you think you have to change the impeller each time you change seals or is it your practice to destroy the impeller when removing it? Or is it that you think when a seal fails you should throw away the pump?

It is little wonder why many owners are mothballing their boats or reconsidering the return on their yachting investment.

My dear friend Marmot

You certainly are an angry young man.

See when you rebuild the pump and change the seals and not the impeller, then the impeller might wear out before the new seals do. Then you might have to rebuild the pump again in another 6 more months or so oppose to another year, wasting more time and money. It does not always work that way and every situation can be different, but this is what some of my experiences has taught me. I try to work smart and not hard.
I am referring to a consent run raw water pump as well, not the original topic of a flex rubber impeller deal..

Not angry, just disappointed at yet another example of why owners so often feel like they are being victimized.

Your attempt at clarification is interesting to say the least. Again , it probably tells more than you really meant it to.

Hi,

If you are only getting 1 yr or some 8000 odd hours of running out of a SW Pumps rotating mechanical parts like the impeller I would hazard a suggestion that either the pump/installatyion or maintenance is incorrect.

C4ENG- Do you ever find that when the impeller on a centrifugal pump ( This is what I am assuming you are referring to here) is worn that most of the wear is around the inlet volute?

There is often a corresponding wear rate around the surface it runs in on the pump end casing so they should really be replaced as a pair, or you will have a premature failure of the same components.

I have not seen a pump in recent years where you can replace the impeller, seal and casing for less than the cost of a new pump, so maybe your maintenance is short sighted due to a lack of real world experience and general engineering knowledge/training.

K1W1 you just answered a question I've had for years. I have never seen a yard bill for a new impeller or seal. It's always for a new pump. I wrongly just assumed they were padding the bill. Thank you for the education.

I really wonder how it makes you people feel good while standing on others with sly condescending un-called for remarks because maybe you do not agree with something said....

Maybe a bronze impeller doesn't last 18 months and seals do last longer than 12 months in consent run sea water pump, Maybe Scott Pump sales techs lied to me about there products and maybe I am mistaken with what I have seen in the ER over the last couple of weeks that I have been working in engine rooms,

But really..........

I think I will go ahead and find something better to do than to fight with you people,,,,, like go to work because I am still employable.

It all depends on the size and type of pump. Some small pumps don't use replaceable wear rings and are not worth the time to weld and machine back to specs. But, unless you have been pumping sand the impellers should last for a long time, certainly far longer than seals, even lip seals. Mechanical seals if installed properly by a competent tech will last for a very long time, installed poorly they don't last long. An impeller has to be pretty far gone before pump output drops low enough to cause real problems in most applications onboard a yacht.

The application where impellers go away rapidly is when pumping a lot of sand or silt or when pumping hot water with a high suction head that causes cavitation. Even then it gives a lot of notice that it is not happy and a prudent engineer will recognize the problem before draining the owner's wallet.

There is still a good chance that they were stiffing you because they don't have the facilities or technicians to rebuild the things or they simply make more money replacing than repairing or simply replacing a seal. That way the warranty is on the manufacturer, not them and they make more money. You need to ask what is going on if they throw the whole thing away, motor included, even most small close coupled pumps can be replaced without trashing the motor.

With these smaller boats it usually is a matter of sand/silt injestion as the owners try to get as close as possible to the beach (can't get the bikinis wet when the girls step off) and often run in marginal depths. One local bay (that's transited by up to a 62 Azimut) has a mid-chanel high tide depth of 4' at one spot. Most yards for small yachts don't have the facilities, techs or time to rebuild, but from what you and K1W1 say I'll be less sceptical of their motves. Sounds like it just makes sense to swap it all out.

Ah yes… impellers.
My first boat + my first outing = my first disaster.
Out on a boating holiday found us anchored in what seemed like 10 feet of water, but we woke up in about a foot.
Needless to say, sand got the better of my leg, and 2 days were spent undergoing repairs at a horrendous price for a young guy back in the 70’s.
The holiday continued with a new respect for paying attention to tide tables.

Hi,

NYCAP- Next time you are looking at replacing a pump, ask the supplier not the yard installing it how much the Shaft, Seal, Impeller and Casing are.

Then ask how much a complete pump is.

When armed with that ask the yard to quote you to repair the one that needs work.

You will no doubt be surprised that once you are replacing the shaft or casing in addition to the Impeller and seal that the whole pump is probably cheaper and you get all the other big part thrown in. ( I have had this experience on Jabsco Raw Water Pumps as used on Caterpillar Gensets and many brands of Centrifugal Pumps used elsewhere onboard)

I do not have much experience with these tiny close coupled pumps so maybe some of these are really throw away models in the cold light of day.

C4ENG- Calm down a bit, when you post obviously mis leading info you should not get upset when someone takes you to task about it.

There are many very skilled people here on this forum who are willing to give advice when it is asked for.

If you have questions about systems you would like some help with don't be afraid to ask. You can PM me or even one to Marmot if you have questions or need some advice with something you have encountered onboard.

Unless he carries liability insurance and has permission from the marina an independent captain can't do mechanical work except for emergency repairs and little stuff like filter or belt changes. He mainly just troubleshoots. It would be somewhat different for a full-time captain and certainly an engineer.

...X2.