Impellers boats,washing machines and ponds.

Vara

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Over the last month I have done three jobs on pumps. <ul type="square"> [*]Changed impeller on Volvo inboard,23Hrs use and signs of deterioration of rubber [*]Scrapped washing machine and salvaged pump (it might come in handy)Rigid plastic impeller goodness knows how many hours and gallons it has pumped over 13 years,no sign of damage or deterioration [*]Cleaned out pump in pond similar impeller to washing machine rigid plastic not touching casing and has pumped about 26280 Hrs no sign of deterioration or wear [/list]

Question is why cant we use rigid non sweeping impellers to push water round an engine,as it would appear to be an intrinsically more reliable way to move water about.Or is there already a better pump on the market I haven't stumbled across?
 

simonfraser

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i guess the boat ones are flexible to cope with marine life and othe bits, or it could just be that it makes more money to fit flexible ones that break . . .
 

david_bagshaw

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Me Thinks unfortunately both pond & washmachine pump dont have to self prime nor cope with variable back pressure.
 

pappaecho

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Yup, he's right. A washing machine impellor does not need to pump a fixed head, as it is self primed. Point is that you are recommended to change the impellor on a Jabsco every year. My boat was owned previously by a tightwad, who believed in changing the impellor every five years... probably because the change job is a nightware on a Perkins 4108 which has the pump directly on a bulkhead. I checked it and after 5 years and about 200 hours, it is OK, but in need of a change.
The point is I think that they should be changed after a given number of running hours, and this also applies to oil, air and fuel filters, and even the engine oil itself, rather than blindly changing every year " just to be safe".
I dont think you would apply the same criteria to a car for example - you service after a given mileage- or possibly at a lower mileage if on a lot of stop /starts etc.

I think marine engines get a comparatively easy life - they are run at constant speed, normally for a reasonable period of time, and seem to have things changed regardless of whether they need it or not!
 

Freebee

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The volvo pump has to self prime the other pumps are called flooded suction they always have a reservoir of water on the inlet to get the pump going they never have to start pumping from a run dry situation.

Its not beyond the wit of man to design a pumping set up for the volvo that would work in the same way but guess what this will cost more hence the manufacturer will go for the cheapest fit for purpose design that will fulfil the function and so as long as it can get through the warranty period thats it. If you are forced to buy expensive replacements thereafter they are even happier!
 
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Anonymous

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Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

The workshop manual for the Yanmar 4JH3-TE and similar engines calls for a check - not a replacement, just a check - on the sea water impeller every 1000hrs or 4 years. Mine is positioned in a heck of a difficult place and I don't see any need to disagree with the manufacturers, though I have checked to see how to do the job and that I have the tools and parts on board.
 

ShipsWoofy

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Re: Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

I check each of mine every time I start the engines, is that too much?
 

Ships_Cat

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Re: Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

Interesting on the 1000 hours - our impellor (in Volvo) has done around 600 hours and I have never bothered to look at it and I can stop feeling guilty now. The flow out the back seems as good as the day the engine was first run.

I wonder if the rapid failures some have are because the engine is not run regularly - ours is run summer and winter? Small commercial vessels may do 3,000 -4,000 hours a year and they would be checking their impellor every week (and replacing their oil every week too) at the frequencies I see some recommend on this forum.

John
 
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Anonymous

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Re: Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

John, I was very surprised. The previous owner, who had put 2800 hours on the engine, left an old one in the spares box (so I'm not alone in keeping apparently good parts when I've replaced them on a time basis and found them to be good!) and the impeller is in pefectly good nick except for a mark where he had obviously had to use a screwdriver to get it out! In all other respects it looks fine.

On my previous engine, a Volvo MD11C, I never had problems until I bought one of the easy-change plates with knurled screws. I had terrible cooling problems after that which stopped when I went back to the original. It seems that the new plate left an unacceptable gap between the impeller and the plate itself, preventing the pump from sucking. I see in the Yanmar manual that they spec the thickness of this plate.

David
 

Stemar

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Re: Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

AFAIK, the biggest problem with yatch engines is that they aren't used enough. The rubber impellors tend to spend several months without moving, so one or two of the vanes stays bent right over. This seems to be what is likely to cause problems. A motor used constantly is far less likely to have problems. I do mine every year; they always look OK, but an impellor is a helluvalot cheaper than a serious overheat.

Most cars of the age I can afford are supposed to have an oil change every 12000 miles or every 12 months, so there are similarities.
 

richardandtracy

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I think you've come across another instance of the type of exceptionally poor design and material selection that occurs almost across the board with boats.

I agree that the little impellors that are found on washing machines and pond pumps are not suitable because of the problems of suction. However, vane pumps found in central heating pumps will lift water (a neighbour who was a plumber used one with a 3ft lift on his pond) and do not deteriorate significantly of not run every day or two.

Regards

Richard.
 
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Anonymous

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Re: Yanmar 4JH3 impeller only needs checking every 4yrs/1000hr

Quote: AFAIK, the biggest problem with yatch engines is that they aren't used enough. The rubber impellors tend to spend several months without moving, so one or two of the vanes stays bent right over. This seems to be what is likely to cause problems.
The engineer who has done all my non-DIY engine stuff for the last five years told me that in her experience it is the bond between the rubber and metal shank that tends to go. Others have mentioned the dangers of impellers disintegrating and blocking water passages - though I have never heard even second-hand an account of that actually happening. I wonder if anyone else has?
 
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