Orientation of impeller blades

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eddystone

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Changing the impeller for the first time on a VP2002, I read the VP manual and it clearly stated "turn the new impeller clockwise as it is inserted" (or words to that effect in Anglo-Swedish). However, taking off the cover plate the blades were orientated the opposite way. I rang KP Marine at Bursledon and they said it doesn't matter, it will sort itself out. So I followed the handbook and turned it clockwise as I inserted it. It's been running for nearly an hour since relaunch without any overheating symptoms including a decent burst at medium/high revs. Anything to worry about? I'm not sure about the VP handbook as the diagram definitely shows the wrong bleed screw for the secondary filter.
 
eddystone said:
Changing the impeller for the first time on a VP2002, I read the VP manual and it clearly stated "turn the new impeller clockwise as it is inserted" (or words to that effect in Anglo-Swedish). However, taking off the cover plate the blades were orientated the opposite way. I rang KP Marine at Bursledon and they said it doesn't matter, it will sort itself out. So I followed the handbook and turned it clockwise as I inserted it. It's been running for nearly an hour since relaunch without any overheating symptoms including a decent burst at medium/high revs. Anything to worry about? I'm not sure about the VP handbook as the diagram definitely shows the wrong bleed screw for the secondary filter.
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No need to do anything. The blades will turn the right way as soon as you start the engine - which you have done and all is well with the world (and your engine).
 
Instructions can be tricky ...

nigelmercier said:
I just fitted a SpeedSeal Life for my raw water pump. I would warn anyone thinking of getting one of these that the instructions leave a lot to be desired.
They [...] tell you that having noted the direction of rotation (quite tricky on your own, I used a video camera): “The impeller blades should be deflected in the opposite direction”; this is ambiguous. If something is opposite, it means it opposes something, so the conclusion is that the blades should oppose the rotation. A picture would be ideal, but failing that something like “the blades should trail behind the direction of rotation” is clearer...
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LadyInBed said:
“the blades should trail behind the direction of rotation”

That sums it up quite clearly :encouragement:
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Agreed.
I think, as pointed out, it does not really matter for the FIRST installation of a new impeller. However if you found a good reason to pull out an otherwise perfectly good impeller, it would not be a good idea to re-fit it in exactly the opposite direction!

I have no idea quite why anybody would want to... but it could be done with some designs...
 
pagoda said:
However if you found a good reason to pull out an otherwise perfectly good impeller, it would not be a good idea to re-fit it in exactly the opposite direction!

I have no idea quite why anybody would want to... but it could be done with some designs...
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With most raw water pump designs I have seen you could install the impeller either way. Whether it would be advisable or not to reverse a good impeller and allow it to wear in the opposite direction is something that has occurred to me occasionally. I think an argument could be made that reversing the impeller is a good idea to even out the wear and reduce the permanent set of the vanes although I've never done it and have never seen any expert opinions on it.

Richard
 
RichardS said:
With most raw water pump designs I have seen you could install the impeller either way. Whether it would be advisable or not to reverse a good impeller and allow it to wear in the opposite direction is something that has occurred to me occasionally. I think an argument could be made that reversing the impeller is a good idea to even out the wear and reduce the permanent set of the vanes although I've never done it and have never seen any expert opinions on it.

Richard
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The danger is that if you reverse an impeller that has become well curled up the vanes, having lost some of their original flexibility , could break off when forcibly curled in the opposite direction.
 
VicS said:
The danger is that if you reverse an impeller that has become well curled up the vanes, having lost some of their original flexibility , could break off when forcibly curled in the opposite direction.
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But what if the vanes have not yet become inflexible? Would reversing the impeller before that stage help to preserve its flexibility and prolong it's service life at a good level of pumping efficiency rather than continue the inevitable deterioration as the the vanes become set and reversal then becomes counter-productive?

As an aside, when I remove the old impeller I coat it liberally with silicon grease which I rub well into all the vanes. I then store the used impeller in the wrapping that the new one came in. When I check the old impeller a few months later it seems to have been "revitalised" and the vanes have regained their flexibility, so perhaps the hardening process can be delayed and reversing the impeller might contribute to longer life in a similar way.

Just a thought!

Richard
 
RichardS said:
But what if the vanes have not yet become inflexible? Would reversing the impeller before that stage help to preserve its flexibility and prolong its service life at a good level of pumping efficiency rather than continue the inevitable deterioration as the vanes become set and reversal then becomes counter-productive?

As an aside, when I remove the old impeller I coat it liberally with silicon grease which I rub well into all the vanes. I then store the used impeller in the wrapping that the new one came in. When I check the old impeller a few months later it seems to have been "revitalised" and the vanes have regained their flexibility, so perhaps the hardening process can be delayed and reversing the impeller might contribute to longer life in a similar way.

Just a thought!

Richard
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Resilience is a property of the elastomer material and usually it is retarded with reduced temperatures. Colder sea water followed by warmer air temperature would be good conditions that allows your impeller to return to its original shape. Beware that silicon is a known reactant with some elastomer products. I have no idea what elastomer impellers are made from. My experience is with elastomer seals used in various oil and gas tools and the advice is never to coat them in any material, store them cool and out of direct sunlight. Elastomer products also tend to have a shelf life as the properties deteriorate over time.

It is still good practise to keep the old one as an emergency spare until you purchase a new replacement but I would not coat the elastomer in anything unless the instructions specifically stated that you could.
 
RichardS said:
But what if the vanes have not yet become inflexible? Would reversing the impeller before that stage help to preserve its flexibility and prolong it's service life at a good level of pumping efficiency rather than continue the inevitable deterioration as the the vanes become set and reversal then becomes counter-productive?

As an aside, when I remove the old impeller I coat it liberally with silicon grease which I rub well into all the vanes. I then store the used impeller in the wrapping that the new one came in. When I check the old impeller a few months later it seems to have been "revitalised" and the vanes have regained their flexibility, so perhaps the hardening process can be delayed and reversing the impeller might contribute to longer life in a similar way.

Just a thought!

Richard
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Possibly if you can find something that will keep them flexible and reverse it regularly.
 
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Replying to the original question. The impeller goes clockwise - the same way as the crankshaft pulley. Quite often when you take one out it looks as though it has been turning the other way. The reason for this is that when you turn off the engine the piston is stopped by compression and bounces back turning the engine backwards for a bit.
 
TRUNDLETRUC said:
Replying to the original question. The impeller goes clockwise - the same way as the crankshaft pulley. Quite often when you take one out it looks as though it has been turning the other way. The reason for this is that when you turn off the engine the piston is stopped by compression and bounces back turning the engine backwards for a bit.
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So, having discovered two vanes facing the wrong way when I changed the impeller recently (and seeing considerably eccentric wear on the Speedseal cover, see...

Worn_Speedseal_Cover.jpg

which I assumed to be as a result of this wrong alignment and thus probably my fault from last time I changed the impeller - the orientation of the impeller blades can be seen as marks on the brass disk), I installed the impeller doubly carefully using a cable tie and with all the vanes correctly aligned. I used the original Johnson cover whilst waiting for a replacement Speedseal cover to arrive. The engine was run for less than an hour from launching to pontoon and then, when the new Speedseal arrived, I took off the cover to install it... to discover that two of the vanes were now facing in the opposite (incorrect) direction to all of the others. I managed to flip them into the right direction and turned the engine over briefly with the cover off, to make sure that all was correct. No, two of the vanes faced the wrong way again. Tried again, four vanes wrong this time. Tried again, two. And so on, see...

Impeller_Vanes.jpg

I have finally managed to get all of the vanes in the correct direction and have refitted the original Johnson cover for the moment. I'm leaving it for a few days to hope that the vanes might get a little set. Regarding engine bounce back - I had realised that this happened and thought it might be the cause - but careful observation as the engine was turned over briefly with the cover off revealed that bounce back was very minor and not sufficient to explain the vane re-orientation. I have talked to Alex at Speedseal, who is at a loss. And to Peachments (the Nanni Diesel agents and suppliers of the impellers) who were a little dismissive and said not to worry if the vanes face the wrong way - hmm. What I don't want to do is knacker another Speedseal cover if I can avoid it. Is it common for vanes to face the wrong direction after being used for a year? Does this indeed cause eccentric wear on a Speedseal cover?
 
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JohnCowan said:
So, having discovered two vanes facing the wrong way when I changed the impeller recently (and seeing considerably eccentric wear on the Speedseal cover, see...

View attachment 55688

which I assumed to be as a result of this wrong alignment and thus probably my fault from last time I changed the impeller - the orientation of the impeller blades can be seen as marks on the brass disk), I installed the impeller doubly carefully using a cable tie and with all the vanes correctly aligned. I used the original Johnson cover whilst waiting for a replacement Speedseal cover to arrive. The engine was run for less than an hour from launching to pontoon and then, when the new Speedseal arrived, I took off the cover to install it... to discover that two of the vanes were now facing in the opposite (incorrect) direction to all of the others. I managed to flip them into the right direction and turned the engine over briefly with the cover off, to make sure that all was correct. No, two of the vanes faced the wrong way again. Tried again, four vanes wrong this time. Tried again, two. And so on, see...

View attachment 55687

I have finally managed to get all of the vanes in the correct direction and have refitted the original Johnson cover for the moment. I'm leaving it for a few days to hope that the vanes might get a little set. Regarding engine bounce back - I had realised that this happened and thought it might be the cause - but careful observation as the engine was turned over briefly with the cover off revealed that bounce back was very minor and not sufficient to explain the vane re-orientation. I have talked to Alex at Speedseal, who is at a loss. And to Peachments (the Nanni Diesel agents and suppliers of the impellers) who were a little dismissive and said not to worry if the vanes face the wrong way - hmm. What I don't want to do is knacker another Speedseal cover if I can avoid it. Is it common for vanes to face the wrong direction after being used for a year? Does this indeed cause eccentric wear on a Speedseal cover?
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Interesting! I assume your outlet hose is the one at the top of your pump. With the cover off, what happens if you turn the engine over by hand using a socket on the crank nut? Can you then see at what point the vanes change direction?

Www.solocoastalsailing.co.uk
 
Yanmar provide little tubes of glycerine to lubricate the impellor while dry. I assumed, as a previous poster pointed out, this was because silicon grease, or stern gland grease, could react with the elastomer. I nicked a wee bottle of the wife's icing glycerin ( don't tell her )
 
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