donm
Active member
Just replaced mine with a new lookalike made to the "same standard" but has 7 vanes rather than the 12 on the original Jabsco impeller. Drags the water through ok, but am I missing something else (in addition to 5 vanes)?
Jabsco impeller
- Thread starter donm
- Start date
pvb
Well-known member
It's obviously not made to the same spec, but it'll probably still work OK.
superheat6k
Well-known member
If the original had 12 vanes and the pattern has only 7 I am not sure the words "same standard" realistically apply.
Might be just fine, but if you suffer premature pump failure Murphy's law suggests it will be at the most inconvenient moment. If a single engine set up this could fail at a place that puts the vessel in danger. Original Jabsco or Johnson impellers are not that expensive so for this specific item why take the risk. (I fully advocate use of other pattern items especially filters, but checking the effectiveness of a rubber impeller is just not feasible and can only be judged by experience).
If you do run with it please come back to the forum in a year or when you next routinely change it and let us know how it has faired at next routine change e.g. Any signs of lobe break up, cracking, etc. Bear in mind that any other deleterious affects, especially a weed blocked strainer will equally knock out a Jabsco / Johnson impeller, so judgement here needs to be objective.
donm
Active member
It is not a matter of cost - this was the only one available at short notice and the difference was not apparent until I took the damaged one out. I am looking for technical/design reasoning to understand why 7 vanes may be (or not be) as efficient as 12
superheat6k
Well-known member
PM sent
donm
Active member
Thanks for the information
pvb
Well-known member
Isn't that the most infuriating response we see on these forums? Why send a PM? Why not post the information here? If it's confidential/scurrilous, why advertise that you've sent something by PM? It is just totally illogical.
VicMallows
New member
AGREE. I simply cannot understand what is to hide - good or bad.
donm
Active member
No secret here. The Gent very kindly sent me some large files containing operating data for pumps and impellers. I guess because of their size he did not want to gum up the Forum works
Very kind of him in my humble opinion and not worthy of such a reaction Gents?
pvb
Well-known member
But he could have done that without advertising the fact on here (which, incidentally, also gums up the forum works to a lesser extent). There's simply no logic in it.
superheat6k
Well-known member
I simply sent the OP two Dropbox links to manuals on Jabsco and Johnson pumps. I do this selectively because I am unsure of the copyright situation on such publications, so avoid open forum dropbox links. I have no wish to be sued or otherwise upset a copyright owner.
I have a sizeable collection of such publications including published reference books, all of which I have found freely on the web, and will share these quite freely with anyone wanting them.
in return I do suggest recipients of such books consider a donation to the RNLI.
In future I will not post 'PM sent' as clearly this causes annoyance.
If anyone reading this post would like the Jabsco or Johnson manuals I hold please PM me. The Johnson manual is very thorough.
I have a sizeable collection of such publications including published reference books, all of which I have found freely on the web, and will share these quite freely with anyone wanting them.
in return I do suggest recipients of such books consider a donation to the RNLI.
In future I will not post 'PM sent' as clearly this causes annoyance.
If anyone reading this post would like the Jabsco or Johnson manuals I hold please PM me. The Johnson manual is very thorough.
theoldsalt
Active member
I had a similar experience recently. I bought a new Jabsco raw water pump and a spare impellor. The impellor in the pump had a different number of vanes to the spare. I took advise from Jabsco and ASAP and a respected mechanic. It appears the number of vanes makes little or no difference to the operation of the pump. However in my case both impellors were Jabsco branded, so quality was not in question.
donm
Active member
Thanks for this. The quantity and temp of the cooling water seems fine so I guess this also confirms that the number of vanes makes little difference
rogerthebodger
Well-known member
Two things come to mind with regard to the number of vanes on a Jabsco pump impeller.
With less vanes the friction between the vanes would be a little lower with less vanes and the swept volume of water would be a little larger with less vanes as there is less space taken up by the additional vanes.
With less vanes the friction between the vanes would be a little lower with less vanes and the swept volume of water would be a little larger with less vanes as there is less space taken up by the additional vanes.
jon711
Well-known member
Except the impeller with less vanes has thicker vanes so volume works out about the same, the difference is that there can be a difference in the head pressure curve, but even then, different flexibilty of materials, systems etc... Even the friction (the biggest problem with a flex impeller pump) is pretty much equal as the thinner blades of the extra bladed impeller is balanced out by thicker and less blades.
End result, no noticible difference in a typical marine system..... (In some industrial applications, more blades or less blades are needed because of products being pumped i.e. foaming, high density, suspended solids etc.... Not what you would expect in a boat)
Jon
rogerthebodger
Well-known member
Point taken
donm
Active member
Thanks Chaps - I feel even happier now!