Pegson Marlow water pump not drawing.

[sidevalve44]

Just recently, my Pegson Marlow 1.1/2″ centrifugal pump has been reluctant to draw any water.

When working, it will pump several gallons in a few seconds but now there does not appear to be any appreciable suction.

The impeller is turning and there is a tiny bit of suction, evidenced by air bubbles in the bin I was pumping into, but not enough to draw any water, even after extensive priming.

I think the problem could be that the suction hose is much too long (at 4 metres) and that there may be air leaks where the suction hose screws into the pump body.

Any ideas ?

[wristpin]

Wouldn’t have thought that 4m was not over long but how much lift are you attempting? Also, you need to eliminate any air leaks on the suction side and make sure that the internal structure of the suction hose is not collapsing. Heavy grease around screw fittings can help.

[hillsider]

Assuming that all checks out ok with the suggestions made so far and the pump is still not working the next place to look is the drive shaft gland seal, if that has failed the pump will not prime no matter how hard you try.

[sidevalve44]

Thanks for the suggestions.

The total lift is only about 1 metre or so, well within its capabilities. The hose is very rigid (too rigid really, makes fitting it very difficult), no problems there. However, the Union is made of nylon and has begun to get a bit worn. Water was dripping out past the threads.

As far as I can remember, there is no gland seal as such although there was a rubber seal that fitted on the outside of the engine crankcase and was compressed when the pump body was bolted up onto the engine body.

When I got the pump, a previous owner had fitted 1.1/2′ to 3/4″ reducers which I removed.
Beginning to think that perhaps I should have left them !

[hillsider]

The couplings don’t rely on the threads to provide the seal, that is normally taken care of by a rubber or leather washer that sits in the bottom of the female half of the coupling.

Re the rubber seal that you described as located on the shaft between the engine and the pump body that is almost certainly just a thrower seal that deflects any leakage from the gland seal preventing it from damaging the engine. The gland seal is possibly a carbon ceramic face type of seal and is totaly contained within the pump if the pump has not been used for some time it may be that the seal has become stuck to the shaft preventing the tensioning spring from pushing the seal faces together.

[sidevalve44]

Thanks Hillsider.

When I stripped and rebuilt the pump there was nothing even remotely resembling what you are describing inside it I’m afraid ! It all seemed very basic but, worked well up to recently.

I think I’ll try greasing the threads, refilling the shaft greaser and giving it a few turns (a well greased shaft seems to act as a kind of seal) and taking it from there. If that fails, then it’s back to the workshop !

[hillsider]

It is most unusual to have no seal at all on a centrifugal pump such as yours but we live and learn.
The fact that there is a grease cup feeding the seal indicates the presence of a seal of some description and yes charging it with grease will improve the seal for a while. It would be a great help if there was a parts diagram that we could look at, failing that perhaps if you do need to open it up you could post a photo or two of the pump and its internals including the area where the shaft enters the back of the pump body.

[sidevalve44]

If greasing it all up doesn’t work I’ll remove the pump and strip. Will photograph as well.

Unfortunately, when I was re-building it, I could find absolutely nothing on the Web or anywhere (even on here) of a technical nature about Pegson Marlow pumps. I guess, being over 50 years old years old (1960) it is unlikely I would !

The only seal on the shaft was the rubber one that squashed up against the crankcase and I could find no evidence that the pump had ever been dismantled before and a seal “lost”. The tab washer on the impeller was intact.

[Author]

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