Multistage pump cleaning

[julianf]

I have a couple of these -



Theyre little grundfoss multistage units.  Not exceptional flow, but a solid unit.


Anyhow, a while back one got choked up with sawdust, and lost flow.  I swapped it out for an identical unit, but the time has come for me to clean out the first part.


The pump is a "CM" but i cant find any service diagrams on grundfoss' site - im thinking they must all be about the same, so im wondering if one of the pumpophiles could advise?


If i undo the 4 allen bolts, the housing splits and will rotate a little in the middle of the stainless section, but thats as far as it gets.  Looking down the inlet, i can see a nut, but i dont just want to go attacking things blindly.

Thanks, Julian

[Tony]

Yes take that nut off the shaft and everything will then slide out. Pay close attention to the order it's all fitted in

[julianf]

Any special way to lock the shaft?

Or take the fan cover off, and lock it at that end?

[Tony]

Very hard to get the force needed to lock it at the fan end.  On multistagers I put one of those oil filter removers over an impeller (the chain ones work well) and lock it that way.

[julianf]

That i dont understand -

In order to get to the impellers, i need to undo the bolt.
In order to undo the bolt, i need to get to the impellers?

[Tony]

Ah.  On the Calpedas the first stage casing just falls off to access the impellers.  I don't own any Grundfos multistagers so have not had the opportunity to do the same 

[julianf]

Found this on yourtube -

http://www.youtube.com/watch?v=hYaHmZBZ7qw

Now need to work out why the cast end does not want to drop off mine...

[julianf]

Got it apart - once id watched the vid, i was happy to use a little more force.  I think it was all the junk inside it making it difficult.

Im now wondering how much effort its going to be to find some of the paper sealing rings, or if i shouldnt resort to the usual "wind it with a load of ptfe" fix... : )

[Tony]

Interesting.  The construction is very similar to the Calpeda, except that doesn't have those sealing rings between stages (just metal on metal) but the whole thing sits inside a stainless outer casing so I guess tiny leaks between stages are not a problem as it just gets recirculated.

Are the rings on yours damaged?

[julianf]

Theyre a thin paper gasket, the OD of the rings, and with an ID only a few mm less (so the 'width' of the paper strip is about 2mm)

They just tore immediately.

[greasemonkey]

You could try cutting the rings out of a cereal box. It's fiddly, but I've done it. No need to get the external the same size, presuming it's poking out the side of the casing. make that a bit thicker, to give it strength. Just get the inside right.
You can also buy proper gasket material. Is the thickness critical? See that it won't pinch the workings up it the gaskets are a bit thin.

[julianf]

The originals are very very thin - they're like office paper, or even thinnner - there's really nothing to them.

They should not cost more than a couple of quid for the whole pump, but i fear that may be optimistic.

I think ill try and get the right parts, but, if not, either cut them from an A4 sheet (easy enough to draw in cad, and then cut along the printed lines) or just do the ptfe one.

I have 2-off these pumps.  One is on the reactor, and one is a spare, so im in no real rush (well, until the one on the reactor gets blocked - and then ill be in a panic!)

[julesandtash]

I'm glad I didn't try to relieve you of one now. My battered and bruised, but still fine, GRC Aquatec pump is so simple with just a single closed impeller and one big O ring - and it gives 80lpm from a 370watt motor.

Why dont you put one of your 110lpm JGS pumps on it?

[julianf]

Why dont you put one of your 110lpm JGS pumps on it?

Cause im saving them for when i finally get that plate done for the base.  Then i will fit them both.

I know that if i fit one now, itll just get covered in s#it, and i wont have the motivation to sort it properly.

The grundfoss pumps are nice.  I was using those Leo units previous, but all 4 of them have developed leaking seals, and damaged electrical housings.  The grundfoss, whilst they dont like pumping sawdust, are as good as new on the outsides, and, save for the sawdust in the impeller of one of them, they work nicely. 

My reactor used to have 2-off the leos attatched.  I have 2-off the grundfoss units, and have only ever bothered running one of them at a time.  The only reason why i plan on fitting the 110lpm unit is to get the venturi to work better.

[Tony]

Having tried single stage vs multistage pumps with the same max flow rating, I have to say when it comes to driving a venturi there is no contest.  The multistager's run like it isn't there, and the venturi performs a lot better as a result.