The Craftmans Shop > New from Old
Resurrection of a CFEI 100 KVA Induction Furnace
awemawson:
So casting all caution to the wind I started dismantling the pump.
The first stage casing was firmly stuck to the inlet casting, somebody has used a thread lock I think. Gentle heating and a tap or two eventually got it loose to the stage you see in the first picture.
The seal / spring assembly is now exposed and actually it turns out the original definitely had bent over ends of the springs going into locating holes, whereas the kit does not, so more investigation needed.
. . .but supper calls . . . !
awemawson:
I got the old seals out. They are quite different from the replacements in the way the spring is compressed and rotated.
The original has the ends of the spring protruding and engaging in a hole in the other parts, with quite a compact arrangement to house the shaft O ring. The replacement has a plain spring and pressed metal parts that is considerably larger. I can see that it probably fits, and may be an upgrade but there is no mention of the difference in the instructions, nor does it mention why there is a black and a green version of both O rings. However the original had green so that's what's going back in!
(Google tells me green O rings are Hydrogenated Nitrile and are intended for high temperatures and stresses!)
Perhaps I should explain that the static part of the seal is sealed to the motor casting with a large thin O ring, and the rotating part of the seal is sealed to the shaft with a small fat O ring. A ring clip sits in a grove in the splined shaft holding the assembly together as the rest of the pump is assembled which gives the final compression to the spring.
Everything needs a good clean up before reassembly - there is a distinct 'tide mark' where it has dried out down to just below the shaft level, leaving a rust and debris conglomerate that needs to be removed from most of the impellers and the end housing to ensure that it doesn't get pumped round the system when it's back together - oh joy !
awemawson:
It seems that ceramic / mechanical seals are a very complicated but fascinating subject. I came across this treatise from Grundfos that I found very informative. Amusingly it illustrates the very pump I'm working one on one of its plates.
A bit of reading for those of you self isolating as I am !
https://api.grundfos.com/literature/literature/Grundfosliterature-5768950.pdf
nrml:
Whoever wrote that paper did a brilliant job of demystifying the science and engineering and presenting it in a very readable and easy to comprehend manner. :clap:
awemawson:
Yes it certainly sorted out my understanding of rotary seals!
So now the big clean up begins. Frankly it's not surprising that the spring and seal failed - all inner stainless steel surfaces are covered in a light coating of deposited rust, as are the two end castings, and there is a 'tide line' of something very varnish like that has set rock hard.
I gently grit blasted the inner surfaces of the cast iron inlet and outlet ports, masking up the motor, seal area and shaft to avoid damaging them. It worked quite reasonably, but I had to hand scrape some as I didn't want the blasting pressure too high to avoid ingress of grit where it wasn't wanted.
I'd intended to continue gentle low pressure blasting of the stainless steel pump vanes and housings, but it seemed a shame to lose the polished surface even though I don't suppose it would interfere with the pump operation. Experimenting with a specialist corrosion remover that came with my Wire CNC EDM machine it worked extremely well apart from the varnish like deposit, so at the moment all the vanes, housings and spacers are soaking in a washing up bowl of hot water and Altrans (by DEB) that is mainly phosphoric acid with a wetting agent added - I had to top up with neat phosphoric acid as the Altrans was insufficient to cover everything.
Probably leave them there for a few hours to cook in their own juice.
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