I would say that 90% of the shaft seals I assemble and test are leak free -- this testing of course is part of the MSD/SD test and certification process each WTC gets here before sending it off to the customer (these days, The Nautilus Drydocks).
Leaking shaft seal assemblies are either repaired or replaced. The major cause of a shaft leak is a crack or scratch of the seal inner bore where the cup-seals outer edge makes contact; that portion of the rubber that makes the watertight seal between seal and inside bore of the shaft seal body. My seal bodies today are machined pieces of polyurethane sprue. A cracked or scratched inside bore would permit water to flow around the outer rubber seal lip, through the crack, letting water into the motor bulkhead.
I see that you are adhering the rubber cup-seal outer lip with adhesive. Stop doing that! Use silicon oil (not silicon grease!) to lubricate the outer and inner seal lips during assembly.
Typically the manufacturer supplies the cup-seal with an inner lip diameter slightly smaller than the stated diameter of shaft it is supposed to seal against. In our sizes that's a few thousandth's of an inch smaller. They don't have to be tight.
Are you using proper cup seals or the spring tensioned seals used by the piston crowd?
David
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Thanks David and everyone,
I have another series of questions that I hope you don’t mind answering, even though some aspects we’ve been over. I suppose I just need a little further clarity.
Leaks in drive shafts.
David, do you guarantee that your shafts don’t leak? Or is this a hot potato? I can vouch I have one of your older SD’s and it don’t leak. But are you that confident in the product?
My latest design hasn’t leaked until today, So I was really disappointed and I am assembling the first ZB2 for a customer and am currently checking the shaft seals and Uh oh, a leak.
Now you know my seal design is similar to yours, I use an Oil lite Bush with an outer housing and a U cup seal lightly glued to the top of the outer housing and the shaft is pushed through. My biggest unknown is how much grip should the lip of the cup seal push around the shaft. Obviously when you push the shaft through the lip it should flex outwards and wrap around as you push the shaft up. I am still trying to work out the fine balance between how tight this should be.
I am guessing that if it’s tighter then the motors just pull more amps? But also if you run the motor for longer periods out of water then the lip rubbing against the shaft will cause wear?. Do you not run the shaft out of the water for any length of time?
I am am convinced that there is something really subtle and tiny that I have missed, maybe it’s just getting the tightness of the lip on the shaft just right? Maybe my lip seal isn’t tight enough?
I have some pics here of my set up if it helps, I have looked at all your photos of the shaft arrangement that many times. I hope my line of enquiry make sense.
Thanks for your time,
david H.
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Beats drilling and grinding
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when it comes to static (Oilite) and dynamic (roller) bearings you want hard against hard or hard against soft. Soft against soft quickly wears away the surface of the bearing AND shaft. Bad ju-ju!
DavidLeave a comment:
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Do believe there are 2.3mm i.d. tubing available.
If not, just take off 0.15mm all around the shaft.
If you're in a hurry get a torch to the brass to soften it and just force fit the shaft.Last edited by redboat219; 09-27-2020, 04:41 AM.Leave a comment:
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How bout using brass tubing instead? 3mm OD; 2mm IDLast edited by redboat219; 09-27-2020, 03:18 AM.Leave a comment:
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Thankyou David,
Im pretty much doing most of that. I should probably use the dial gauge a bit more. Definitely doing step one. Step two grinding Down the outer shaft with motor spinning and fixed grinding. Wheel, am doing this but using a way to big grinding wheel. Will use small disc and third ,standing by for unspeakable business.
thankyou David for your schpeedy -ness..
dave hLeave a comment:
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Hello David,
its been a while while since I asked you some questions, but right now I am stumped. I am still having a problem with shaft extensions, they are the single biggest drama I’m having at the moment with my cylinder design. I know that you posted a heap of pics a couple of months ago about how to turn then and press fit them with a hammer onto the motor shafts.( I cannot for the life of me find those pics or which thread it is in.)
Anyway, I am finding them near impossible to get them absolutely centered so there is no vibration. I drill a hole in the stainless steel shaft and then lightly grind the motor shaft and then tap them with a hammer, but unless I concoct some kind of extremely tight accurate jig to hold everything absolutely in line I cannot see how I’m going to get the shafts absolutely centric...
it it makes me want to drop the ZB-2 design and just go with geared end caps...
i could take pliers and try bend it slightly that either makes it slightly better or a lot worse. I am worried if I do that then I could slightly bend the shaft inside the motor.
Help..
Thanks
David H
First is to insure your lathe is set up so the head stock and chuck are centered (run-in) so that the work does not spin 'wobbly'. You bore out one end of the stainless steel shaft extension with a bit that will produce an interference fit to the motor shaft -- that bit held in a chuck supported on the carefully dialed in tail-stock. You shave the motor shaft as the motor rotates at high speed to a slight tapper. Use a hammer or hand-press to set the extension to the motor shaft.
The second is to use a dial-indicator to find any offset of the motor-shaft extension unit -- correcting it by slightly bending the motor shaft itself.
If need be I'll impart onto you the secret, discusting, out-of-left-field third method of insuring shaft extension unity with the motor shaft -- too horrible to relate at this time.
David
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Hello David,
its been a while while since I asked you some questions, but right now I am stumped. I am still having a problem with shaft extensions, they are the single biggest drama I’m having at the moment with my cylinder design. I know that you posted a heap of pics a couple of months ago about how to turn then and press fit them with a hammer onto the motor shafts.( I cannot for the life of me find those pics or which thread it is in.)
Anyway, I am finding them near impossible to get them absolutely centered so there is no vibration. I drill a hole in the stainless steel shaft and then lightly grind the motor shaft and then tap them with a hammer, but unless I concoct some kind of extremely tight accurate jig to hold everything absolutely in line I cannot see how I’m going to get the shafts absolutely centric...
it it makes me want to drop the ZB-2 design and just go with geared end caps...
i could take pliers and try bend it slightly that either makes it slightly better or a lot worse. I am worried if I do that then I could slightly bend the shaft inside the motor.
Help..
Thanks
David HLeave a comment:
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Hello David,
I’m gone back to looking at vac pumps and am confused by the stats needed. I realize 29 inches of mercury and also -1 bar with about 8 CFM. However when I look up pumps, they all say how many cfm but none tell the amount of vacuum pulled in any meaning ful reference I can get my head around.They certainly don’t mention 29 inches or -1 Bar , they may mention microns. I’ve looked up conversion scales but I’m just getting more confused. Any further advice?
regards
David H
OK, that out of my system …...….
Kevin Rimrodt is a calibration technician. If there's a conversion scale that converts microns per whatever-to-inches, he's the guy. I'll get back to you, Dave.
DavidLeave a comment:
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Hello David,
I’m gone back to looking at vac pumps and am confused by the stats needed. I realize 29 inches of mercury and also -1 bar with about 8 CFM. However when I look up pumps, they all say how many cfm but none tell the amount of vacuum pulled in any meaning ful reference I can get my head around.They certainly don’t mention 29 inches or -1 Bar , they may mention microns. I’ve looked up conversion scales but I’m just getting more confused. Any further advice?
regards
David HLeave a comment:
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I would cut down int the number of vents you are using. I try to position the parts as such that I only need one vent. For the hinge for example if you angle the part you will not need a vent at the hinge.
Below the mould I made for the new diveplanes I did for the AKULA, only one vent/part.
Grtz,
Bart
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