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post #23 of Old 11-13-2012
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Re: Stuffing box & grease fittings

Originally Posted by Omatako View Post
I am contemplating making a dripless seal for my propshaft. Yes I know you can buy them but they're expensive and besides it's not only about saving money, it's about the sense of satisfaction.

A Marelon tube with three double-lipped oil seals as used in vehicle wheel bearings but the type that is fully rubber encased to prevent the shell from rusting. Between each seal a collar with a groove running around to distribute grease to the bleed-through hole.

The first two seals face the incoming water, the third at the other end of the tube faces the other way to contain the grease.

Then a zerk (? - I call them grease nipples) between the seals that allow the whole assembly to be pumped full of waterproof grease. From outside it would look like this:

It will take up less space on the shaft than the stuffing box I have now which I actually consider to be pre-historic and I reckon it will work really well.

Any reason why this would not work? The total cost excluding my labor (which when invoiced to me is really inexpensive ) would be about $40.

Your drawing looks just like the rotating center column of a beverage filling machine from a bottling plant. This type of design has been in use for a very long time and it works great.

A couple of things: Because you want to eliminate water intrusion, the grease has to have some miniscule amount of flow (leeching is more appropriate than flow) past the rubber seals to lubricate them. The grease must move into the water side and not the opposite as the water will ruin the grease and bearings over time. It looks like you will accomplish this by basically packing the entire thing with grease. That will work fine, but make sure with that much grease that you allow for grease changeout. (weep holes) You will get some water in the grease. It's going to happen. I'm sure you are planning for it as evidenced by your seal arrangement.

The RPM of the shaft is probably the driving (pun intended) factor of how long your seals will last. Engine crank seals / transmission seals sound like a good place to start since that's what they effectively do.

I see you plan to add zirks for the bearings. I also suggest putting the zirk on the face of each seal. pump grease around the curcumferenace of the seal. Grease will overflow the seal and will fill the cavity between the seals. But you need a channel to contain the seal anyway, and that channel needs to be filled with grease. (wet the seal on all four sides, since you're talking square seals). My suggestion is to add small weep holes on the opposite side of your seal journals. (In other words, the zirk is at 12 o'clock on the seal journal, and the weep hole is at 6 o'clock. The grease will follow the journal around on both sides and push out at 6 o'clock.) You need to see fresh grease oozing out to know you are getting grease all the way around the seal. Also, if there are no weep holes, there is no way for the journal to excrete the soap (used grease leftovers) and accept new grease. If that happens the old soap will just dry up and the seal won't be lubricated- then the shaft will eat the seal up right away.

Every grease channel needs a weep hole. So, for each zirk, factor in a weep hole on the opposite side. With a liquid like oil or transmission fluid this isn't necessary because you always have flow. With grease you need weep holes.

Do you have a grease in mind? I would suggest Lubriplate NLGI 2 or similar.

Just my .02 I love your design.

Last edited by ShoalFinder; 11-13-2012 at 04:43 PM.
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