shaft gland

[Deleted member 36384]

No Experience With Goretex or Teflon - But Comments On Graphite Packing

I am looking to replace the packing in my stuffing box while the boat is out this winter. I have read from time to time about "dripless" packing material being available- I think using Goretex or Teflon? Anyone tried this material?

I have used graphite packing in industrial applications. The reason we use them is to do away with the grease. However, you have to get the packing pressure correct and adjust it as it wears otherwise they leak too.

In my experience with pumping brines, similar viscosity to water, the packing will pass much easier than gelled drilling muds.

 

[vyv_cox]

Sticking can be an issue and just like not burping a Volvo you would soon know about it because it usually makes a horrible noise. There is also an issue with the faces parting either because the bellows is not set up properly or excessive forward movement of the engine when going into gear - or a combination of the two. I have heard of such cases and also cases of water pressure opening the faces when surfing, but only at the bar talk level.

I vaguely remember the stories but find them rather difficult to believe. I can't imagine how a PSS could stick - what's the adhesive that will stick polished carbon to polished stainless steel? Whatever it is could make lots of money if marketed. My boat is on the hard for half the year, plenty of time for it to dry out. There is never a suggestion of sticking when I get back to it in the spring. Salt deposits accumulate around it, especially in the Med, but I don't see salt crystals being much of an adhesive.

Unfortunately there are many examples of failures where poor setup, maintenance or plain abuse are the fundamental cause, but a perfectly good product gets the blame.

As for 'a piece of wood floating in the bilge jammed between the faces???' Enough said.

 

[Tranona]

As I understand it from the "stories" usually secondhand of course, the "sticking" more often occurs when the boat is idle in water with high fouling, although also possible with boats out of the water.

A little bit of history. When face seals were first used in this type of application about 25 years ago, there were several manufacturers and failure was more common, not so much the faces (although not unknown) but the the bellows and clamping arrangements which were not adequate for the job. They have all disappeared from the market with the exception of PSS which is much better engineered and to an extent Deep Sea Manecraft, but this is not actively marketed here. I wonder why? and why the design has never been taken up by builders.

The only possible advantage of not having the seal on the actual shaft, but in the housing, is perhaps reduction in wear on the shaft. However, not sure wear was ever a big issue. Other than that I can see no advantage over lip seals or even a stuffing box (except for the drips) and the disadvantage in that failure can be catastoiphic - however remote the possibility.

As I indicated in an earlier post, my ideal shaft seal is the oil bath type with lip seals, but this is expensive, heavy and bulky. The elegance and simplicity of the Volvo seal, plus low cost must make it the preferred choice for small shafts. There may be a residual issue over life, particularly as Volvo indicate a 5 year service life - the reality is that they last a very long time and are simple and cheap to replace should there be any signs of wear on the seals.

BTW the "piece of wood" was a first hand account and is as reliable as the individual who reported it - no intention of making things up!

Not sure I would agree that a product that can fail for reasons of poor set up, maintenance and abuse in this crtical situation would justify the description of a "good" product! Surely it should be idiot proof, low maintenance and stand up to "abuse" without failing - catastrophically!

 

[doug748]

I vaguely remember the stories but find them rather difficult to believe. I can't imagine how a PSS could stick - what's the adhesive that will stick polished carbon to polished stainless steel? Whatever it is could make lots of money if marketed. My boat is on the hard for half the year, plenty of time for it to dry out. There is never a suggestion of sticking when I get back to it in the spring. Salt deposits accumulate around it, especially in the Med, but I don't see salt crystals being much of an adhesive

Well I must agree, never seen the sticking problem myself.

I feel that there are issues will all stern gear. Too sharp a focus on the seal itself ignores the fact that all depend on the itegrity of some form of rubber fabrication, bellows, moulding or construction. When that fails leaks are inevitable. Leaking stern gear has always been one of the more common forms of flooding, ask any surveyor.

Of more interest in terms of the OP is the first hand report that a member had a problem with a PSS and vibration on his Yanmar single cylinder. He felt it lent less support to the shaft allowing it to rattle on the stern tube of his Spring 25. The noise was so bad on tickover that it convinced him to swap back to a stuffing box. One to bear in mind on small engines

 

[wotayottie]

Not quite - every drilling rig I work on including brand new rigs all have a stuffing box with packing on centrifugal transfer pumps. All now use non lubricated graphite packing. The reason for this is low cost reliability and the ability fix without pulling the motor off the pump.

They also offer good shaft sealing on non toxic slurry mediums in preference to a more engineered elastomer type lip seal.

Stuffing boxes offer simple, effective, reliable technology with inherent redundancy in the 4 wraps of packing.

Thats interesting. All the equipment I came across in heavy engineering was lip seal based but then we wernt dealing with slurry. Incidentally, a large French built container ship I sailed on a few years back had lip type seals on its twin shafts.

 

[vyv_cox]

Not sure I would agree that a product that can fail for reasons of poor set up, maintenance and abuse in this crtical situation would justify the description of a "good" product! Surely it should be idiot proof, low maintenance and stand up to "abuse" without failing - catastrophically!

Like an engine? I can think of many ways of wrecking a perfectly good engine through poor setup (tappets for example) maintenance (oil, filters, belts) abuse (too many to mention - see PBO forum pages!)

My own problem with the Volvo seal was the condition of my shaft. I doubted that it would seal on the scratches and burrs that were already there. Assuming they made one in my size, of course.

 

[Tranona]

Like an engine? I can think of many ways of wrecking a perfectly good engine through poor setup (tappets for example) maintenance (oil, filters, belts) abuse (too many to mention - see PBO forum pages!)

My own problem with the Volvo seal was the condition of my shaft. I doubted that it would seal on the scratches and burrs that were already there. Assuming they made one in my size, of course.

The point I was making (I thought quite clearly) is that in this critical situation simplicity reliability and security are perhaps rather more important than in other situations!

Yes, Volvo do make a seal in your size and of course will only seal on a good shaft. A new shaft and Volvo seal would still be an economical solution.

 

[Deleted member 36384]

Thats interesting. All the equipment I came across in heavy engineering was lip seal based but then we wernt dealing with slurry. Incidentally, a large French built container ship I sailed on a few years back had lip type seals on its twin shafts.

Drilling rigs do tend to be quite conservative with regards to up grades. I used to get approached quite often by seal salesmen asking me to consider upgrading but it just isn't economical for these applications.