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Flossdog
12-03-14, 17:12
What's best for a non greased stern gland? If one is far better than the other why are two types available?
Thanks guys.

GHA
12-03-14, 17:37
What's best for a non greased stern gland? If one is far better than the other why are two types available?
Thanks guys.
I've had very good results with Ptfe from ASAP. Though the was in a greased stuffing box. Except it wasn't really, never remembered :)
Interestingly, I just ordered a new stuffing box from tnorris who mentioned they use graphite now after a few customers mentioned the Ptfe was causing more heating. Not heard that before and my last one ran virtually drip free and cool.

ksutton
12-03-14, 19:04
I had graphite packing in my water cooled (non grease) stuffing box from new and changed it to PTFE stuffing after 10 years. Was in the Med at the time, had huge problems just 2 months after changing to PTFE. It got hot and found it impossible to adjust, either dripped too much or got mad hot with only minute changes of the gland adjustment, it even leaked melted PTFE blobs out.
I changed it again after 3 months and used "greasy hemp" stuffing material. Worked perfect from installation, didn't even have to re adjust anymore and is still perfect 300 eng hours later.
I believe the only PTFE you may get now is old stock, many stuffing box seal suppliers have taken PTFE off the market. I suppose if you have a greased stuffing box you may get away with PTFE, but given the choice I would go for graphite or greasy hemp, (if you can get it).

Mel
12-03-14, 19:09
I think the PTFE one would last longer as the properties of the PTFE are able to deal with high temperatures.
Both have been in use in industry a long time. I recall PTFE coming onto the market in the 1960's and the material survived difficult applications where abrasives were present in the water being pumped.

Alpha22
12-03-14, 19:13
Just done both of mine with PTFE, now running too hot to touch!!! Will have to haul out and replace... annoying as they are both very inaccessible.

GHA
12-03-14, 19:23
I had graphite packing in my water cooled (non grease) stuffing box from new and changed it to PTFE stuffing after 10 years. Was in the Med at the time, had huge problems just 2 months after changing to PTFE. It got hot and found it impossible to adjust, either dripped too much or got mad hot with only minute changes of the gland adjustment, it even leaked melted PTFE blobs out.
I changed it again after 3 months and used "greasy hemp" stuffing material. Worked perfect from installation, didn't even have to re adjust anymore and is still perfect 300 eng hours later.
I believe the only PTFE you may get now is old stock, many stuffing box seal suppliers have taken PTFE off the market. I suppose if you have a greased stuffing box you may get away with PTFE, but given the choice I would go for graphite or greasy hemp, (if you can get it).

Maybe the grease is a factor after all..

Flax PTFE gland packing must be regularly lubricated with quality water resistant grease, such as Drive Force 807680 and 807684.
http://www.asap-supplies.com/marine/ptfe-flax-gland-packing

Alpha22, is yours greased?

ksutton
12-03-14, 20:02
What's best for a non greased stern gland? If one is far better than the other why are two types available?
Thanks guys.

Floss dog I think the reason why there are different types of stuffing box materials is that the stuffing box was not initially designed for marine prop shaft applications. It has been widely used in the chemical industry for packing and sealing shaft seals on various sizes of valves for ages. In that application the shaft speed is very slow and not continuous as in marine use. The types of packing originally came form that industrial application as did the application, before it was used extensively on boat prop shafts. Hence different material seals became available for various industrial applications in fluids, pressures and materials.

parsifal
12-03-14, 20:39
I last repacked mine several years ago, and I used ptfe instead of hemp. The gland ran quite hot, too hot to leave your hand on it for long.

I thought this was due to me putting too much grease in and so preventing any cooling water getting near the bearing. I cut down drastically on the greasing and the bearing ran cooler but it's still hotter than I think it should be.

Maybe the ptfe packing is the culprit, as suggested above.

Alpha22
12-03-14, 21:26
Alpha22, is yours greased?

Yup! They appeared to be OK at slow speeds, but got astonishingly hot when opened up a little.

NormanS
12-03-14, 21:43
Floss dog I think the reason why there are different types of stuffing box materials is that the stuffing box was not initially designed for marine prop shaft applications. It has been widely used in the chemical industry for packing and sealing shaft seals on various sizes of valves for ages. In that application the shaft speed is very slow and not continuous as in marine use. The types of packing originally came form that industrial application as did the application, before it was used extensively on boat prop shafts. Hence different material seals became available for various industrial applications in fluids, pressures and materials.

Packing glands have been, and still are used in all sorts of pumps etc, some with shaft peripheral speeds well in excess of small boat prop shafts.

GHA
13-03-14, 08:43
Yup! They appeared to be OK at slow speeds, but got astonishingly hot when opened up a little.
What sort of shaft revs do you think? After the success of the last Ptfe stuffing I was going for the same, but a few alarm bells ringing now. My shaft revs will be about 1400rpm max.

Ta

NormanS
13-03-14, 09:07
What sort of shaft revs do you think? After the success of the last Ptfe stuffing I was going for the same, but a few alarm bells ringing now. My shaft revs will be about 1400rpm max.

Ta

It's not just shaft revs. The revs and the shaft diameter determines the peripheral speed. At one time I was involved with large turbine pumps, which rotated at 1500rpm, and the shafts were about 100mm. Originally we used graphite packing, and at some stage changed to a Teflon based packing. It didn't seem to make any appreciable difference.

charles_reed
13-03-14, 09:13
I thought I knew a little about gland-packing materials and, on reading this thread became increasingly confused (as the posters appear to be).
As with many things in the life we look for sound-bite answers, which are as likely to farther confuse than to elucidate. Hence, I suspect, many revert to the ultimate low-tech answer - greasy string.
I will confess that I have no answer for the OP - his question offers inadequate information and appears to be based upon a simplistic perception of a fairly hi-tech branch of industry;-

http://www.sealrite.co.uk/gland_packing.htm?gclid=CM3swPOTj70CFSUUwwod8GoArA

GHA
13-03-14, 09:16
It's not just shaft revs. The revs and the shaft diameter determines the peripheral speed. At one time I was involved with large turbine pumps, which rotated at 1500rpm, and the shafts were about 100mm. Originally we used graphite packing, and at some stage changed to a Teflon based packing. It didn't seem to make any appreciable difference.
Ah, yes, that makes sense. Thanks

25mm prop so 1400/60*0.025=5.83 m/s

Anyone who's had hot Ptfe stuffing care to shaft revs & dia ?

Ta

savageseadog
13-03-14, 09:28
I've never used gland packing nor am I an expert but when I was selling some at a boat jumble I was told that PTFE packing can score shafts.

vyv_cox
13-03-14, 09:30
An interesting thread. I recently repacked the stern gland on Cecilia, using PTFE. The shaft diameter is about 30 mm and rotational speed I guess is pretty low. The previous packing was in very poor condition, leaking badly. Since repacking the shaft rotates very freely, the yoke bolts are as loose as they can be without falling off, but the gland overheats badly within a few minutes of motoring. Greasing seems to improve it briefly but overheating then recurs. No idea of the reason as yet.

KellysEye
13-03-14, 09:36
I have used PTFE tape to seal compression fittings for Copper water pipes, as far as I know it is not made for rotating shafts so it no wonder it gets hot and breaks up. Our boat had two greasers, for the front and back shaft bearings, and I used waxed flax in the stuffing box. Without greasers waxed flax should work but I would expect it will have to to be replaced regularly. I have no experience with graphite.

DerrickHigton
13-03-14, 09:42
Another factor is that you need to be aware that you can have electrolytic corrosion using graphite packing with stainless steel shafts. Crevice corrosion is a potential problem with any packing, due to the exclusion of oxygen, even with a nickel aluminium bronze (NAB) shaft, as in my case. There are some relatively exotic packings available that are worth considering, many combining PTFE and graphite!


After considerable research I decided to use Gore GFO packing. Although clearly the answer to the maidens prayer, I still had some concerns about the risk of electrolytic corrosion between the noble carbon and the less noble nickel aluminium bronze (NAB) shaft (not approved by the American Bureau of Shipping for this reason). I contacted the W L Gore Associates UK office and they assured me that it would not be a problem.

The carbon is actually impregnated in the PTFE; running fingers over it leaves no residue.

Not a drip since!

GHA
13-03-14, 09:48
An interesting thread. I recently repacked the stern gland on Cecilia, using PTFE. The shaft diameter is about 30 mm and rotational speed I guess is pretty low. The previous packing was in very poor condition, leaking badly. Since repacking the shaft rotates very freely, the yoke bolts are as loose as they can be without falling off, but the gland overheats badly within a few minutes of motoring. Greasing seems to improve it briefly but overheating then recurs. No idea of the reason as yet.
What's going on?? Seems to be a common experience so somethings up, yet I had years of drip free cool motoring, using ASAP stuffing. Could there be differences in different types?are there different types?

This was the stuff I used.. http://www.asap-supplies.com/marine/ptfe-flax-gland-packing
PTFE Flax Gland PackingDrive Force PTFE flax gland packing rope is ideal for packing out shaft bearings and glands.
PTFE impregnated flax 'Sturntite' packing is ideal for boat prop shaft applications, as the PTFE makes it 'super slippery' while the flax material reduces wear on the shaft when compared to graphite cotton or asbestos rope type gland packing.
We sell PTFE flax gland packing either on an 8 metre roll, or per metre for maintenance. Most glands or bearings require three rings of gland packing, so a one metre length is enough to provide three rings for shafts up to 100mm (4”) in diameter.
Flax PTFE gland packing must be regularly lubricated with quality water resistant grease, such as Drive Force 807680 and 807684.

Alpha22
13-03-14, 09:54
My shafts are an inch and a quarter... quite chunky and at fast cruising speed are rotating in the order of 2000 to 2500 rpm.
Looks like an order from ASAP is on the cards.

vyv_cox
13-03-14, 09:55
Another factor is that you need to be aware that you can have electrolytic corrosion using graphite packing with stainless steel shafts. Crevice corrosion is a potential problem with any packing, due to the exclusion of oxygen, even with a nickel aluminium bronze (NAB) shaft, as in my case. There are some relatively exotic packings available that are worth considering, many combining PTFE and graphite!


Close to scare-mongering, I fear. Galvanic corrosion is theoretically possible between graphite and stainless steels but the reality is that it is almost unknown, particularly where the graphite is such a minor part of the packing mix.

I have been researching crevice corrosion in stainless steels for some years and have never come across it in a packing, although there are photos of it under cutless bearings on my website. Considering how many hundreds of thousands of boats use packed glands without suffering this problem it cannot be considered a genuine risk.

So far as nickel aluminium bronze is concerned, the copper Development Association says this:
Any crevice corrosion of aluminium bronzes, however, takes the form of minor selective phase dealloying ....... which results in little reduction of strength and practically no impairment of surface finish. Aluminium bronzes are, therefore, very widely used for pump shafts and for valve spindles - situations where pitting corrosion in crevices makes stainless steels, for example, unsuitable.

ksutton
13-03-14, 13:37
I thought I knew a little about gland-packing materials and, on reading this thread became increasingly confused (as the posters appear to be).
As with many things in the life we look for sound-bite answers, which are as likely to farther confuse than to elucidate. Hence, I suspect, many revert to the ultimate low-tech answer - greasy string.
I will confess that I have no answer for the OP - his question offers inadequate information and appears to be based upon a simplistic perception of a fairly hi-tech branch of industry;-

http://www.sealrite.co.uk/gland_packing.htm?gclid=CM3swPOTj70CFSUUwwod8GoArA

Greasy string or "Greasy Hemp" as its know admittedly more in southern hemisphere countries than northern is far from being a low tech answer. It has been used for decades, new materials principally developed because of the commercial competition in industrial use, they don't have to be necessarily correct for our boats. (If it wasn't broke, why did it need fixing) comes to mind.
As you can see from the posts here, many of us have tried PTFE packing, a large percentage of those have reported hot running and difficulty in finding a balance between being too tight and too loose.
PTFE and its lack of compressibility may be a factor, it does seem to go hard (or solid) and lacks give very quickly. Initially when installed with some kind of lubricant it seemed fine to me, and it was initially cool to touch while running. The problem with mine began after about 20 hours motoring it then got hot and began to smell, it then started extruding pieced of white PTFE pieces.
At that point it was no longer possible to adjust it either leaked or ran so hot it began to partially seize the prop shaft.
I was in Minorca at the time and had a conversation with a Kiwi marine engineer in a marina. He told me about greasy hemp packing and quoted that as being the preference with both NZ and Australian boat builders and maintenance companies.

This comment is based on an experience, I would never try to persuade or convince anyone, its entirely up to individuals, just in case you still think there is an element of confusion with responses.

vyv_cox
13-03-14, 13:41
I believe the problem may be partly due to the very low thermal conductivity of PTFE. Once it begins to heat up, maybe due to a small rub or a shaft deflection, the heat accumulates quickly as it cannot be conducted away. PTFE also has quite a high coefficient of thermal expansion, which then exacerbates the problem.

rob2
13-03-14, 16:16
I was thinking about the comment earlier that PTFE gland packing promotes excess wear of the shaft. I would imagine that this would be due to the fact that it is a relatively soft material and particulates of hard materials can become embedded in the surface, scouring the shaft.

Rob.

ksutton
13-03-14, 16:31
I was thinking about the comment earlier that PTFE gland packing promotes excess wear of the shaft. I would imagine that this would be due to the fact that it is a relatively soft material and particulates of hard materials can become embedded in the surface, scouring the shaft.

Rob.

All the sales info written on PTFE seals suggest they cause less shaft wear. However further to my post above number 22, when I dismantled the gland with the PTFE seal after only 20 hours some of the PTFE had stuck solid to the shaft "in rings". I suspected then that the water injection cooling may have been blocked because they looked to have been running dry. I connected an external water hose and water gushed out into the dismantled gland, so it hadn't been blocked. It proved difficult to clean the baked on PTFE rings from the shaft which were 20 or so mm inside the gland casing. I disconnected the prop shaft from the engine and moved the prop rearwards out of the cutlas bearing and cleaned the shaft at that area thoroughly,thankfully there were no score marks or shaft wear.

vyv_cox
13-03-14, 17:11
I was thinking about the comment earlier that PTFE gland packing promotes excess wear of the shaft. I would imagine that this would be due to the fact that it is a relatively soft material and particulates of hard materials can become embedded in the surface, scouring the shaft.

Rob.

A fellow student in my final year did a sponsored project on the wear associated with PTFE on stainless steel. Surprisingly the steel wore a lot and the PTFE hardly at all. I then joined Shell, who turned out to be the sponsors of the work. It was for the seats of very large ball valves, originally intended to be PTFE until it was found that the balls were wearing badly. I now know that raw PTFE is colourless but the white stuff that we mostly call PTFE is filled with powdered glass to improve its mechanical properties. It's the glass that wears the steel. PTFE intended for reciprocating duties, e.g. dry running gas compressors, is filled with graphite plus lead, bronze and other materials.