gland packing. graphite or ptfe?

[XLD]

Not sure which to order. I don't understand why graphite is used when it's near the top of the noble scale of metals, so should cause corrosion in steel!

[Tracy D'arth]

Being old fashioned, I go for graphite every time. Old school, long proven record.

[BEngo]

Depends what you are packing.  PTFE lasts much better in the governor glands than does graphite, whereas the water pump and stern gear last well, once  settled down,  on a tallow substitute  type stuff.

 

N

[jonathanA]

2 hours ago, XLD said:

Not sure which to order. I don't understand why graphite is used when it's near the top of the noble scale of metals, so should cause corrosion in steel!

Last time I checked graphite is carbon and not a metal. It's a good conductor but I don't think that means it will cause corrosion. It's not on any list of noble or transition metals as far as I know. 

[Alan de Enfield]

26 minutes ago, jonathanA said:

Last time I checked graphite is carbon and not a metal. It's a good conductor but I don't think that means it will cause corrosion. It's not on any list of noble or transition metals as far as I know. 

 

 

Graphite is about the most 'noble' on the charts and sits above gold and Platinum

 

 

 

 

[David Mack]

Some reported problems using graphite packing with bronze shafts or some grades of stainless steel. I guess its probably worse in salt water too.

https://forums.sailboatowners.com/threads/stuffing-box-packing.159570/?highlight=bronze%20shaft%20damage

[jonathanA]

Graphite still isn't a metal and it's  interesting depending on which site you look on graphite May or May not be listed... where it is listed it's always at the noble end...  

So you live and learn...

[Bargebuilder]

Coincidentally, I've just changed from graphite which I've always used, to PTFE, but only because I couldn't get graphite in the size I needed at the time. 

 

I've repacked many a stern gland and with graphite based packing I've always found it easy to adjust to get a drip or two per minute whilst motoring and a barely warm stuffing box, but I've really struggled with the PTFE.

 

Even with the packing 'pusher' just hand tight with almost no friction on the prop shaft, the stuffing box temperature climbed to about 80⁰c: I couldn't keep my finger on it!

 

I unscrewed the pusher by two full turns and it made no difference. I changed the grease to a lighter one and that made no difference either.

 

After 30 hours motoring to settle in, it's a bit cooler now.

 

PTFE packing, for me at least, ran hotter than graphite base packing, even when compressed less.

 

 

 

 

[XLD]

9 hours ago, jonathanA said:

Graphite still isn't a metal and it's  interesting depending on which site you look on graphite May or May not be listed... where it is listed it's always at the noble end...  

So you live and learn...

Graphite is a non-metal and it is the only non-metal that can conduct electricity. You can find non-metals on the right side of the periodic table and graphite is the only non-metal that is a good conductor of electricity.

7 hours ago, Bargebuilder said:

Coincidentally, I've just changed from graphite which I've always used, to PTFE, but only because I couldn't get graphite in the size I needed at the time. 

 

I've repacked many a stern gland and with graphite based packing I've always found it easy to adjust to get a drip or two per minute whilst motoring and a barely warm stuffing box, but I've really struggled with the PTFE.

 

Even with the packing 'pusher' just hand tight with almost no friction on the prop shaft, the stuffing box temperature climbed to about 80⁰c: I couldn't keep my finger on it!

 

I unscrewed the pusher by two full turns and it made no difference. I changed the grease to a lighter one and that made no difference either.

 

After 30 hours motoring to settle in, it's a bit cooler now.

 

PTFE packing, for me at least, ran hotter than graphite base packing, even when compressed less.

 

 

 

 

Is this “One drip a minute” a bit misleading? Does a tiny drop of water really cool the prop shaft down?

My prop only averages 300 rpm but the shaft never gets warm even without the magic “ one drop a minute”

Is that just because it’s such a low rpm?

[Bargebuilder]

It might be misleading if you think it's the drip of water that does the cooling, it seems to be the reduction in friction that the film of water produces at one or three drips a minute that reduces the build up of heat.

[XLD]

Good point.

[Bargebuilder]

Interestingly, try as I might, I've not been able to sustain any dripping at all with my new PTFE packing, one reason I suspect why it runs much hotter than my previous graphite packing.

 

I've even removed the packing whilst afloat and re-done it a second time ensuring that it dripped enthusiastically once installed. Once the shaft started spinning, after 15 minutes or so, the dripping slowed and stopped and the temperature increased and this was without tightening the 'pusher' at all; very odd characteristics indeed.

 

It's settled down now, but at 80⁰c or thereabouts it was unnerving.

 

I do turn the greaser every few hours of motoring as I did with the graphite, so perhaps I shouldn't.