Replacing a PSS Shaft Seal with a Stuffing Box?

[skipperpete]

I have a few issues that crop up from time to time with dripless seals , but since the topic is PSS I’ll only mention specific problems with that brand. I actually think they’re pretty good but they definitely have some fragilities.
I often have trouble with the grubscrews in the stainless steel collar and usually fit a hose clamp or shaft anode to the shaft as a safety measure if the collar gets loose. Occasionally the carbon face and the collar get stuck together after long periods of layup and require very delicate handling to separate them. A frequent issue is leaking under full power against soft engine mounts,the movement can be substantial and can’t always be accommodated by over adjusting the bellows tension. PSS’s are annoying if an engine alignment needs to be done for several reasons, first off , if the alignment was bad and its adjusted back to where it should be, the seal takes a lot of coaxing ( and sometimes lapping) to stop it leaking in the new position and because the coupling needs to be opened up to check pilot alignment/engagement and gaps, that stainless collar has to be moved to allow the shaft to be slid back, there’s a risk of rounding out those( loctited) grubscrews or damaging the pair of orings if some previous mechanic (or owner) has used a pipe wrench or vycegrips to turn the shaft at some point in the past. I made up a pair of short threaded rods to go into those grubscrew threads to easily wiggle the collar back and not flood the bilge. If the PSS is far down the shaft outside the engine room bulkhead there’s a real risk of it being damaged by a mechanic who’s never seen one before and uses a crowbar to force the coupling apart to do a gearbox seal, yes this can and does happen. Having said all of that, I’m going to put a PSS on my own propshaft in the very near future because the old fashioned conventional stern gland is so close to the coupling that it can’t be re packed without moving the engine forward…. and I don’t like the drip,drip,drip.
Anyone else had these problems with their PSS?

[markxengineerin]

Walter Schulz (of Shannon) summarized dripless shaft seals very well when he called them "a solution to a problem no one ever had". I hate my PSS- as mentioned above it burps water when motor mounts are soft or engine is not perfectly aligned, loctiting tiny set screws is ridiculous, and it's theoretically not good to block all waterflow anyway- means the same stagnant water is going to be touching the shaft for years on end and and I read somewhere that this can cause crevice corrosion quicker due to lack of oxygen. Not sure if that's true, but I will be switching back to a regular stuffing box.

[Fuss]

Probably all valid points.
On the subject of carbon face stuck to the collar, yes this is important to separate them by hand after more than 3 weeks layup...but look at it like this, once you know it...it kind of forces you to do a mini inspection before it goes back in the water. On the older ones if you did not separate them, the risk was that the boot was split.

[stormalong]

Originally Posted by skipperpete

I have a few issues that crop up from time to time with dripless seals , but since the topic is PSS I’ll only mention specific problems with that brand. I actually think they’re pretty good but they definitely have some fragilities.
I often have trouble with the grubscrews in the stainless steel collar and usually fit a hose clamp or shaft anode to the shaft as a safety measure if the collar gets loose. Occasionally the carbon face and the collar get stuck together after long periods of layup and require very delicate handling to separate them. A frequent issue is leaking under full power against soft engine mounts,the movement can be substantial and can’t always be accommodated by over adjusting the bellows tension. PSS’s are annoying if an engine alignment needs to be done for several reasons, first off , if the alignment was bad and its adjusted back to where it should be, the seal takes a lot of coaxing ( and sometimes lapping) to stop it leaking in the new position and because the coupling needs to be opened up to check pilot alignment/engagement and gaps, that stainless collar has to be moved to allow the shaft to be slid back, there’s a risk of rounding out those( loctited) grubscrews or damaging the pair of orings if some previous mechanic (or owner) has used a pipe wrench or vycegrips to turn the shaft at some point in the past. I made up a pair of short threaded rods to go into those grubscrew threads to easily wiggle the collar back and not flood the bilge. If the PSS is far down the shaft outside the engine room bulkhead there’s a real risk of it being damaged by a mechanic who’s never seen one before and uses a crowbar to force the coupling apart to do a gearbox seal, yes this can and does happen. Having said all of that, I’m going to put a PSS on my own propshaft in the very near future because the old fashioned conventional stern gland is so close to the coupling that it can’t be re packed without moving the engine forward…. and I don’t like the drip,drip,drip.
Anyone else had these problems with their PSS?

The collar is clamped to the shaft with two sets of set screws. The second set screwed behind the first to lock them in. When you get a new bellows they include new setscrews and O rings for the collar. The new set screws have a locktite product already applied. Contrary to their instructions I use some Teflon grease on the shaft. Makes assembly easier.

As for the graphite ring sticking to the SS collar it breaks free easily with hand pressure. Then spin the shaft by hand and it will seal just fine.

If the engine mounts are so soft that under high power the PSS leaks try over compressing the bellows a little bit. If you have that much movement what does it do to the alignment?

[stormalong]

Originally Posted by markxengineerin

Walter Schulz (of Shannon) summarized dripless shaft seals very well when he called them "a solution to a problem no one ever had". I hate my PSS- as mentioned above it burps water when motor mounts are soft or engine is not perfectly aligned, loctiting tiny set screws is ridiculous, and it's theoretically not good to block all waterflow anyway- means the same stagnant water is going to be touching the shaft for years on end and and I read somewhere that this can cause crevice corrosion quicker due to lack of oxygen. Not sure if that's true, but I will be switching back to a regular stuffing box.

Conventional packing glands can get hot if adjusted wrong. The friction wastes horsepower.

I once met a guy that had his conventional packing gland so over tightened that he was complaining about low engine power. Then one day he noticed that the shaft log was hot enough to fry eggs. The penny dropped and he adjusted the packing. Sudden increase in engine power. Fortunately his was a steel boat and it could take the heat without damage.

I prefer PSS. Adjust it once and forget it. Get the high speed version and there is no burping or dry face. Replace the bellows every 5 to 10 years and you are good to go.

[skipperpete]

Conventional packing glands have their own set of vulnerabilities with the over adjustment at the top of the list..... running a bit hot is the least of the problems, running very hot leading to seizure and shearing the flexible connection with the ability to sink the boat is a much scarier event, once long ago the bronze stern gland on the rubber extension had a 10mm bronze rod threaded into it to stop this very thing. Then there’s the problem that arises after the gland is over tightened......it’s not enough to back off the adjuster, usually it requires digging out the old packing and installing fresh flax.
The problem with dripless packings (and stern glands generally) is that while the members of this forum are abundantly aware of how to look after them, the majority of the boating community don’t even know what type of stern gland they have or what the consequences are of knowing nothing about it ....until!

[deblen]

Originally Posted by stormalong

These people are idiots. If you have to replace a shaft seal while in the water first go for a swim. Tightly pack a rag between the shaft and the shaft log in such a way that you can pull it out later. Then the inflow will be a trickle. Don't forget to remove the rag.

Up north here,the water temp varies from 32 -45F(0-12C)
Us idiots avoid jumping in the water at all by doing our best to figger dumb ways to avoid it
Ch- Ch- Cheers /Len

[sailorboy1]

Originally Posted by Fuss

Ok, What seal problems, installed correctly they work very reliably. Are they better than a stuffing box....

I would be interested to hear what faults you had?

You would look, at them different if you showed mid week to find the boot split, water spraying, an c the bilge pump waiting for the battery to die.

[canvasman]

My last boat came with a shaft seal. It was in a difficult place to access, which is why it was probably installed to begin with. I've always tried to avoid anything that can result in catastrophic failure. I replaced it with a tried and true stuffing box when I hauled the boat a few months later.

[stormalong]

Originally Posted by sailorboy1

You would look, at them different if you showed mid week to find the boot split, water spraying, an c the bilge pump waiting for the battery to die.

Did than happen to you? How old was the bellows?

[sailorboy1]

Originally Posted by stormalong

Did than happen to you? How old was the bellows?

Yes it happened to me and I don't know how old the bellows was. But it will never happen with a stuffing box!

Btw for those that say to just replace the bellows every X years that means need to remove the coupling. If you do that the right answer after would be to replace it. Which means you need to have the new one fit and faced, which means you need to pull out the shaft. On my boat that means dropping the rudder or pressing out a replacing later the cutlass bearing. All to not have a few drops of water while motoring.

[stormalong]

Originally Posted by sailorboy1

Yes it happened to me and I don't know how old the bellows was. But it will never happen with a stuffing box!

Btw for those that say to just replace the bellows every X years that means need to remove the coupling. If you do that the right answer after would be to replace it. Which means you need to have the new one fit and faced, which means you need to pull out the shaft. On my boat that means dropping the rudder or pressing out a replacing later the cutlass bearing. All to not have a few drops of water while motoring.

There is no need to replace a coupling just because it was removed from the shaft. It should be keyed so that it can go back in the same position from which it was removed.

If you can move the shaft back 4 inches (100 mm) you can replace the PSS bellows. It seems that that you have an unfortunate design.

Due to the design of my engine installation - V drive and the flex coupling I can remove the transmission and coupling in about an hour. Easier than disassembly of the three blade Maxprop which is best re-assembled with two people.

[skipperpete]

Originally Posted by sailorboy1

Yes it happened to me and I don't know how old the bellows was. But it will never happen with a stuffing box!



Btw for those that say to just replace the bellows every X years that means need to remove the coupling. If you do that the right answer after would be to replace it. Which means you need to have the new one fit and faced, which means you need to pull out the shaft. On my boat that means dropping the rudder or pressing out a replacing later the cutlass bearing. All to not have a few drops of water while motoring.

Why would you replace the coupling after removing it to do routine maintenance?
This is a topic about PSS seals and I already outlined the problems I have with them from day to day, nothing too dramatic and generally the various dripless seals work quite well but there’s one that I have absolutely no love for and will actually advise the owner to get rid of this particular seal. Its the only one I’ve ever seen fail catastrophically ( more than once)and is the best argument for going back to a conventional flax packing type shaft seal.
Here’s a pic of my worst dripless and don’t start hammering me if you have one that “still works perfectly” after X number of years, I’ve replaced a lot of these that have failed or were about to fail.

[sailorboy1]

I am not going to explain or debate the coupling issue and leave it to each boater to look up etc. I did say it you want to do it right.

[Jim Cate]

Originally Posted by skipperpete

Why would you replace the coupling after removing it to do routine maintenance?
This is a topic about PSS seals and I already outlined the problems I have with them from day to day, nothing too dramatic and generally the various dripless seals work quite well but there’s one that I have absolutely no love for and will actually advise the owner to get rid of this particular seal. Its the only one I’ve ever seen fail catastrophically ( more than once)and is the best argument for going back to a conventional flax packing type shaft seal.
Here’s a pic of my worst dripless and don’t start hammering me if you have one that “still works perfectly” after X number of years, I’ve replaced a lot of these that have failed or were about to fail.

Pete, what has been the failure mode on these?

Jim