PSS shaft seal life expectancy

[bobsadler]

Hi. I had a PSS shaft seal installed in 2016. Manufacturer recommends replacing the bellow every 6 years. Boat has had very little use since PSS was installed (Covid etc etc) and has spent 80% of the time out of the water. I'm interested in hearing how frequently others have replaced the bellows. All help appreciated. Regards,

Bob

[Hartleyg]

On our Tayana 48, the original PSS seal was installed in 2001 when the boat was being commissioned.
Because of several issues introduced by the incompetent original installation, we completely replaced it in 2010. It has been functioning well since then (30,000nm and about 4000 engine hours) but it is now beginning to fail - it leaks enough drops while underway with power that a crust of salt crystals builds up on the muffler and other objects around the seal.
I fear we will be replacing at least the bellows again soon


Hartley
S/V Atsa

[SailFastTri]

Originally Posted by Hartleyg

On our Tayana 48, the original PSS seal was installed in 2001 when the boat was being commissioned.
Because of several issues introduced by the incompetent original installation, we completely replaced it in 2010. It has been functioning well since then (30,000nm and about 4000 engine hours) but it is now beginning to fail - it leaks enough drops while underway with power that a crust of salt crystals builds up on the muffler and other objects around the seal.
I fear we will be replacing at least the bellows again soon


Hartley
S/V Atsa

You can renew the seal by cleaning and polishing the interface between the carbon bellows side and the stainless steel disk. The disk can become pitted (and that can cause leaks) by the electrolytic action of the carbon against it in salt water. The easy remedy is to reverse (flip direction) the steel disk so the worn side is out and you get a fresh surface contact using the opposite side.
You can renew the carbon disk surface using 600 grit wet sandpaper laid out horizontally on a piece of window glass or mirror (to assure a perfectly flat surface). The rubber bellows should last at least 10 years or more unless it’s been over-compressed.
Edit - don’t forget that the set screws in the stainless disk are stacked.

[skalashn]

Our PSS lasted 9 seasons, then we started seeing a bit of black dust residue and maybe some light mist when underway. PYI recommended replacing the bellows, which I did, and now it is as good as new. Our sailing season is 4 months in fresh water, about 100 engine hours.

[mikereed100]

We replace ours at 6 years as recommended by PSS. While highly unlikely, a cracked bellows could be problematic.

[barnakiel]

When it failed (x2) on the boats I sailed, it was never the bellow but both times the seal (the rotor/stator interface).


If I were to replace the bellow, I would just replace the whole thing with something that is more robust.


PS Other brands rate their rubber bellows at 10 years (Volvo) but note theirs are flat, not ribbed, designs.



b.

[NorthCoastJoe]

I had a bellows lose its elasticity and failed to provide proper pressure on the seal. It got a little scary, the amount of water that came in until I replaced everything new. Sometimes it leaked a little and sometimes a lot just could not predict how it was going to behave.

I do not think it's worth trying to reuse any old parts. Just get a new kit and go with it. I will stick with the 6 year plan for the entire kit.

If the set screws sockets strip out use a reverse ( left hand ) drill bit for stainless steel to remove them. I think 3/16 bit was perfect for the job, the set screws are 1/4 20. That way you don't risk damaging the prop shaft.

[SailingHarmonie]

This is one of those cases where engine hours have almost nothing to do with the failure mode of the bellows. It is just aging of the rubber. No matter how little you use the engine, I would absolutely follow the recommendations. The idea here is to replace them BEFORE they fail, while they still work fine and look good! If you wait to replace until they start leaking, YOU WAITED TOO LONG!

If your engine room has a lot of electrical equipment, especially brushed motors or anything else that generates an internal arc, you can have shorter than expected life from rubber parts from the ozone generated. Not so much when the engine is running (hopefully you have good ventilation at that time) but while at anchor or otherwise moored you can get a build up of O3.

[wrwakefield]

We replaced our PYI dripless coupling bellows [Type A; Nitrile] 8 years after it was replaced by the previous owners, who maintained a 6-7 year replacement schedule.

The bellows looked like new and the entire coupling assembly was functioning as expected with no issues- but we were hauled-out and had a spare bellows in hand.

Attached is a photo of the old vs. new bellows. [1.75 inch prop shaft for reference.]

There was a small amount of pitting on the SS rotor [at 18 years old; full time cruisers…] so I reversed it to expose a new surface as well. The stationary graphite stator looked fine. Next time I will likely have both surfaces on the rotor renewed in a machine shop- or just replace it outright.

The bottom line is the bellows appears to loose compressive strength over time by taking on some memory, so the manufacturer suggested change interval seems like a prudent guideline.

FWIW

Cheers, Bill

PS: I don’t know why this forum software insists on rotating some images seemingly at random…

PPS: I scrutinized the old bellows for cracks/tears/wear, etc. and found nothing. It was still like new except for taking on some compressive memory.

[PippaB]

Originally Posted by wrwakefield

...PS: I don’t know why this forum software insists on rotating some images seemingly at random…

Because the EXIF information contained in the photo file tells it to

There are disagreements about how orientation should be coded, the biggest outlier is Apple, but there are others as well that differ from what these software developers assumed/used.

The photo you uploaded lists "height" at 963 and "width" at 1264, and that is how it is being displayed, with height being the smaller edge.

[wrwakefield]

Originally Posted by PippaB

Because the EXIF information contained in the photo file tells it to

There are disagreements about how orientation should be coded, the biggest outlier is Apple, but there are others as well that differ from what these software developers assumed/used.

The photo you uploaded lists "height" at 963 and "width" at 1264, and that is how it is being displayed, with height being the smaller edge.

Thanks. As I suspected; old school… I have even tried editing photos in other posts before attaching. No joy. Sometimes they are posted upside down. I think we need to move towards software more recent than the 1990’s…

Cheers, Bill

[toddedger]

I just replaced my bellows last year with an upgrades silicone bellows made for the new Pro model. It's supposed to have twice the lifetime. They're interchangeable but requireir different rotor adjustment on the shaft. Also added their new shaft retention collar for added safety. My original was over ten years old and still going strong, but why push it.

[Greg K]

Have no idea how frequently such seals should be replaced, so can't help you there. But for the sake of others, particularly newbies who have bought older traditional boats and are thinking of changing out their traditional bronze stuffing box for one of these fortified shaft condoms, I would say don't do it. These rubber shaft seals are a perfect illustration of a highly technical solution to a non-problem. Aside from the very real possibility of such rubber shaft seals getting irreparably damaged and the risk they pose to a yacht off shore or in remote areas, just the idea that one has to pull the shaft every 6 years or so to install a replacement should be a deal-breaker when a traditional bronze stuffing box is practically indestructible and can be maintained at sea if necessary without having the shaft pulled.

[GreenWave]

Replace it at least after 10 years. Bellows, set screws etc. and while disassembled clean the carbon disc. If it is leaking you can try to compress the bellows some more but that is a losing battle.

[KelseyB]

Replace the bellows, and inspect the rest of the DSS. I’d suspect that it’s actually worse for the bellows to have been out of the water more than they’ve been in.

If you want to eke a few more years out and just check the bellows to be safe, loosen the hose clamps on the shaft log side and decompress the bellows. 1) see if they want to decompress or if they’re now pretty molded into place and 2) look inside the folds for teeny tiny cracks.

But, I’d still recommend replacing them at the recommended interval even if you don’t see any tiny cracks, because they may be there even if you don’t see them. A DSS that decompresses slightly, or becomes a water sprinkler because there’s gunk between the faces, etc. is annoying. A DSS whose bellows fail can sink the boat - it’s one of the only catastrophic failures a DSS can really have. For the relatively low price of preventative maintenance, it’s just not worth gambling it.