Pss seal failure

[vyv_cox]

I had a pss seal with a water feed, fail yesterday. This was fitted professionally, just over a year. I was told by the engineer that it did not need squeezing and didnt need to do anything with it. The engineer attending breifly yesterday said that the ceramic seal showed signs of getting hot. I am going to have to fit a new one. Has anyone had a similar problem. Should I be still be squeezing the seal despite the water tube being fitted? Thanks in advance

I always open the faces on first launching to ensure they are wet but throughout the season I never touch them. However, as liveaboards we are running the engine frequently, at least every two or three days. If the engine was not run for two or three weeks I can imagine that the faces could dry out.

 

[rogerthebodger]

Some time ago I had the collar move back that allowed water ingress, so I made a spit collar to back up the Rotar no more issues since then.

The SS grib screws supplied are soft so IMHO the lower grub screw needs to be hardened steel grub screw fitted with grease followd by the locking (upper grub screw) being SS so the lower grub screw will bite into the prop shaft better

 

[IanCC]

Thank you. This is all very useful.
I have a sailing boat speed approx 6-7 knots but sometimes I need to put a few re s on the boat handle the wind and tide.

Is it easy to replace a pss seal? Dropping the shaft back makes me a bit nervous. How do you know that it is realigned properly?

The tricky bit, depending on access, is compressing the pss seal. I had to build a tool from bits of wood and threaded bar. Also be careful not to scratch the faces of the seal, they work on surface tension. Mine does not leak a drop after i redid the 'professional' installation.

I really recommend phoning the pss guy in the uk, he is really, really helpful and may volunteer to come and have a look.

 

[BabaYaga]

The seal looks way over compressed, was this done to try and stop the leak?

If not it could well be the cause of the problem. The amount of squeeze is really quite small, on the smaller sizes I think only about 10mm or so - check the handbook.

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Recently bellows may have been redesigned to be stiffer. I replaced the bellows a couple of years ago (at +15 years) and the new one was not easily compressed the correct amount. Ended up making a tool from threaded rod, as mentioned above. 25mm shaft.

 

[Tranona]

Every time I read a thread like this I am pleased I have been able to fit Volvo/Radice seals. Latest in post#12. Fraction of the cost and trouble free.

 

[vyv_cox]

Every time I read a thread like this I am pleased I have been able to fit Volvo/Radice seals. Latest in post#12. Fraction of the cost and trouble free.

As ever, the few failures that occur receive considerable attention whereas the thousands of successes go unnoticed. A year or two ago I found a list of boatbuilders who fit PSS seals as original equipment. It filled an A4 page double columns in a small font.

 

[Tranona]

As ever, the few failures that occur receive considerable attention whereas the thousands of successes go unnoticed. A year or two ago I found a list of boatbuilders who fit PSS seals as original equipment. It filled an A4 page double columns in a small font.

Yes, but the failures are consistent around the weak points of making the face seals work reliably in this application. To me it is an overly complicated and expensive way of solving the problem. I expect your list is mainly US builders and larger sizes whereas in Europe in smaller sizes like the ones we use, Volvo seals dominate as the 2 builders who produce boats in volume with shaft drives under 40mm fit them. In larger sizes.

Retrofitting of course is not so straightforward as the Volvo type has a limited size range for the shaft log fitting, but often bronze fittings like mine in the photo can be machined to take it.

 

[doug748]

As ever, the few failures that occur receive considerable attention whereas the thousands of successes go unnoticed. A year or two ago I found a list of boatbuilders who fit PSS seals as original equipment. It filled an A4 page double columns in a small font.

What do you think about the photo in post 1? Zoom in.

It seems to have been crushed so tight that it may have buckled. If this was not done to try and stop the leak it might explain the overheating.

Looks dodgy to me. The OP should be wary of the original installer till it eliminated as a possibility.

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[vyv_cox]

What do you think about the photo in post 1? Zoom in.

It seems to have been crushed so tight that it may have buckled. If this was not done to try and stop the leak it might explain the overheating.

Looks dodgy to me. The OP should be wary of the original installer till it eliminated as a possibility.

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Pity the focus is not better but I agree the convolutions look closer than I would expect.

 

[zoidberg]

Vyv Cox's comments give, as always, helpful perspective. But the statistics are of little consequence to someone who has just had a failure that could sink the boat, and those in her. For them, it's a 100% life-threatening emergency.

And they don't always occur when one is in a safe haven with the RNLI on hand nearby with a soddin' big salvage pump. We should have been halfway across the Channel towards Ushant.... but were 300m. from Falmouth's Lifeboat Station when we discovered our floorboards floating - and our Single Point of Failure.

I hold that we - er, those of us with a PSS seal lurking silently in the bilges like a ticking time-bomb - need to keep, on board and to hand, simple and reliable means to mitigate, constrain and choke off water ingress from a failed PSS seal. This is now a 'known risk'.

We accept and do that for the remote possibility of a through-hull hose failure. IMHO we must apply the same logic....

* In event of Rotor Slippage/set screws failure, a s/s hoseclip with butterfly nut closure - already fitted.

* In event of Bellows Rupture, ( perhaps ) a larger s/s hoseclip with butterfly nut closure - large enough to fit around and stored handily nearby.

These seem 'cheap and cheerful' readily-affordable precautions that few except the Yorkshiremen among us would cavill at.

Of course, a better solution is to fit a bespoke collar, or a shaft anode. I understand the PSS Company provide such collars for their larger commercial units. It quite escapes me why they don't provide the same for their smaller, 'leisure sailor' units..... but that's likely cynical US marketing thinking.

 

[noelex]

If you are replacing your PSS seal they have released a new "pro" version with more durable bellows that is worth considering.

 

[srm]

I hold that we - er, those of us with a PSS seal lurking silently in the bilges like a ticking time-bomb - need to keep, on board and to hand, simple and reliable means to mitigate, constrain and choke off water ingress from a failed PSS seal. This is now a 'known risk'.

Manecraft Deep Sea Seal has built in such a device. They have been criticised on here for having it as some keyboard warriors interpreted it as an admission of potential failure. When challenged no one could give an authenticated example of a total failure such as described above; annoying leaks but nothing requiring a salvage pump.
I replaced mine in 2019, the old one being of indeterminate age and a lot more than the ten years I had owned the boat. Only done as I had to pull the shaft to change the cutless bearing. I tried the emergency seal after taking the old one off and it would certainly reduce water ingress to a manageable rate and probably stop it totally.

 

[Roberto]

I replaced my pss bellows after about 7 years, just for precaution as it was showing no sign of wear. The sturdiness of the material is such I think all other underwater parts of the hull (itself included) might break before the bellows, it could possibly be cut if hit with an axe.
The distortion in the OP photograph might be due to the connection to the stern tube not being made exactly perpendicular (?)
Anyway, pss worked for me and cannot see any reason to change, whatever happens elsewhere after pro/not pro installations

 

[vyv_cox]

I replaced my pss bellows after about 7 years, just for precaution as it was showing no sign of wear. The sturdiness of the material is such I think all other underwater parts of the hull (itself included) might break before the bellows, it could possibly be cut if hit with an axe.
The distortion in the OP photograph might be due to the connection to the stern tube not being made exactly perpendicular (?)
Anyway, pss worked for me and cannot see any reason to change, whatever happens elsewhere after pro/not pro installations

The reality is that no seal is totally safe from failure. There are examples of fails of just about every type on my website.

Packed glands are probably the safest of all. In the refinery that I worked at there were about 3000 pumps. Every one had a mechanical seal of the PSS type, except for fire pumps that had packed glands. These would continue to pump even if the gland packing was destroyed. This is true on the boat, even if the packing is removed afloat the incoming flow can easily be arrested by wrapping a rag around the gland.

 

[Roberto]

The reality is that no seal is totally safe from failure. There are examples of fails of just about every type on my website.

Packed glands are probably the safest of all. In the refinery that I worked at there were about 3000 pumps. Every one had a mechanical seal of the PSS type, except for fire pumps that had packed glands. These would continue to pump even if the gland packing was destroyed. This is true on the boat, even if the packing is removed afloat the incoming flow can easily be arrested by wrapping a rag around the gland.

I think there can be some statistical relevance in one's own experience, at least there is for me.
If I have spent Xthousand happy nights with a given type of anchor, X thousands engine hours with a seal, or a mechanic device of whatever sort, there can surely be alternate choices but I see no reason to change (nor to advise anyone to do so, simply relating my experience which is what I think forum are for). No way I would change anything if my personal statistically relevant experience is disputed by say a three-try Panope anchor test, or some leaking distorted bellows on a seal. I used clove hitches for fenders without that ever-reassuringly-seamanlike additional locking half hitch and never lost a fender, go figure why that knot has never come undone
Of course nothing is totally failsafe, but I have more confidence in my experience/mistakes when obtained beyond normal operating periods, than anything one can read here and there, which of course can be useful suggestio ns when one is unhappy with what they are doing.

 

[zoidberg]

There is always room for a prudent Plan B.