Pss seal failure

[sailygirl]

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

 

[rogerthebodger]

I have a pss seal for over 10 years without any issue,

The vent pipe looks like is goes down so could restrict any water flow. Mine is feed upwards to way above the waterline fo have feed from the raw water pump if its a high speed boat

 

[sailygirl]

Thanks you Roger. I will check the feed. Do you squeeze the seal after it has been out of the water?

 

[Crinan12]

Wow unlucky. Do you have a y piece with a water feed and a breather? I can only see one pipe coming from yours? What boat? I understood that on a boat with a speed of less than 12 knots you dont need a water feed.

Does it only leak when the shaft is rotating ?

 

[srm]

I have a similar type of seal, Maincraft (I think). This has a "Y" tube on the connector. One side takes a feed from just after the engine raw water pump and the other an open tube to well above the waterline. This will bleed any air out of the seal when launching. I replaced the seal a few years ago as had to remove the shaft to change the cutless bearing. I suspect the original seal had done about 20 years without problems.
In your case a Y connector and bleed tube may be worth adding.
Also, check that you are actually getting a water feed when the engine is running. If you have a waterline filter on the engine intake topping this up with sea valves closed when the boat is ashore should leak out of the stern tube.
Burping the seal on launching will not do any harm, and may help if you do not fit a breather/air bleed tube.

 

[Tranona]

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

If it is fed by a bleed from the engine then you need to check that the stern tube and rear bearing has enough clearance for the water to exit. There should be no need ever to squeeze the bellows as there should be ample clearance in the stern tube for water to flow either in from outside or from the feed. Squeezing is often required on a Volvo type seal because that does not normally have a feed or vent. However the PSS design is different.

Common problems with restricted flow are stern tube blocked with grease if the PSS replaced a stuffing box, tight clearance non fluted composite rear bearing and limited clearance between rear bearing housing and propeller - ideally 20mm minimum.

What boat is it in?

 

[rogerthebodger]

Thanks you Roger. I will check the feed. Do you squeeze the seal after it has been out of the water?

No newer need to squeeze the the seal hens the boat has been out of the water in fack my boat is in the water all year round and only come out once every 2 years for antifouling.

I just check that water flows out of the vent pipe if i have been away from the oat for some time to check if the vent becomes blocked

 

[vyv_cox]

I have owned my PSS for many years with the only problem being crevice corrosion of the stainless steel face. I rinse the faces with fresh water at haul out and again before launching (which PSS advise)

 

[Hoolie]

I`ve had a PSS seal for several years now without problems. It does have a feed form the raw water pump and does`t need squeezing. But I always break the seal between the stainless face and the carbon disk as it tends to get stuck after a period of not being used. This not only prevents the bellows being twisted but also allows some water to escape to lubricate the seal.

 

[sailygirl]

I have a similar type of seal, Maincraft (I think). This has a "Y" tube on the connector. One side takes a feed from just after the engine raw water pump and the other an open tube to well above the waterline. This will bleed any air out of the seal when launching. I replaced the seal a few years ago as had to remove the shaft to change the cutless bearing. I suspect the original seal had done about 20 years without problems.
In your case a Y connector and bleed tube may be worth adding.
Also, check that you are actually getting a water feed when the engine is running. If you have a waterline filter on the engine intake topping this up with sea valves closed when the boat is ashore should leak out of the stern tube.
Burping the seal on launching will not do any harm, and may help if you do not fit a breather/air bleed tube.

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?

 

[Crinan12]

I don't have much mechanical knowledge and I fitted one to my boat recently (while out of the water). My shaft just unbolted from my gearbox coupling and I drew it back and installed the PSS seal and re attached the shaft to the coupling. I didn't need to re align anything and it was reasonably easy.

I would have fitted a volvo seal because I prefer their design but they don't fit my stern tube. Maybe they would fit yours though.

 

[Tranona]

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?

See post#6. You should not need a positive water feed on a sailing boat. It is primarily power boats that need it as the speed can suck water out of the tube. However there are some boats - Contessa 32 for example - where the tube is very restricted as is the space for water to exit at the aft end so a water feed is used. Non drip seals require more water cooling than traditional stuffing boxes which rely on water slowly seeping into the packing.

From your phot there seems to be enough space to fit a Volvo type seal and the Radice version has a vent so no squeezing. you will need to check the size of your stern tube and shaft as the choice of sizes is more limited than the PSS.

Photo is of a Radice seal in my boat on a 30mm shaft.

 

[srm]

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?

My boat is a cruising sailing boat so modest speeds, but as I said, not a PSS seal.
As @Crinan12 said removing and replacing the shaft is straight forward. Alignment should only be needed if you have moved the engine.
Before removing the shaft check the stern bearing for play as it can be replaced at the same time if worn.

 

[zoidberg]

Reports in yesterday from a friend of his PSS faceseal failing while anchored in Hope Cove, Devon. Lotsa seawater above the floors. Salcombe l'boat attended with salvage pump, and tow to Salcombe yard. A near-sinking....

Sounds like a re-run of a similar incident I experienced in Falmouth Harbour some years back. Then the problem was traced to the 2 crucial grub screws which hold the collar in the right place. These had slipped, permitting the collar to move along the shaft, which also breaks the 'face seal' . Result - water entry in volume and a potential sinking. By the time the problem was discovered, there was >2 feet of water in the boat and it was impossible to trace the source of ingress.

In theory, forcing the collar - and thus the rubber bellows - back into position should re-establish the 'face seal' effect. The problem with that is the grub screws.

Lotsa 'research' afterwards - including in here - elicited that NEW GRUB SCREWS should be used every time.... and that tightening them to the exactly-correct manufacturer's SPECIFIED TORQUE is crucial. It also emerged that many eng fitters simply use the International Bodgers Standard of 'That Feels About Right'. And it isn't. Further, other club members report similar encounters, so it is not a vanishingly-rare event.

The idea of one's boat and her occupants being so vulnerable to a Single Point Of Failure is not compatible with my ideas.

For those with PSS devices who may feel a twinge of concern, one 'fix' would be to fasten one or more s/s wormdrive hose clips around the shaft to restrain a PSS collar from wandering. Another is to fit a shaft anode to do the same.

 

[iamtjc]

Rather than a hose clip as backup to the collar grub screws, I have installed a stainless split collar on the shaft with a measured 1mm gap from the back of the PSS seal. That way, if the grub screws slip, the collar will keep enough pressure on the seal to prevent a leak and gives me a way of periodically checking the gap with a feeler gauge so I can confirm that the grub screws are holding.

 

[vyv_cox]

316 stainless steel is pretty soft stuff and the grub screws are hardened. Any average bodger should easily be able to indent the shaft sufficiently that the screws will never slide, although of course they might loosen. Which is why a second screw should be tightened down onto the first.

 

[zoidberg]

316 stainless steel is pretty soft stuff and the grub screws are hardened. Any average bodger should easily be able to indent the shaft sufficiently that the screws will never slide, although of course they might loosen. Which is why a second screw should be tightened down onto the first.

One wouldn't argue against that, as that's how the kit is ( I think ) supplied. There should be no problems and many years of effective service if installed exactly as the manufacturers intend. However, the string of reported failures - of which this ^ is one and my experience is two - suggest that doesn't always happen.

The simple fact is that while one may pay professional rates for a professional to do the work, one doesn't always get a professional outcome. And it's next to impossible to check/confirm that the grub screws have been secured exactly as specified, without removing them and doing it again with new ones.

It's a Single Point Of Failure design which threatens loss of the boat.

A 'belt and braces' approach is warranted.

 

[mikegunn]

In yachts and other low speed craft the PSS seal installation often relies solely on its vent pipe, to ensure the presence of water at the seal’s face. In such instances it is vital that the vent pipe exits well above the heeled waterline and does not form a “U” anywhere along its length. If a “U” exists it is possible for water to sit in the “U” bend creating an hydraulic lock. This can prevent air from venting from the seal face and in turn water from entering the seal’s cavity. This scenario does not occur where seals are fed by a portion of the engine’s raw cooling water.
Mike

 

[doug748]

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

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.

.

 

[wingcommander]

Another point is the grub screws are a one time use only, i have the early version PSS with no vent . So mine requires burping after re floating. I do carry spare grub screws , however fortunately, not had any need to use .
Hope I've not jinxed myself.