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Installing PSS dripless shaft seal


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We are wanting to install a PSS seal to replace a old packing gland.

 

The old packing gland is threaded on to the stern tube and has a internal grease lubricated plastic/rubber bearing as part of it. The stern tube has no bearing in it. The PSS seals have no bearing so I'm wondering if that bearing in the old packing gland is needed and if so how do I substitute it and also install the new PSS seal?

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Hey Kestrahl.

 

I have just been through this with the Marshall but ran out of time to do it. The PSS seal has a kit that screws onto the stern tube in place of the packing gland apparently. In the end I just re-packed the stuffing box with new packing and plenty of grease and it is nice and dry. Remember the PSS glands need a cooling water line, and if the seals craps out, the water comes in fast, with no quick fix. At least you can re- pack the stuffing box...

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Yes the PSS seal is great when new and working nicely. But no so when worn. Expensive and the standard packing type seals are cheap and easy as smithy has said. Pump or two of grease and you are set.

The other issue with PSS is they are fine in clear water, but will wear faster than normal if you have to work the boat in the dirtier waters like the Rivers etc. The grit can be very hard on them.

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Hey Kestrahl.

 

I have just been through this with the Marshall but ran out of time to do it. The PSS seal has a kit that screws onto the stern tube in place of the packing gland apparently. In the end I just re-packed the stuffing box with new packing and plenty of grease and it is nice and dry. Remember the PSS glands need a cooling water line, and if the seals craps out, the water comes in fast, with no quick fix. At least you can re- pack the stuffing box...

 

Thanks for the reply smithy.

Our stuffing box has been repacked but is very sensitive, to little pressure and water pours in, to much and it overheats, I suspect the shaft is worn and really can't be bothered with it anymore!

 

I can't find any reference to the kit that screws on to the stern tube - have emailed PSS about it. Did the NZ agents have the kit? The other option is to cut the bit of the old stuffing box that threads on to the stern tube and use that.

 

As far as needing a forward bearing goes apparently it depends on a number of factors including length of unsupported shaft and clearance between shaft and stern tube etc..... I can only assume since it already had a forward bearing it should probably still have one.. but then how to have that and a PSS... unless the kit you talk of allows for a forward cutless bearing.

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PSS is a face seal rather than a lip seal isn't it? It relys on compressing two faces together by a rubber bellows arrangement. That type has more flexibility than the newer lip seal types which absolutely have to have a forward bearing in the shaft log.

 

I believe personally that face seal type dripless seals are much more suitable for fitting to existing or older installations than the lip seal types, which require that extra bearing and no history in the form of wear and tear or scratches on the propshaft

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PSS is a face seal rather than a lip seal isn't it? It relys on compressing two faces together by a rubber bellows arrangement. That type has more flexibility than the newer lip seal types which absolutely have to have a forward bearing in the shaft log.

 

I believe personally that face seal type dripless seals are much more suitable for fitting to existing or older installations than the lip seal types, which require that extra bearing and no history in the form of wear and tear or scratches on the propshaft

 

Correct PSS is a face seal so a worn shaft is no problem. And at $300 US the price isn't bad.

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What about a blue water seal? I have one on my shaft and they are great.

 

I got mine from chatfields but I think they have recently gone into receivership. Real shame as they were good.

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Our stuffing box has been repacked but is very sensitive, to little pressure and water pours in, to much and it overheats, I suspect the shaft is worn and really can't be bothered with it anymore!

I suspect the packing hasn't been placed in properly. The method is to cut pieces (that wrap once around to meet and Butt up with itself) and place each piece in so as one overlaps the join of the other. Do not spiral wind the material as this Grabs the shaft and tightens on it.

The only issue with Gland packing is that you should have a drip when it is running. Which is why the face type seals have a big plus being water tight....when they are working correctly.

 

Chatfields in receivership?? that would truly be a sad thing.

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Our stuffing box has been repacked but is very sensitive, to little pressure and water pours in, to much and it overheats, I suspect the shaft is worn and really can't be bothered with it anymore!

I suspect the packing hasn't been placed in properly. The method is to cut pieces (that wrap once around to meet and Butt up with itself) and place each piece in so as one overlaps the join of the other. Do not spiral wind the material as this Grabs the shaft and tightens on it.

The only issue with Gland packing is that you should have a drip when it is running. Which is why the face type seals have a big plus being water tight....when they are working correctly.

 

Chatfields in receivership?? that would truly be a sad thing.

 

The packing was placed in as you described. 5 or 6 rings.

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Hi Kestrahl.

 

Sorry, it was a kiwi shaft seal, not a PPS. These are probably a little better. The carbon face seals can crap out spectacularly, but lip seals (Kiwi) tend not to, but still require water feed like the PPS... They had a specific kit to fit to the screwed stern tube. I was talking to the engineering shop over at West Harbour. Very helpful.

 

Strange with your packing. I run a similar stuffing box on a 25mm shaft. It was leaking big time. I used only 3 (I think 6mm/1/4") rings. Cut them at an angle and heavily greased them. Hardly any pressure on the bolts and not a drip, but only motored for an hour so time will tell. The old packing was in too tight and had glazed...

 

You might want to read this blurb: http://www.kiwishaftseal.co.nz/wawcs0158117/history.html Hope this helps!

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I have had a look at their site.. Very interesting. Pinched this test report on running the seals dry.. Good research and sounds like a quality NZ product!! Nice!

 

 

Case Study 4 - Trial Report: 29/8/11

KSS serial: #175029 & #175034:

 

15m Planning “Altair” Henley’s test vessel.

Auckland, NZ.

Engine: Twin 250 Cummins.

Shaft: 1.75”

 

Test:

 

KSS fitted at 2384 engine hours – September 2009.

2430 hours seals checked running at approx. 12c OK.

2531 hours seals checked running at approx. 12c OK.

2558 hours seals checked running at approx. 12c OK.

2601 ZERO water coolant test, seals squealing after approx. 5 minutes, too hot to touch at 450srpm. Remove water feed line, allow water to flow thru seal to cool – approx. 10 minutes, re connect water feed line, run up to 1100srpm. ZERO leaking

2648 ZERO water coolant test, seals squealing after approx. 5 minutes, too hot to touch at 450srpm. Remove water feed line, allow water to flow thru seal to cool – approx. 10 minutes, re connect water feed line, run up to 1200srpm. ZERO leaking.

2754 ZERO water coolant test, seals squealing after approx. 5 minutes, too hot to touch at 450srpm. Remove water feed line, allow water to flow thru seal to cool – approx. 10 minutes, re connect water feed line, run up to 1250srpm. ZERO leaking.

KSS serial: #175029 & #175034 continued use up to 2796 hours with ZERO leaking temp measured 12c port, 18c starboard.

 

Result:

 

Seals were run dry on three occasions. Seals ran without leakage from 2601 hrs. To 2796 hours over a range of 450srpm to 1250srpm = 195 hours in damaged condition without failure.

Shafts checked for wear – no damage to 1.75” shafts, no damage to lip seal. No damage to KSS nose cone or hose. Internal KSS bearing shows signs of excessive heat due to zero coolant.

 

Outcome:

 

The test Kiwi Shaft Seals were removed and replaced with new KSS seals fitted with new design lip seals for further testing.

 

Conclusion:

 

The Kiwi Shaft seals enabled the vessel to run for 195 engine hours after three dry run incidents created. There is no doubt that a vessel fitted with a Kiwi Shaft Seal will be able to return to dock with paramount safety while working under extreme conditions.

 

There is no doubt that the vessel could have founded under various other brands of shaft seals.

 

PLEASE NOTE: The above report was undertaken under test conditions – the results should not be used as a running guide. Should a KSS run without water coolant – with similar test results – the vessel should return to dock and the seal should be sent to KSS ltd for refurbishment or replacement.

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I got a reply from PSS regarding fitting it to a threaded stern tube (shaft log). They said to just put some gasket sealant on the threads and clamp it straight on...

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Hey Phil, we fitted a dripless, greaseless Volvo seal in Sala when we had to cut out some of the shaft log due to electrochemical rot. The thought of putting the messy, drippy, maintenance-intensive stuffing box back in was just too much to bear!

 

There's no water feed (you just 'burp' it when it goes back in the water), and lubricate with a dab of expensive blue Volvo grease (probably exactly the same stuff that comes in tubs for next-to-nix at Burnsco...) It's totally self-contained and pretty much zero maintenance, although I am led to believe the lifespan isn't what you would get with a lubricated seal. That's a trade-off I'm happy to live with though, as it was only about NZ$100 or even less if I remember rightly.

 

Re. the bearing issue, we had the same thing, but were told that our prop shaft was short enough that we didn't need to worry about it - on Sala there is a bearing in the P-bracket and a thrust bearing at the gearbox, which I was led to believe was adequate. Not sure about Sophia's setup, but can't imagine it's too much different?

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Thanks for all the replies, all done and fitted now.

 

I emailed the KSS people about an adapter to screw onto the threaded shaft log to house a bearing and that a dripless seal would clamp onto and they said nothing like that exists but did give me the length the bearing they recommend. I ended up getting a local engineering shop here in Malaysia to make one for me out of bronze ($100) and sourced a local cutlass bearing ($30 per ft) which was pressed into the housing. All good now and just have to remember to get a new rubber bellows every 6 years!

 

It seems the forward bearing was required in this case with the PSS because I have a very soft mounted 3cyl volvo that moves around a lot. It has a very flexible coupling which I presume is there so it doesn't transfer to much pressure to the forward bearing, but without the forward bearing it would cause the shaft to rattle.

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