Stern gear seals

[catmandoo]

As I have a catamaran with packed glands on the hydraulic drives in each hull I am considering fitting mechanical seals getting fed up with water in the bilges etc . I have been looking at PSS and DSS versions and I am undecided . Has anyone any opinions as to which unit I should select . I will need two one for each hull.

I like the DSS seals emergency feature but dont like having to pipe both an air vent and a flush from and to the seal

The PSS seal on the other hand is much simpler with only an air vent which I could combine with my cutless bearing vent . Supplier now recommends this feature to release air as an alternative to pulling back the bellows from the rotor when the vessel is returned to the water. The rotor also appears to be fixed to the shaft with round headed grub screws with additional screws to lock in the ones under neath

DSS on the other hand use CRANE mechanical seals which are well known in the Petroleum and Chemical industry and used extensively in hazardous and agressive environments but for my application they seem a little overengineered and the number of Jubilee bands makes it look like a Xmas tree

What should should I do with my glands . Any advice ?


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[Robin]

Do a forum search and then you will see why perhaps you should favour the PSS one or the similar French one called Stopelo. Our DSS is being replaced this winter with a PSS one.

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[catmandoo]

Had done forum search and conclusion was that problems were mainly due to application,how installed and frequency of maintenance / inspection . Only items attributable to DSS seals were splitting of rubber (perhaps application problem ie engine vibration ) ,corrosion of seal surface and slipping of rotor perhaps due to vibration - violent reversing etc

In your particular application are you installing replacement yourself and what was the particular reason for your DSs seals to fail ?

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[Robin]

We suffered from an intermittent leak under sail in heavy weather that was eventually traced to the seal opening as the engine moved on its (soft) mounts. There was no leaking under engine at any load ahead or astern. The temporary cure late last season was to adjust the face pressure more than stated. This was a new seal fitted two seasons back to replace one fitted when we bought the boat and which leaked on the delivery trip, though the adjustment had slipped or had been wrongly adjusted by the yard who serviced the engine beforehand. Our club engineer who fitted the replacement for us says the DSS seal is very difficult to set the face exactly at 90 degs to the shaft, whereas the PSS has a rigid S/S rotor which clamps consistently at 90 degs, the corrugated PSS hose also seems to apply more consistent pressure than the softer DSS one. We backed up the DSS with an extra hose clip to prevent slippage, but the shape of the rubber is such that this tends to provide an uneven support (ie could result in a non 90 deg fit) whereas on the PSS it would bear directly on the S/S rotor.

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[catmandoo]

Thanks for the concise reply . I know know what to do .

Its probably also a matter of scale too since some DSS seals seem to work . perhaps those with bigger shafts are more easily lined up

Im also not too happy with the need to provide a separate water flush from the engine cooling water in my case one to each hull. Another leak source !!!





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[charles_reed]

Imitation being the sincerest form of flattery - I'd suggest going for the PSS seal, the French imitation is however about 50% of the price.

Mine has been far more successful than either the Bukh (similar to the DSS) or the Halyard seals fitted previously. Two drawbacks, the collar can move on the shaft, allowing the seal to leak and, after about 6 hours at 1400 rpm the seal starts to overheat and the carbon pressure plate starts to pick up. In theory the high-speed bearing should avoid the latter problem.

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[pvb]

Keep it simple...

Several years ago, I changed my simple, reliable, cheap, Volvo rubber seal for a sparkly, high-tech Halyard seal. Great! No drips (although the Volvo seal hardly dripped). But now I find that the Halyard seal has a limited life and can't be repaired. When it finally gives up the ghost, I'll replace it with a simple, reliable, cheap, Volvo rubber seal. Maybe you should check out the simple option first, and save yourself some money.

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[Robin]

Charles, do you have the French Stopelo or the PSS itself? I must admit to some concern at 'pick up' after 6hrs at 1400rpm (shaft revs I assume) which admittedly would be more than we ever use on our Yanmar for any length of time, being normally nearer 950 - 1100 srpm. We would intend backing up the S/S rotator collar with a jubilee clip as with the DSS but would expect it to work better on the PSS (solid v rubber).

Robin

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[johnq]

Have you looked at the Shaft seal sold by Ambassador Marine (the people who do the rope cutter). It is similar to the Halyard and PPS seal but longer lasting

I fitted one on my boat 6 years ago and have done a transatlantic since with a free wheeling shaft and with no leaks. The local ferry also fitted one at the same time and has had no problems.

Only problems I have had is the reservoir was fitted to low – user error and I have to bleed it if the boat has been out off the water for any length of time (10 minute job)


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[catmandoo]

Re: Keep it simple...

Where does one get details of Volvo Seals ? Have searched internet with no success

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[catmandoo]

Re: Keep it simple...

where does one get details of Volvo seals . Have searched internet but no success?

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[catmandoo]

Uk supplier of PSS recommended fitting High speed version anyway to allow air to vent automatically - as Charles says in theory spin off is cooling feature provided by flow through vent

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[charles_reed]

Mine is an actual PSS

I'd have done better to get the watercooled one - the ss collar gets hot enough to instantly vapourise water.

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[pvb]

Details...

Any Volvo Penta dealer will give you details - should be full info and dimensions in the VP Accessories catalogue. VP call it a "rubber packing box". It's only available for 25/30/35/40mm diameter shafts, and each size only has one stern tube diameter, so it might not fit your installation. Worth checking out.

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[Robin]

Re: Mine is an actual PSS

Thanks Charles. Our DSS doesn't have the water inlet as for the high shaft speed version yet doesn't get hot, I wonder why your PSS does? Maybe on your installation the water in the sterntube is sucked down a bit, like on a self bailer?

I have just come back from checking on the boat and also spoke to our club engineer - he tells me we have DSS seals on all the club launches/workboats and they frequently slip on the shafts, then drip, he prefers the PSS but they do need a touch more shaft space to fit them.

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[Cantata]

Re: Details...

Suspect the VP seal may also be available in imperial sizes? I do hope so, I have one on a 1-inch propshaft and it's probably getting to the point when I ought to replace it!
Excellent seal, had them on 2 boats, never any trouble. And soooo simple.

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[Robin]

Re: Mine is an actual PSS

According to PSS website the PSS is designed to withstand a maximum operating temperature of up to 500 degs F, so maybe yours is normal!

See www.shaftseal.com

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[Mudplugger]

Re: Keep it simple...

Back up what has been said about the Volvo seal, about the only volvo product I would wish to be associated with....fantastic piece of kit....and this from a guy who went thru 3 DSS in 5 years (nobody bothered to say they don't like muddy water). If you are having problems try French Marine @ Brightlingsea ( Mike French) 01206 302133

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[theia]

Try Volspec Ltd. Tel 01621 869756. Part no for the seal to suit a 25mm shaft is 828254. Just bought one which cost about £85 including package and postage.

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