PSS Shaft Seals

[jim rosenthal]

Just to put this out there... McMaster-Carr sell a clamp that will work with this, I think it is stainless, the one in the photo might have come from them. But we used a hose clamp, on each side.

The instructions ARE clear. And when mine loosened, all four setscrews were in place. But the points wear off the setscrews, and I didn't check it like I ought to have done. Now, this spring, you can bet they will get checked.

[DCMY #92]

Some timely information: My neighbor hauled his 43 Saber MY today (unplanned) to diagnose and repair a badly failed Lasdrop seal. Don't know what initiated the failure yet, but it wasn't loss of cooling water. The seal that failed is 15 months old with 120 hours on it. He previously had PSS seals. Went to Lasdrop because of a PSS failure 15 months ago.

Correction of the previous preliminary information: My neighbor's Lasdrop seal failure was attributed to loss of cooling water after full investigation. The seal cooling water was acquired downstream of the main heat exchanger. Crud from the HE fouled the cooling water tube, starving the seal. The seal cooling water tap has been relocated to just downstream of the raw water pump on both engines.

[krush]

Size matters. Whats the od of the tube and the shaft size. I may even know where some are.

So crawled around and vacuumed out bilges yesterday and various other slave work. Shafts 2", Logs 3". I have a Duramax (20yrs?) on one and a Tides (10+ yr old) on the other. I want to install something new on both while out. Haven't decided to go stuffing box with duramax packing or go PSS or other mechanical seal. I'd like to get away from the need to have pressurized water to the seal...I think my gears can freewheel so I can run on 1 engine to save hours and fuel









......there's a joke in there.

[jim rosenthal]

If you want a recommendation, I would go with the PSS units. If you want regular packing glands, Buck-Algonquin would be your best bet. They are actually located here in MD. Groco may also make regular shaft-log/packing gland units, I can't recall, but they are up here, too.

[Boatsb]

So crawled around and vacuumed out bilges yesterday and various other slave work. Shafts 2", Logs 3". I have a Duramax (20yrs?) on one and a Tides (10+ yr old) on the other. I want to install something new on both while out. Haven't decided to go stuffing box with duramax packing or go PSS or other mechanical seal. I'd like to get away from the need to have pressurized water to the seal...I think my gears can freewheel so I can run on 1 engine to save hours and fuel









......there's a joke in there.

Wise ass. I almost dropped the phone when I read that.

[krush]

Of the face seals (axial "mechanical seal") there are PSS, Lasdrop Gen II (must be genII model), and Duramax.

The Gen II and the Duramax both look to be built strong and better than PSS. LasDrop Gen II uses exhaust hose like a stuffing box. Duramax has ABS classification cert and a big spring inside it's "bellows". I got more info, I have a 10yr old tides seal and about a 10yr old duramax lol. I don't really think lip seals are the best solution in this case...I have really silty water where I run.

Also, though this is a marketing flyer, it does have general information on shaft sealing types: http://www.duramaxmarine.com/pdf/ShaftSeal.pdf

[jim rosenthal]

Since you already have one Duramax, you should probably just get a second one. Any spares you have to carry would fit both.

[Dan Mapes]

I can't see a reason to change from Duramax to anything else and agree that upgrading the other to match would seem to be the best approach.

I have to admit their drawing (page 6) is a bit confusing because the arrows that point to the seal ring and friction ring point to the same ring? The smaller diagram on the same page seems to back up my interpretation.
Then there is the sea gasket. I get it that the friction ring slides inside the adapter. But that sea gasket, if it is tight to the shaft, will prevent the supplied water from escaping the assembly? If that bellows fails you're still going to get a mess of water in the bilge but you could probably wrap it with "rescue tape".

It looks pretty much like Lasdrop Gen II except they mounted the spring on the rotating assembly thus making it susceptible to the hose collapsing beyond the ability of the spring to maintain seal pressure.

I like this one better than Lasdrop, but still have reservations if the shaft clamp is not stainless. My experience has me concerned that these will slip since they are not keyed. But then if they were, they could spin the whole assembly and make a real mess out of everything. The mating surfaces of the seal seized on ours and the shaft spun inside the clamp. Sounds really weird but trust me it happened. Salts or calcium caused the faces to lock to each other. I was able to bust it loose but it left me wondering just how much force a non metallic shaft clamp could supply.

[krush]

I can't see a reason to change from Duramax to anything else and agree that upgrading the other to match would seem to be the best approach.

I have to admit their drawing (page 6) is a bit confusing because the arrows that point to the seal ring and friction ring point to the same ring?

Once it gets above 10F, I'm going to go inspect the duramax on the boat closer, and give them a call to ask about renewal parts. After research and independent analysis, I think the duramax design is probably the most robust. It's the only one, as far as I can tell, that has ABS class rating--if they failed and sunk a lot of vessels, they wouldn't have this LOL.

As for how it works, it took me a couple minutes and looking at page 6 and 7 to fully understand it.

The "shaft clamp" rotates with the shaft and is two pieces. A nylon clamp is tightened on the shaft (instead of set screws like PSS). The "seal ring" is 316SS and is attached to the shaft clamp AXIALLY with 3 compression screws. The SS seal ring does not touch the shaft...it is insulated from the shaft with an o-ring. This reduces electrolysis problems.

The SS Seal Ring spins with the shaft and rides against the "friction ring" that is stationary and made out of "oil impregnated nylon" (instead of graphite/etc on PSS). Look at page 7 and you can see the friction ring is actually very long, almost looking like a cutless bearing shape. On the engine end, it seals against the rotating SS "seal ring". Pretty simple and just like other systems.

The difference is on the prop end, the friction ring has a "sea gasket" attached to it that connects to the "adapter ring" (adapter ring is attached to shaft log). What this means is that there IS NOT water inside the yellow bellows under normal situation. Very different than the other designs out there. If the "sea gasket" fails or the "friction ring" cracks in the body, it will leak water, but the yellow bellows will now be holding the sea water out, like the PSS bellows.

"The Duramax Main Seal Body has been
designed to eliminate the use of a rubber
bellows or spring-loaded hose. It employs
a rigid, spring-loaded, composite body
that cannot be knocked off the seal face.
The main seal body is attached to an
adapter ring by a neoprene sea gasket.
If this sea gasket were to fail, the seawater
would enter the sealed spring chamber.
This special design feature provides
a secondary seal to the main body seal
and would prevent the entry of seawater
into the vessel."

[Dan Mapes]

The drawing does not show that sea seal riding on the shaft. It mates with the friction seal assembly. There won't be water in the bellows but it will come all the way up to the friction/seal ring and Lasdrop has similar capability but the components are reversed.