PSS Operation

[steve stark]

Interesting recent threads on PSS design. Reminds me of a curiosity I have had since installing PSS on my H340 last year. We use the boat every couple of weeks and during the down-time, some small amount of salt crust appears around the interface of the rotor/seal. Then upon startup, I notice that the bellows take a fair amount of rotational load to 'break' this crust. Occasionally I have, before starting up, while opening the raw water intake, spun the shaft by hand to impart this load slowly in order to observe it. I presume that the bellows' design must accomodate this rotational load but thought you all may have some thoughts on this.

Maybe the crust buildup on my installation is abnormally high. I have always had a teaspoon or so of leakage around the seal during a day's running and have attributed this to the abnormally high vibration my shaft has in certain RPM ranges. I am addressing this with alignment and a new 3 blade prop, but am still curious about others' experience with small leakage and crusting.

 

[Sam Salter]

I don't get any leakage whatsoever - been on since 2003.
Only time water gets in the boat is when I "burp it" in the spring after launch.
If you get drips while it's going it may not be compressed enough!
sam

 

[Ross]

I would break it loose by hand without rotation before start-up. And as Sam suggests you may noy have enough compression on the bellows.

 

[sailaway78]

Is it possible

Is it possible that the collar is not down tight enough, allowing a tiny bit of seepage to come through, thus the salt crust. I have had a PSS installed for a fairly good while now, and have had absolutely no issues with it. Does not leak a drop.

 

[petersea]

Ditto on no water at all. As others have suggest maybe the seal needs more "compression" Check the archives there are several people who either put a zinc collar or a SS clamp just a 1/4 in front of the seal to see if it has slipped and to prevent too much slippage. If you have to reset make sure to use new set screws (double set) as well as some loctite. As far as the salt crust you could always put a wet rag (hot) to help break the crust but it should not be necessary if the seal is working correctly.

 

[kloudie1]

No experience with PSS, but lots with mechanical face seals.. Couple of things.. Compression is a good one to check and it can be increased fairly easily.. If a very small (invisible size; less than about 40 microns) piece of abrasive (sand or similar) got between the faces, it could "phonograph" the soft face and cause slight leakage when shut down, and while running. Increasing the face pressure (tension) should help and eventually, it may lap itself back in. Lots of engine bounce is definitely bad for a face seal and again, that would call for a bit more bellows compression during set-up.. Seal faces are really flat, like two-three light bands on an optical flat using monochromatic light. This is about 0.3 to 0.9 microns.. so if the seal is running well, particles larger than that can't get in to harm the face.. If the engine is bouncing around a lot, the seal may momentarily lose the ability to track, and open slightly, allowing a larger particle in, which will then scratch a spiral in the soft face as it crosses the face to get out. More face compression (maybe like 1/8" or a smidge under that?) will help it track better and may help it to heal if it is already scored. Ya probably want to remove it at next opportunity and inspect it for face damage.. A shop that handles mechanical face seals, someone like John Crane seals, or a local seal shop can lap both faces back to flat.

 

[steve stark]

Good advice all, thanks.