PSS Shaft Seal - Bellows Degradtion

smokey73

smokey73

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Oct 26, 2010
2,023
Hunter 40.5 Beaufort, SC
Roy S wrote: "If you installed your bellows any time after 10/13 you should take a close look. The replacement bellows that I bought last week from Defender was actually manufactured in 4/17, three years ago."

Very interesting :huh: Have you notified PYI of this issue that two with the exact same manufacture date had a similar problem? Secondly, considering that the manufacturer recommends frequent inspection of the bellows and in addition recommends a replacement schedule based on "time" one would assume that there is a storage/shelf life on these bellows to get a reasonable service life out of them. How they are stored would make a difference too I assume. In my, and most all, boats the bellows, once installed, would be out of direct sunlight or any light, for that matter, so UV degradation should not be a factor.

Frankly, I'm disturbed that Defender would sell a product with a known service life on the order of years (not decades) that is already 3 years old. :eek: I imagine the retailer bought in bulk to get a price break and have a bunch of old ones. They may not even check manufacture date before they pull from stock. It would be interesting to know if the manufacturer has established a "use by" date for this item and taken that into account for the recommended replacement cycle. This may be one of the products that needs to be bought directly from the manufacturer rather than a retailer who may not rotate their stock. Just saying, but the plot thickens.
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,456
Hunter 30T Cheney, KS
They always warn folks to check the dates on tires when purchasing. What's an acceptable age when buying your bellows? The bellows age, not the buyer.
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,713
Hunter 430 Waveland, MS
Nitrile Rubber or Buna N has a shelf life per Goodyear Rubber [5-10 years]
Nitrile Polymer Manufacturer | Goodyear Rubber Company
One reason Ozone generators should be used with caution.

The bellows are the "spring" used to compress the mechanical seal surfaces together.

If compressed too much, then you might see the flexural cracking.

All springs must flex back and forth. [forward and reverse Engine thrusts]
My PSS is purged by my engine sea water pump.
Lack of a purge can result in over heating when running high RPM.

If boat is on the hard, then there is no water inside the bellows.
Putting it back in the water leaves the air trapped.:(

Where does the friction heat from shaft seal go?

Sea water is expected to lubricate the stator/rotor.
Jim...
 
dmax

dmax

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Jul 29, 2018
1,091
O'Day 35 Buzzards Bay
The later PSS seals have a vent that allows air to escape so they do not have to be purged of air.
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,713
Hunter 430 Waveland, MS
dmax said:
The later PSS seals have a vent that allows air to escape so they do not have to be purged of air.
Click to expand
That is the point!
No vent or purge, how do you get water in the bellow?
Many use the vent method, that has to be about 2 feet above the boats loaded water line.
I chose the water purge method after discussion with PYI technicians.

Why?

Putting my engine in reverse can suck up silty muck from a river bottom that I traverse to get to my marina.
Then when back to clear water, that silt is purged out of my bellows.

Purging the "grit" from the stator/rotor surfaces too.;)
Jim...
 
dmax

dmax

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Jul 29, 2018
1,091
O'Day 35 Buzzards Bay
While the pump sounds better, I haven't had a problem with the vent - as soon as the boat is dropped in, the bellows fill up with water, I check. My vent tube rises about 3 feet above the water line.
 
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L

leo310

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Dec 15, 2006
643
Catalina 310 44 Campbell River BC
Just replaced my PSS unit, bellows was ok but the carbon disk was at the end of life. This unit was installed back in 2003 so 17 years is a good return. Total engine hours just under 2k.
 
M

Mike Oldak

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Jan 22, 2008
325
Hunter 34 Herrington South, MD
one of the things that my new knowledgeable diesel mechanic found was that due to engine vibration,etc. the diesel fuel return hose was cracked where it connected to the engine. I replace the entire fuel line just to avoid the potential diesel spill. but probably could have just cut off an inch or two and replaced the old line.
 
smokey73

smokey73

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Oct 26, 2010
2,023
Hunter 40.5 Beaufort, SC
JamesG161 said:
My PSS is purged by my engine sea water pump.

Jim...
Click to expand
Jim, can you explain this setup or a picture if you have one? I have a vent tube but it goes to a loop well above the loaded water line but it is just a "loop" When you say "purged" by my engine sea water pump what do you mean?
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,456
Hunter 30T Cheney, KS
smokey73 said:
Jim, can you explain this setup or a picture if you have one? I have a vent tube but it goes to a loop well above the loaded water line but it is just a "loop" When you say "purged" by my engine sea water pump what do you mean?
Click to expand
Dripless seal manufacturers show an alternative way to connect the vent barb. One is to vent it like you have, the other is to tap into the engine cooling system for water to flow back thru the seal. It is supposed to prevent an air pocket that might burn out the seal surfaces. LasDrop said the latter was only required on boats over a speed. Sailboats were not required.
 
RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
I notified PYI that my cracked bellows had the same manufacture date as Walmsleyc's. They asked that I send them the bellows for examination. Regarding shelf life, PYI stated that the bellows was wrapped in plastic and inside a cardboard box. They thought that my bellow's three years on Defender's shelf, so protected, was not a concern. Regarding the recommended compression of 3/4"; I used a screw jack to accomplish this while installing the set screws. In my opinion, that compression requirement is probably excessive and is near the limit of what is possible. Despite all that my first of three bellows was in service for about ten years and then in my basement for four years. Examining that old bellows today revealed two facts: 1) There are no cracks. and 2) The design has changed. The original one permitted more compression as the configuration of spring section was longer (2-1/4" vs. 2") and more compressible, and perhaps, less likely to crack. I will attach a photo showing the differences below.
 
Justin_NSA

Justin_NSA

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Jul 7, 2004
8,456
Hunter 30T Cheney, KS
Interesting development. I'm interested in how this plays out.
For anyone following who are on the fence regarding dripless seals, check out the LasDrop Gen II. Practical Sailor liked it and the PSS best.
 
njlarry

njlarry

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Sep 23, 2009
1,475
O'Day 34-At Last Rock Hall, Md
My pss has a vent hose but I don't recall ever seeing a water line in it. As for burping it I 've never been able to compress it to accomplish that.
 
JamesG161

JamesG161

SBO Weather and Forecasting Forum Jim & John
Feb 14, 2014
7,713
Hunter 430 Waveland, MS
njlarry said:
My pss has a vent hose but I don't recall ever seeing a water line in it
Click to expand
If it is installed correctly and your hose is not black, you should see a water line.
In fact it will be the static water line/level of your boat, at berth.;)
_____
This is my hose/bellow and how do I know what I say is true?
IMG_3252-1.jpeg

_______
If I disconnect the other end of the purge line and hold it higher than my boat water line, no flow.

If I lower the hose end, below the Boat water level, it will start to back flow from bellows, and bypass the mechanical seal.

The PSS or
Justin_NSA said:
LasDrop Gen II [ Uses a SSteel spring, but they have a bellows version]
Click to expand
Use the bellows as a spring to provide the sealing pressure.
The more the forward thrust of your engine, the tighter [looser] that mechanical seal becomes. [less {more} flow bypassing].

In Reverse, you bellows expand [contracts] and allow more [less] bypassing.

Why is it called "Dripless" seal?
It is dripping, so to speak, inside the Bellows.

But it always "Drips":cool:
Jim...

PS: @Justin_NSA and I discussed, in detail, before he installed his. He picked the Stainless Steel spring version.:biggrin:

PSS: Corrected the above after drinking 2 cups of coffee and hearing from @smokey73 in next post below.
Duh... I did have right before self quarantine. :banghead:
 
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smokey73

smokey73

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Oct 26, 2010
2,023
Hunter 40.5 Beaufort, SC
JamesG161 said:
The PSS or

Use the bellows as a spring to provide the sealing pressure.
The more the forward thrust of your engine, the tighter that mechanical seal becomes. [less flow bypassing].

In Reverse, you bellows expand and allow more bypassing.
Click to expand
Jim, your assertion does not make sense to me:

When the engine in in forward, the thrust from the propeller, pushing back on the water is transferred to the shaft which wants to "move forward" applying the thrust to the shaft coupling and thus to the transmission thrust bearings and finally to the engine motor mounts, hence moving the boat forward. The stainless steel collar on the PSS shaft seal is firmly fixed to the shaft and moves "forward" with forward thrust (transmission in forward) which would seem to relax the or "expand" the bellows since the carbon ring and bellows "float" and are not attached to the shaft. Correct me where I am wrong on this concept.
 
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RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
OK, so this thread has been quiet for a while. I had composed a letter to PYI on April 8th explaining the problem here in detail. I also included my two bellows, one old and and one new, for them to compare. They had asked for this via telephone. I followed this up with a phone call alerting them that they should have received the package and asking what they thought. They responded that the virus had upset the office and that they would look for the package. It has now been almost five weeks since they received that and still nothing from them. Wasted my time, I guess.
 
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