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-   -   PSS Vent Leaking (https://www.cruisersforum.com/forums/f114/pss-vent-leaking-38062.html)

noelex 77 20-03-2010 13:27

PSS Vent Leaking
 
For the first time today I had some seawater leakage out of the top of the vent line for my PSS shaft seal.
It was only a small amount (perhaps 5 table spoons worth), but I have 2 questions
Why now?
What do I do to stop it happening again ?

The vent line (a simple tube no pressure feed) leads up to just below the cockpit floor about 1.1m above the waterline and 0.35m from the centerline.

The puzzle is it has never happened before (the engine and vent arrangement was changed about a year ago). I went for a 30 mile sail in light conditions and anchored in a new location. My theory is the reverse thrust from the propeller when setting the anchor forced the water up, but I always set my anchor the same way.

The boat has just been re-launched with new antifouling but nothing with the vent or stern tube was changed. The propeller a maxiprop was re-greased and one anode changed (same size and location)
The vent would be difficult to locate higher I am thinking of a simple water trap on the top
Any theories or solutions ?

GordMay 20-03-2010 13:51

From PSS:
"If the PSS seal drips while at rest then it is likely that foreign material is on the face of the seal between the stainless steel rotor and the carbon flange.To clean this foreign material from the seal,insert a clean rag carefully between the two faces (Note:some water will come into the boat at this time if the boat is in the water)and work the rag around the seal.As you do this,the incoming water will flush the impurities.Remove the rag from the seal and the leak should stop."

noelex 77 20-03-2010 14:01

Thanks for the reply Gord, but its not the shaft seal thats leaking its the vent (that lets air out of the saft seal ) thats leaking. It is open at the top, but should be high enough that seawater doesnt come out.
Hope thats clearer.
John

GordMay 20-03-2010 14:20

Do not run a loop at the top end of the vent hose, as this could promote a siphon, and water could enter the boat.

AnchorageGuy 20-03-2010 14:56

noelex, Is this the first and only time or is it happening or on more than one occasion. You may be getting concerned for something that is an isolated case. If in launching the boat you got some air in the vent that filled a portion of the tube and it was finally purged pushing some water out ahead of it, you have no problem. I would think you need to wait and see if it happens on more than one occasion. WG

noelex 77 20-03-2010 15:31

Quote:

Originally Posted by Waterwayguy (Post 421972)
noelex, Is this the first and only time or is it happening or on more than one occasion. You may be getting concerned for something that is an isolated case. If in launching the boat you got some air in the vent that filled a portion of the tube and it was finally purged pushing some water out ahead of it, you have no problem. I would think you need to wait and see if it happens on more than one occasion. WG

Thanks for the comments.
It is the first time it has occurred.
Its an Interesting theory of yours about air in the vent tube. The tube has a reasonably straight run and with an open top I would have expected a bubble of air to simply rise to the top and dissipate, but the tube is narrow and it is possible surface tension held trapped some water above a bubble which subsequently rose to the top of the tube carrying the water with it. Hard to imagine, but who would think you could “float” a metal pin on top of water using surface tension.
.

Capn Morgan 23-03-2010 20:56

Hi Noelex

The bleed line on my PSS seal is short and it is plugged at the end. I only bleed it after launching and never seem to have a problem with it. Something to consider, perhaps?

Cheers

Wotname 24-03-2010 01:41

I agree with Waterwayguy. Was the boat re-lauched quickly and/or went astern quickly after re-launch. I could envisage a small rush of water being forced out of the vent tube under such conditions

noelex 77 24-03-2010 02:31

Thanks for everyones comments. It could have been at the launch (lowered down on travel lift). I did not notice it then and although it was only a tiny amonut of water my bilges are dry so even drops stand out.
Motored yesterday and set the anchor as usual and no water from the vent so hopefully it was one off.

Blue Stocking 24-03-2010 03:39

Have installed a number of PSS units, including my own 2 boats. The Reliant does not have the vented seal because we are less than 10 knots boat speed. The power boat uses the fitting for water injection, bled off the raw water pump, because the planing speed evacuates the shaft log of water. Never seen one used as just a vent--but makes sense.

noelex 77 24-03-2010 03:55

Quote:

Originally Posted by Blue Stocking (Post 423688)
Have installed a number of PSS units, including my own 2 boats. The Reliant does not have the vented seal because we are less than 10 knots boat speed. The power boat uses the fitting for water injection, bled off the raw water pump, because the planing speed evacuates the shaft log of water. Never seen one used as just a vent--but makes sense.

Thanks. The PSS website is a bit confusing. My old engine had water injection, but I removed this with my new engine as it was one less fitting to leak and corrode.
My yacht cruses under motor at about 7.5K. Max speed under motor is less than 10K, but undersail we can occasionally reach 10K. I have a feathering Maxiprop, so the PSS is not turning when sailing, but I assume sailing at 10K it could suck air in and subsequently motoring even at a lower speed could case an overheat situation without a vent.
Is the above correct?
Is a vent Ok or does it need water injection?

Maine Sail 24-03-2010 04:26

Quote:

Originally Posted by noelex 77 (Post 421935)
For the first time today I had some seawater leakage out of the top of the vent line for my PSS shaft seal.
It was only a small amount (perhaps 5 table spoons worth), but I have 2 questions
Why now?
What do I do to stop it happening again ?

The vent line (a simple tube no pressure feed) leads up to just below the cockpit floor about 1.1m above the waterline and 0.35m from the centerline.

The puzzle is it has never happened before (the engine and vent arrangement was changed about a year ago). I went for a 30 mile sail in light conditions and anchored in a new location. My theory is the reverse thrust from the propeller when setting the anchor forced the water up, but I always set my anchor the same way.

The boat has just been re-launched with new antifouling but nothing with the vent or stern tube was changed. The propeller a maxiprop was re-greased and one anode changed (same size and location)
The vent would be difficult to locate higher I am thinking of a simple water trap on the top
Any theories or solutions ?

And when you anchored you backed down? The reverse thrust CAN send water up the shaft log, out the vent tube and out the top of the vent hose, if you've given her enough reverse..

I use a Taco "hi vent" for a hydronic heating system. It has worked flawlessly for nearly 5 years though I do disassemble it and clean out any salt at the beginning of each season. I used to feed it into a bicycle water bottle mounted to catch the drips but I got sick of looking at it.

The hi vent is the brass looking round unit next to my siphon break arrangement.

https://www.pbase.com/mainecruising/image/118092458.jpg

Wotname 24-03-2010 16:35

Quote:

Originally Posted by noelex 77 (Post 423695)
Thanks. The PSS website is a bit confusing. My old engine had water injection, but I removed this with my new engine as it was one less fitting to leak and corrode.
My yacht cruses under motor at about 7.5K. Max speed under motor is less than 10K, but undersail we can occasionally reach 10K. I have a feathering Maxiprop, so the PSS is not turning when sailing, but I assume sailing at 10K it could suck air in and subsequently motoring even at a lower speed could case an overheat situation without a vent.
Is the above correct?
Is a vent Ok or does it need water injection?

I have also just fitted a PSS seal and was initially a little confused about the venting, water injection or otherwise. With some CF help (i.e. one of Gord's links), it became much clearer.

Water Injection:
) On low speed boats (<12 kts) like you and me; the PSS seal does NOT need any additional water injection other than the natural injection of water coming in through the log.

Venting:
) Again on a low speed boat; the venting is ONLY there so you don't have to "burp" the seal (i.e. remove any air locks) on re-launching. The vent has no effect one way or another when motoring. If you can remember to "burp" the seal every time you re-launched, you could do away with the vent and seal it off. If you can't be sure of remembering, then the vent automatically ensures any air lock is removed when re-launching.


I understand that PSS changed their recommendations about venting some years back after users have forgotten to "burp" their seals and complained about poor design or service life. However, this explanation could just be another internet myth.

noelex 77 25-03-2010 02:36

Quote:

Originally Posted by Maine Sail (Post 423703)

The hi vent is the brass looking round unit next to my siphon break arrangement.

https://www.pbase.com/mainecruising/image/118092458.jpg

Thanks Maine sail that looks like a good solution.
Is it a simple vented expansion tank? If so I could DIY something similar from plumbing supplies which would be much easier than trying to purchase the real vent.
Is it brass? Some of the fittings you have on the siphon break also look like brass plumbing fittings which are easy to get here.
Have you any idea how long it will last in a salt water environment. I always thought brass had a very short life, but reading some posts on a recent on watermaker thread, the life expectancy of brass high pressure pump heads was listed as years.

noelex 77 25-03-2010 02:44

Quote:

Originally Posted by Wotname (Post 424021)
I have also just fitted a PSS seal and was initially a little confused about the venting, water injection or otherwise. With some CF help (i.e. one of Gord's links), it became much clearer.

Water Injection:
) On low speed boats (<12 kts) like you and me; the PSS seal does NOT need any additional water injection other than the natural injection of water coming in through the log.

Venting:
) Again on a low speed boat; the venting is ONLY there so you don't have to "burp" the seal (i.e. remove any air locks) on re-launching. The vent has no effect one way or another when motoring. If you can remember to "burp" the seal every time you re-launched, you could do away with the vent and seal it off. If you can't be sure of remembering, then the vent automatically ensures any air lock is removed when re-launching.


I understand that PSS changed their recommendations about venting some years back after users have forgotten to "burp" their seals and complained about poor design or service life. However, this explanation could just be another internet myth.

Thanks for clearing that up.
As I need to seal up the vent anyway, and a hose is the only way of doing this, I think I will keep the tube. It should alow air to escape if I do get up to 12k which may be possible as I have done a bit over 10k and not been game to have the spinnaker up yet. (the spinnaker on my old smaller boat was enough of a handfull for my wife and I)


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