PSS Seal lubrication question

[seadog30]

We have a PSS Seal on a 1 1/2" shaft. No problems it just works.

The Seal is lubricated by from the water take-off pipe on the Volvo exhaust manifold as
per standard practice.

Today (with the engine stopped) I pulled the pipe off the manifold (while still attached at the PSS end)

Question - is it normal for water to flow back up the tube when the un plugged end is at the same height as the manifold take off ?, will this not fill up the water trap and eventually backflow into the engine?

Should I route the water pipe up into a loop or put a non return valve into the pipe ?

Thanks

 

[john_morris_uk]

Is this a high speed craft? I'm sure I remember the instructions saying a water feed was only necessary if it was a high speed planing type boat?

Otherwise why not make a loop in the forced feed pipe well above the water line and you'll solve the problem?

 

[pcatterall]

What are the relative heights involved? If the manifold is below water level then, yes, I guess there will be backflow potential.
depending on engine size I believe that it is possible to just vent that pipe by feeding it up above water level.
I guess also that a loop in your connected pipe would eliminate backflow potential.

 

[sarabande]

from the installation instructions.

15A. Low speed boats: (Under 12 knots of boat speed under power and no bearing
in the shaft log).
Using a ⅜” (8 or 9 mm) ID “underwater rated” hose (not provided with the PSS),
connect the hose to the hose barb fitting installed on the carbon and secure the hose
with two (2) hose clamps. Run the hose to a point in the boat at least two (2) feet
above the waterline, making sure that the hose does not apply any load on the carbon
part of the seal. Keep the hose as close as possible to the centerline of the vessel so
the top of the vent hose is never below the waterline, even if the boat heels. Secure the
hose in place with the necessary fittings that insure it will not pull free and drop. This
hose is now a venting hose that will help ensure that no air is trapped in the seal.
WARNINGS: Do not run a loop at the top end of the vent hose as it could start a
siphon action in some extreme conditions. Also, make sure the vent hose is properly
secured from falling below the waterline. If the vent hose were to fall down below the
waterline, water would come in the boat. Also, do not plug or block the end of the
vent hose, as this would prevent the line from venting.


That's not clear and is carelessly written.

 

[john_morris_uk]

That's different to the instructions that came with ours twelve years ago. I've blocked ours off and from memory the instructions said to push the bellows back to ensure there is water getting to the seal every time you launch or dry out.

I might change it to a breather pipe as described.

 

[seadog30]

Thanks all

It is a slow 30' sailboat.

The yard fitted the PSS when we re-engined so I did not see the instructions however we had discussions about the engine being low, so I agreed to the extra cost of a high rise manifold. We also agreed to water lubricate the PSS as our water is often sandy mud and the water lubrication once at sea would clean the mud etc that might have got in while in our river mooring.

Unfortunately the water feed pipe was run in an almost stright line between the PSS and Manifold.

I will "re-pipe" with an upwards loop at least 12" above the water tke off point on the manifold.

Fortunately no damage has been done to date.

Thanks for advice.

 

[vyv_cox]

Mine has an open vent pipe that runs to the top of the engine compartment. As said, my instructions advise to wet the seal faces when launching or after not having run for some time (months). In addition I flush mine out with fresh water at the end of the season to avoid a crevice corrosion problem that I encountered early in the seal's life.

 

[boatmike]

There is a little confusion here methinks. The OP has a positive feed from the engine to the seal which is designed to produce a positive flow of water through the shaft tube and out of the stern bearing. This cools the seal and helps to avoid crevice corrosion of the shaft by re-oxygenation of the water that would otherwise be stagnant. This feed is often taken from the gearbox oil cooler or elsewhere on larger engines to produce positive flow. On smaller engines it is sometimes seen from the exhaust manifold where no other feed is present. In this case if the engine is below the waterline it may well be necessary to put in an anti-syphon loop. If it's above obviously no need. On smaller auxiliaries where no positive water feed is provided the pipe to the PSS (or any other watercooled seal) should be vented to atmosphere above the waterline to allow water to freely flow in through the stern bearing without an airlock in the tube which would prevent water flowing up to cool the seal. In the OPs case it appears that the manifold has been taken above the WL to prevent cooling water running back when stopped but the cooling pipe has gone straight back to the engine side of the manifold below the WL. If a loop is installed in this pipe it could still syphon unless a syphon break valve is installed in the top of the loop.

 

[Hoolie]

I'm just about to install a PSS seal. Our boat is slow and although it doesn't require water flow I think I can use the connection used by the current Deep Sea (?) seal. It has a take-off on the output from the raw water impeller, well above the waterline on the anti-syphon loop. This loop of course has a syphon break device.

 

[john_morris_uk]

I'm just about to install a PSS seal. Our boat is slow and although it doesn't require water flow I think I can use the connection used by the current Deep Sea (?) seal. It has a take-off on the output from the raw water impeller, well above the waterline on the anti-syphon loop. This loop of course has a syphon break device.

Won't do any harm.

 

[boatmike]

Won't do any harm.

Indeed not and this is an excellent arrangement even if the original design does not call for it

 

[Hoolie]

Thanks - I thought that too! Hopefully it will avoid the crevice erosion mentioned by vyv-cox.

 

[vyv_cox]

Thanks - I thought that too! Hopefully it will avoid the crevice erosion mentioned by vyv-cox.

The crevice corrosion happened to mine, and that of another forum member who had the same problem, during winter layup. Nothing to do with flushing rates when the engine was driving, which of course could never lead to crevice corrosion. There is a photo of it very near the bottom of this page https://coxengineering.sharepoint.com/Pages/Sternglands.aspx Seawater between the faces could remain wet for a long time as the evaporative surface is very low, but salt concentration would increase as it did so. That incident was several years ago, since when I have flushed it in fresh water at the end of each season and had no recurrence.

Although I think it looks like crevice corrosion there may be a galvanic contribution due to the graphite/stainless steel combination.

 

[Hoolie]

Thanks. Something else to do at the end of the season! But if the boat's still in the water how can you prevent seawater seeping back?

I know PSS say nothing should be put on the carbon face but would vegetable oil keep the stainless collar free of salt over the winter? It would soon disappear when running.

 

[macd]

I know PSS say nothing should be put on the carbon face but would vegetable oil keep the stainless collar free of salt over the winter? It would soon disappear when running.

If I remember correctly, PSS are very specific that no oil or grease should be allowed near the faces.

 

[vyv_cox]

Thanks. Something else to do at the end of the season! But if the boat's still in the water how can you prevent seawater seeping back?

I know PSS say nothing should be put on the carbon face but would vegetable oil keep the stainless collar free of salt over the winter? It would soon disappear when running.

I wouldn't risk it but it might work. Detergent is OK but does have a small salt content, much less than seawater I think. It doesn't seem to be a big problem, the makers denied that it ever happened.

 

[boatmike]

Vyv, Crevice corrosion during layup while boat was in the water or out? If out I would have thought you were correct about the galvanic contribution. The main corrosion would then be at the bearing of the Pss seal itself I guess. In my shipbuilding days I have seen really aggressive crevice corrosion on 316 shafts left in the water with no water flow and not just at bearings either! In some cases a secondary pump has been used to keep the flow running while alongside. This was on shafts with quite long tunnels though..
If possible on new builds I always tried to persuade designers to specify High Molybdenum Duplex stainless for vessels that were at risk of crevice corrosion It's a while back now but I think 2205 has 3% molybdenum? Interestingly it was never screamingly expensive compared with 316 and the performance was so much better...... If I had to have new shafts on my boat because of crevice corrosion I would definitely specify it.

 

[vyv_cox]

The boat was laid up out of the water. I don't think it has been wintered afloat since I fitted the PSS. It was working fine in the October and I happened to notice that it felt a bit rough in the following spring and found the damage. I agree that 2205 is far better, although not immune, especially in Middle East water temperatures. For ultimate protection 904 is used, high nickel stuff used for Rolex watch cases as it has good dermatological properties. No doubt not cheap but I know of seacocks made from it.

 

[superheat6k]

PSS installations instructions here.

https://www.dropbox.com/s/ku3cvw4lujemvhp/PSS installation instructions (low res).pdf?dl=0

 

[pcatterall]

Vyv, Crevice corrosion during layup while boat was in the water or out? If out I would have thought you were correct about the galvanic contribution. The main corrosion would then be at the bearing of the Pss seal itself I guess. In my shipbuilding days I have seen really aggressive crevice corrosion on 316 shafts left in the water with no water flow and not just at bearings either! In some cases a secondary pump has been used to keep the flow running while alongside. This was on shafts with quite long tunnels though..
If possible on new builds I always tried to persuade designers to specify High Molybdenum Duplex stainless for vessels that were at risk of crevice corrosion It's a while back now but I think 2205 has 3% molybdenum? Interestingly it was never screamingly expensive compared with 316 and the performance was so much better...... If I had to have new shafts on my boat because of crevice corrosion I would definitely specify it.[/QUOTE

Following my own issues with crevice corrosion ( Tides marine lip seal) I investigated getting a new shaft and read about the different Stainless steels available The extra cost of the High Molybdenum steel was not so great and I recommend anyone getting a new shaft to consider it. Thanks Boatmike !!