PSS shaft seal - what do I use for the vent hose?

Bob 04 H260 · Apr 27, 2015

Hey Chris, I replaced my PSS this year, it was so old it did not even have a vent ! The new one has the S/S barb. I think they went that way because the nylon ones could fail. I used a heavy grey fabric reinforced rubber fuel hose for the drain. It runs forward into a plastic bottle I bought at Homedepot. It came with a bracket to hang on the wall. It was designed to hold small parts, the bottle could be removed from the wall to access them. It sits right above my engine so easy to see and empty if needed. So far not enough water to bother with in 100 hrs of motoring. I also have my vacuum breaker from the raw water pump draining in there.
Do you know when the bellows was changed last ? I talked with the PSS guy at Miami boat show. He said the bellows last along time unless they get exposed to an ozone generator or fumes from wet cell batteries.
Bob

Bob 04 H260 · Apr 27, 2015

Chris, I replaced the whole thing on mine. I also added the s/s backing ring suggested by Mainesail. I like the idea of something more than a couple of setscrews protecting the boat from sinking ! It also makes the job much easier I think.
We are back in Florida now. We came back a bit sooner than planned. Just getting things cleaned up and will probably haul her out in a week or so. Hope it has warmed up by the time we get home.
Have you launched yet ? My friends in Toronto went in the past weekend. I think Ottawa will launch this weekend.
We had a great cruise through the Abaco's, starting to plan next years trip now.
Take care, Bob

Bob 04 H260 · Apr 27, 2015

They are at the Mimico Cruising Club, they have a Hunter 36. They flew down to Marsh Harbour and sailed with us for a week this winter. We all really enjoyed it, and so easy having sailors stay on the boat with you. They plan to come south after retirement so wanted to check it out.
He has a stuffing box issue and will install a PSS next fall.
Bob

seadaddler · Apr 27, 2015

PSS

I have heavy clear hose on a plastic barb for many years and have the vent hose high into water bottle.
Nick

dziedzicmj · May 1, 2015

Sorry to hijack the thread, but I was wondering if it would make sense to connect the vent hose to e.g. the sink drain from the galley (it would have to be high enough that it is always above water level). This would eliminate the bottle (and the need for emptying it).

Or am i missing something here.

RHUMB RUNNER · May 1, 2015

Had one on my 420, it was feed raw water from the engine to keep it cool and you did not need to burp it when you hauled out. I don't think it is used as a vent.

Bob 04 H260 · May 1, 2015

I think under about 12 kts they use a vent on the PSS. Above about 12 kts they have to feed water under pressure to the PSS.

I just put 100 hrs on my engine and have about 3 oz of water in the bottle. I think you just get a bit when shifting into reverse. I think it will evaporate before needing to be emptied.

Bob

seadaddler · May 1, 2015

PSS

I agree that the only time I had water out the vent hose was when putting
the boat hard into reverse when trying to slowing or stopping the boat.
If the vent hose is put up high than water rarely comes out the vent hose
and I have a bottle just as caution not to have water enter the rear cabinet
above my engine where the vent hose is secured.
nick

Dan_Y · May 3, 2015

Re: PSS

Unfortunately, I found out today that on my H30, the bottle for the vent overflow won't work after spending the time to install it. The distance between the prop and shaft log is about 40", close enough for water to pressurize the PSS and start to file the bottle rapidly when the engine is in reverse. At 1800 rpm out of 3600rpm max (Yanmar 2GM20F), the water is pushed 24" up the vent tube into the bottle! At 1600 the water was hovering an inch or two below the bottle at about 22" up the vent tube. What tipped me off was that I filled the 1 qt. bottle about 1/3 full at 2400rpm for about 7-10sec, like I was setting/testing my anchor. So I am going to run the vent line to sink drain. Still allows the vent to work and no worries about reverse on my small boat. It probably not an issue for 35-36ft boats. But I would test it. The PSS works great, BTW.

dziedzicmj · May 4, 2015

I found that the vent tube spits water when you do quick forward/reverse maneuvers (like when you are docking in a tight spot). Last year I had situations (tight spot, side wind), when I managed to fill a 500 ml bottle during one docking.

I ran the vent line to the sink drain and the boat still floats.

I am still wondering if there are any reasons why not to do that.

JamesG161 · May 18, 2015

I just fixed my badly install purge line to the PSS seal and talked to the PSS technician at the factory.

The seal purges are to "insure" there is always water on the seal plates to lubricate the rotor.

If your boat is less than 12 knts by engine then you don't have to force sea water into the bellows.

But....

You must "vent" the seal purge line to allow sea water to "back flow" into the bellows.

They recommend the seal vent line top to be 2+ feet above boat water line.

Now...

I didn't like an open pipe from sea inside my boat that may be in heavy seas. Plus i only had 9" of vent space AWL.

So...

I installed, with high temp neoprene hose, on to a sea water pump line at my siphon break. PSS tech, said "perfect"! Now my 8 knt boat has assured PSS purge, no chance of back flow, and is part of the engine sea water system.

If this is confusing call PSS direct. They are good and patient.

They sell all adapters to tee into sea water hoses and matches their purge barb.
Solid brass tee and 2.5" length and $50.
Jim...

Bob 04 H260 · May 18, 2015

JamesG161 said:
I just fixed my badly install purge line to the PSS seal and talked to the PSS technician at the factory.

The seal purges are to "insure" there is always water on the seal plates to lubricate the rotor.

If your boat is less than 12 knts by engine then you don't have to force sea water into the bellows.

But....

You must "vent" the seal purge line to allow sea water to "back flow" into the bellows.

They recommend the seal vent line top to be 2+ feet above boat water line.

Now...

I didn't like an open pipe from sea inside my boat that may be in heavy seas. Plus i only had 9" of vent space AWL.

So...

I installed, with high temp neoprene hose, on to a sea water pump line at my siphon break. PSS tech, said "perfect"! Now my 8 knt boat has assured PSS purge, no chance of back flow, and is part of the engine sea water system.

If this is confusing call PSS direct. They are good and patient.

They sell all adapters to tee into sea water hoses and matches their purge barb.
Solid brass tee and 2.5" length and $50.
Jim...

Jim, I like it ! Smart solution, may be my next project, thanks, Bob

Dan_Y · May 22, 2015

I considered a 3/8 tee in my 5/8 raw water line between the heat exchanger and mixing elbow, just after the siphon break. Had two issues though for my 2gm20f. First is the pss can take 10psi max and I didn't have a easy way to measure the pressure out of the tee. Second issue is the ratio of the area of 3/8 tube to 5/8 tube is 0.36, meaning about 36percent (worst case) of the flow area is diverted away from cooling the exhaust elbow, tubing and muffler. I thought about a flow restrictor in the 3/8 line (1/16 hole drilled thru a 1/4"slug clamped in the line, but figured venting to the head sink drain was less risk. PYI did say hot water was ok going to the pss. The open line to the sea does make me uneasy, so its a new routine inspection point with other thruhulls. Any solution short of a valve in the 3/8 line at the pss has the same "always open to the sea issue". But I think the pss is better for a SS shaft versus packing due to less chance of oxygen starvation of the surface and crevice corrosion when the boat sits in the water unused through the winter (I think Mainsail illustrated that issue on his site). But that might be a stretch.

JamesG161 · May 23, 2015

Had two issues though for my 2gm20f. First is the pss can take 10psi max and I didn't have a easy way to measure the pressure out of the tee.

My solution was done after consulting with a PYI (pss seal maker) technician. I suggested doing the same before implementing the purged "tee" solution on any boat.

But...

On my boat, my exhaust muffler is above water line and there is a water "seal loop" to keep the muffler flooded by the exhaust riser water. On my Hunter 430 this loop is about 24" high to set the minimum back pressure on engine exhaust and sea water pump. The exhaust pressure builds up slightly higher to "burp/spit" that seal loop water, my guess is about 36" of water pressure but no more than 24" times 2 or 48" water pressure.

I purge my "drip less" with the cool side water. If my PSS was "starving" the engine cooling, it would be quickly apparent, by high engine temperatures or no "burp/spitting" exhaust. That would be a sign of PSS seal shattering or engine exchanger plugging.

BTW 10 psig is 279 inches of water pressure, much much more then my normal sea water pump can deliver.

So...

You analysis of 3/8 vs 5/8 (mine is 1 1/4") tubing is correct if they are both open to air, but the PSS has a flow area of near zero (space between rotor and stator) and hopefully my open engine exchanger flow area is bigger than my supply hose (which is the back pressure).

Lastly...

I seriously doubt my "rubber flex vane" sea water pump can deliver much more the 2 psig or it would bypass or blow the hose clamped water line off.

All should verify your own boating needs.
Jim...

Dan_Y · May 23, 2015

JamesG161 said:
You analysis of 3/8 vs 5/8 (mine is 1 1/4") tubing is correct if they are both open to air, but the PSS has a flow area of near zero (space between rotor and stator) and hopefully my open engine exchanger flow area is bigger than my supply hose (which is the back pressure).
Jim...

Excellent points Jim. I'm not sure what you mean above though regarding the near zero flow. When I swapped the existing 3/8 vent tubing for the new one that ran to the head sink drain, water continuously squirted about 4-6" (maybe more) in the air out of the stator's 3/8 barbed SS fitting. I let probably two cups in the bilge while I took a few seconds to marvel at how much water can flow through such a tiny hole! It sits about 14 - 18" below the water line. While I understand the flow between the rotor/stator is miniscule, the stator bore is somewhat larger in diameter than the prop shaft so the PSS can flex with engine vibration. My stator bore diameter is probably 1.25 - 1.5" and the vent hole is flush with the inside of the stator bore, leaving a 1/8 - 1/4" layer of water around the 1" shaft inside the stator, enabling the free flow of sea water out of the vent. But as you point out, the back pressure in the 5/8 line as it dumps into the mixing elbow is probably very low and little water would be diverted through the 3/8 tee. It's still a future option.
Dan

JamesG161 · May 24, 2015

I should have said "flow clearance", but was comparing the inside area of the 3/8" tube barb and the flow of water by the seal (at sea pump pressure).

BTW...:dance:

You just measured your pressure drop around a stationary seal thru the 3/8" tube barb.

water continuously squirted about 4-6" (maybe more) in the air out of the stator's 3/8 barbed SS fitting. I let probably two cups in the bilge while I took a few seconds to marvel at how much water can flow through such a tiny hole! It sits about 14 - 18" below the water line.

Pressure drop is = 18"-6" or 12" of water or near 0.43 psig

GOOD JOB!

The bellows are compressed when it is installed to act like a compression spring, therefore you measured that compression clearance DP, if your seal graphite is evenly worn.

Now....

When your prop is thrusting forward the bellows compress even tighter which should increase that seal pressure drop even more (near zero clearance).

My guess is that 99.9% of my sea water goes to my exhaust and the seal just dribbles from bellows to sea.

To prove it...

If your head sink is AWL underway, and there is no flow...then DP is the difference in top of sink to the water line.

Take care and happy sailing.
Jim...

Dan_Y · May 24, 2015

JamesG161 said:
I should have said "flow clearance", but was comparing the inside area of the 3/8" tube barb and the flow of water by the seal (at sea pump pressure).

BTW...:dance:

You just measured your pressure drop around a stationary seal thru the 3/8" tube barb.

Pressure drop is = 18"-6" or 12" of water or near 0.43 psig

GOOD JOB!

The bellows are compressed when it is installed to act like a compression spring, therefore you measured that compression clearance DP, if your seal graphite is evenly worn.

Now....

When your prop is thrusting forward the bellows compress even tighter which should increase that seal pressure drop even more (near zero clearance).

My guess is that 99.9% of my sea water goes to my exhaust and the seal just dribbles from bellows to sea.

To prove it...

If your head sink is AWL underway, and there is no flow...then DP is the difference in top of sink to the water line.

Take care and happy sailing.
Jim...

You bring up another good point I need to consider regarding prop thrust. Per installation instructions, the bellows is compressed 0.75 and It would be difficult to compress it much more, maybe 0.25 in. In forward gear, the prop transmits thrust to the boat thru my old motor mounts and the engine moves forward in the mounts a small distance, which moves the rotor away from the stator, allowing the bellows to lengthen to maintain the seal with the stator. But in reverse, the bellows cannot be compressed much more as the proper tries to pull the shaft out of the transmission, pushing the rotor against the stator...but I'm sure it has some give. I'm wondering if spongy mounts could cause trouble, especially in reverse. I'm all about finding the failure modes you know...

PSS shaft seal - what do I use for the vent hose?

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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