Dripless seal - water injection needed?

[Delfin]

I believe the answer on whether injection is required is, as noted in the installation instructions for the PSS dripless seal, a matter of boat speed. Above 10 knots, yes. Below, not essential as long as you remember to burp the seal after haul out.

On mine, I split the difference. Unless I fall off the end of the Earth, I'll never see 10 knots. But I went ahead and plumbed the vent line to the only inlet through hull I have so water is always available and the system is self burping. Since I close that through hull when we leave the boat for any period of time, I'm far less concerned about leakage than otherwise.

The purpose of water injection is cooling and providing lubrication for the seal. If your IR gun shows no heat buildup, and the seal had been burped, providing injection doesn't really accomplish much.

[a64pilot]

On at least most Yanmar’s there is usually a drain petcock in the raw water supply after the pump, just unscrew the petcock, screw in a nipple and connect to the vent line, you now have water injection, seems to easy to not do it?

[mlydon]

On my boat (Columbia 50), the entire engine is below the cabin sole, and the sole is at least a fout below the water line. I think i’m going to install a vacuum break for the raw water line before the injection elbow just on principal. If the impeller shredded itself, the engine would flood itself as soon as you shut down (I think this happened to the P.O. - I know he paid big bucks for a rebuild that looked like it was caused by water intrusion, going by the labor descriptions).

I will put a tee in before the break for the seal, or from the stopcock as pointed out, so that the seal tap can’t backflow into the injection elbow. The idea of having it be on the suction side, drawing water INTO the stern tube is kind of interesting as well, but I think pressure is better, as my prop sits directly behind the tube and cutlass bearing - the post regarding low pressure from the prop comes to mind - I could see the ‘prop suction’ and raw water pump suction competing, cancelling each other out and resulting in no water movement

Keep ‘em coming, guys, this is great stuff!

Matt

BTW Groco makes a very nice looking vacuum break - the HVL series

https://www.defender.com/product.jsp...294&id=2753431

They state if used in exhaust system, the vent should be run outside. I suppose this counts, as if you lost water, AND the valve stuck open, you could get some exhaust coming out of it.....

[jamhass]

If water comes out when you "burp" the seal, you will be fine just venting it. Assuming of course you are a sailboat topping out below 8-ish knots.

In either a vented seal, or the older style non-vented seal, there wasn't any significant water flow. Just having water in the bellows region (burping) was and is plenty.

[mlydon]

I'm thinking the same - the original gland on this 50 year old boat stayed wet enough to not burn up packing, I've got to assume the same with a new dripless...

Matt

[Pizzazz]

I also believe that you do not need water injection or venting below 10 knots. Just burp the rubber hose by pulling it backwards every couple of months or before a long motoring session. I do it once a year just to have a piece of mind. The last time I changed the rubber hose, three years ago, I spoke to the PSS folks and they told me, fell free to replace the hose very five years but in our experience, it is only needed on commercial vessels after 20,000-30,000 hours. I believe I would need to replace my engine three times before I get to those usage rates.

Fast moving vessels (as in planing vessels) is more complicated.

SV Pizzazz

[a64pilot]

I won’t get into the argument about needing it, but many manufacturers say you do IF you have a cutlass in the shaft tube and Lasdrop recommends it for all installations.

But I’m not understanding this need for a vented loop? The water level is the same on both ends and the middle of the boat. So knock up a T that goes into the water supply line from the pump and take water from there, this is before the engine vented loop and water is there from the thru hull, so why do you need a vented loop?
Tides marine makes such a water injection T to do exactly what I am saying If you don’t want to build your own. https://www.tidesmarine.com/shaftsea...p_overview.php
However it’s made from yellow brass that they claim to be corrosion resistant, but you should never, ever use brass below the waterline correct? I have seen it fall apart.
But it seems many manufacturers use brass?
I’m ordering stuff off of Amazon to do it with 316 SS and change the brass nipple out to 316 SS too.
I believe that I will install a Lasdrop Gen II as well.

The problem with the black packing is that it’s Graphite impregnated, and graphite will cause corrosion, see Maine Sails article on packing.
https://marinehowto.com/re-packing-a...-stuffing-box/

[slug]

The bearing must be water lubricated

Water injection ...positive water pressure ...is the most reliable because you are confident that no air pocket exists at the bearing

[Andreas W]

Originally Posted by a64pilot

On at least most Yanmar’s there is usually a drain petcock in the raw water supply after the pump, just unscrew the petcock, screw in a nipple and connect to the vent line, you now have water injection, seems to easy to not do it?

That's what I used on my Yanmar to get water injection to my PSS seal. My stern tube bearing I made of Vesconite (which is water lubricated and very low friction), with two spiral grooves machined in for better water flow.