Dripless Shaft Seal Waterline on a 2 GM20F?

[Dan_Y]

Just installed a PSS dripless shaft seal on our H30 with 2GM20F and vented the unit per the instructions. Used Maine Sails idea of using a water bottle because my boat will easily push water up and out of the tube (tube top about a foot above the water line) at only 2200 RPM in reverse. The prop is only about 38 inches from the shaft log.

Has anyone tee’d off the output from the heat exchanger (between the siphon break and mixing elbow to push water into the seal? I can’t imagine the hot water would matter much, especially if the flow was low from a restrictor of some sort. Interesting though I can’t find anything in the archives about this on a 2GM20F or 3GM20F...I know...we go less than 12 knots...
Thanks
Dan

 

[ALNims]

Just installed a PSS dripless shaft seal on our H30 with 2GM20F and vented the unit per the instructions. Used Maine Sails idea of using a water bottle because my boat will easily push water up and out of the tube (tube top about a foot above the water line) at only 2200 RPM in reverse. The prop is only about 38 inches from the shaft log.

Has anyone tee’d off the output from the heat exchanger (between the siphon break and mixing elbow to push water into the seal? I can’t imagine the hot water would matter much, especially if the flow was low from a restrictor of some sort. Interesting though I can’t find anything in the archives about this on a 2GM20F or 3GM20F...I know...we go less than 12 knots...
Thanks
Dan

I would be careful with where you t-off the water source from. I suggest you contact the seal manufacturer and ask their advice.

 

[DougM]

I have a 2GM20F in my Beneteau with a Volvo shaft seal. The prop shaft is contained in a skeg which houses the cutlass nearing. Between the water that enters through the Pickup tube when the through hull valve is opened and any capillary flow through the cutlass bearing. There is always water at the seal when I burp it at launching. It has not really occurred to me that there would be a concern about a lack of water at the seal regardless of slow speed operation. I would be interested in what others might think about this.

 

[sesmith]

I have the non-vented pss seal on my boat. It is lubricated from water on the sea water side of the seal and you have to burp the air out of the seal when the boat is first put in the water. I thought the only difference with the vented seals is that the vent gives the air a place to go, and burping the seal is unnecessary. Do you have to feed water in from another source to lubricate your pss seal?

 

[jlp0217]

My Jeanneau is like Doug's Beneteau. I've always wondered what the purpose of the pickup tube is. The cutless bearing leaks, right? That's why seals are needed. So what does the tube do? Water pressure will be the same on both sides of the cutless bearing, so will there be any flow? Is that little scoop on the pickup tube through hull enough to create water flow? If there is little or no flow, the water will not cool the bearing and seal, it will just get hot.
Jim

 

[Meriachee]

The vent is to release any air that may get in there so that the faces maintain a water seal. Cavitation will (may) force air up the shaft tube, and if you run the carbon face dry, it will get hot, in a hurry, and destroy the mate. I'd be really careful about connecting that hose to anything other than a catch bottle. Your boat, your choice.

 

[Dan_Y]

I was just trying to avoid emptying the bottle but sounds like an easy wy to go. Below is from PYI's PSS installation manual for sources of lubricating water. Doesn;t seem like warm or hot water matters.

"For high-speed vessels it is required that a water supply be plumbed to the PSS for the purpose of cooling and lubricating the seal faces (i.e., at over approximately 12 knots of speed a vacuum is created in the stern tube and water is drawn away from the PSS resulting in a loss of cooling water that may cause the carbon to over heat). There are multiple sources of water for the supply. The following are a few non-exhaustive examples. These are examples only and they may or may not apply to your particular boat.
-T-off the engine raw water-cooling line. (Note:T-kits are available separately from PYI Inc for internal hose ¾”, 1” , 1¼”, 1½”)
-Thread a barb fitting into the drain plug of the heat exchanger if applicable.
-Thread barb fitting into the drain plug of the exhaust manifold if the manifold is raw water-cooled.
-Add a small scoop under water for keel-cooled boats or T-off another water pick up. (Note: A valve must be installed to regulate the water flow as too high water flow may over pressurize the PSS seal). Use an appropriate “underwater rated” hose from the fittings on the boat and the fitting on the PSS and secure them with two (2) hose clamps at each end.
NOTICE: All plumbing must follow the standards and practices of proper boat plumbing. For example, if the pick-up on the engine is located under the waterline, an anti-siphon fitting must be installed, in addition to other standards and practices."