Dripless Shaft Seal Inspection & Maintenance?

[chala]

Originally Posted by noelex 77

I still get a few drops of water out of the tube when setting the anchor in full reverse.
The backwash from the propellor is obviously enough to raise the water head well above the waterline.

And in the same time bring silt into the stern tube. Another reason for having a feed line to the stern tube as Sailmonkey point out.

Originally Posted by Sailmonkey

I ran the engine water to ours to keep the bearing clean.....I figure the more silt I can keep from accumulating in the bearing the better.

Originally Posted by noelex 77

I must be missing something

If you look at the picture showing a plumbing principle of engine cooling you will see that the backwash from the propeller is in direct opposition with the sea water pump. It is more likely that more water will come out of the vent (relief ) tube. If for some reason the pressure could not be relieved into the vent tube then the flow of water from the stern tube will join the flow of (raw?) water from the engine pump to the mixing elbow and escape normally to sea via the water lock, gooseneck, ETC to sea. It is more likely that the backwash pressure may not be sufficient to reverse the flow of raw water from the pump and silt raised by the propeller will be prevented from entering the stern tube.

[rebel heart]

Originally Posted by eyschulman

I don't think we are going to get a meaningful answer here just opposing opinions. Time will tell as the drip less units age many not getting any maintenance we will see if they are as safe as what came before. While lack of maintenance of a standard packing box has caused many a wet bilge I am not aware of many catastrophic sinkings. I for one went back to the standard box with modern packing material because my dripless was anything but dry. I never had a problem with dripless in low powered sail boat motors but on big diesels with pressurized water ports they can be tricky to keep dry in my experience no better than standard box with modern packing. Both systems can fail as is the case with almost everything that goes on a boat.

The only times I've heard of someone nearly sinking their boat from the saft gland was on a dripless system. Seems like a really silly product to me which solves a problem that really isn't a problem.

[Sailmonkey]

Originally Posted by rebel heart

The only times I've heard of someone nearly sinking their boat from the saft gland was on a dripless system. Seems like a really silly product to me which solves a problem that really isn't a problem.

There are boats that I'd agree with you on this point. There are others where accessing the gland are problematic at best. On our boat I need to empty the starboard cockpit locker, crawl into the keel cavity upside down, them break my ribs to reach the shaft. We do however carry the old gland, with new packing, just in case.

[Sailmonkey]

Originally Posted by Sailmonkey

There are boats that I'd agree with you on this point. There are others where accessing the gland are problematic at best. On our boat I need to empty the starboard cockpit locker, crawl into the keel cavity upside down, them break my ribs to reach the shaft. We do however carry the old gland, with new packing, just in case.

And yes, I can change it in the water if the need arises.

[chala]

Mechanical seals, (PSS) provide dry bilges which is advantageous to boat equipment and to some boats. There is nothing wrong with a good mechanical seal.

I have read with interest the thread http://www.cruisersforum.com/forums/...ar-107705.html and particularly post 101 and 103. The boat in question appears not to have a mechanical seal. If I was to accept that the engine was damaged by (water hammer) then I would look primarily at the design of the mixing elbow and the possibility that raw water is aspirated by the engine at shut down. Diesel engines are notorious for (kicking back) when shutting down. This is most noticeable when replacing the impeller in a raw water pump. For the many times that I have replaced impellers I have never seen one whose compressed vane was compressed in the right direction. If there was a possibility of raw water entering the engine then the mixing elbow would be of an inadequate or faulty design.

Originally Posted by sy_gilana

On a practical note, did you see any pitting on the sleeve of the lowest piston? and was that piston the one with broken lands? if so...Yanmar are going to say that hydraulic hammer (water in the cylinder) is what broke the lands.

Originally Posted by roverhi

Water enters the combustion chamber through an open valve. Doesn't matter what the height of the cylinder in relation to others. It'w where in the rotation cycle that the engine stopped if and when water floods in through the exhaust. Still no reason to assume that the problem was caused by water ingress without evidence.

[wingless]

On my boat, the "pressurized" raw water feed to the Tides dripless shaft seal is tapped from that circuit right at the water line level.

The exhaust ports are higher, by about an inch.

The path from this raw water inlet / outlet to the exhaust port is about a foot up / down, along a convoluted path.

There is not a risk to hydrolock from this water path.

Also, there is not a sinking risk if this small diameter hose became loose. The water flow is small. Any one of my three automatic bilge pumps would have no problem staying well ahead of this flow. Sometimes they do stay ahead when I intentionally drop the hose to perform service.

[Sailmonkey]

I have seen several instances of the pss seals being plumbed to the incorrect side of the vented loop. Plumbed to the upstream side of the loop, flooding of cylinders isn't possible. But I have seen many examples of the seal connected between the loop and the mixing elbow. One may ask why even bother with a vented loop at all if this is the case.