Volvo deep water seal stern gland

[Pagetslady]

hi Here is a new one I think, I have been using a 25 mm Volvo stern gland for more than 20 years now, not the same one, after fitting a new Beta 35 engine to My Westerly Corsair winter of 2013 I fitted a new prop shaft and Bruntons prop together with a new Volvo stern gland. It has never let in a drop of water since fitting, but some how it gets air into the stern tube without being lifted out of the water, I have to burp it every time I go out and after an hour maybe I get a strange noise from the shaft which is stopped by BURPING the seal it is not getting over hot, the shaft is aligned as well as is possible with an engine on rubber mounts, I have over the years had plenty of practice with aligning my old VP 2003 after rebuilds and new mounts, In the past I have done a lot of hours motoring 6000 hrs over 20 years. so has anybody any idea why my stern gland needs BURPING so often.
Regards Mike

 

[Tranona]

Check that the clamp holding it onto the stern gland is tight. There is air getting in (or water draining out). As you know the main part of the seal is a fluted rubber bearing and it is this being dry that makes the noise. It only needs a very small amount of air to get in to drain the water out, and of course burping it purges the air past the seals and lets water in.

 

[CaptainBob]

We always had air in ours after every trip so I added burping it to the routine shutdown after any passage, or something to do every hour or so on longer passages.

It did this when working dripplessly so I have no idea where the air was coming from. Some kind of vortex creating suction within the gland, sucking air in past the vanes, like a dyson? Or cavitation bubbles from the prop? Remarkable amount of gas whatever the mechanism.

Many others have reported the same.

 

[superheat6k]

Underway the stern tube can experience a slight vacuum and the labia like lip seals facing the wet end allow the air to pass through the seal. Perhaps squeezing a little extra VP seal grease might help, but do not overdo it as the seal doesn't like to be over greased - the MacDonald's straw method seems to work well. I would be a little more generous with the amount just outside the seal where the shaft enters (inside the boat obviously).

 

[tyce]

Mine always does this after a rough passage when I guess the stern lifting up and lots of air going under when it comes down again some must find its way up the gland. A quick burp sorts it but I must admit the noise it makes before I burp it is a little disconcerting but it's never damaged it.

 

[Concerto]

I would also expect the micro bubbles of air in the water passing under the hull are finding the stern tube hollow and then rising. The only real solution is to fit a water fed seal and this stops the problem completely. I fitted a Tides Marine seal from Sillette to my Fulmar and I have had no water entry and never needed to displace any air. The difference in price is minimal, so when you next need to change the seal consider using a water fed one instead.

 

[Tranona]

The difference in price is minimal, so when you next need to change the seal consider using a water fed one instead.

It is actually double the price - hardly minimal. It is also substantially longer which makes it impossible to fit in some installations.

A better alternative is the Radice seal, identical to the Volvo except it has a built in vent to avoid the need for burping. Similar price to Volvo.

 

[Piddy]

It is actually double the price - hardly minimal. It is also substantially longer which makes it impossible to fit in some installations.

A better alternative is the Radice seal, identical to the Volvo except it has a built in vent to avoid the need for burping. Similar price to Volvo.

I fitted a Radice seal last winter and it seems to be as good as advertised. No water and no issues.

 

[Pagetslady]

Thank you all that is very reassuring, i have never experienced this in over 20 years using this Volvo seal (not the same one) so it looks as though I need to Burp frequently or use a Radice seal in future.
Regards Mike

 

[[10753]]

I have to burp mine all the time, still going strong after 12 years.

 

[ghostlymoron]

I thought these were fit and forget unless you come out of the water. My illusions are shattered. I've got a stuffing box but might consider the Radice if the size is available.

 

[pandroid]

I've never heard of all this. I've had one for over 10 years and I burp it once a year when we put the boat in the water. If you are having to do this more often that sounds like its not set up properly or an alignment issue.

 

[CaptainBob]

I've never heard of all this. I've had one for over 10 years and I burp it once a year when we put the boat in the water. If you are having to do this more often that sounds like its not set up properly or an alignment issue.

Maybe. Wasn't obvious how it could be changed in any way in our case though. Shaft was dead centre and didn't oscillate. Gland didn't drip. Worked perfectly well if we forgot to burp it or not. We had to put a new one on after installation of a new cutlass bearing which resulted in the previous one beginning to drip. The new one did it too.

 

[Birdseye]

Weird. The Volvo seal is designed to operate below the water level so no amount of alignment issues should put air into it - to the contrary, alignment problems can only cause water leaks into the boat. The OP changed the prop at the same time so I wonder if he is now getting some cavitation with air being sucked down from the surface and then bubbles of it getting into the stern tube from the prop end.

 

[Happydaze]

Also on a Corsair i changed the Volvo seal a couple of weeks ago because of a slight drip and have the same problem. Yesterday i was out for 10 hours, half motor and half sailing and needed to burp it on 3 occasions to stop the shaft noise. I guess the leaking old stern gland allowed a slight flow of water in to self bleed but can't see how the air gets in the new one.

 

[ghostlymoron]

Some authorities say that a traditional stuffing box needs slight leakage to cool it, others say the gland should be adjusted to eliminate leaks completely. They can't both be right.

 

[Tranona]

Some authorities say that a traditional stuffing box needs slight leakage to cool it, others say the gland should be adjusted to eliminate leaks completely. They can't both be right.

They are mostly very crude devices and are very sensitive to getting the pressure on the packing just right to run cool enough and still seal. Also some have the housing filled with grease which can actually cause it to run hotter because water cannot get to the back of the packing. Some types of packing seem to run cooler than others so rquiring less water for cooling.

So, some stuffing boxes need a constant small water flow to keep cool and others don't.

The use of lip seals as in the Volvo, Radice and Tides Marine seals (as well as other designs not seen so often) means the seal is made over a small area and does not require pressure. Water in the tube is often enough to keep it cool in low powered installations. The requirement for burping is to ensure there is no air in the fluted rubber bearing behind the seals stopping water from getting up to the back of the seal. A vent or water feed from the engine is one way of ensuring there is no air, but many installations (like mine) only require burping if the boat has been out of the water.

 

[Pagetslady]

I've never heard of all this. I've had one for over 10 years and I burp it once a year when we put the boat in the water. If you are having to do this more often that sounds like its not set up properly or an alignment issue.

I have had one of these stern glands on my Corsair for 20 years and never burped it only after lifting back into the water.
But this new one on a new shaft prop and engine needs burping frequently.

 

[Appleyard]

Same here... Old one burped once when launched and that was it. Fitted new one this spring and it needs burped occasionally.Not a big issue, but I guess as the old 'un was dripping a bit ,it self burped, new one does not drip so any air reaching the seal perhaps due to cavitation needs expelled.

 

[Pagetslady]

They are mostly very crude devices and are very sensitive to getting the pressure on the packing just right to run cool enough and still seal. Also some have the housing filled with grease which can actually cause it to run hotter because water cannot get to the back of the packing. Some types of packing seem to run cooler than others so rquiring less water for cooling.

So, some stuffing boxes need a constant small water flow to keep cool and others don't.

The use of lip seals as in the Volvo, Radice and Tides Marine seals (as well as other designs not seen so often) means the seal is made over a small area and does not require pressure. Water in the tube is often enough to keep it cool in low powered installations. The requirement for burping is to ensure there is no air in the fluted rubber bearing behind the seals stopping water from getting up to the back of the seal. A vent or water feed from the engine is one way of ensuring there is no air, but many installations (like mine) only require burping if the boat has been out of the water.

Hi I ordered a new Radice stern gland yesterday and it arrived this morning, and it was cheaper than the Volvo one looks well made and has a proper system for greasing and an outlet for any air so prevents the need for Burping, just need the time now to change over to the new one thanks for your help.Mike