Volvo shaft seal burping

[pete]

Looking at a boat that has just had the shaft seal replaced with a Volvo seal that has a water spigot pointing upwards, this is piped horizontally about 12" then down through the hull via it's own sea cock, the owner said it has to be burped if the boat is ever dried out.
I know that the seal has to be lubricated and cooled with water but what is the pipe doing ? it isn't connected to the engine cooling system so no pump is involved and under static conditions water would not escape from the seal as there would be air trapped in the pipe above the seal.
Does the boat moving through the water form a suction on this pipe to create flow and if it does will it need to be burped every time I dry out (I have a drying mooring).

Thanks Pete

 

[Plevier]

My previous boat which was designed for drying out had a vertical spigot in the tube immediately behind the Volvo seal, but it was simply led up to well above the waterline (alongside the vacuum breaker on the cooling water inlet pipe) so that it was self-burping.
I can't see what is achieved by the arrangement you describe. You said replaced with a Volvo seal, do you mean it had something different before, is this a leftover?

 

[Tranona]

Volvo seals do not have a vent as you described. That sounds like the new Radice seal. Unless of course the vent is not actually in the seal but in the stern tube. If it does have a vent the purpose is to allow air to escape when you launch the boat. This is necessary because the seal housing ahs a water lubricated bearing inside. You can also vent by squeezing the end of the seal until a trickle of water comes out. Provided the boat does not dry out there will always be water in the seal.

 

[VicS]

Instructions for the Volvo seal

 

[pete]

Thanks for your replies

Troubadour
It was a direct replacement (about a year ago) and it seems Beneteau build them this way, I also would have thought that if the pipe was extended well above the waterline it would vent without the need for the extra skin fitting and seacock hence the question.

Tranona
The instructions I was shown had Volvo printed on them and explained the burping process but nothing else. the spigot was black plastic and looked like part of the seal to me ?

Pete

 

[pete]

Thanks VicS

The seal does not look like that
I think Tranona is right and it is a Radice seal and maybe the owner showed me the old user's instructions ? it was fitted by the marina but I'm pretty sure that they haven't fitted an extra skin fitting and seacock ?

Pete

 

[Tranona]

The vent should not go to a seacock. It should go well above the waterline, or should be used as a feed for water from the raw water cooling circuit. Latter is not really necessary on a yacht. Neither is the vent really if the seal is easy to access for burping once you are in the water.

Think there might be some confusion in the installation with the Vetus seals which also use lip seals, but housed in a bronze casting. They cannot be burped so require a flow of water which comes either from a bleed from the engine or an external scoop through a seacock.

 

[dje67]

Looking at a boat that has just had the shaft seal replaced with a Volvo seal that has a water spigot pointing upwards, this is piped horizontally about 12" then down through the hull via it's own sea cock, the owner said it has to be burped if the boat is ever dried out.
I know that the seal has to be lubricated and cooled with water but what is the pipe doing ? it isn't connected to the engine cooling system so no pump is involved and under static conditions water would not escape from the seal as there would be air trapped in the pipe above the seal.
Does the boat moving through the water form a suction on this pipe to create flow and if it does will it need to be burped every time I dry out (I have a drying mooring).

Thanks Pete

I've just been through exactly the same thought process on my Beneteau. Volvo seal with a pipe that rises above the height of the tube, then drops down through the hull. Photo attached. Under the hull the hose is connected to a strainer that looks to be fitted backwards (compared the direction a cooling strainer would be which helps to "push" water into the cooling system). I reckon it must produce enough suction to pull the air out of the tube breather when the boat is moving - never proved it though. In any case, I'm replacing all the seacocks and have shortened the strainer/skin fitting so that the valve and hose are now mounted at the same height as the tube, not higher.

 

[Plevier]

Troubadour
It was a direct replacement (about a year ago) and it seems Beneteau build them this way, I also would have thought that if the pipe was extended well above the waterline it would vent without the need for the extra skin fitting and seacock hence the question.

To clarify, with respect to Tranona's comment too, the vent tube on my former boat - also a Beneteau, 1985 First 29 lift keel - was built into the shaft tube just behind the boot of the seal, not in the seal itself which was standard Volvo with no vent provision. There was no connection to a skin fitting, just the extended vent tube.

 

[pete]

It is the same as dje67's set-up.
Just to clarify the situation The owner said it was a Volvo seal and was replaced because Volvo recommended replacement every 5 years (but I think it is a Radice seal) now.

The info he showed me was just for re greasing and not installing the seal and did not appear to show the spigot. (I think these may have been for a Volvo seal)

The spigot looks to be built into the seal (will try to get a better look at the weekend and a picture)

Thanks for all the info
Pete

 

[[10753]]

Not sure about all the piping stuff but I certainly burp my VP every time - boat is on a drying mooring. Squeezing the seal creates hiss for about 2-3 seconds before the water arrives.

 

[vyv_cox]

Both types, and many others, can be seen on my website. Look here.

 

[Plevier]

So is the Radice seal with the vent interchangeable with the Volvo seal in an existing installation and is there a UK supplier, anyone know please? I've drawn a blank on Google. It would save me burping the seal on my drying mooring.

 

[Pye_End]

So is the Radice seal with the vent interchangeable with the Volvo seal in an existing installation and is there a UK supplier, anyone know please? I've drawn a blank on Google. It would save me burping the seal on my drying mooring.

Sillette: http://www.sillette.co.uk/shafts_seals_and_sterntubes_list.html

 

[Plevier]

Thanks. Website not working though. Company still shows as active at Companies House - will keep trying.

 

[Norman_E]

Its working now. This is the page you want, scroll down to see the Radice seal.

 

[Plevier]

Yes OK now.
For 25mm shaft the VP is 42mm sleeve dia, the Radice is 39.42 (funny number) wonder if it will stretch? I will ask.

 

[HunterWanderer]

I think burping is only necessary if you have a long stern tube between the seal and the hull.
The idea of a vent tube from the top of the seal seems dangerous to me as there is no seacock to close on the top of the seal.
A friend has a Bene 257 and that has a vent that goes up behind the bulkhead at the nav table. After a bit of a rough passage he found seawater behind this bulkhead and had damaged his radio and several other instruments. just the action of the boat in the swell had forced water up though the vent.

He has now fitted a seacock just in case the hose splits and the vent is now extended down and exits into the cockpit.

 

[Plevier]

I think burping is only necessary if you have a long stern tube between the seal and the hull.
The idea of a vent tube from the top of the seal seems dangerous to me as there is no seacock to close on the top of the seal.
A friend has a Bene 257 and that has a vent that goes up behind the bulkhead at the nav table. After a bit of a rough passage he found seawater behind this bulkhead and had damaged his radio and several other instruments. just the action of the boat in the swell had forced water up though the vent.

He has now fitted a seacock just in case the hose splits and the vent is now extended down and exits into the cockpit.

I have wondered whether burping every time is necessary as the stern tube is very short, but it still takes a few seconds hissing to let the air out. However I did once forget for 30 mins or so with no apparent ill effects. I did then burp it and it still had air in.

I think the risk of the vent tube is small. I'm perhaps more concerned about the security of the greasing plug in the Radice. That seems unnecessary, it's only once a year.

 

[ccw]

Looking at a boat that has just had the shaft seal replaced with a Volvo seal that has a water spigot pointing upwards, this is piped horizontally about 12" then down through the hull via it's own sea cock, the owner said it has to be burped if the boat is ever dried out.
I know that the seal has to be lubricated and cooled with water but what is the pipe doing ? it isn't connected to the engine cooling system so no pump is involved and under static conditions water would not escape from the seal as there would be air trapped in the pipe above the seal.
Does the boat moving through the water form a suction on this pipe to create flow and if it does will it need to be burped every time I dry out (I have a drying mooring).

Thanks Pete

With most Beneteau type boats that have a grp skeg housing the cutlass bearing and a volvo seal at the inboard end to stop the yacht from sinking. The arrangement is such that the tube coming up from the through hull fitting (normally with a scoop fitted) is there to create a continual flow water down the shaft tube and out of the cutlass bearing thereby cooling the cutlass bearing and Volvo seal. With a Volvo seal to ensure there is no air lock and thus preventing the flow of water it is important to squeeze the rubber seal by the shaft until you get rid of all the air and you get a good flow of water.