submerged gearbox seal arrangement

[linares]

Hello experts,

I am designing a gearbox that needs to be submerged in water at 10 psi with a shaft coming into the water. My biggest challenge here is how to seal that shaft completely. I need to keep water from the area where the gears are in order to guarantee life and lubrication quality.

I am no seal expert and ask for your help. Right now I have thought of two possible ways of making this happen. One is to have a slightly higher internal pressure so the leak is always towards the water. Other arrangement is to use seals in tandem and have some kind of trap in between perhaps.

Right now I am using mechanical bellow seals. The shaft RPMs are in the order of 150 RPM and the diameter is 4".

Many thanks,

 

[JJPellin]

This is a common problem with submersible pumps and mixers. We have a number in our plant. All of them use the conventional solution. They have multiple mechanical seals with a moisture detector in a cavity between. We have mixers with the manufacturer of Air-o-Later (spelling?). They have three seals. One keeps the oil in the gearbox and the other two keep the water out. The moisture detector is between the two outermost. Search for submersible pumps and you will find a number of references

I have never heard of any similar machines with pressurized gearboxes. It might work. I assume you would plan to have a line down from the surface to provide constant pressure.

Johnny Pellin

 

[micalbrch]

To pressurize the gearbox will only shift the problem to the other side. Then you have to seal against the other side and against a pressure higher than 10 psi if you want to keep the pressure inside the gear constant. I agree with Johnny, submersible pumps work with a special seal arrangement. Check the following link for a first overview:

http://net.grundfos.com/doc/webnet/waterutility/_assets/downloads/shaft_seals.pdf

 

[flexibox]

Linares
I have worked on a seal for a submersible motor for a Dredge and the solution was a dual pressurised seal however you need a reliable pressurisation system with the correct instrumentation and alarms. The barrier fluid needs to be compatible in both directions. As this is low pressure and low speed it should be easy however I am not sure that you will have the axial space to fit the ideal design.
In the event of a seal failure you should still be in a position whereby no water enters the G/B

cheers

 

[linares]

Thank you for your answers. Micalbrch, thank you for that document. I think 2 mechanical seals with a flush fluid (oil?) going through is the way to go. It seems like a back to back arrangement guarantees no leakage, but I would prefer a tandem arrangement. Is it possible for water to leak through even do you are flushing between the seals with a flushing fluid?

Also what kind of sensors do you have in place to deternmine seal failure?

Thank you