sealing piston ballast tanks

[itolond]

Dear Forum peeps,

I have been looking at a number of ballast systems, in particular -piston type. I ave a question, how is the threaded rod sealed on the housing....I see it rotates with the motor on what appears to be a fixed thread- drawing the piston in and out.is there a specific sealing magic here?

[Ralph --- SSBN 598]

Re: sealing piston ballast tanks

The piston is a closed container.
The threaded rod that move the piston end is external of the piston volume.
The motor, gears and threaded rod are not in side the piston area.
The piston moves back and forth drawing in water in.
This in turn produces a pressure increase in the rest of the wtc.

This might help visualize it all.

Pistol ballast system inside wtc

[itolond]

Re: sealing piston ballast tanks

Ah yes i see.

Have you seen or have reference to a threaded rod being sealed to prevent water (e.g. rotating threaded shaft)

[Guest]

Re: sealing piston ballast tanks

Ron Perrott's tanks work with a sealed gland on a fixed threaded shaft.

[salmon]

Re: sealing piston ballast tanks

Andy,
How does that work? How do you seal a thread? Can you show me?

Peace,
Tom

[itolond]

Re: sealing piston ballast tanks

Ron Perrott's tanks - do you have reference for this os email for Ron?

[Guest]

Re: sealing piston ballast tanks

Ron is one of the pioneers of model submarines here in the UK. He did produce a small range of kits back in the eighties and early nineties, and now makes bits and pieces on a more limited basis, mainly for modelling colleagues he knows well.

Regarding sealing against a thread, I haven't owned one of Ron's models or his tanks, so not had one apart, however he did tell me that basically it's a threaded gland set-up as a stuffing box. To seal the thread you can use either waxed hemp or PTFE cord. Probably a good idea to polish the thread to remove any sharp edges.

Tanks using this system have been in use for over 30 years, so they're well proven and reliable.