Bellows Seal

A picture would be worth a thousand words. It is easier to visualize than to explain. Off the top of my head I don't know any brand names, but some Websites probably have good diagrams.

To describe an example, imagine a globe valve, with the disk attached to an inner stem extending into the bonnet. The lower O.D. of a bellows is welded/brazed to the valve body; the upper I.D. of the bellows is welded/brazed to the top of the inner stem. As long as the bellows don't leak, this perfectly isolates the fluid in the valve and piping. Outside the bellows, the stem continues with a threaded extension, which is moves up and down by a handwheel or other actuator.

If the fluid is hazardous or expensive, or if fugitive emission standards apply, this type of valve is better than those with traditional packings, which can leak. I think there are also motorized valves with the motor and gear train encased in a hermetic "can" integral with the valve.

thanks tornado ;-)

Thanks! I tried to give it a GA, but the system is overloaded or something.

Thanks for your appreciation. In fact the same picture I've submitted for an earlier discussion on 'Double gland packings for Globe valves'. So I could recall immediately.

Our OP will be benefited more by going through this thread as well, since many other experts have given good points therein...

http://cr4.globalspec.com/thread/34879/Double-Gland-Packing-for-Globe-Valves

thanks yesyen...appreciated the inputs