Swagelok Ball Valve performance

[SCUBA_Phil]

Steve,
I'm missing something. If I shut off first using the needle valve, I have pressure between the O2 bank and the needle valve. Shutting off the ball valve at this point keeps pressure between the ball valve and the needle valve. At his point, I would close off the storage bank valve. When opening, I would open the bank valve (pressure between the ball valve and the storage bank), then the ball valve (which has the same pressure on both sides. Last would be the needle valve. Where in this conops does O2 slam into a dead end?

 

[divingtactics]

Ball valves have no place in oxygen systems - period. The more complex our panels become, and the more valves that have to be opened and closed in specific orders with these complex systems, the easier it is for us to make a human mistake that can cost a life.

 

[Akimbo]

Steve,
I'm missing something. If I shut off first using the needle valve, I have pressure between the O2 bank and the needle valve. Shutting off the ball valve at this point keeps pressure between the ball valve and the needle valve. At his point, I would close off the storage bank valve. When opening, I would open the bank valve (pressure between the ball valve and the storage bank), then the ball valve (which has the same pressure on both sides. Last would be the needle valve. Where in this conops does O2 slam into a dead end?

I guess I am missing something. What is the point of using a ball valve in this scenario? It seems redundant. Ball valves have two major characteristics. Rapid opening with minimal flow control and excellent visual on/off indication. A lot of ball valves can also be more reliable than many of the low-grade rotating-stem (needle, rising stem, spindle, etc) valves out there.

Also note that not all rotating-stem valves have needle orifices. Many are shut-off valves with simple flat seats that have high initial flow rates when cracked open. True needle valves have seats with tapered flow restriction and a fairly flat flow-to-turn ratio — the best choice for high pressure oxygen systems.