Quote:
Originally Posted by Alan Anderson
If you use a flow control valve to completely isolate a portion of your pneumatic system, you are not in compliance with R78.
|
I think it is important to highlight a nuance to the flow control valve function that seems to be missing in this thread. Most pneumatic flow control valves (including
this in-line one mentioned by Sean) only restrict flow in one direction. For fittings attached directly to actuators, most are meter-out, although you can find meter-in types. For in-line types, its all in which direction you install it.
This means that the air has two pathways inside the valve, flow in one direction is restricted through the adjustable needle valve. In the opposite flow direction, it can either travel back through the needle, or through a separate internal check valve, which is not restricted.
In the case of using one of these flow controls as suggested in this thread, at no time would the needle valve isolate a portion of the circuit, or prevent complete draining of all pressure when the one relief valve is opened. The check valve integral to the flow control would always allow pressure to be drained completely, even if the needle is fully closed. This is fundamentally different from the use of a ball valve.
As Daniel suggested, you may find the needle valve starts to leak after repeated shut-offs. You will also likely find your one-touch fittings leaking after several re-connections, as they are only good for a dozen or so insertions before the tube needs to be cut shorter.
I would also argue that there are better legal ways to accomplish this (such as a single-acting valve at this connection). A main concern I would have with using a flow control valve is that the team should always drain their pressure completely after the match, before attempting to disconnect this mechanism (regardless of closing the needle valve).