Air flow to control valve
Air flow to control valve
(OP)
I need to calculate the available flow rate of instrument air to a control valve. The tubing is 3/8" SS and the pressure is 80 psig minimum. I do not know the velocity of the air or the pressure drop in the line so I'm having a hard time applying Bernoulli's. What assumptions/method should I use?





RE: Air flow to control valve
RE: Air flow to control valve
RE: Air flow to control valve
RE: Air flow to control valve
RE: Air flow to control valve
Good luck,
Latexman
RE: Air flow to control valve
RE: Air flow to control valve
If you calculate the initial velocity with max dP, you'll find a huge friction loss (which reduces the dP so you have to iterate on this step a few times). When you get a stable value, determine how much air got into the actuator in 50 mS at that velocity and recalculate the pressure in the actuator. With the new dP you can start over and calculate a new velocity. It is interesting to put a 100 Hz datalogger on the actuator to see the pressure traverse, it is impressive to see the real data match the theory.
A rigorous solution to this problem has eluded engineers throughout all time. You can get an answer that will work with the above process, but it is kind of a pain. I've done it when I was trying to determine if I had a problem with a slow-acting valve or if the latency really was that long. Once when I was doing this arithmetic I found that the valve really was taking far too long to operate and discovered that it had the wrong main spring in it. Replaced the spring and the valve worked as advertised.
David