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Air Pressure drop

  1. May 20, 2013 #1
    I am having a problem with an air pressure drop. I have a supply of 100psi of around 4scfm. I have it regulated down to 90psi, but when I turn on an air turbine motor my regulated pressure drops momentarily (1-2sec) down to 80psi. This drop in pressure is unacceptable to other components in my system. Do I need to to run a seperate regulator, or can I put an accumulator into the line to take up this sudden demand on available air?
  2. jcsd
  3. May 20, 2013 #2


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    Staff: Mentor

    Welcome to PF.

    How does the air turbine motor get turned on? Is there a valve too far from it that some tubing has to fill with air before it starts the turbine motor? Can you make the valve open slower? An accumulator should definitely help, as should a regulator. Or even an orifice or other flow restriction like a circuit setter, calibrated to only let the required flow for the turbine motor through.
  4. May 20, 2013 #3
    Thanks Russ. The turbine gets started via a solenoid through 4' of 1/2" air line. I used to use smaller diameter air line (which worked like a restrictor), but changed to larger air line when having intermittent problems with turbine not starting. Now, I have the turbine starting everytime, but other components in the system can't tolerate the drop in pressure.
  5. May 20, 2013 #4


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    The drop in pressure caused by the increase in flow through the regulator is called droop, falloff and probably a few other things. It's caused by the fact that as more flow demand is put on the regulator, the valve poppet must open further to maintain pressure and increase flow. But the reg is most likely spring loaded and the spring load is a function of how far the spring has to extend. Even for fairly small movements of the poppet, the spring load (F = k dx) can change significantly, and as it does, the pressure opposing the spring (pressure on the diaphragm) has to change with it. So the pressure drops as the spring load falls off and the poppet opens.

    Yes, the easiest thing to do is simply add another regulator to either the turbine or the rest of your system that can't tolerate the pressure drop.

    There are other solutions such as
    1. increasing upstream pressure on the regulator
    2. install a more sensitive spring loaded regulator
    3. install a dome loaded regulator
    4. install a control valve
    but I suspect those aren't as practical as simply adding another reg.
  6. Jun 5, 2013 #5
    Problem solved

    Thanks Goest for your explanation. You hit the nail on the head with what is going on. The momentary drop in air pressure caused a pressure sensor to send a signal to the PLC telling everything else to stop due to the pressure loss. I installed a sensor with a time delay or 2 seconds, and since the droop is less then that, I am good to go. Thanks again.
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