Air Pressure Drop Problem: Solutions Explored

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Discussion Overview

The discussion revolves around a problem related to air pressure drop in a pneumatic system, specifically when starting an air turbine motor. Participants explore potential solutions to mitigate the momentary pressure drop that affects other components in the system.

Discussion Character

  • Technical explanation, Problem-solving, Debate/contested

Main Points Raised

  • One participant describes experiencing a momentary drop in air pressure from 90psi to 80psi when starting an air turbine motor, which is problematic for other components.
  • Another participant questions whether the distance of the air line and the method of starting the turbine (via a solenoid) could contribute to the pressure drop, suggesting that a slower valve opening might help.
  • A suggestion is made that adding an accumulator could help manage sudden air demand, along with the possibility of using a separate regulator or flow restriction methods.
  • One participant explains the phenomenon of pressure drop, referred to as droop, and describes the mechanics behind it, including the behavior of the regulator's poppet and spring load.
  • Several alternative solutions are proposed, including increasing upstream pressure, using a more sensitive regulator, or installing a control valve, though one participant suggests that adding another regulator may be the simplest solution.
  • A later reply indicates that the original problem was resolved by installing a pressure sensor with a time delay to accommodate the momentary drop, thus preventing system shutdown.

Areas of Agreement / Disagreement

Participants generally agree on the existence of the pressure drop issue and the mechanics behind it. However, there are multiple proposed solutions, and no consensus is reached on the best approach, as different participants suggest various methods to address the problem.

Contextual Notes

Participants discuss the implications of the pressure drop on system components and the potential effectiveness of different solutions, but the discussion does not resolve which solution is definitively superior.

JimatDAC
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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 separate regulator, or can I put an accumulator into the line to take up this sudden demand on available air?
 
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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.
 
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.
 
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.
 
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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