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ronald
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Instrument air pressure regulators...

04/29/2008 9:26 PM

As Test Method Validator/Contractor i have a point that i'm trying to get across a manufacturing and test team...After they build the machine it goes thru a rigorous test procedure where 95-97% Pass with no problems. Final test area then receives the equipment where they calibrate and retest for market. The problem i'm having is that a high number keeps returning from final test claiming that the pressure regulators are off by 5-15% below rated pressure settings. Today i had a test technician run a pre-test and observed every step. i noticed that, every time, they were adjusting the regulators downward from a high pressure (59psi or 60psi) to a desired pressure (30psi). i believe that pressure regulators should be regulated by starting at a low end and increasing by turning CW until the desired pressure is achieved! Can someone help me to convince the manufacturing engineer that i'm right?

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Electroman
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#1

Re: Instrument air pressure regulators...

04/30/2008 9:40 AM

All the 'normal' pneumatic pressure regulators I've come across state that they should be pressurised with the control at maximum anticlockwise i.e. lowest pressure.

This isn't because its the safe way to start them up, its because the internal spring against the diaphragm is loose and the application of pressure allows the spring to 'fall' into its correct position before having stress applied to it by the control knob.

So I would agree with you, the pressure should be at minimum before the air is applied and the pressure turned up to the target outlet pressure...

John.

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Andy Germany
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#8
In reply to #1

Re: Instrument air pressure regulators...

05/01/2008 7:16 PM

I gave you a GA for a good answer (there may be more but yours was the 1ST!!)

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Poison
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#2

Re: Instrument air pressure regulators...

05/01/2008 6:28 AM

I definitely agree. When adjusting pressure on a regulator down from a high pressure I've noticed that the actual pressure in the system will not be indicated on the regulator until the air cylinder has fired at least once. To defeat this, I've always gone below my target air pressure and then come back up.
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betomachine
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#3

Re: Instrument air pressure regulators...

05/01/2008 8:27 AM

I'm confused (imagine that), so you are saying that the regulator should start closed and be opened until the desired downstream pressure is reached?

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Electroman
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#4
In reply to #3

Re: Instrument air pressure regulators...

05/01/2008 8:44 AM

Yes... the regulator should start off with the spring in a relaxed state , which means the downstream pressure will be as near zero as makes no difference. Then when the inlet pressure is applied the diaphragm will engage with the spring, locating it in the correct position.

Then as the knob is turned clockwise the spring is put in compression against the diaphragm to increase the outlet pressure...

Increasing the pressure is by far the best way to set a pressure due to the fact that not all pneumatic systems have a pressure leak / flow-rate, so as most pneumatic regulators aren't self relieving you can only get good accurate pressure setting by increasing the outlet pressure - NOT decreasing it...

John.

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betomachine
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#7
In reply to #4

Re: Instrument air pressure regulators...

05/01/2008 4:12 PM

Thank you for the information, I will apply it in a future opportunity I am sure.

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Poison
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#5

Re: Instrument air pressure regulators...

05/01/2008 9:18 AM

If you still need to convince the engineer, that what we are saying is correct. Take one of your failed instruments and redo the test using our method of starting with low pressure and then increasing. If the part now passes will he/she be satisfied?
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Trigger
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#6

Re: Instrument air pressure regulators...

05/01/2008 3:41 PM

I am a retired USAF Aircraft Instrument Technician and you ALWAYS start at the lowest setting. Not doing so risks the chance of overstressing the spring and other internal mechanisms which will then require recalibration or replacement , as all readings will then be inaccurate ( not just the range but incremental ).
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ronald
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Technical Fields - Technical Writing - Validation Specialist-Medical Devices United States - Member - From the Big Apple! Hobbies - Model Rocketry - Rockets should go nuclear! Fans of Old Computers - PDP 11 - Studied computers at W.H.Taft H.S., Bronx, NY. Popular Science - Cosmology - Radio Science Observing

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#9

Re: Instrument air pressure regulators...

05/11/2008 1:11 AM

I have convinced them with your input;

I Thank You All!

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Users who posted comments:

Andy Germany (1); betomachine (2); Electroman (2); Poison (2); ronald (1); Trigger (1)

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