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Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 6:34 AM

My friends, I have been using pneumatic actuated instrumentation over many years and have had little or almost no problems . However, of late one of the actuators controlling Steam through a Modulating Globe Valve at a pressure of 30 barg had a ruptured diaphragm. Upon inspection, it was also noted that there were signs of oil within the actuator internals. My immediate response was to check the air compressor for any worn piston rings , but upon opening up, there was not signs of oil leakage. The discharge air delivery has a RFL system . Pressure setting was also as per recommendations. I am a bit puzzled and would welcome anyone if you can throw some light regarding this.

Very grateful and thank you.

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Anonymous Poster #1
#1

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 6:46 AM
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#3
In reply to #1

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 7:53 AM
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#2

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 7:51 AM

Although it is good practice to lubricate instrument air it sounds as though there was an incompatibility between the diaphragm material, the number of cycles it has endured, the temperature, and the lubricant.

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#4

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 8:05 AM

It's been my experience that there is some oil usually found after several years of operation in pneumatic controls....You might want to check your filtering system and clean out the controls during any repairs or adjustments...I would check with the manufacturer for any bulletins on diaphragms premature failures, or compatibility issues with lubricants...So did you notice anything unusual about the diaphragm?

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#5

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 8:44 AM

You need a coalescing filter to remove the oil. Oil and dirt will clog the small orifices in the instrumentation, the I/P or the positioner.

See pages 32, 33 (pdf) 925, 26 paper) in the NRC's Instrument Air Systems regarding coalescing filters used to filter oil out of the air.

https://www.nrc.gov/docs/ml0037/ml003767039.pdf

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#7
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Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 2:03 PM

that is a really good answer, and dead on with root cause, I expect.

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#6

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/05/2017 10:32 AM

Thank you, guys for all the input. I will follow up on all your suggestions to resolve this issue.

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#8

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/06/2017 8:15 AM

Don't know about your section of industry, but in the instrument control portion of the pharmaceutical industry, that is a FRL.

Well if that is a "RFL" or FRL, the "L" is lubricator, so what would you expect to find?

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#10
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Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/06/2017 12:20 PM

The ones we have around here are "ROFL" type. We roll on the floor laughing if the thing actually operates as expected.

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#9

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/06/2017 11:37 AM

Hi Satish,

If there is in fact a lubricator in the air supply then check that the correct lubricant is used. People put all sorts in the lubricator, machine oil, compressor oil even in one case I had they put brake fluid any of the above can have a detrimental effect on rubber parts.

Best regards,

John

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#11
In reply to #9

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/06/2017 10:40 PM

Thank you, John. Your point duly noted.

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#12
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Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/07/2017 3:37 AM

Hi Satish,

Just a thought, what pressure is the air? If it is the control air (15 psi /1 Bar) it is not normal to have lubrication.

And "one" more (final) point. A diaphragm actuator does not need lubrication as there are no sliding seals so depending on any other parts in the circuit it might be wise to remove any lubricators where not needed.

Best regards,

John

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#13

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/11/2017 4:22 AM

You don't say how long it has been working, but if it's several years why not just replace the actuator, it can't be very expensive.

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#14
In reply to #13

Re: Failure of Pneumatic Actuator for a Steam Control Modulating Valve

09/11/2017 8:32 AM

Sorry, I meant replace the diaphragm, not the complete actuator.

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