What is the difference between instrument air and plant air? What is the importance for inst air.

pspandi

 

Plant air is basically for machinines that require air that does not need to be extremely clean or dry, and usually require large volumes.

Instrument air needs to be clean and dry, for pneumatic istrumentation. This is important for say, a control valve positioner where the feedback baffle/nozzle can be plugged off by dirt.

If the instrument air is used in a northern climate where valves may be located outside, dewpoint is a major consideration, because of freezing.

If someone tells you there is no difference tell them to get they're head examined!

 

The above is true and in some cases instrument air may nitrogen fed from liquid nitrogen cylinders if the instrument air consumption is low, remote, or is important that is remains 'dry'.

 

Above explanation is short and good.

I would like to add that in US most of Instrument Ait pressure is 20-25 psi in the system and Plant (Service) Air pressure is 80-120 psi (about 7 atm)
Both system require dryers, filters and some other equipment to do air conditioning. Controls are in Center and in distribution manifolds.

 

All above are valid. I might add that safety (fail safe) considerations might be more stringent for instrument air. Process components using plant (service ) air may be designed to fail in a safe position. INstruments losing air may cause hazardous transient conditions upon loss.. Instrument air may also be "piggybacked " on service air with additional regulation, drying and backup.

 

Plant air generally runs anywhere from 60 to 150 psig, and usually has considerable condensate and sometimes particulate.

Instrument air is clean and dry, having been filtered for both particulate and moisture, and runs a normal maximum of 20 psig at the drop, since the typical pneumatic instrument is looking for 3-15 psig.

It is never advisable to use plant air directly as a source of instrument air without filtration and de-humidification.

Walt Boyes

---------SPITZER AND BOYES, LLC-------------
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I think instrument air is for instrument signal, it only for signal. Plant air is for driving actor through amplify signal. Instrument air requires more clean than plant air but both need filter. Their pressure is different sure. plant air changes to instrument air through filter and decreasing pressure i think.

 

Clean and water free.

Regards

cww

 

Generally, instrument air is dryer, and contains no oil. I beleive their is an ISA standard for it.

Bob Peterson

 

Hey Walt:

Was just doing some reading and was wondering what you were referring to in the "Pasted" exerpt from your previous email.

"and runs a normal maximum of 20 psig at the drop, since the typical pneumatic instrument is looking for 3-15 psig."

Thanks In Advance:

Stephen Bennett

Kawasaki Robotics (USA), Inc.

 

In our plant, "plant" air is called "service air."