GENERAL

This subsection will discuss compressed air requirements for pneumatic instruments and control purposes. Instrument air is compressed air used to operate pneumatic controllers, pressure transmitters, pneumatic information transmission systems, pressure transducers, and other similar devices. Control air operates automatic temperature control (ATC) systems and associated heating, ventilating, and air-conditioning (HVAC) devices used to control and condition air for comfort in facilities. This section will describe instrument air quality, production methods of air for use in pneumatic instruments.

CODES AND STANDARDS

The Instrument Society of America (ISA) is the major organization writing and issuing standards. The principal standards concerning the creation and use of air are:

1. ANSI/ISA S7.3, Quality Standard for Instrument Air

2. RP S7.7, Recommended Practice for Producing Quality Instrument Air

AIR QUALITY STANDARDS

There are four elements of quality that must be considered: moisture content, oil content, particulate size, and other toxic contamination.

If any instrument air lines are located outside a building, then the maximum allowable dew point at which the instruments will continuously function satisfactorily is 18 F (10 C) below the lowest temperature that any part of the instrument air system will be exposed to. When the instrument air system is completely indoors, the dew point shall not exceed 35 F (2 C).

The oil content shall be as close to zero as possible, with the maximum allowable content of 1 ppm under normal operating conditions. This requires the use of an oil-free compressor to generate the compressed air rather than the type...