InstrumentationProcess Control



The air used must be cleaned, dry and oil-free to ensure that small lines,  restrictions and nozzles will not be plugged by dirt, oil or water.  In this course you will learn about basics of instrument air supply system.  This unit will teach you what an instrument air system is, what its components are and how they function


The System Concept

Figure shows the components of an instrument air supply.  In this system you see 12 major components.  Instrument air supply systems are not all the same.  But they all perform the same function.  They supply a sufficient  volume of clean and dry air at the constant pressure required by all plant instruments.

The major parts of an instrument air supply system are:

  • The Electric motor
  • The Compressor
  • The Inlet Air Filter
  • The After Cooler
  • The Moisture Separator
  • The Condensate Trap
  • The Air Receiver
  • The Safety Relief Valve
  • The Pressure Gauge
  • The Oil Remover
  • The Dryers
  • The Air Distribution System


The Electric Motor

The primary function of the electric motor is to provide a rotary motion to drive the compressor.

The Compressor

The Compressor converts the mechanical energy provided by a prime mover (e.g.  an electric motor)  into the potential energy of compressed air.

The Inlet Air Filter

This removes dust and dirt from atmospheric air before it enters the suction inlet of the compressor.

The After Cooler

This cools the air leaving the air compressor.  This is done by passing cooling water over the after cooler chamber.

Moisture Separator

This removes most of the moisture from the air.

Condensate Trap

This collects the condensed liquid from the moisture separator and drains the liquid periodically when the Condensate levels gets too high.

Air Receiver

This stores large volumes of the compressed air.  It also provides an emergency supply of air for a short period of time in the event of compressor failure.

Safety Relief Valve

A Safety Relief Valve is used to discharge excess pressure automatically if  maximum pressure develops in the air receiver.

Pressure Gauge

This indicates system output pressure.

Oil Remover

This is used to remove oil carried out by the air during the compression cycle.  If the oil vapour is not removed from the compressed air it slowly forms into droplets large enough to plug up tiny instrument tubings and nozzles.


These dry any moisture that is left in the air.

Air Distribution System.

This is the final step in producing a properly balanced instrument air system.  It should provide delivery to all air users with a minimum supply variation of approximately 125 to 150 psi or 8.618 to 10.342 bar of pressure.



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