P&ID diagram for Basic Air supply system and it's operation

The pneumatic instrument in an industry needed a clean and sufficient air supply for their operation. An air supply system will be implemented in all industries to achieve this task consisting of an air compressor and other air conditioning system. An array of instruments are used to condition air supply, each component has a specific task.

P& ID diagram for Air supply system:

NOTE: Not all the instrumentation air supply systems are the same but perform the same function. A typical air supply system is shown here.

The P&id diagram for air supply system is shown below.


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 Electric Motor:

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

The Inlet Air Filter:

This removes dust and dirt from the 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 through the aftercooler 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 get 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.


  • The compressor takes air from the atmosphere through a filter and compressor compresses the air. The filter cleans the air. It removes the dirt and oil content in the air.

  • Always the compressed air will be hot, the hot air is cooled using coolers. Hot air is passed through aftercoolers.

  • Moisture developed in the air due to cooling is separated using moisture separator

  • Now the air is sent to a receiver. A receiver removes the dirt and oil content in the air supply.

  • Then the air is sent to the dryers. Dryers remove the remaining moisture content in the air. The dryers use desiccants to absorb moisture from the air.

  • The regulator regulates the air pressure to the required air supply pressure for plant instruments.