Pneumatic pressure regulators


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What is the Pneumatic pressure regulator?

Air pressure regulator is a device which regulates and filters air for a stable source of air to process control equipment such as a I/P converter and control valve positioner

Pressure regulator construction:

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Instrument air enters through the inlet port and then to the drip well. Any dirt or moisture carried along with air will be collected at the bottom of the drip well and can be drained through the drain cock (valve).

A supply cum exhaust valve supported by the inlet valve spring controls the air pressure. The inlet valve spring and the supply cum exhaust valve are housed in spring housing. The valve sub-assembly comprising of parts are separated by a filter element. Practically clean air is available at the supply valve port.

The upper section of the filter regulator comprises of an adjusting screw, a lock nut, spring case, range spring, spring button and a diaphragm sub-assembly. The orifice (exhaust valve seat) at the center of the diaphragm is in contact with the exhaust valve plug.

Working and Operation pressure regulator:

Adjust the adjusting screw by turning the screw clockwise it compresses the range spring, which applies a definite amount of force on the diaphragm. This closes the exhaust port and pushes down the supply valve to open the supply port admitting the filtered air to pass through the passage in the
filter body and then to the outlet port.

The air pressure in the outlet port is also communicated to the underside of the diaphragm through the aspirator hole to produce the necessary balancing force to counteract the force generated by the range spring.

When the downward and the upward forces on the diaphragm are equal, the exhaust valve is closed and the supply valve is open to supply the set pressure through the outlet port to the downstream equipment. The outlet pressure is also tapped to a pressure gauge, which is mounted on the regulator to indicate the set pressure.

In case of a decrease in air pressure in the outlet port, the force acting on the under side of the diaphragm will reduce and the spring force will push the supply valve to open the supply port to admit more air to meet the new requirement and the increased pressure will restore the equilibrium condition of the diaphragm assembly.

In case of an increase in the output pressure, the force acting on the under side of th diaphragm will overcome the force generated by the spring. This unbalance in forces will move the diaphragm upwards to make the exhaust valve seat to lift off from the plug to allow the excess air to bleed to the atmosphere through the bleed hole (B) in the spring housing. This process will continue automatically till the forces acting on the diaphragm are in equilibrium. The lock nut on the adjusting screw prevents it from turning due to vibration and not to cause any changes in the set point.