The proportional valve is used in conjunction with the butterfly-type inlet control valve. When the system pressure increases due to a decrease in air consumption and reaches the set pressure of the proportional valve, the proportional valve activates, reducing the controlled air output. This decreases the thrust on the servo cylinder valve stem of the air compressor inlet valve, causing the valve stem to retract under the force of the spring. When the spring force balances with the gas thrust from the cylinder, the valve stem remains in a semi-open state, reducing the air intake of the air compressor to match the system’s air consumption.

Adjusting the proportional valve is relatively simple, but achieving sensitive operation of the servo cylinder requires multiple adjustments. The purpose of adjusting the proportional valve is to ensure that the air pressure activates the proportional valve when it is within 0.02MPa of the upper and lower limits of the pressure switch action. This helps to reduce or increase the air intake to close or open the inlet valve correspondingly in advance, thereby adjusting the air compressor’s capacity and minimizing the number of times the air compressor operates at idle load. To increase the air intake of the servo cylinder, turn the proportional valve clockwise; conversely, turn it counterclockwise to reduce the air intake.