The leveling control needs air pressure. A two stage vacuum operated compressor produces this pressure. For intake stroke, the sliding distributor valve, which is operated by linkage attached to the piston, applies engine vacuum to compartment ‘B’ and atmospheric pressure to compartment ‘A’. This forces the diaphragm to move the piston toward the reservoir. This opens check value No.1 and fills the first stage with air.
When the piston reaches the end of intake stroke, it causes the distributor valve to admit vacuum to compartment ‘A’ and atmospheric pressure to compartment ‘B’. This moves the piston back toward check valve 1 causing it to clocks. As the piston continues its movement it compresses the air ahead of it. The air is now under pressure. It travels through the hollow piston opening and check valve 2 allowing the air to enter the second stage when it completed its stroke, the distributor valve again reverses the vacuum to opposite side of the diaphragm compartment ‘B’ and the piston is forced to travel toward check valve-3. As it travels, it does two things.
1. It compresses the air in the second stage cylinder. This closes value 2 and opens valve 3, which allows the compressed air to flow in to the reservoir. At the same time, a fresh charge of air is drawn in through valve-1.
2. The compressor piston cycles (moves back and forth) until the pressure built by in the reservoir is equal to the pressure generated by the second stage cylinder. When this point is reached, a balanced condition exists and compressor will not operate until some air has been used by the system.