VEE BELT SET (4 belts) 4N4773 - Caterpillar

During the down stroke of the piston, a vacuum is created in the cylinder. The vacuum causes the inlet valve to open. The discharge valve remains closed.Atmospheric air is drawn through the open inlet valve. The air flows past the inlet valve and into the cylinder.When the piston begins the upward stroke, the air in the cylinder begins to compress. The air pressure in the cylinder closes the inlet valve.The piston continues the upward stroke. The piston compresses the air until the discharge valve opens.When the discharge valve opens, the compressed air rushes through the discharge valve. The air then flows into the discharge line.The compressed air acts upon the unloader piston. The air pressure and the spring for the unloader piston holds the unloader piston against the seat for the unloader piston on the valve plate.When the piston reaches the top of the upward stroke, all of the compressed air has left the cylinder. The piston begins the down stroke and the cycle begins again.