Pressure operated changeover switch - has central spring piston operating between two end switch positions but with central null point

摘要

The switch body (1) has a central cylinder bore (2) in which the pressure difference piston (3) moves between the two end cavities (3,4). End chambers (6,7) are connected to the hydraulic or pneumatic door drive lines. The pressure difference piston (3) is held centrally by a spring (8,9) on either side. Pressure leaks around the springs are prevented by sleeving (16,17) and guides through the end walls (14,15) of the pressure difference cylinder (2,3,4). The sleeving guides (16,17) have end lips (16a,17a) to prevent excessive piston (3) movement. The pressure difference piston (3) carries the switch control contacts (20,18a,19a) to operate the valves and pumps in the hydraulic or pneumatic system as wired to the pressure difference switches (18,18b,19,19b).