Time relay is a control appliance that uses electromagnetic principle or mechanical principle to achieve time delay control. It has many types, such as air damping type, electric type and electronic type. Time relays can be divided into two types: energized time delay type and power-off time delay type. Air-damped time relays have a large delay range (0.4 ~ 60s and 0.4 ~ 180s) , it is simple in structure, but less accurate.
When the coil is energized, the armature and pallets are attracted by the core and move down instantaneously, making the instantaneous action contact on or off. But the piston rod and lever can not follow the armature together with the drop, because the upper end of the piston rod is connected to the rubber membrane in the air chamber, when the piston rod in the release of the spring began to move down, the rubber membrane down concave, the air chamber above the air becomes thin and the piston rod is damped and slowly fall. After a certain period of time, the piston rod down to a certain position, it will push the delay contact action through the lever, so that the dynamic break contact off, dynamic contact closed. From the coil energized to the time delay contact to complete the action, this time is the relay delay time. The length of the delay time can be changed by adjusting the size of the air chamber inlet hole with a screw. After the attraction coil is de-energized, the relay recovers by the action of the recovery spring. The air is rapidly discharged through the air outlet hole.