The Allen-Bradley 849A-ZOB25 Pneumatic Timing Relay is an 849 series on-delay timer, which means it waits for a preset time interval before changing its electrical contacts from the off status to the on status after the relay coil is energized. This pneumatic timing relay’s time delay setting is user-configurable by turning a screw-type adjustment knob clockwise to increase the time delay or counterclockwise to decrease the time delay. The actual physical activation of the electrical switch is achieved by a mechanical system which includes a pneumatic bellows that is filled with air that is activated by the incoming pressure signal and the electrical contact driver. The speed at which the bellows of the Allen-Bradley 849A-ZOB25 Pneumatic Timing Relay is completely filled is directly proportional to the position of the adjustment knob, which is mechanically linked to a needle valve for controlling the release of the air from the bellows.

The electrical contact block of the Allen-Bradley 849 series 849A-ZOB25 Pneumatic Timing Relay can be replaced as part of a maintenance procedure or in the event of damage. Additional or auxiliary contacts can be added if more circuits need to be controlled from the pneumatic timing relay according to the final users’ application needs. The electrical contacts of the Allen-Bradley 849A-ZOB25 Pneumatic Timing Relay are normally open and they have a mechanical spring return mechanism that brings them back to their initial position after the electrical signal which activates the coil changes its state. This type of pneumatic timing relay is very commonly employed as industrial control components for hazardous or even explosive applications such as installations with oil, natural gas, or any type of flammable materials in suspension.