The Allen-Bradley 849-Z0D321 Pneumatic Timing Relay is a heavy-duty 849 series relay that has been designed for applications even in the most difficult outdoor applications and for trouble-free operation in heavily polluted industrial environments. It has a set of pneumatic bellows that is mechanically attached to a set of electrical contacts in order to engage or disengage an electrical circuit according to the condition of a remotely energized coil. The Allen-Bradley 849-Z0D321 Pneumatic Timing Relay is completely adjustable by the users by means of a calibration screw that works by restricting or augmenting the flow of air out of the device’s pneumatic chamber. These variations in the speed of airflow determine a change in the amount of time it takes for the switch to move from one electrical status to the other.

The Allen-Bradley 849-Z0D321 Pneumatic Timing Relay is an on-delay timer, which means it is not designed to change from the off to the on electrical status immediately when the coil is energized. Instead, when the coil in the Allen-Bradley 849-Z0D321 Pneumatic Timing Relay is energized, the device waits for a user-configurable time before actually changing the status of the electrical contacts. A set of auxiliary contacts is included from the factory on this pneumatic timing relay. This relay comes as a normally open switch that needs an external control signal to energize the coil to close the electrical circuits that are connected to its terminals. The device is designed to be immune to external electric disturbances or interferences, and it is an ideal solution to implement in environments where a high degree of atmospheric contamination is expected.