Selector relays connect to multiple sensors or components with signal outputs, compare the two signals against each other, and pass through either the higher or lower pressure signal. They are used to verify equipment is operating correctly and can act as a fail-safe to prevent unsafe operating conditions.

Snap-acting relays respond instantly to changes in signal pressure and change between different states. They are commonly used as shutoffs or high/low limits to ensure safe equipment operation.

Two-position switching relays connect to two different pneumatic HVAC systems and switch their output between them, depending on the status of the control signal.

Capacity relays respond to control signals and combine two air inputs to increase the flow rate of a single airline to allow them to supply components with higher air demands.

Reversing relays monitor the pressure of a control signal and provide the opposite of the signal they receive. They are used to monitor equipment and will send a signal when they sense that connected device is no longer providing air pressure.