Model 90 Low Pressure Selector Relay is designed to select the lower of two signal pressures to provide a continuous output pressure to a control device. The Model 90 is recommended for dead end or low flow service in critical applications such as control loops requiring precise, automatic monitoring of signal pressures.

Model 91 High Pressure Selector Relay is designed to select the higher of two signal pressures, and to provide a continuous output pressure (or pressure range) to a controller. The ability to precisely control pressure switching and pressure monitoring functions make the Model 91 the logical choice in dead end or low flow applications such as precision control loops.