Robertshaw R503-1 Pneumodular Diverting Relay, a component used in pneumatic control systems for heating, ventilation, and air conditioning (HVAC) applications. It converts a proportional pneumatic signal into a positive pneumatic switching action. 

• Function: It is designed for switching and interlocking functions, such as feeding and exhausting branch lines, or diverting a supply line to either one of two branch lines based on signal strength. 

• Set Point Range: This specific model operates within a 3–20 PSIG input range.