| Control or Indicator | Purpose |
|---|---|
| Discharge check valve | Cuts off the reverse flow of air/fluid mixture through compressor discharge system at compressor shutdown. |
| Thermal valve | Regulates flow of fluid to and around the cooler. Designed to maintain a minimum operating temperature (180F); used for fast warmup on startup. (Aircooled only) |
| Discharge temperature switch | Shuts the machine down when the compressor discharge temperature exceeds maximum design temperature. |
| Minimum pressure valve | Maintains minimum pressure level in compressor sump (40 PSI is a common setting). Valve piston restricts receiver air discharge from receiver/sump when pressure falls to 40 PSI. |
| High pressure shutdown switch | An added feature designed to shutdown the machine when the pressure becomes too high (135 PSI is a common setting, unless the compressor is a high pressure unit). |
| Pressure relief valve | Opens sump pressure to the atmosphere should pressure inside the sump become too high. (140 PSI is a common setting) Operation of this valve indicates that the high pressure protection system is either faulty or out of adjustment. |
| Check valve | Prevents line pressure backflow into the sump during unload conditions and after shutdown. |
| Pressure regulator | Opens a pressure line between the sump and control to regulate air delivery according to air demand. |
| Pilot valve | By-passes the pressure regulator valve causing the control to close the inlet valve when the machine reaches maximum operating pressure. |
| Pirate Parts | Counterfeit or copies of genuine parts. Usually supplied by an unscrupulous vendor. Should be avoided. Rarely comes with warranties. |
| Pressure switch | Senses service line pressure. When line pressure reaches maximum setting, the pressure switch signals the control valves to unload the machine. |
| Blowdown valve | Vents sump pressure to the atmosphere during unload conditions and shutdown. |
| Water regulating valve (water-cooled only) | Regulates the amount of cooling water used in the heat exchanger to keep the machine running at a normal operating temperature. |
