As soon as the vehicle is started (in neutral), main pressure is established by the ______________.

As soon as the vehicle is started (in neutral), main pressure is established by the ______________.

• A. Priority valve
• B. Hold regulator valve
• C. Spring-loaded MPRV
• D. Trimmer regulator valve

Answer: (C)

The main pressure in the system is established by the spring-loaded Main Pressure Regulating Valve. This valve sits in the path between the compressor and the main reservoir and it sets the regulated pressure the system will try to maintain. When the engine starts and the compressor builds air, the MPRV opens to allow air into the main line until the pressure reaches its set value, at which point it closes to hold that pressure steady. If the pressure starts to fall—due to braking or leaks—the spring pushes the valve open again to admit more air and restore the level. Other valves handle different roles, like prioritizing air to critical circuits or holding pressure in certain lines, but the device that actually establishes the main system pressure is the spring-loaded MPRV.

The main pressure in the system is established by the spring-loaded Main Pressure Regulating Valve. This valve sits in the path between the compressor and the main reservoir and it sets the regulated pressure the system will try to maintain. When the engine starts and the compressor builds air, the MPRV opens to allow air into the main line until the pressure reaches its set value, at which point it closes to hold that pressure steady. If the pressure starts to fall—due to braking or leaks—the spring pushes the valve open again to admit more air and restore the level. Other valves handle different roles, like prioritizing air to critical circuits or holding pressure in certain lines, but the device that actually establishes the main system pressure is the spring-loaded MPRV.