Mitsubishi 6M60-TL Service Manual page 313

STRUCTURE AND OPERATION
61-8
2.4 Operation when tank pressure
reaches lower threshold level
• When the air pressure A from the air
tank drops below the lower threshold
level, the piston is pushed downward
by the spring such that the inlet valve
closes and the exhaust valve opens.
As a result, air pressure flows through
the exhaust stem and escapes to the
atmosphere.