🔍 Key Concepts

• Trace the pilot air path from the solenoid air valve, through the pinion-engaging line, past both pinion mechanisms, to the air relay valve in the illustration. • Understand when pilot air is supposed to be sent to the air relay valve: is it when the pinions are engaged with the flywheel, or when they are retracted? • Notice the series relationship between the upper and lower pinions: one must move first so air can continue on to the other and then to the check valve.

💭 Think About

• When you press START and the solenoid opens, what physical movement has to occur at the pinions before the relay valve can get pilot air and admit main start air to the motors? • If pilot air never reaches the relay valve, which kind of malfunction would block it before rotation ever begins: a failure to engage or a failure to retract? • Looking at the arrows and piping, which pinion appears to be first in the pilot-air path, and how would its failure affect the second pinion and the relay valve?

✅ Before You Answer

• Confirm from the sketch whether pilot air is routed through BOTH pinion housings before it reaches the check valve and air relay valve. • Decide whether engagement or retraction of the pinions is the interlock condition that allows pilot air to flow onward. • Verify which pinion (upper or lower) is upstream in the pilot-air path and therefore, if it fails, would prevent the other pinion from moving and stop pilot air from reaching the relay valve.