The main engines on your harbor tug utilize...

Question 1 / 2066636eef28f7522a1c51fe4c

Question 1 of 2066636eef28f7522a1c51fe4c

The main engines on your harbor tug utilize a starting system with two air-start motors similar to that shown in the illustration. Upon pushing the start button, the solenoid air valve energizes open, but the air start relay valve fails to receive pilot air, and thus the starter motors and engine fail to rotate. Which of the listed conditions would most likely be the cause of the failure to start? Illustration MO-0200

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🔍 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.

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Question 1 of 20

The upper pinion fails to retract, which in turn does not allow the lower pinion to retract. Because retraction of both pinions is required to supply air to the air-start motors, the engine does not start.

The lower pinion fails to engage, which in turn does not allow the upper pinion to engage. Because engagement of both pinions is required to supply air to the air-start motors, the engine does not start.

Question 1 / 2066636eef28f7522a1c51fe4c

Question 1 of 2066636eef28f7522a1c51fe4c

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Question 1 of 20

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💭 Think About

✅ Before You Answer

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