The admission valve, shown in the illustration, is fitted to an air supply manifold for opening and closing off the supply of compressed air to the starting valves, as well as air distribution to the main propulsion diesel engine. The admission valve is opened by __________. See illustration MO-0055.
• Understand the difference between control air (CA), start air (SA), and exhaust air (EA) in the illustration. • Notice how the springs are arranged versus the pistons connected to the CA inlet. • Think about whether the valve moves to the OPEN position when force is applied by air pressure or by a spring.
• In the illustration, which force is acting to KEEP the valve closed when there is no control signal: the spring or the air pressure? • When control air (CA) is admitted on the small upper piston, does that tend to move the main valve spindle upward or downward? What position (open/closed) would that create for the start air passage? • Do any of the choices mention a condition that would actually REMOVE air pressure rather than apply it? Would that normally OPEN or CLOSE a safety‑critical admission valve?
• Trace the path from the CA inlet to the small pilot/guide piston and then down to the main valve piston. • Verify which direction the return spring is trying to move the valve (toward OPEN or toward CLOSED). The opening action must OPPOSE this. • Eliminate any choices that rely on vacuum or venting the system, since the illustration shows a design based on positive control air pressure and spring return.
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