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Q6. What is "virtual tappet" in the hydraulically actuated air spring return exhaust valves, and how is it set. Explain why the damage occurs to the seats of the exhaust valves due to furrowing and cutting and how an incident of "valve drop" leading to extensive damage to running gear can occur.

Q9. (a) Explain why variable exhaust valve closing can be advantageous in the operation of large slow speed main engines.

(b) Explain, with the aid of a sketch, how variable exhaust valve closing is achieved.

(c) Explain how high impact is avoided as the valve closes. (2)

Q3. What is "virtual tappet" in the hydraulically actuated air spring return exhaust valves, and how is it set. Explain why the damage occurs to the seats of the exhaust valves due to furrowing and cutting. How an incident of "valve drop" leading to extensive damage to running gear can occur.