Exam Question

### (a) Clearances to Check When Lapping Valves to Seats
When lapping safety valve discs to their seats, the primary objective is to achieve a perfect, pressure-tight metal-to-metal seal. However, several critical clearances and adjustments must be checked to ensure not only this seal but also the correct and reliable operation of the safety valve. Failure to observe these can lead to valve sticking, premature lifting, chattering, or failure to reseat correctly.
* **Valve Spindle to Guide Bush Clearance:**
* **Reasoning:** This is perhaps the most critical clearance. The valve spindle must move freely within its guide bush without excessive play. Lapping the seat is only effective if the valve disc can descend perfectly concentrically onto the seat. If the clearance is: