Final answer:
Manufacturers recommend grinding the valve face to 45.5 degrees when the valve seat angle is 45 degrees.
Step-by-step explanation:
When the specified valve seat angle is 45 degrees, most manufacturers recommend grinding the valve face to 45.5 degrees.
This is because a slightly smaller angle of 45.5 degrees allows for better sealing between the valve and the seat, preventing any leakage. It also helps to reduce wear and tear on the valve face and seat, thereby increasing their lifespan.
Grinding the valve face to a positive angle of 45.5 degrees ensures optimal performance and longevity of the valve assembly.