Which type of valve is not recommended for on-off service?

The globe valve is primarily designed for throttling flow, which means it is typically used to control the flow rate in a piping system rather than to provide a complete shut-off. The seating surface in a globe valve is not flat; instead, it has a more complicated shape that allows for precise control of flow, but this design does not facilitate a tight seal when the valve is in the closed position.

In contrast, other valve types such as gate valves and ball valves are designed for on-off service. Gate valves provide a straight-line flow with minimal resistance and are effective for isolating sections of piping, while ball valves have a spherical disc that provides a very tight seal, making them suitable for both on-off service and quick operation. Check valves, on the other hand, are used in applications to allow flow in one direction only and prevent backflow, so they are not typically used for on-off control of flow.

Thus, the globe valve is not the ideal choice for situations requiring a reliable on-off control due to its intended design and functionality.