What type of valve provides good throttling action but does not seal well?

The type of valve that provides good throttling action but does not seal well is the double seated valve. This design consists of two seating surfaces, which allows it to control flow effectively over a range of conditions, making it suitable for throttling applications. However, the presence of two seats can lead to challenges with achieving a perfect seal, especially under certain pressure conditions.

In contrast, single seated valves typically offer better sealing capabilities because they use only one seat to close off the flow, resulting in less opportunity for leakage. Reverse acting and direct acting valves are more concerned with executing specific actuator functions than with providing throttling action or ensuring seals. Hence, the focus on throttling effectiveness makes the double seated valve the correct choice for this question, highlighting its balance between flow control and sealing characteristics.