Which of the following is NOT a type of plug valve gland?

In the context of valve design, particularly regarding plug valves, a gland is a component that serves to secure the valve stem while also providing a seal to prevent leakage. The types of glands listed are generally recognized in valve engineering.

Single glands are designed to provide sealing with a single packing arrangement around the stem. Double glands employ two sets of packing, which can enhance the sealing capability and is especially useful for applications requiring higher reliability.

Bolted glands are a further enhancement where the gland is mechanically fastened with bolts, allowing for even tighter sealing and easier maintenance. They can provide greater pressure handling capability and maintain alignment better under operational stresses.

Screwed glands refer to glands that utilize threaded connections. While this design is possible, it is less common compared to the others mentioned. In typical plug valve configurations, single and double glands along with bolted options are more standard and recognized due to their effectiveness and reliability in valve sealing functions.

Thus, the selection indicating that double gland is not a type of plug valve gland is not accurate, as double glands are indeed a valid type. The recognition of single, bolted, and screwed glands aligns better with conventional practices in valve design, making it clear that double glands are indeed a recognized type of valve gland.