What type of valves utilize a stem that extends through a bonnet?

Gate valves are designed to control the flow of liquid or gas in a system and typically utilize a stem that extends through a bonnet. The bonnet is the part of the valve that encases the stem and provides a secure seal. This design allows for easy operation of the valve and ensures that the moving parts are protected from external elements and contaminants.

In a gate valve, when the handwheel or actuator is turned, the stem moves the gate (or wedge) up and down to either open or close the valve. This up-and-down movement provides a clear pathway for liquid or gas flow when the valve is open and effectively blocks the flow when closed.

Other types of valves, such as check valves, pressure relief valves, and butterfly valves, have different mechanisms and designs that do not typically include a stem extending through a bonnet in the same way gate valves do. For instance, check valves are designed to allow flow in one direction and have a different internal mechanism to prevent backflow. Pressure relief valves are primarily focused on safety and are designed to release pressure without the need for a stem extending through a bonnet in the traditional sense. Butterfly valves utilize a disc that rotates to control flow, which is also a distinct operation compared to gate valves.