Bonnet

Valve bonnet is a component that covers the opening of the valve body.  It is typically bolted or screwed onto the valve body and provides several important functions.

• Enclosure  -  The bonnet encloses and seals the internal components of the valve, such as the stem, packing, and other moving parts, protecting them from external contaminants and environmental factors.
• Pressure Containment  -  In pressure containing valves, such as gate valves, globe valves, and check valves, the bonnet plays a crucial role in containing the pressure within the valve body.  It helps to reinforce the structural integrity of the valve and prevents leakage.
• Access for Maintenance  -  Valve bonnets are designed to allow easy access to the internal components of the valve for inspection, maintenance, and repair.  They can be removed to facilitate servicing of the valve without requiring the disassembly of the entire valve body.
• Connection Point  -  In some valve designs, the bonnet serves as the connection point for the valve actuator or operator.  It provides a mounting surface for actuators, handwheels, or other devices used to control the valve.

Valve bonnets come in various designs and configurations depending on the type of valve and its intended application.  They can be bolted, threaded, welded, or pressure sealed onto the valve body.  The choice of bonnet design depends on factors such as the pressure rating, temperature, fluid characteristics, and service conditions of the valve.