Method: Sand Casting, Investment Casting or Lost Foam Casting
Materal: Carbon Steel, Ductile Iron, Gray Iron and stainless steel.
A Valve bonnet acts as a cover on the valve body. Generally made by casting ( Sand Casting or Invesment Casting). It is commonly semi-permanently screwed into the valve body. During manufacture of the valve, the internal parts are put into the body and then the bonnet is attached to hold everything together inside. To access internal parts of a valve, a user would take off the bonnet, usually for maintenance. Many valves do not have bonnets; for example, plug valves usually do not have bonnets.
Casting Valve Bonnet