In addition to simply acting as a regulatory device, a cast iron butterfly valve can also be used to control the flow of water into the pipe, which can actually start and stop the flow as desired. Butterfly control valve is a well-known and appreciated design, which is incredibly effective in its extremely simple design.
Small forged steel ball valve is the popular electromagnetic device that controls the flow of media, usually water or gas. The solenoid coil uses energy to mechanically open and close the valve from the flip of the switch. Sometimes they can use metal or rubber seals and interfaces that allow you to handle them more easily. A spring can also be used to keep the valve open or closed when activated. The diaphragm is used to prevent media from passing through the valve. The pressure on both sides of the diaphragm is the same which closes the valve with any flow.
As you can imagine, small pressure relief solenoid valves have such small functional parts that there are plenty of chances for things to go wrong. Although it is rare, sometimes it is necessary to know the basics of how to serve them. If any holes in the diaphragm climb in any way, it can seriously affect the device working properly.