Hydraulic control valves can be divided into two types according to their structure: diaphragm type and piston type. They work on the same principle, using the pressure difference △P between upstream and downstream as power, controlled by pilot valves (including bellows shut-off valves), enabling hydraulic differential operation of the diaphragm (piston), and fully automatically regulated by water force. This causes the main valve disc to be fully open, fully closed, or in a regulating state.
When the pressurized water in the control chamber above the diaphragm (piston) is discharged to the atmosphere or the downstream low-pressure area, the pressure value acting on the bottom of the valve disc and below the diaphragm becomes greater than the pressure above it, thus pushing the main valve disc to the fully open position.
When the pressurized water in the control chamber above the diaphragm (piston) cannot be discharged to the atmosphere or the downstream low-pressure area, the pressure value acting on the top of the diaphragm (piston) becomes greater than the pressure below it, thus pressing the main valve disc to the fully closed position.
When the pressure value in the control chamber above the diaphragm (piston) is between the inlet pressure and the outlet pressure, the main valve disc will be in a regulating state. Its regulating position depends on the joint control action of the needle valve and adjustable pilot valve in the pilot system. The adjustable pilot valve can adjust its own small valve opening based on the outlet pressure downstream and its changes, thereby changing the pressure value in the control chamber above the diaphragm (piston), controlling the regulating position of the valve disc.