Pneumatic diaphragm shut-off valves (referred to as shut-off valves for short) are the executing units in pneumatic unit combinations. They directly control the cut-off and flow of media based on signals output by the regulating instrument, achieving automatic control over parameters such as pressure, flow rate, or liquid level. The main difference between shut-off valves and regulating valves lies in the fact that the former are used for two-position on-off regulation, while the latter are used for multi-position continuous regulation.

This product features a simple structure, convenient operation, a compact form, light weight, and an innovative valve body design. It has low flow resistance, a large valve capacity, and excellent sealing performance, and it is fire-resistant and explosion-proof. Cage-type shut-off valves adopt a balanced valve core structure, which can increase the allowable pressure difference. The valve cores are available in soft-sealed and hard-sealed types, which can be selected according to performance requirements. Therefore, they are widely applied in automatic control and remote control systems for production processes in various industrial sectors such as petroleum, chemicals, metallurgy, electric power, light industry, and textiles.

Structure and Principle

Shut-off valves consist of two parts: a pneumatic diaphragm actuator and the valve body, connected by three vertical rods or a bracket. Shut-off valves come in three forms: single-seat (P), cage (M), and three-way (3). Their structure and principle are shown in the figure below.

The actuators have two forms: positive and reverse. When the signal pressure input is 0.2 MPa, the push rod extends out of the diaphragm chamber (moves downward), which is called the positive action, and forms a gas-open type when combined with the valve. When the signal pressure input is 0.2 MPa, the push rod retracts into the diaphragm chamber (moves upward), which is called the reverse action, and forms a gas-close type when combined with the valve. For three-way valves, since the valve opens and closes simultaneously, there is no distinction between gas-open and gas-close types. The principle is as follows: when the signal pressure is "0", due to the pre-tightening force of the spring, the valve core is in the initial state, either normally open or normally closed. When a signal pressure of 0.2 MPa is input, it generates a thrust on the diaphragm, compressing the spring and driving the push rod and valve rod to move the valve core to the limit position, achieving full valve closure (full opening) or changing the flow direction of the medium. When the signal pressure returns to "0", the force acting on the diaphragm disappears. Due to the reaction force of the spring, the valve core returns to the initial state