The functions of solenoid valves and pneumatic valves

Solenoids are used relatively rarely in process pipelines. It is generally used in pneumatic pipelines. We sometimes use solenoid valves in the DN20 flushing piping as shut-off valves. To use this, one needs to consider the requirements regarding medium temperature, pressure, and leakage level; other aspects are not clear

Definition: A solenoid valve is an automated basic component used to control fluids, and it belongs to the category of actuators； It is not limited to hydraulics or pneumatics. Solenoids are used to control the direction of hydraulic flow. The mechanical devices in factories are generally controlled by hydraulic systems, which is why solenoids are used. Working principle: The solenoid valve contains a sealed chamber with holes opened at various positions; each hole leads to a different oil pipe. At the center of the chamber is the valve, with two electromagnets on either side. When the coil of the magnet on one side is energized, the valve body is drawn toward that side. By controlling the movement of the valve body, it is possible to block or allow fluid to pass through different oil outlet holes. The oil inlet hole remains open, allowing hydraulic oil to flow into the various oil outlet pipes. The pressure of the oil then pushes the piston inside the cylinder, which in turn drives the piston rod, and the piston rod activates the mechanical mechanism. In this way, controlling the current to the electromagnet controls the mechanical motion. Classification and Principles: Electromagnetic valves worldwide can be divided into three main categories based on their principles (i.e., direct-acting, step-by-step direct-acting, and pilot-operated). Based on differences in valve disc structure, materials, as well as principles, they are further divided into six subcategories (direct-acting diaphragm structure, step-by-step diaphragm structure, pilot-operated diaphragm structure, direct-acting piston structure, step-by-step direct-acting piston structure, and pilot-operated piston structure). ①Direct-acting solenoid valve Principle: When powered, the electromagnetic coil generates an electromagnetic force that lifts the closing element away from the valve seat, thereby opening the valve ； When power is cut off, the electromagnetic force disappears, and the spring presses the closing element against the valve seat, causing the valve to close. Features: It can operate normally under vacuum, negative pressure, or zero pressure, but the diameter generally does not exceed 25 mm. 　 ②Direct-acting solenoid valve – Principle: It operates on a combination of direct-acting and pilot-operated mechanisms; when there is no pressure difference between the inlet and outlet, upon power application, the electromagnetic force lifts the pilot valve and the main valve’s closing element upward one after another, thereby opening the valve. When the pressure difference between the inlet and outlet reaches the starting value, upon power application, the electromagnetic force acts on the pilot valve; as a result, the pressure in the lower chamber of the main valve rises while the pressure in the upper chamber drops, and this pressure difference is used to push the main valve upward ； During a power outage, the pilot valve uses spring force or medium pressure to push the closing element downward, thereby closing the valve. 　　 Features: It can operate at zero pressure difference or in vacuum as well as under high pressure; however, it requires a higher power level and must be installed horizontally. ③Principle of pilot-operated solenoid valve: When electric current is applied, electromagnetic force opens the pilot hole, causing the pressure in the upper chamber to drop rapidly. This creates a pressure difference with higher pressure below and lower pressure above the closing element; the fluid pressure then pushes the closing element upward, thereby opening the valve ； When power is lost, the spring force closes the pilot hole; the inlet pressure rapidly creates a pressure difference around the valve closing element, with lower pressure at the bottom and higher pressure at the top. The fluid pressure then pushes the closing element downward, thereby closing the valve. 　　 Features: High upper limit for fluid pressure range; can be installed in any position (customization required), but must meet the fluid pressure difference requirements. When using it, its various characteristics should be taken into account, such as the properties of the medium, ambient temperature, operating frequency, power supply, and other factors.

I feel that whether it’s electric or pneumatic, it’s just a matter of the different sources of energy that drive the valve’s movement; the conditions under which it’s used are determined by the characteristics of the valve itself, I guess. Hehe, not necessarily true though

The solenoid valve operates on the same principle as air control valves, such as 2/3-way and 3/5-way valves. The only difference lies in the control signal: solenoid valves use electricity as the control signal to regulate the opening and closing of the valve, while air control valves use air pressure as the control signal for the same purpose. Solenoids are used for general interlock control, and solenoids are used for two-position shut-off valves. A flow control valve can be connected to a solenoid valve to create more complex control systems. Since the wind itself cannot operate automatically, it generally needs to be used in conjunction with solenoid valves. Or in combination with other devices that control wind signals.

The solenoid valve is merely an accessory to a control valve or a shut-off valve. It is mainly used to implement interlocking functions. And the pneumatic valve you mentioned is just one of the ways in which energy can be supplied to a valve. It is commonly used in explosion-proof environments.