The development of electromagnetic valves has a long and evolving history. Today, solenoid valves at home and abroad are generally classified into three main types based on their operating principles: direct-acting, step-by-step pilot, and pilot-operated. Additionally, depending on the structural design and material differences, they can be further divided into six subcategories: direct-acting diaphragm type, step-byreshold diaphragm type, leading diaphragm type, direct-acting piston type, step-by-step piston type, and pilot piston type.
A **direct-acting solenoid valve** operates by using an electromagnetic coil to generate a magnetic force when powered. This force lifts the closing member off the valve seat, allowing the valve to open. When the power is turned off, the magnetic force disappears, and a spring pushes the closing member back onto the valve seat, shutting it off. These valves are capable of functioning under vacuum, negative pressure, or zero-pressure conditions, making them ideal for low-pressure applications. However, their flow path is typically limited to about 25mm in diameter.
The **distribution-type solenoid valve**, also known as a combination direct-acting and pilot valve, works by combining two principles. When there is no pressure difference between the inlet and outlet, the electromagnetic force directly lifts both the pilot valve and the main valve’s closing member, opening the valve. Once the pressure difference reaches a certain level, the solenoid opens the small pilot valve, increasing the pressure in the lower chamber of the main valve. This pressure difference then pushes the main valve open. When power is removed, the pilot valve closes due to spring force or media pressure, allowing the fluid to return to the upper chamber, which forces the main valve to close. These valves can operate at zero pressure, vacuum, or high pressure, but they require more power and must be installed horizontally.
A **pilot solenoid valve** functions by using a pilot mechanism. When the coil is energized, the pilot valve opens, allowing the pressure in the upper chamber to drop quickly. This creates a pressure differential around the closing member, which causes the fluid pressure to push it upward, opening the valve. When the power is off, the pilot valve closes due to spring force, and the inlet pressure flows through a bypass into the upper chamber, creating a low-pressure area that pushes the closing member down, thus closing the valve. These valves are suitable for high-pressure applications and can be customized for different installations, though they require a minimum pressure condition to function properly.
Overall, each type of solenoid valve is designed for specific working environments and performance requirements, making them essential components in various industrial and commercial systems.
GNEE (Tianjin) Multinational Trade Co.,Ltd , https://www.suppliersteel.com