Differences Between Direct-Acting and Pilot-Operated Solenoid Valves

Differences Between Direct-Acting and Pilot-Operated Solenoid Valves:
Solenoid valves are widely used in industrial automation due to their simple operation and strong market demand; they serve as key solutions for automated fluid control. Based on their operating mechanism, they are generally categorized into two types: direct-acting and pilot-operated. Improper selection can lead to malfunctions, such as failure to open or close correctly. The following section details the differences between the two types and explains their respective operating principles and characteristics.

1. Direct-Acting Solenoid Valve – Product Introduction:
Direct-acting solenoid valves are typically used for small-bore, low-pressure applications. This type of valve does not require a pressure differential (i.e., no minimum starting pressure) to open; it can operate at zero pressure. Consequently, it offers faster actuation speeds compared to pilot-operated valves, making it particularly suitable for pipelines requiring rapid shut-off.

Characteristics: Power consumption is relatively high (typically 15–30W), but control is simple and the application range is broad. They function correctly under vacuum, negative pressure, zero pressure, and low-pressure conditions, though the nominal diameter (DN) generally does not exceed 50mm.

Direct-Acting Solenoid Valve – Operating Principle:
When energized, the electromagnetic coil generates a force that lifts the closing element directly off the valve seat, opening the valve. When de-energized, the electromagnetic force vanishes, and a spring presses the closing element back onto the seat, closing the valve.

2. Pilot-Operated Solenoid Valve – Product Introduction:
Pilot-operated solenoid valves are generally used in applications involving pressure differentials, high pressures, or large diameters. This type of valve requires a certain minimum starting pressure to open; without sufficient pressure, only the pilot orifice opens, while the main valve port remains closed.

Characteristics: Power consumption is lower (10–25W), and they are energy-efficient and suitable for frequent or prolonged energization. They support higher maximum fluid pressures and offer customizable installation orientations, though they strictly require a specific fluid pressure differential to operate.

Note: Impurities in the fluid can cause wear on the sealing surfaces, leading to poor sealing; therefore, these valves are not suitable for fluids containing impurities or particulate matter.

Working Principle of Pilot-Operated Solenoid Valves
When energized, the electromagnetic force opens the pilot orifice, causing the pressure in the upper chamber of the valve to drop rapidly. This creates a pressure differential-lower pressure above and higher pressure below the closing element-allowing fluid pressure to push the element upward and open the valve. When de-energized, the spring force closes the pilot orifice; inlet pressure quickly fills the chamber via a bypass hole, creating a pressure differential-higher pressure above and lower pressure below the closing element-whereby fluid pressure pushes the element downward to close the valve.

Comparing direct-acting and pilot-operated solenoid valves, pilot-operated valves can withstand higher pressures, whereas direct-acting valves offer faster actuation speeds and do not require a minimum operating pressure. Direct-acting solenoid valves are recommended for applications requiring rapid shut-off or low-pressure operation, while pilot-operated valves are recommended for applications involving high pressure differentials, high operating pressures, and large port sizes.