| Definition | Electrically controlled hydraulic valve | An electro-hydraulic valve uses an electrical input signal to control the direction, pressure, or flow of hydraulic fluid in a pressurized circuit. |
| Energy Conversion | Electrical signal to hydraulic action | An electronic command energizes a solenoid or drives an electro-mechanical actuator, which changes the position of a hydraulic control element. |
| Main Control Variables | Direction, pressure, and flow | Directional valves control actuator movement, pressure valves regulate system force, and flow-control valves adjust actuator speed. |
| Primary Components | Valve body, spool or poppet, actuator, spring, seals, and ports | The valve body guides hydraulic fluid, while the spool or poppet opens, closes, or restricts flow paths. Springs commonly return the valve to a defined position when the signal is removed. |
| Electrical Actuation | Solenoid, proportional actuator, or servo actuator | On/off solenoids provide discrete positions. Proportional and servo actuators allow more precise control of spool position, flow, or pressure. |
| Hydraulic Ports | Pressure, tank, and working ports | A typical directional circuit includes a pressure port connected to the pump, a tank or return port connected to the reservoir, and one or more working ports connected to an actuator. |
| Operating Sequence | Command, actuation, flow change, and response | The controller sends a signal, the actuator shifts the internal control element, hydraulic flow is redirected or metered, and the connected cylinder or motor responds. |
| Control Signal Types | Digital or analog | Digital signals generally produce an on/off response. Analog signals, such as voltage or current commands, can produce variable valve opening and smoother motion. |
| Common Valve Functions | Directional, pressure, and flow control | Directional valves determine movement direction; pressure valves limit or regulate pressure; flow valves control the rate of hydraulic fluid movement. |
| Typical Hydraulic Medium | Mineral-based or synthetic hydraulic fluid | The fluid transfers power, lubricates internal parts, and helps remove heat. The selected fluid must be compatible with the valve seals and operating conditions. |
| Response Behavior | Fast response with possible switching transients | Electro-hydraulic valves can react quickly, but response is affected by electrical delay, spool movement, fluid compressibility, pressure changes, and load characteristics. |
| Pressure Rating | Application-specific; commonly specified in bar or MPa | The allowable pressure depends on the valve design and must not be exceeded. The system rating is determined by the lowest-rated connected component. |
| Flow Rating | Application-specific; commonly specified in L/min | Flow capacity indicates how much hydraulic fluid can pass through the valve under defined pressure-drop conditions. Excessive flow can increase heat and reduce control accuracy. |
| Neutral or De-Energized Position | Normally closed, normally open, or defined center condition | When the actuator is not energized, the valve may block flow, connect ports, or unload the pump depending on its internal configuration and spring arrangement. |
| Feedback Options | None, position feedback, pressure feedback, or external sensor feedback | Feedback enables a controller to compare the desired and actual condition, improving accuracy in position, pressure, speed, or force control. |
| Advantages | Remote control, automation, precision, and high power density | Electrical control allows integration with sensors, programmable controllers, and safety systems while hydraulic power provides high force and compact actuator size. |
| Limitations | Fluid cleanliness, heat generation, leakage, and tuning requirements | Contamination can damage precision parts, throttling can generate heat, seals may wear, and proportional or servo systems may require careful adjustment. |
| Common Applications | Mobile machinery, industrial automation, presses, lifting systems, and material handling | Electro-hydraulic valves are used where electronic control and hydraulic power must work together to manage motion, force, speed, or load holding. |
| Maintenance Priorities | Filtration, fluid condition, electrical connections, seals, and leakage inspection | Regular maintenance helps preserve response quality and service life. Hydraulic cleanliness and correct fluid level are especially important for reliable operation. |
| Basic Safety Principle | Relieve stored hydraulic and electrical energy before servicing | Hydraulic systems can retain dangerous pressure after shutdown. Lockout procedures, pressure release, suitable protective equipment, and manufacturer-approved methods are essential. |
