The Difference Between Proportional vs. Directional vs. Servo Valves

As our understanding of hydraulic systems advanced, so did our desire to enhance and fine-tune their performance. In response to this need, different types of valves were developed to meet specific requirements. This article provides a concise overview of the three major categories of hydraulic valves.

Directional Valves, also known as "switching valves" or colloquially referred to as "bang-bang valves" due to their noise during switching, have evolved from simple left-right decisions to more sophisticated valves capable of containing multiple outputs. Some directional valves also have the capability to moderate the speed of hydraulic fluid by adjusting the aperture through which it flows.

While directional valves are simple and effective, each change in direction, flow, or pressure necessitates its own valve, resulting in large and costly hydraulic circuits for even moderately complex systems.

Proportional Valves utilize solenoids to allow the valve to assume any desired position between 'closed,' 'left output,' and 'right output.' This adjustability grants them the ability to provide variable flow volumes in any proportion between the two outputs. By consolidating flow and directional controls into a single valve, proportional valves significantly reduce the space requirements for complex circuits.

Furthermore, proportional valves can alter the speed by adjusting the electrical signal level, eliminating the need for additional hydraulic components. Their proportional controls, coupled with electronic systems, offer additional features like acceleration and deceleration. As a result, machines equipped with proportional valves experience improved overall cycle times, enhanced production rates, and the ability to safely operate at higher speeds with controlled start and stop characteristics.

Servo Valves, one of the oldest and more expensive valve types, operate through a combination of input pressure from the hydraulic line and electronic controls. Unlike "bang-bang" valves, servo valves move smoothly and with high precision.

Servo valves are known for their exceptional accuracy, repeatability, low hysteresis, and high-frequency response. These characteristics contribute to the long-lasting nature of servo valves, their quick response to controls, and their minimal hysteresis compared to other valve types.