Proportional Valve

Proportional valves in hydraulics are used for precise and controlled regulation of hydraulic pressure. These valves do not merely “open” and “close” but also enable all other pressure states between these two endpoints. This makes the actuators connected to the proportional valve particularly well controllable.

Design and Functionality of a Proportional Valve

A proportional valve belongs to the group of “continuous valves.” This group also includes pressure, throttle, flow control, and directional control valves. Strictly speaking, the proportional valve is a directional control valve, as it is controlled by an internal spool. Other directional control valves include the servo valve and the control valve.

The challenge in designing the proportional valve is to gradually change the volumetric flow rate through the spool movement. Partially opening a normal directional control valve is technically difficult because pressure contributes to opening the valve.

To ensure proportional control of the volumetric flow, an exact counterforce must be applied to the thrust. This is achieved in proportional valves either via electromagnets or a separate hydraulic control circuit.

The electromagnetic design is technically simpler, but it has high power consumption. When the valve opens, the volumetric flow and the position of the blocking piston are measured. Its exact position is determined from this. The electromagnet builds up a correspondingly high counterforce, which prevents the piston from opening abruptly. This allows the proportional valve to be opened and closed very precisely manually. The further the valve opens, the higher the pressure rises and the faster the volumetric flow.

Purely hydraulic proportional valves have the advantage that they do not require additional electrical energy.

Application of the Proportional Valve

The proportional valve is used wherever actuators are not intended to assume defined states. For hydraulic cylinders, this means, for example, that their extension movement must stop at any desired position. Furthermore, the extension speed must always be precisely controllable. Rotational motors can be precisely adjusted in their rotational speed by the proportional valve.

A common application for proportional valves is in the control of construction machinery. Excavators, in particular, have separate hydraulic circuits with an interposed proportional valve for the movement of the boom and the attached work tools. This always allows the excavator operator to move the entire arm to the desired position with high precision. This is very important, for example, for careful demolition of a building, lifting and lowering loads, etc.

Maintenance of Proportional Valves

Proportional valves have an additional seal between the hydraulic circuit and the electromagnets mounted on both sides. These must always be perfectly sealed. If the electromagnet is flooded with hydraulic fluid, this can lead to malfunctions. Regular inspection of the proportional valve is therefore advisable.