Hydraulic valve: Universal component in fluid systems

Hydraulics is the study of power transmission through fluids. It is based on the fact that fluids are incompressible. Applied pressure is therefore distributed evenly throughout hydraulic systems. Hydraulic valves are used to direct hydraulic pressure specifically to a certain point.

Purpose and function of a hydraulic valve

A hydraulic valve controls the flow rate in a hydraulic system. Control ranges from targeted flow restriction to complete shut-off. Hydraulic valves can also be expanded with convenient control systems. These can act on the valve indirectly via electromechanics. However, for many applications, the valve itself already offers numerous options for largely autonomous control.

Types of hydraulic valves

The simplest hydraulic valve is the ball valve. It consists of a block with a flow bore into which a similarly bored ball is inserted. The ball is connected to a lever. When the lever is moved, the flow is opened or shut off. The standard dictates that the flow is open when the lever is parallel to the line. If it is turned 90°, the flow is blocked. The ball valve also allows for a certain degree of throttling. The further the lever is moved toward a right angle, the more the ball valve restricts the flow.

Other types of hydraulic valves include:

• Pressure valves open or close when a minimum or maximum pressure is reached
• Shut-off valves immediately block the flow rate
• Throttle valves gradually restrict the flow rate
• Load-holding valves maintain pressure at a specific point in the system
• Non-return valves allow the flow rate to pass in only one direction
• Directional control valves switch the flow rate between two segments of a system
• and much more.

Advantages of hydraulic valves

Hydraulic valves are manufactured in a wide range and for all pressure ranges. Continuous loads of up to several hundred bar can be easily handled by most hydraulic valves. Their robustness and the wide variety available allow for highly complex hydraulic circuits, enabling extremely safe and convenient systems.

Disadvantages of hydraulic valves

To process high pressures reliably and permanently, hydraulic valves are always designed to be quite massive. They must either be elaborately milled from a solid block or manufactured using die-casting and then precision-machined. This makes them complex and expensive components.

They have two weak points: the seals can fail after several years under permanent high pressure. However, this is usually repairable without great effort. Hydraulic valves can normally be completely disassembled and resealed.

A major problem is cavitation. If the flow rate, along with its pressures and flow velocities, is not calculated precisely, the inner wall of a hydraulic valve can be destroyed. This damage usually goes unnoticed until the dislodged chips have caused significant damage within the hydraulic system.

Maintenance and care of hydraulic valves

Therefore, a complex hydraulic system fundamentally requires filtration. In addition to regular maintenance of the particle filters, an oil analysis should also be performed. This ensures that the internal wear of the hydraulic system is always precisely monitored. Since hydraulic valves can consist of different materials depending on their type and task, oil analysis usually allows defective components to be identified quite accurately.