Valves Used in Hydraulics

Hydraulic Valves are a vitally important part of hydraulic systems, all of which consist of hydraulic pumps, oil reservoirs, hydraulic motors, and/or hydraulic cylinders. Hydraulic valves regulate the flow and direction of hydraulic oil to hydraulic motors and cylinders to control their linear or rotary motion. Hydraulic valves can be actuated directly by equipment operators by moving or flipping levers or knobs, or by automated actuators such as solenoids or pneumatic signals from control systems or computers.

Construction

Hydraulic valves are most often constructed of steel or stainless steel because of the very high pressure of hydraulics, although high grades of billet aluminum are also common. Valve sealing surfaces may be elastomeric or plastic. O-ring seals and gaskets are common also because of the pressure.

Valve Action Types

As with all valve classes, hydraulic valves are available in a number of valving types from simple on-off to throttling, to crossover valves where two hydraulic signals can be cross-exchanged to selector valves where a single output can be sourced from any of a number of inputs at one at a time. Many of these actions are made possible with multiple port spool valves, which can be configured or connected in a number of ways to achieve the desired valve action.

Valve Use

As implied by their designations, valves are designed to perform specific functions within hydraulic systems, the simplest of these being the on-off valve, which either blocks or allows the passage of hydraulic oil to the cylinder or motor. Throttling valves are variants of these which allow regulation of the flow of oil to either speed up or slow down the motor or cylinder. Reversing or crossover valves essentially exchange the two signals--high pressure and return either extending or retracting a cylinder rod or reversing a rotating motor from clockwise to counter-clockwise or vice versa. Check valves are usually spring loaded and biased valves that only allow flow in one direction. Biasing means that the oil pressure must exceed a pre-set value before the valve will allow flow in the correct direction. Relief valves relieve hydraulic pressure.

Levers and Knobs

Many advances have been made in the area of ergonomics, making it easier for human operators to optimally operate machinery safely and efficiently. Watching an expert hydraulic excavator operator dig a foundation with their power shovel is a marvel of almost balletic precision as both hand and foot operated valves are actuated in precise unison. There are also safety systems such as for presses where two isolated valves must be independently operated by two hands to keep them out of harm's way.

Automated valves

Automated valves mimic human motion with hydraulics, but as the part of an automated program that may be controlled by a machine's programmable control system or manufacturing computer system.

References

• Hydraulic valves
• Hydraulic valves and systems