Hydraulic valves contain and transfer the flow and pressure of hydraulic fluid in hydraulic power systems. They range from simple shutoff valves to precision control valves.

In their unpowered state, hydraulic valves can be normally open (open center) or normally closed (closed center). Hydraulic valves with a tandem center connect the pressure and tank ports, but block the service ports to allow system unloading and isolation of the service lines. Devices with a float center allow the supply to be shut off and enable the load to move to other services.

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Explaining Directional Control Valves: Types and Terminology. Video Credit: Bailey Hydraulics / CC BY-SA 4.0

Types of Hydraulic Valves

Hydraulic valves can be almost any valve, i.e., check valve, drain valve, control valve, and many more, as long as the valve restricts hydraulic fluid they can be classified as hydraulic valves.

For a full description on types of valves and their actuators please read Industrial Valves.

Specifications

Performance specifications for hydraulic valves include:

• Valve sizes are typically measured in inches (in).
• Pressure ratings are usually measured in pounds per square inch (psi).
• Ports are available as both double-port and multi-port hydraulic valves.
• Media temperature is the maximum temperature of the media the valve is designed to accommodate expressed in degrees Fahrenheit.
• Flow coefficient equals the number of gallons of 60° F water that flow through a valve at a specified opening with a pressure drop of 1 psi across the valve.
• Connection type - there are several connection types for hydraulic valves. Some devices have internal or external threads for inlet or outlet connections. Others use a bolt flange, clamp flange, union connection, tube fitting, butt weld, or socket weld. With compression fittings, tightening a nut on one fitting compresses a washer around the other. With metal face seals, a gasket is sandwiched between two fittings.

Standards

• ISO 6403—Flow and pressure valves for hydraulic systems

• ISO 6263—Hydraulic fluid power - compensated flow-control valves - mounting surfaces

• SAE J748—Hydraulic directional control valves, 3000 psi maximum

• SAE J1235—Measuring and reporting the internal leakage of a hydraulic fluid power valve

Image Credit

Carr Lane Manufacturing