Hydraulic Valves Information
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
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.
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.
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
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Butterfly valves control flow through a circular disc or vane by turning the valve's pivot axis at right angles to the direction of flow in the pipe. They are normally used as throttling valves to control flow.
Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves.
Globe valves are linear motion valves with rounded bodies, from which their name is derived. They are widely used in industry to regulate fluid flow in both on/off and throttling service.
Needle valves are small valves used for flow control in liquid or gas services. The fine threading of the stem and the large seat area allow for precise resistance to flow.
Pinch valves include any valve with a flexible elastomer body that can be pinched closed, cutting off flow, using a mechanism or fluid pressure.
Solenoid valves are devices that use a solenoid to control valve activation.
Solids valves are used to control or regulate the flow of powder, granular and other bulk solid materials along a process line, or to and from process units, storage bins, conveyors and product packaging.