Image Credit: The Hydraulic Centre | Harrier Fluid Power | Bailey International LLC
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.
Hydraulic Valve Types
There are many types of hydraulic valves, including:
- Angle valves admit media at an angle and permit maximum flow.
- Ball valves provide tight shut-off and reliable control.
- Block and bleed valves use a small port to depressurize the space between the inlet and outlet.
- Check valves prevent flow reversal. Control valves modify fluid flow.
- Control valves or proportional valves are power-operated devices used to modify fluid flow or pressure rate in a process system.
- Cartridge valves are directional control valves that are inserted into manifolds to provide a cost-effective, compact system design.
- Directional valves steer process media through selected passages.
- Drain valves are used to remove surplus fluid from a system or container.
- Needle valves have a slender, tapered point at the end of a valve stem.
- Poppet valves open and close ports with a sealing device that includes a disk, cone, or sphere.
- Pressure relief valves remove excess upstream pressure. By contrast, regulators maintain a constant outlet pressure.
- Safety valves contain a thermal sensing component that opens or closes in response to temperature changes.
- Shut off valves close a line to stop flow when a pre-set condition occurs.
- Solenoid valves are electro-mechanical devices that utilize a solenoid to control valve activation.
- Spool valves are actuated by a rotary or piston-like spool that slides back and forth to cover and uncover ports in the housing.
- Stack mounted, sandwich, or modular valves can be assembled to create a valve block.
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.
Explaining Directional Control Valves: Types and Terminology
Video Credit: Bailey Hydraulics
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 - both double-port and multi-port hydraulic valves are available.
Media temperature is the maximum temperature of the media the valve is designed to accomodate 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.
Hydraulic Valve Standards
ISO 6403 - HYDRAULIC FLUID POWER - VALVES CONTROLLING FLOW AND PRESSURE - TEST METHODS
ISO 6263 - HYDRAULIC FLUID POWER - COMPENSATED FLOW-CONTROL VALVES - MOUNTING SURFACES
SAE J748 - HYDRAULIC DIRECTIONAL CONTROL VALVES, 3000 PSI MAXIMUM
SAE J1235 - MEASURING AND REPOTING THE INTERNAL LEAKAGE OF A HYDRAULIC FLUID POWER VALVE
Related Products & Services
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.