Senior Editor Mary Gannon discusses the various styles of hydraulic valves—including pressure, directional, relief, flow control, and proportional valves—and where and why they are most commonly used.
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Hi, I’m Mary Gannon, Senior Editor with Design World, here with a look at hydraulic valves, which govern direction, pressure and flow of hydraulic fluid, enabling smooth, safe and controlled use of actuators.
Directional control valves help to control the path of fluid flow. Their construction ranges from cartridge valves to monoblock valves, or subplate mounted valves to inline valves.
The most basic directional valve is the check valve; it allows flow into one work port, and blocks flow from coming back through the opposite work port. Pilot-operated valves are more complex directional valve designs.
Directional valves are often described by the number of “ways” fluid can travel through them, and also by the positions available to be shifted into. For example, one would describe a double-acting single monoblock valve as “4-way, 3-position,” or simply a “4/3 valve.”
Directional valves are available in monoblock or sectional valves, common to the mobile industry, as well as subplate mounted industrial type valves. Cartridge valves installed into manifold blocks are common in both mobile and industrial applications.
A pressure valve is any component designed to limit pressure. They are usually based on a poppet being pushed against a seat with an adjustable spring.
A relief valve controls maximum pressure for the entire system or a sub-circuit of it. Most other pressure valves, including sequence valves, counterbalance valves and brake valves, are based on the relief valve’s spring-loaded ball or poppet. Pressure-reducing valves limit pressure downstream of themselves, rather than upstream.
Flow control valves control or limit flow. They can sometimes have multiple ports, such as with a priority flow control. They are able to provide controlled, fixed flow to one part of the circuit.
Flow controls are ideally pressure compensated, which allows the valve to maintain its set flow regardless of load-induced pressure changes. Pressure compensators are a type of flow control valve.
Proportional valves are considered both flow and directional valves, and are able to meter flow and control the direction that flow is metered in. They use pulse-width modulation to maintain voltage and control current.
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