HYDRAULIC VALVES
What is Hydraulic valves?
Asking “What is a hydraulic valve?” is like asking “how long is a piece of string?” The variations available to the hydraulic designer are absolutely astounding, not only because of the myriad types of valves on the market, but also because of the numerous manufacturers making them.
A hydraulic valves properly directs the flow of a liquid medium, usually oil, through your hydraulic system. The direction of the oil flow is determined by the position of a spool. A hydraulic system can only function - as per requirements - by using valves. Thus, you should always look for the correct type of hydraulic valve to serve your intended purpose. The required size is determined by the maximum flow of the hydraulic system through the valve and the maximum system pressure.
The most basic description of a valve is a mechanical device that opens and closes, most often to control the flow of fluid—liquid or air. Valves exist in nearly every industry, from automobile engines to the foundries that cast the engine’s valves; yes, there are valves on the machines that make valves.
So a hydraulic valve is just a device that opens and closes to allow the flow that will move actuators and loads. It sounds simple, but there are various techniques used in hydraulics to allow this to occur. Valves can be mechanically operated (by handle, knob or cam), electric solenoid-operated, or pilot-operated (air or hydraulic pressure actuates the valve). Some valves use the pressure of the circuit’s fluid to actuate themselves, like with relief valves. Valves can also be actuated with cables, levers, plungers, torque motors and so forth.
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Hydraulic valves help regulate the flow of fluid within a hydraulic circuit. They can be used to completely close a line, to redirect pressurized fluid or to control the level of flow to a certain area. Designed in a wide range of styles, they can be controlled manually or automatically, by physical, mechanical, pneumatic or electrical activation.
Hydraulic valves are manufactured in the same categories as other fluid control valves, including ball, bypass relief, check, regulating, pilot-operated, proportional and directional. Manufacturers use a wide range of materials, such as carbon steel, stainless steel and various synthetics. The choice of valve type and material is dependent upon the application, as different materials and designs have different pressure and flow ratings. Valve manufacturers will list the valves pressure rating at a certain temperature, as well as the minimum and maximum temperatures that the device can withstand. Also provided will be valve diameter, typically measured in inches, as well as the mounting flange dimensions and specifications, which should both be matched to your system.
Ball valves are generally among the more simple hydraulic valves available. They involve a handle or similar control that is linked by a metal stem to a ball within the valve. The ball has a central hole and allows fluid flow when properly aligned. When the ball is turned so that the hole is perpendicular to the flow of the pipe, it stops the movement of fluid. Relief valves provide an alternate passage for fluid when it reaches a certain pressure, thereby helping to regulate the pressure of the entire system.
Other, more complex valves are available, which can be activated by compressed air, electricity or other remote means. These control valves can be used to specifically regulate the parts of the system receiving hydraulic fluid, as well as the level of fluid being supplied.
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A hydraulic valve properly direct the flow of a liquid medium, usually oil, through your hydraulic system.
Hydraulic valves are available in a variety of sizes and according to multiple International Standards. Hydraulic valves are available with many different mounting styles: e.g. mounting in pipe lines, with threaded connection as cartridge valves, subplate mounting or flanged mounting. Hydraulic valves are subdivided into three main categories: directional control valves, pressure control valves and flow control valves. All valves operate a different function in the hydraulic system.
You can use hydraulic valves to switch at a certain pressure or adjust the direction and flow of the fluid.
Different valves function in different ways. Check valves permit free flow in one direction and block flow in the opposite direction. The directional control valve is used to pass on the pressure medium (i.e. flow) in an orderly fashion to a particular direction. Pressure control valves switch (or control) at a certain pressure; the switching pressure may be adjusted on the valve. Flow control valves regulate the flow this is done by adjusting the size of the bores (orifices).
How many types of hydraulic valves are there?
There are nearly as many types of hydraulic valves as there are ways to actuate them. You have solenoid valves, flow control valves and pressure control valves as the three primary groups of valves, but each of those also have their own sub-species. Solenoid valves can be poppets or spool valves, and either of those can be electro-proportional or servo-controlled. Flow control valves can be hydrostats (also known as pressure-compensators) or simply needle valves, and can be used to meter-in or meter-out fluid.
Directional Control Valves
Directional control valves can control the start, stop and change in direction of flow of a pressure medium (i.e. hydraulic oil). Hydraulic valves as poppet or spool valve.
As the name suggests, the directional control valves are used to direct the flow of fluid through the system. These valves can pause and restart the movement of fluids. Also, they can change the direction of fluid flow. Check valve, prefill valve, spool valves, etc. are the various directional control valves used for ensuring proper flow of fluids within the system. The check valves and prefill valves are non-return valves. Check valves block bidirectional fluid flow and control the pressure. Whereas, the prefill valve pass the fluid through the hydraulic cylinder and tank. Spool valves control the fluid flow within the system.
The 2-way directional control valve is the simplest directional control valve that has two ports called inlet and outlet. These valves are used in water faucet and it can start or stop the fluid flow. A 3-way directional control valve has 3 working ports called inlet, outlet and exhaust. They are used in single acting cylinders and the third working port can block the flow of all ports. Similarly, there are 4-way valves and 5-way valves used in double acting actuators and air circuits respectively.
Pressure Control Valves
Every pressure control valve switches at a predetermined pressure setting. This occurs either gradually with variable throttle (control) or suddenly with a fixed throttle (switch).
The hydraulic pressure control valve plays a vital role in controlling the leakages and bursting of pipes. Pressure control valves regulate the pressure of the fluid passing through the pipe by releasing the excess pressure. These valves maintain the pressure as entered manually by the operator.
Hydraulic pressure relief valve, sequence valve, counter-balance valve and pressure reducing valve are the different types. The counter-balance valve creates dynamic control within the system and the sequence valve, detects the extreme pressure. The pressure relief valve is one of the important types that set the pressure limit by transferring excess back to the tank.
Yuken hydraulic pressure
Pressure control valves are the most varied of the three primary groups. They open and close, just as other valves, but these are more dynamic, with linear rise and fall of performance, based on the pressure acting upon them. Most pressure valves (like relief valves, sequence valves, counterbalance valves, and so forth) are normally closed, meaning that it takes a rise in pressure to open them. However, the pressure-reducing valve is the only one that closes when pressure rises above a set point.
Proportional Control Valves
Proportional hydraulic valves are able to control the opening to flow proportionally instead of gradually, as is the case for most standard hydraulic valves.
Flow Control Valves
Flow control valves manage the flow by decreasing or increasing the opening at the throttling point. This helps to determine speed of movement for the hydraulic actuators.
The flow control valves are used for controlling and adjusting the fluid or gas flow through the system. These valves can optimize the hydraulic system performance. Flow control valves will monitor and regulate pressure fluctuations in the system. It prevents the flow towards ill-founded system components.
Diagram of hydraulic valve operation
Hydraulic valves image
Yuken hydraulic valves
Hydromax hydraulic valves
Parker hydraulic valves
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