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Posts tagged: Hydraulic Valves

Hydraulic Valves: Directional, Proportional, and Servo

For  decades, hydraulic valves have operated in more or less the same simple way: they flipped back and forth, opening first one line, and then another. Normally, one pipe was the ‘do nothing’ line, and one was the ‘do something’ line. But as our understanding of hydraulic systems increased, our desire to manipulate them in more precise manners piqued — and in response, different kinds of valves developed. Here’s a brief summary of the three major types of hydraulic valve.


Directional Valves

Also known as ‘switching valves,’ or more colloquially, ‘bang-bang valves’ because of the noise they made when switching, these are the valves described above. Directional valves have evolved over the past decades, however, from a simple left-right decision to a single valve that can contain several different outputs. Many also moderate the speed of the hydraulic fluid by altering the aperture through which it can flow.


Directional valves are useful, but simple: every change in direction, flow, or pressure requires its own directional valve, making even modestly complex hydraulic circuits enormous in size and expensive to produce.


Proportional Valves

Proportional hydraulic valves use solenoids to allow the valve to take any desired position between and including ‘closed,’ ‘left output,’ and ‘right output.’  This means they can adjust the flow to any proportion between the two outputs. This gives the ability to put speed, flow, and directional controls all on a single valve, dramatically reducing the space taken up by a complex circuit.


In addition, the ability of a proportional valve to adjust the speed of a circuit anywhere between ‘stop’ and ‘full power’ means that a single source and a single hydraulic pump can be used to power a wide variety of hydraulic devices, even if they require entirely different flow speeds and/or pressures to operate. That meant not only were circuits smaller, but there were fewer circuits necessary for any given set of jobs.

Servo Valves

Servo valves aren’t new — they’ve been around since the 1940s — but they’re rare, because they’re expensive. They operate using a combination of input pressure from the hydraulic line and electronic controls to create a valve that doesn’t ‘bang-bang’ — it moves smoothly and accurately. The net effect is that a servo valve lasts a very long time, responds quickly to controls, and has low hysteresis compared to the other two valve types.


Three Points on Understanding Hydraulic Valves

Hydraulic valves are an important part of machines and certain equipments. If you do not work with these valves on a daily basis, you may not understand the importance of the hydraulic valve, the way it operates, and the different parts involved in the process of a working valve.

Point 1: The Functions of the Hydraulic Valve

Hydraulic valves are responsible for directing the flow of fluids beginning from the input port of the valve and coming through the output port. The commonly used fluid is oil. The spool position inside of the valve determines the direction that the fluids flow through the valve. The force of the fluids flowing through the valve is driven by a force motor.

Point 2: The Specific Parts of the Hydraulic Valve

Hydraulic valves have three specific parts that are included along with the valve in order to create the right amount of pressure to allow the fluids to flow quickly, powerfully, and easily. Below are the parts and their primary function:

  • Power Conversion: this part gives isolation between the power valve, external field bus, and the auxiliary supplies. It is also the source of voltages to regulate functional blocks that may occur while the valve is at work.
  • Field Bus Interface and Control: this part gives isolation between the control system and the signals that come from the field bus. The control system turns all information coming from the field bus into instructions for the DSP.
  • Valve Control: this part takes a role in positioning the spool and measuring temperature and pressure. This part is also responsible for indicating certain alarm conditions.

Point 3: The Primary Uses for Hydraulic Valves

The hydraulic valve is a necessity for carrying out certain hydraulic mechanisms. Most typically, hydraulic valves are used in machinery and equipment that lifts heavy objects. But hydraulic valves are also present in heavy machinery, like vehicles, military machinery, and aircraft. If you work on a construction site, in a manufacturing facility, or do everyday normal activities like drive a car, you are most likely using some type of hydraulic valve.

Hydraulic valves are an essential part of major tools, machines, and equipment. The valves are responsible for transporting fluids from one end of the valve to the other. It gives off high pressures and power which makes it powerful enough to manage its role in big machinery and equipment.