Friday, 29 April 2016

DIRECTIONAL CONTROL VALVE AND ITS CLASSIFICATION

DIRECTIONAL CONTROL VALVE AND ITS CLASSIFICATION

We were discussing various types of pressure control valve such as Pressure reducing valve, Pressure sequence valve, Pressure relief valve, Pilot operated pressure relief valve and Counter balance valve in our previous posts.

Now we will see here the direction control valve in this post, we will start with brief introduction of directional control valve and further we will see the various types of directional control valves in this post. 

 
Let us see first here, what is directional control valve? 

Directional control valve (DCV) is a device which is used in hydraulic units in order to permit, restrict or block and change the direction of fluid which is flowing through this. Directional control valve will be operated by receiving the signal and signal might be manual, hydraulic pilot signal, electric signal or electronics signal.

Direction control valve, as name indicates, will have to control the direction of fluid by moving its movable components in a hydraulic unit.
4/3 Directional control valve

Directional control valve internal construction

Classification of directional control valve

Let us see here the various types of directional control valve used in hydraulic system.
If we look the design features of internal moving components of directional control valves, we will see that directional control valves will be of the following types.
Moving element of DC valve

Poppet type directional control valve

There will be one ball or piston that will move on and off a seat. Such types of valves will be operated usually by manual method.

Rotary spool type directional control valve

There will be one spool which will rotate about their axis in order to change the direction of flow of fluid in hydraulic unit. Such types of valves will be operated usually by manual method.

Sliding spool type directional control valve

There will be one spool which will move to and fro i.e. spool will slide in the bore in axial direction. Such type of directional control valve require good practice of maintenance as dirty hydraulic fluid will damage the valve land mating surface and therefore accuracy will not be secured as desired. Valve spool may stick and may not work as desired if condition of working fluid is poor.

 
Let us see the various types of actuation method to actuate the valve element of directional control valve and on the basis of valve element actuation method, directional control valves are basically classified in following types as mentioned here.

Method of actuation of DC valve

Manual actuation directional control valve

Spool of directional control valve will be operated with the help of manual actuators for example push button, pedals and hand lever

Mechanical actuation directional control valve

Spool of directional control valve will be operated with the help of mechanical elements such as roller and plunger, rack and pinion or roller and cam.

Electrical actuation directional control valve

Spool of directional control valve will be operated with the help solenoid action.

Hydraulic actuation directional control valve

Spool of directional control valve will be operated with the help of pilot pressure and therefore such types of valves are also termed as hydraulic operated directional control valve.

Pneumatic actuation directional control valve

Spool of directional control valve will be operated with the help of compressed air. Compressed air will apply the force over a piston which will be attached either end of the valve spool.

Let us the directional control valve types on the basis of the number of switching positions and number of connection ports.

 
Normally directional control valves, used in hydraulic units, will have two or three switching positions. Usually directional control valves are displayed as NP/NS. NP is the number of connections ports with directional control valve and NS is the number of switching positions. 

Let us consider one directional control valve specified as 4/3 DCV, it indicates that there are four ports connected with directional control valve and there are three switching positions. Out of four ports of DCV, one port will be connected with pump and hence termed as pump port, one port will be connected with tank and hence termed as tank port and rest two ports will be connected with actuators and hence termed as working ports of DC valve.

Directional control valve each individual switching position will be displayed by one square and flow directions will be displayed by arrows. Blocked ports will be indicated by horizontal lines. Direction control valve with 3 switching position will be indicated by three adjacent squares. Middle square will indicate the neutral position and rest two squares will represent the extreme positions of DC valve.

Let us see the symbolic picture of directional control valve 4/3DCV

Directional control valve 4/3DCV

On the basis of path of fluid and working ports, DC valves are classified in following types as mentioned here
  1. Shuttle valves
  2. Check valves
  3. Two way valves
  4. Three way valves
  5. Four way valves
Do you have suggestions? Please write in comment box.
Image courtesy: Google

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