# Hydraulic Directional Control Valve – Complete Lecture.!

hello everybody in this lecture we are going to see about the directional control valves we all know that any hydraulic or pneumatic system will have various important components like pumps pipes or pipelines filters or strainer hydraulic oil storage tanks heating elements electric motors which drives the pump and the hydraulic motors which performs the work now out of all these one important component which renders the hydraulic system useless is the directional control valves the directional control valves alters the direction of hydraulic fluid within the system such that there is no additional pipelines are required the control of the hydraulic fluid can be obtained precise and smooth so this lecture is all about construction symbolic representation and step-by-step procedure of learning all about the directional control valves so in any hydraulic system how do you represent or how do you identify a directional control valve usually these are represented by a square symbol just draw a square this means this is a control valve for two position ones draw one more square and for three position valves draw one more square now each square represents a position remember this so if you have a single square there is only one position valve if you have two squares but it’s two position valves if you have three squares that has three position valves now something must be running through your mind what is a position are what are these positions a control valve slides within a cylinder and then it alters the flow of the fluid so if you have a three position valve as indicated by three squares so the what it means that the valve can operate in three different positions which can connect the ports in different ways so that’s the meaning of it now you would be asking a new terminology which I used ports what are ports ports are nothing but drilled passages are holes through the control valve within which the oil passes through let’s see you have a three-position valve block like this or let’s draw a simple square if I have this valve in the hydraulic system without any passages there will be no oil flow through the system the oil will stop at this point and stop at this point so you require ports to connect the passages so that the oil flows through it so in this case I can make the connection like this so that the oil flows from this port to this port so in this case this is the entry port and this is the exit port entry and exit so on the valve block of the directional control valve somewhere the oil should enter and somewhere the oil should exit so with that in mind let’s proceed with the basic three position valves we have seen that to recap we have seen what our directional control valves what our positions and how to identify the number of positions which is three square means three position now we are talking about ports what are ports ports are nothing

but drilled passages through the valve block so that the oil or any fluid can enter and exit to perform work so we have seen what are ports the next is how many ports can a control valve have how many boats ok so a control valve based on the number of positions it can have as many boats as possible let’s let us take a square in the square it can have two ports three port and four port and rap scenarios you will have five ports so a single block a single square or a single position can have five ports depending upon the type of application now you must be wondering why I have drawn an inverted T over here so to represent in any hydraulic drawing we have to draw each and every port as inverted T so I will draw once more a three-position valve so that’s one square one position the second Square and let this be the third square there is a three position valve so to indicate the ports it is usually represented in the centre that a central block this is a single port the second port the third and fourth port so now we can always say that this valve is a three position four port directional control valve this is how we give the nomenclature for this control valve if the valve is having just two squares or two positions we say that it is a two position four port directional control valve you have to count the number of ports and number of positions and say that it is a directional control valve now in this case we have four ports so let’s name the boards so that we can identify them because we have to connect the inlet of high-pressure fluid and exit and then the return so it is always better to name them let’s name it as B the port B the port T port a and port B now we have a new terminology which is coming into place that is tandem Center this is very common in any hydraulic circuit or if somebody asks you in an interview what is a tandem Center it it means a position there is a directional control valve with the ports P and T connected like this and a and B are blind or open like this this means any high pressure fluid from the pumping system this means any high pressure fluid a the hydraulic oil or high pressure air can enter through the port P and then it returns back to the tank T so that’s I that’s why I indicated it as port P that is pressure and T back to the tank reservoir we can put the tank or represent it as like this and then just scribble like this this means it’s going back to the tank running back to the tank now port a and B are connected usually to a piston or a hydraulic motor which performs the work now this position where the port P and D connected in a and B left disconnected our tandem Center let’s have a recap we have seen what are the basic components of hydraulic system out of which directional control valve are very important and we have seen water directional control valves with regards to directional control valves we have seen the position that is what our positions are how will you count the position with the 2 square it’s two position 3 square it is 3 position and then we move on to ports the number of ports means the number of drilled passages through which oil can flow in this case this is for port 3 position

directional control valve and after which we have named the port’s P stands for pressure T stands for returned back to the tank a and B are the ports which are connecting to any hydraulic piston of motor and then we saw what our tandem center or what is a tandem Center which is this position let’s move on to the next topic Springs on control valve let’s say I take a classic example of a three position four port directional control valve these are the ports pressure back to the tank or drain you connect it and this becomes the tandem Center now how does the valve closed our get centered I’m going to put Springs here which means if the valve is going to move either way the springs are going to bring it back to the center that’s why I have indicated Springs at the both the ends now let’s see how does that work so to understand the working of the springs we have to actuate or shift the valves how do we shift it we can draw the ports like this now I’m going to have a lever or a button like this and here are your Springs now before that we have to understand what are the ways through which the oil can travel we have seen position that is position 1 2 & 3 ports for port PT and a B now you have to now you have to draw or understand the positions what are these positions conventionally these will be the direction okay so now with this in mind here you have the tandem Center and here are the first position that is this is the first position the second is the tandem Center the third now I have Springs I have an activating lever this is right side out the lever and this is the left side when I’m going to push this lever to the right what is going to happen the boats are the cylinder the spool valves inside the cylinder of the control valve are going to shift which means this particular position the ports are going to shift a will come here B will come here P will come here and T let me use other color so that we can understand better when I move it to right what happens is the valve shifts so that the port a comes here the port B comes here P and T there is pressure and back to the tank comes here so the high-pressure fluid from the pump goes through this direction through this arrow goes to port B so these are the passages through which the oil or fluid passes through to B and then there might be some piston or motor the hydraulic fluid and the pressure performs work and then the return exhaust of drain comes through port a and this is connected back to tank that goes to the tank so let me indicate the high pressure fluid which is entering through both P as red and color that’s high pressure it goes through both B and then the low pressure or the egg sauce comes through let’s say let me use black color the exhaust comes through sorry I music Brown exhaust comes through both a and back to the tank T so this is what happens when I move the lever to right

now it performs some work as I move the lever now what happens when I release the lever as I release the lever the spring pushes back and brings the valve to this position that is standing center position then the flow of fluid stops going to the passage B or the both DNA and the high-pressure fluid goes to P and comes back to the tank which means this is just circulating no work is being performed either moving the piston or the pump because these two ports are disconnected so as I move the lever the wall shifts and the spring is compressed and thus it is charged I said release the lever the spring pushes back and thus you get the tandem Center position again now I can have one more lever that is the same lever can be moved to the left and then valve can be shifted however for clarity I am drawing one more lever over here now what I’m going to do is move this lever towards the left so that the parallel arrows this comes to here which means let me explain it clearly to you you have the three position control valve you have the ports here pressure back to the tank both a and B you had the cross which we have seen in the last light and now we have the parallel stuff or parallel ways here and you have the activating lever and you have one more activating lever on this side I’m sorry it doesn’t come straight now I’m going to add the spring here okay now we have seen oh sorry I forgot to draw this a tandem Center usually because the pump will be running high-pressure fluid will pass through and then circulate back to the tank until and unless you give an order for the valve to shift or move we have seen the movement of the valve and it’s working when I move it to the right now we are going to see the movement of the valve when I’m going to move it to the left as I push the slaver like to the left the spring is going to get charged as the valve shifts to this position so here comes the boat eh here comes the boat B just directly it comes and here comes the pressure and here comes back to the tank so the high-pressure fluid which I will use our red color the high-pressure fluid from the pump passes through this boat and then goes to a and then the exhaust will come from the boat B back to the tank so in the previous slide we saw the high-pressure fluid going through a cross that is B – B I’ll write it for you in the previous that is right shift or the right lever when you operate it the ports P and B are connected and a and T are connected when I move it to the left here P and a are connected B and T are connected so it just high pressure oil goes and then comes back as I said earlier the spring gets charged or compressed when the valve shifts when I release the lever the spring pushes back and thus it attains the tandem center position that is the neutral position which means the high pressure oil now circulates back to the tank so with this in mind here is a three position four port four-way spring-loaded manually operated directional control valve so let’s recap it once again how do we name it we name it as three positions that is one first square the second square the third square so three position and for port number of ports on each

position is for four ports then you can always say this is manually operated or lever operated manually operated spring-loaded a spring centered spring-loaded directional control valve so that’s how you name a hydraulic or pneumatic directional control valve here is the nomenclature now you can also say that it’s a three position four port for vay which means you have four different ways in this valve it can operate with the first way is this second way is this third is this and for testers so these are four ways in this valve that has two ways across and two ways are parallel so that’s why we can always say four-way so that concludes the first lecture on the basics and construction with symbolic representation of a directional control valve you