 Welcome to the lecture, this is on the symbols in oil hydraulics. In lecture 2, we have already discussed about this, how the hydraulic symbols are built and against the components what is the symbols. Also in the last lecture this earlier to this in the tutorial section I have also discussed that ISO symbols and the glossary. And here we will show some simplified symbols who are not strictly the ISO standards, but used in industries. Now, first of all we will recapitulate the some symbols that as I have told this is a puppet type cheque valve, but it is pilot operated so that we can make the line through. That means the normally oil is coming from this side and it cannot go from this side whereas we can move this puppet to have the flow in this direction. So, which is operated actuated by in this case it is a armature means it is a solenoid operated. If we move this one in this directions then oil will grow from this to this. If the oil come from this sides and if you do not move this one then oil cannot go in the other sides. And this is a single plate valve and it is a pneumatic valve or pneumatic actuated not pneumatic valve may be pneumatic actuated to have this 4 by 2 position valve. And this is 4 by 2 position valve and spring return and may be solenoid solenoid it is solenoid solenoid operated and this is just the opposite of this one. And in this case this is solenoid operated no spring return no spring positioning whereas some detent positions are there. Similarly, if we look into the rotary actuator which we have discussed earlier that this is a symbol for rotary actuator in this case the triangle is not filled means this is for the gas or air that this means that this is in compressor. In this case this compressor of 2 stage in the first stage it is the gas or air is pumped with a certain pressure and then in it goes through the second stage and ultimately the output is of high pressure to make such develop such pressure in a single stage size of the compressor will be used. In this case the this is rotary pump and hydraulic pump and this is a fixed displacement this is a double pump by a single shaft both the pump is being operated one is of low flow one is of high flow and this has usually to off the load when there is high flow is required or sorry low flow is required such pump are used or even for low flow both the pumps are work sorry high flow low pressure both the pumps are working and high pressure relatively low flow either of this pump is working. So, this is basically used with proper circuit for energy saving. Now we will go for much simpler symbols which are strictly may not be ISO standard but used in industries. Now first of all we shall consider the symbols for hydraulic tubes pipes hose etcetera. Now this is of course not the symbol for the hydraulic symbol component symbols rather this is the central line in a system if we would like to maintain a central line usually this line is used dashed line is pilot line also this is the sorry the top one is used enclosure outline that means if we sometimes we would say that there are a manifold actually manifold means it consists of few valves together and sometimes the symbols is like that all the symbols for all the components like a pressure valve direction valves these are drawn separately and then it is put in a envelope enclosed by this line this means that it might be a manifold. If you look into the component this is as if a single component but inside that there might have a directional valve a check valve and a pressure relief valve pressure control valve and so on. Now this dashed line means this is usually pilot line why usually I would say this pilot pilot line now there is a dash but small dotted line exhaust or drain line. So, in a drawing suppose only these two lines are given you may not be able to distinguish which is the exhaust and which is the pilot line but in a drawing if these two lines are used careful study will show that this line is for pilot line and this line for drain line. Now very often we will we have to use the line one pipeline is crossing other while we are drawing the circuits in physically we can say that these are severed to 5. Now suppose a line is like that and a line some lines are like that what does it mean line crossing 90 degree intersection not necessary this means that this are usually suppose these two lines are crossing each other but they are not intersecting in that case we present like this or we may present like this this line is crossing over this line like this depending on which one is crossing over this but as well sometimes these are presented like this and of course this is a confusion if you use this one and this one you may we may find we may think that this might be a connected lines but if these lines are basically not connected they are crossing each other even this one is also like that if we would like to show that there is a junction point four lines from four direction and connected we should better use this one this indicates they are actually connected at a point this is a single point you can say where they are connected this might be also like this this is three point connection is like this of course suppose if we do not provide this dot and line is like this this means that this is connected if we increase the line then there will be confusion whether it is a crossing point or connecting point but if simply without dot if we mean this the three lines are connected at a point so that you should understand and sometimes looking into the components and function we shall not confuse that this one either whether is a crossing or junction point this is usually crossing point not a junction point so these are for all junction point you can say these few are and then if it is a flexible hose it is like that now this is a flexible line now this is usually this flexible line means it is I would say not the main hydraulic lines this might be even electrical lines or some other lines which is flexible but in a system particularly in hydraulic system if we use the flexible lines it is presented like this however while we are making such a drawing then you will find that this line is also a straight line not like this and while we are mentioning this components so looking into a line straight line it does not mean whether it is a flexible or a solid line I mean solid conduit pipe only thing we have to mention that component separately but one can use such symbols now this solid line means usually main line then if this arrow is given this is a flow directions usually hydraulic medium why usually if it is filled with hydraulic sorry if this triangle is filled then this is hydraulic and if it is not filled then it should be air or gas now this is a connected usually this quick connector quick connector or disconnector it is like that called so that is symbolized like this say quick connector means usually you will find that when the machine is under operations particularly for training purpose we need to open a line and it is connected and again need to connected now this hydraulic line connections we must take care so that there is should be no leakage and other things and also in many cases we have to use the ferrule properly pipe connections solid pipe connections in that case to just dismantle that connection and to give a new connections it may take lot of time so instead of that usually such ends are with a flexible hose and a quick connector what is quick connector it is like that even if this is under pressure in operating conditions if you connect then these two will be connected first of all in the connections that outer leakage path will be prevented then internal connection will occur to give through passage of the oil from one side to other side that means a good mechanics a good user he can quickly connect this connector without a single drop of oil to the outside and the so this already I have discussed these three lines and then this is a plug point if many in circuit sometimes you will find that a line is there and then this is a cross so looking into this we can suggest a plug point usually such plug points are kept not very often but time sometimes we can have another system to be connected there or may be some measuring point we can put some gauge there and we can measure the pressure etcetera. Now other symbols which is hydraulic connector check valve etcetera now if in the line such arrows are given then this flow can be restricted that flow can be regulated now solid lines means main lines and this is usually for the pilot lines and this is with a fixed restriction and this one is the flow divided this flow is being divided into two directions now what is there you can say that any T connections can be done but this divided is designed in such a way there will be equal resistance so if the pressure demand and both the line are same then flow will be exactly divided into two parts equal parts so flow divided is used for that purpose now this is a throttle valve in that case just a restriction in that case this is throttle fixed or variable adjust but these are usually used to control the flow now this is check valve with a spring return this is a check valve without spring return and this is again quick disconnect with check valves this one the quick connector and check valve and this is a connected and this is disconnected this means that in a circuit if we present this one that means that line is connected by quick connector and if we show that this symbols this means that normally it remains disconnected now in this case what we find that this is same as before only thing this is only one check valve is then another has no check valve then this is quick disconnect without check valves there is no check valve depending on the purpose these are used say for example if we use this one in a line then normally what we find that oil from this side cannot move this side and oil from this side cannot move the other side then what is the use of such connections usually these valves are being operated by an external operation is there pilot operated that means normal condition is a check valve but if you send a signal through the pilots then it will be connected in this case suppose we do not need such pilot operations simply connect and to disconnect then this will be used now filter in the filter I have we have not shown that ISO glossary but in case of this filter or even simple strainer filter or strainer we use this diamond like a block this line is the through line and here one dotted lines now in this case this filter separator with manual drain there is this is basically a separator and manual drain is there and this is automatic drain if we put this one automatic drain and if we use this filter separator with automatic drain and this one oil lubricator with manual drain and this one oil lubricator less drain there is no drain is there I think this one one of that should be drain line means dotted line should be there I think so this is oil lubricator with automatic filling this is a cooler when you see this arrow is going outside it will be cooler when you this is also cooler but this is basically it is also shown that some liquid is flowing through why liquid because this arrow are completely darkened now when this arrow is going inside then heater just look at the difference between the heater and cooler this is also heater inside arrows indicates introduction of heat yeah it might be like this or it might be like this we can put in any direction these are basically heater now if we look into this what we have already studied in IOS symbol some glossary you can see this is cooler because the arrow is outside the heat is going out so you can compare with this only thing in this case this is filled and this is not filled that means this is air cooled or something like this in this case as we find this we can again compare with this one but we get some additional two lines here and then this must be either cooler or heater and then we can see that these are the two components what we can what it looks like this is the main system oil in and out and this is the cooling agent in or out now a reservoir may be a simple tank do not confuse with this the accumulator because accumulator will have no line in the other directions and this is a small reservoir and these are reservoir so if it is shown that it is open then it is usually vented no reservoir will be without any cover there will be cover has to be because when the oil is exposed to the air so more oxidations and more deterioration will be of oil will occur to prevent that it should be closed but usually it will be vented that means inside if there is a gas that gas will automatically come out when certain pressure will increase but in some cases we need to this reservoir is pressurized and closed and their venting is only may be it is again regulated by some pilot system some system signal is there which will vent normal venting is not there so for that pressurized we can show that the reservoir is like this now this reservoir is baffle what is baffle usually you will find inside the separator is there so first oil is coming over here and then it is going this side so many contaminants will reduce remain at this side and suction is usually in the opposite side so return in one side and suction is other sides and again such baffles are like that so this is connected at the bottom then you will find another baffle is top portion is clear oil can flow then next baffle you will find it is connected with the top and oil can flow like this so these baffles are used with a one is connected with the top and one is the bottom so that return oil when it is coming over there first of all the heavy particles that will be remain here then oil will flow and then it will flow like this then again flow like this by that process first of all the better heat exchange will be there secondly the adhesion will be removed that mixing of the air that will be removed it will also act somewhat anti foaming and in other sides you are getting relatively stable fluid for again for the suction so when you would like to mention that the reservoir with baffle is required you can present like this now this is reservoir with connecting lines the connecting lines are there above fluid level sometimes the connections are above fluid level and if you show this below fluid level not lever this is this should be level now this connections you can show then you can mention here that one is for suction another is for return such things but you should remember in both cases both the suction and suction has to be within the oil obviously but return line also to be within the oil otherwise there will be too much foaming but this is a special case where you are keeping some lines above the oil some pressure purpose in that case you have to indicate like this this is air bleeding this in that case if you present this one the air bleeding is necessary now this you see do not confuse with this pump other thing this is a pressure gauge with an arrow inside in a circle this is a pressure gauge again if you draw a straight line and with these symbols means it is a flow control but once you present like this these two lines in a circle and this inside it this is flow meter now accumulator will be will look like this these are look at this reservoir and accumulator if you add one line there that will be reservoir if you do not add a line there and if you simply put like a bearing then this will be accumulator this is also an accumulator but it is a gas charge this side a gas is there now if this accumulator is spring loaded then in that case this line and there will be a spring accumulator means that here this will be gas or air and here the liquid so while we are trying to present an accumulator either you can put simply and you can specify this or if you are if you are specific about this to show that this is a gas charge you can use this one it is a spring loaded you can use this one now as well we have to present the prime over normally you will find in most of the cases this electric motor then you can just put like that em or if you use that engine then you put M engine we call engine but usually it is also called motor electric motor and IC engine is also a motor so you can specify like this and you can see this this not much difference but it is a power line usually you will find with a pump sometimes this symbol is given power source oil or air or oil no this is a power source with air or oil so this will be filled in case of oil or not filled in case of air and this will be filled in case of oil or oil and where is power line this is a line is like this but very very difficult to distinguish with this main hydraulic lines a coupling is shown like this then the crossing power lines we have learn earlier we can use this one this is non-connected if you would like to show at a junction point connect what you have to do move one of that slightly right side or left side and show the connection that means this is junction point otherwise this is a crossing line but best way is that you can cross like this or you can cross like this now this is a drive shaft not so much meaningful but this is a drive shaft and rotating coupling is designated by this one and this is a on of simplified switch that means this on of switch usually not pilot operated it is normally manual operated and this is just to stop the line you will find that either it is a just single lever a ball joint is inside a ball is inside ball with a hole that if you make the line connected to the hole then it is being operated or you just simply rotate in the 90 degree directions it is off. So, this is sometimes used in the hydraulic lines now another important aspects in many cases the color codes are used red means operating at system pressure blue means return line or exist flow green means intake or drain flow yellow means measure usually meter flow or control line flow and then if you use orange then it is reduced pilot pressure reduced pilot pressure and violet means intensified pressure very high pressure and if there is a blank that usually inactive lines that means this is filled with water sorry filled with liquid but no pressure is there this is mainly used for hydraulic lines. Now we have to make this orange and difference between orange and red usually you will find in a same drawing this you can understand the difference but where only say suppose red line is there do not confuse with orange looking into a little studying to the components will give you the idea whether it is pressure line or the ordinary line. Now the then the lever cam etcetera these are designated by as you have seen say this with this double lines with a component say this is the main component with that if this symbol is added what it is this is a practically rectangular box with one line is going outside that is a hand lever. Say in earlier when we are learning the ISO symbols and glossary we I was telling that this extended line means hand lever. So, this is an indication of hand lever then this is a if it is slightly inclined and one line is left side in this is a foot pedal and when this rectangular is just rounded the end is rounded then it is a cam follower. Now if it is a bottom sort of things then it is a roller operator. Now if it is with a symbol like this then it is a lever this a lever is fitted over there. Now this hand operated means in many cases you will find that lever say a manual valve there a lever is given. The lever means that usually one point it is fixed and some intermediate point or may be the extreme point is there to move the other component the one is fall component another is to move the component. So, that is lever and hand lever may be that one also so hand lever may includes this hand this type of lever also. But hand lever means it is for operation a lever is there it might be a simply shifting or with a fall crumb like that. Such details you have to mention perhaps by writing or showing the little design. Now this is again this may be this general symbol is that manual it is like that. So, I think this line will be completed up to this point. But only important is there the other side is extended this line is extended and say this is a cam or toggle it is meant by this one this is again pedal this is foot pedal this is any sort of pedal or pedal. So, this is indicated by this one and this is push button this and this has a difference if you say this is actually cam roller operator and but this one is a push button say reverse D you can say. Now hydraulic valves particularly direction control valves in that case earlier in second lecture we have learned first of all we can have three icons like this. In that icons intermediate one is having zero that means this is the neutral positions A is one operating condition B is another operating condition usually any valve either it will be on off type that means either A or B no intermediate positions. But in most of the cases hydraulic systems and directional control valve where we need to stop the systems for a while or we need to keep the idle system for a while then there must have a neutral positions. So, first we can have while we are designing a valve then the middle one is the neutral then A and B and then there are few icons from there we can select say in neutral conditions it might be like this all are not connected should bring this one and put here. So, we are trying to construct a symbol for DC valves suppose it is complete fully open then we can put it here this one we can put here. We can have also that only supply line is closed other three are connected that means the two ends of the actuator and the reservoir is connected. So, we can take this symbol here and most popular you will find say suppose this is a closed center keep this one at the center this is A and this is B or open center keep this one at the center this one end this is this one at other end. So, this will give four by three closed center four by three open center four ports three positions now you can put this one also at the middle sometimes this is put at the middle suppose you can choose this one this is at the at one end and then this is at the other end or this is this one at the this end and this one at the other end. This is for one specific requirements, but most common we will find either with the closed center or with the open center then cross connection straight connection. So, in that way which these two groups of icons we can build several valves now say for example this first one what we have seen the T indicates is going back to tank P indicates this is for pressure line usually a connected the P means not pump usually pressure line it is called pressure lines A and B two ends of the actuator this capital A and capital B you can mention A B or may not mention you can simply make this valve this is called four by three tangent one valve. So, what is standard that this connection is there that means when it is in the ideal conditions the all will go to the tank without any resistance. In this case what happens this usually with this pressure lines there is a relief valve. So, relief valve is set at a maximum system pressure. So, what will happen in this neutral condition the oil pressure will be up to the maximum system pressure and then it will go through the tank through the relief valve. So, it is a huge power loss, but the advantage is that oil is always ready for work and such systems will be closed center is usually required for when the very weak stop and on and off one and off we are operating some system like that then this system is preferred. So, depending on that requirements also we have to select a super proper valve. Now, this is you see the six by three dc valves what does it mean in that case say this is neutral position that means there is this oil is actually these two are connected together the oil is going from this side to this side and it is doing some main system work. What you can do you can give this line that system main system is off and you can divert this for this operations to a only particular size and also you can use this one then when the means system is off say for example, this valve you can use for a forklift track. In the forklift track main line is going for the hydrostating transmission system which is moving the car. Now you want to lift something once you move the lever first of all your the car will be stopped then it will start operating lifting and while again you are wearing that movement will be off and then this is for an example say it can be made like this. However, in forklift tracks many times it requires that slight movement of the vehicle when it is being lifted or lowering say you would like to take something from the rack. So, you have to take it and move out while you are lifting or lowering you have to take out in that case definitely this valve will not be suitable, but I have given an example where the 6 by 3 valves is used. Now this is 2 by 2 valve say simply it is a on of valve. Now this is also two position but as you see these 3 ports are there that means if we consider the main port then main port this pressure port in that case when this pressure port is stopped this oil from the actuator going back to the tank and when you are connecting to this actuator then your drain connection is off. So, you may need such valve for some operations. Now here of course I have shown this valve, but none of this can compared in this one only thing say this is basically 4 by 2 positions valve spring liter and detent solenoid operated forget about the detent part this is 4 by 2 this is one position this is other positions but what we can do by detaining we can make the all ports are connected. So, in a detent positions we can make this one otherwise normally either this or this positions. Now if you would like to compare with this valve suppose with this connections let us consider this connection is here and these two what is the difference in that case if you leave the valve then automatically this will come back to this position suppose we are using full open center, but in this case it will be full open center only if you use the detent positions that means you have to regulate this actuator in such a way that it will be at the detent positions. So, it is operating conditions no neutral positions either this position or this position only in detent positions it will be there. So, for that what is there this you find that this is not a full line whereas in this case this will be full line the difference between this and this is there and apart from that these we are using only the showing the valve operation we have not using this symbols that is whether it is being written or the armature driven that we are not showing that of course always to be added to show the full form of the valve and this is the other one which I have also discussed this is closed crossover this is this one actually this is having also detent now 3 by 2 dc valve of different configurations the other configuration and this is this configuration is different you have to depending on the applications you have to select this is also 3 by 2 half have this to this is basically not off either this condition or this say if we connect to a rotary actuator then in that case either it will rotate in clockwise direction or anticlockwise directions may be it is like that this valve is directly fitted to the actuator we are operating this way or that way if you would like to off the machines then whole main line is disconnected by some other this is as you see this 5 by 2 4 by 2 5 put a dc valve as you see we have 5 ports how 1 2 3 4 5 the 5 ports but basically this is 4 by 2 valve because we have 2 positions and we use 4 ports so sometimes it is called 4 by 2 5 ported valve now in that case the pressure line is blocked in this case drain is blocked the other cross connections are there from some applications now you see this another interesting thing is that this valve as you see this we have not used any arrow here not to show any directions but say suppose if we take this block that means basically 3 icon together and then if you put an arrow then this will indicate that at neutral position pressure is connected and pressure is closed pressure line is closed and other 3 ports are interconnected that means reservoir and 2 sides of the actuator are interconnected and this is for cross connection and this is for straight connections so that is simple valve now what we find along with that these 2 lines are there this indicates this is infinite positions valve now this is usually for copying machines and other things it is you can say this is a some sort of servo valve so infinite positions means this is some sort of servo working valve now here again 4 by 3 5 ported cylinder ports open to pressure in center positions DC valves as you can see this one 5 by 2 so depending on the purpose this valve is also used now symbols for hydraulic valves again some examples and not exclusive we have exhaustive not this one this is again some repetition of that only thing that you can use this spring say this symbols of repetition but once it is shown that if you add this one this is called spring center if you add spring one side it is called usually spring return if you show this one this is the hand lever if you show this dotted line with field arrow hydraulic pilot and if you show this symbol this is solenoid operated and you can use the spring like this or maybe with a cap like this and this is obviously spring center and solenoid operated both side and here spring return solenoid operated one side so with this addition with more little symbols we what we can add this is basically 4 by 2 DC valve and we have used one spring here what we have used a triangle plus a triangle field with completely field and this is in a box and then a dotted line that means this is pilot operated and maybe hydraulic driven also together it is hydraulic pilot operated spring return valve that means this is hydraulic operated hydraulic pilot as well as spring return in that case both the side hydraulic driven and hydraulic pilot operated here this is solenoid pilot operated and there is also hydraulic actuation is there but this is spring return in that case as you find in both the sides we have added this one so by adding such symbols with this main valve symbols we can also indicate how it is being operated whether it is spring center or not so many things and as you can see this is the 4 by 2 single acting DC valve in this case hydraulic pilot and pneumatic operation might be there in that case solenoid is there and as well as hydraulic pilot is there. Now in case of servo valve as you see in case of servo valve we will find that this with this arrow flow control is also shown because the variable orifice in case of with respect to the directional valve direction control valve the servo flow control valve we will have the variable orifice that is meant by this adding this now also we are adding this one that means this is also pilot operated and this is also variable as well as this is there is a solenoid apart from that we have to put two other lines. So once we put these two lines along with such things this means that it is completely two stage electro hydraulic servo valve why two stage there will be pilot stage there will be main stage and it is a servo valve. So for that we can use this symbol now say we are coming to the pressure control valve in case of pressure control valve the simplest one is that puppet function first of all we will show this puppet functions you will find that in many cases a valve is drawn like this that means it is normally closed in some cases you will find this is there and it is shown like this that means this is open normally open now the direct acting pressure relief valve are shown like this. So this will be there normally closed and along with that there will be a symbol like this and this is the you can adjust the capacity and in this case if it is a pilot operated in that case you will find a straight lines which can come here and here means it is open and here means at the top not on that line is closed. Now this is again pilot operated pressure relief valve but this one is having one is that this is a closed one this is also another closed one but this is operated by the pilot as well as it is a flow control this is a special feature but you can show this with this together this is a complicated one but base better maintenance better pressure relief conditions. Now this one is that pilot operated relief valve external pilot internal drain this is pressure reducing valve this is pressure fixed and variable adjustment this one indicates pilot operated relief valve pressure reducing valve fixed and variable displacement that means once you use these two sign pressure reducing valve is also a pressure control valve pressure relief valve is also a pressure control valve. In case of pressure relief valve oil is flowing from this side to this side you will find that the pilot line is from the upstream but there is no pilot from the downstream if there is a pilot from the downstream also then this is a pressure reducing function in all pressure reducing functions you will find that it is acting as a pressure reducing valve as well as pressure relief valve. So, a pressure reducing valve with pressure reducing valve totally meant by this one usually you will find wherever you are using a pressure reducing valve there is also a separate relief valve which is connected near the pump. So, forget about that part but then again where the pressure reducing valve is there the this will be a relief valve in built there because some flow has to go through the pressure relief valve there. Now this is what is the difference between this and that in that case pilot operated relief valve external pilot external drain you see there is no line from the downstream. So, this is a relief valve but it looks like only thing this line is not there external pilot is there as well as external drain is there and this one pilot operated pressure reducing valve in that case the relief valve function is not shown. So, this is a pressure reducing whenever this pilot connection is from the downstream it is a pressure reducing valve and it is very difficult to remember all such symbols we do not expect that you will remember all such symbols but it is just to have an idea. Now this is as you can see this pressure reducing valve with a check valve here this is a remote pressure adjustment direct operated and counter balance valve looks like this one sequence valve looks like this ones and unloading valve. So, while you are trying to study such valve you should study the circuit along with this and you should spend more time to study such valve this is for your instruction I am just going through that but you should spend more time to learn how this symbols are justified with their function. Now as you find that pressure reducing valve three positions this is pressure switch as you can see this is one two three positions it is either connected with two or connected with one and three. So, this is a pressure switch depending on the pressure this will be connected this way or other way the sequence valve external drain sequence valve external drain load varies with back pressure in the tank line. So, there are many things to understand and then to remember such symbols. However, if you go for circuit design this will be available in your hand you can simply put there but you have to know where to use which one. Now, this is a flow control valve the it is a two way pressure compensated flow control valve. So, this line this arrow is there means this is the directions of the flow and this is the three way pressure compensated flow control valve. If the box is there perhaps this is a pressure compensated and if it is used without this box perhaps it is not pressure compensated this is a throttle valve throttle valve and the flow control valve is almost the same function but in case of throttle valve you may not find it is a simply a flow restrictor. So, that is called throttle valve whereas, flow control valve there is some device the control is there and the excess flow will go to the tank from that valve. In that case this throttle valve that excess flow has to go through this pressure relief valve which is set again a system pressure. That means, in between this throttle valve to pump the pressure will be always to the system pressure it is something like that. So, you have to study in details while you are designing such circuits. The check valve with spring check valve without spring which I have shown earlier also in that case in now we come to the pump in this pump what we find the circle and the triangle inside is completely filled in this is a constant flow fixed displacement pump single outlet unidirectional input shaft rotations and with this one we have not shown shaft it is not necessary always. Now, in this case it is double outlet that means bi-directional input shaft rotation. This is usually either bi-directional shaft rotation is also possible or bi-directional flow is possible simply by changing the swash plate angle this is complicated, but you can once you find this symbols you can think of this designation. Now, with this if you use an arrow then with this feature this will be variable displacement in that case in this case it is a flicks displacement here it is bi-directional with variable displacement and you can see this is the ISO symbol is like that for a pump you can compare this with this one. Now, the motor it just reverse the arrow are put in the opposite directions and other designations remain same this is motor arrow going out means pump arrow going inside means motor hydraulic motor. Now, very often we use this term HST that hydrostatic transmission. Now, total hydrostatic transmissions this term meant there is a pump and there is a motor. Now, if it is connected like this this is a closed circuit all systems are say there is a pump and actuator with a directional valve that is also a hydrostatic transmission, but that is open circuit. Now, this is a closed circuit with a variable pump and fixed displacement motor. Now, if in many cases you will find that instead of pipe connections are there this has simply one input and another output and you will find that this is a pump side you have connected to and prime over it is rotating at a constant piece where by switch by manipulating something in between you may find variable output also. So, that is basically inside there is a pump and motor. So, this construction is also possible. Now, some sophisticated and hybrid units are like that that both pump and motor you can use that this as a pump as well as motor, but this is only unidirectional whereas, this is hydraulic pump or motor single flow that means this is either you can use for pump and motor if you just reverse the flow directions here. In that case you can use perhaps for both directions to have this pump and motor features there is some difference between this and that this is detailed you have to study in details with the component and machine. Now, in this case this is dual rotation no perhaps this one I will tell you this one perhaps that if you rotate in one direction it will act as a pump if you rotate in the opposite directions that means with the same flow directions if you use the flow and try to have the output then it will act as a motor. In that case you rotate in one way and you can have this as a pump and also this can be used as a motor by changing the valve configuration something like that, but this is you can say this is added together if you this both side is pump and motor. So, this will be this will work for dual rotation and also we can have such configuration with variable displacement then there are some more that is the some simplified symbols are there these are usually we would say for example, this already we have learnt in that case this is a bi-directional variable displacement pressure compensated. So, pressure compensated means there will be a arrow like this in that case there is an external drain and this is a pump unidirectional variable displacement and this is of course, non compensated in this case this is compensated arrow is there and this is bi-directional. Now, these are the actuators in this actuators there is no spring return here is some spring is there in that case double acting cylinders thin piston rod not usually under compressions. So, this one we do not use for under compression but this we can use for used in under compression. Now, if we add something like this then there is a cushion effect this cushion effect means physical cushion may not be there it is like that when it is reaching towards the end of the pistons then there will be a flow restrictor through which the flow will be in such a way very slowly that piston will touch the cylinder. So, there will be some cushioning effect. Now, this is cylinder with adjustable cushions this cushion can be adjusted that means you can allow to collapse faster or later. Now, this is again double acting cylinder with adjustable cushions you can see that if it is a single acting cylinder with adjustable cushions only no mention whether it is a single acting or double acting usually it is a single acting because no compressive force is applied here for thin rod. In that case this is double acting you will find both the lines are here and this is a thick cylinder because this is this can give compressive load as well as tensile load. Now, in this case double rod cylinder now this cylinder again may be very thick or thin. Now, this is a telescopic cylinder in that case it is like that if you allow the oil to go inside then first this one will move because this is having a larger area. So, with a small pressure it will work then when this will be fully extended pressure will gradually increase and with this because this is handling the same load. So, with this smaller cylinder it will move. So, this is a we will get telescopic action where it is used where we are we need very long extension in that case we use the telescopic one and this is intensifier what we find that if we allow the flow this side with a low pressure which will you can have much higher pressure this side. And this is we have followed one book this book is available in our library and this is of course the from the net you can download this and you can learn about the ISO symbols. So, thank you for listening.