 Welcome to 2-z lecture on Hydrolix and Neumatics. Today's topic will be selection of HST that is hydrostatic transmission units and components. Now, HST stands for hydrostatic transmission. We have already known that why it is called hydrostatic transmission, because in this case we can neglect the hydrodynamic part or performance of such machines only mostly with hydrostatic not hydrodynamics except when we are analyzing flow through any orifice or any capillary passages. Now, also we have known what is hydrostatic transmission. Essentially hydrostatic transmission should have one motor and pump. In that way any hydraulics and pneumatics drive is hydrostatic drive, because in that case there will be a pump or source of flow and pressure and that flow and pressure is sent to an actuator which gives some motion. So, in that way we should say every system hydrostatic transmission in hydraulics and pneumatics. However, when we mean HST transmissions then basically we mean there is a rotary pump and rotary motor and these pumps and motors they are they may be identical looking. They are body, the reciprocating units, valve etcetera they may look alike. In fact, the same components can be used for pump and motor except there is some differences in the flow distributor valves and even it is possible that we can combine that pump and motor together and that unit can be used both as pump and motor. Anyway this what we look in this figure that there is basically a pump is there. This is driven by some prime mover and then there is an reservoir and oil is going in. Then oil is transmitted to the motor part and which acts this means that that rotates and the oil goes out to the reservoir. So, this we should say an open circuit. It is also possible that we can instead of using that reservoir we can drive this pump which can be rotated in both directions by some arrangement is there and that is driving a motor and depending on the direction of flow that motor will rotate in both the directions. That means it can be rotated in clockwise direction as well as in anti clockwise directions. It is not necessarily that prime mover is rotating in both directions. Prime mover may be rotating in one directions only and there is a mechanism in the pump by which we can change the direction of flow. That means it can be flowing out this way or it can be flowing out it is flowing out from the other side. So, this is called closed circuit. So, if we mean that hydrostatic transmission then either we mean to this open circuit or to the closed circuits. Now this is open circuit also open loop without feedback. There is no feedback open circuit and open loop. Then we would say this one is the closed loop a closed circuit and open loop. That means without any feedback. If there is feedback then we will call it is a closed circuit closed loop etcetera. We are coming to that. Now this is already we have seen. So, this is open circuit open loop without feedback. Then we can have the open circuit closed loop with feedback. So, there is a feedback. So, this means that depending on the output of the motor this pump can be controlled. So, this is open circuit closed loop. Similarly, we can have the it is a closed circuit, but open loop and finally, we can have closed circuit closed loop with feedback. That means this is not only closed circuit as well as closed loop. So, first part this term is the circuit term and second part is the control term. In that way we can name like this. So, if we are asked usually in the classroom question classroom question paper or the examinations. These are a popular questions that describe the hydrostatic transmission system. Then you have to write all such things with such simple diagram. And finally, we can make a block diagram like this hydrostatic transmission systems. You see when we use HST term many people write that hydrostatic transmission system. No it is not for hydrostatic transmission system. HST word comes from hydrostatic transmission only the S the static that S is here. Now, when we add the systems then S will come here. So, this HST S means hydrostatic transmission systems. Now, as we have seen the piping term or circuit term open circuit discontinued flow interrupted flow and closed circuit continued flow uninterrupted flow. And then both may be open loop no feedback closed loop with feedback. This part is also same. Now, in reality circuit will look like this. This is a simple open circuit consists of the following major elements. What is that? There is a reservoir. Then suction strainer these are called suction strainer too. This is filtration is usually 100 to 200 micron in general purpose while hydraulic applications. Now, what does it mean? This mesh of the usually the wear mesh is used also filter papers are used. Then it is 100 to 200 micron say if we consider the 100 micron that means within 1 inch there will be 100 mesh it is like that. So, you can imagine how small particles they are being filtered. This particle size say maximum size is 200 micron that means if you think of a square mesh then diagonal length is equal to 200 micron approximately you can imagine in that way. Now, third one is the pressure relief valve. This one is the pressure relief valve. In this case system is like that. We have a pump source there is a filter and then it is going into a valve which is in fifth item seventh actually. Then pump fixed or variable this one. This may be fixed or may be variable also and then motor fixed or variable displacement. This one may be fixed or variable that means that swept volume may be fixed or may be varying. Now, this conduit etcetera means this piping this may be rigid as well as flexible. Then return line filter this is usually 10 to 25 micron now why it is like that. Now, actually this trainer is used it has practically it is not required. Only thing due to safety reason we put it there. That means if there is any big particle that is being filtered that should be filtered otherwise pump will be damaged. But actual filtration is done in the return lines because why in the return lines. If we put such a strainer at the inlet then this pump will need very high power. So, to avoid that and then there will be loss. To avoid that we put in the return line and this is also justified because there is no exposure up to this motor part that the dirt can come inside. But in case of motor usually that output shaft is rotating and then through that some that particle may come inside because there is a exposure the output is that external to the from the included body. Although there is the ceiling, but there is a possibility of dirt coming inside and that is being filtered in the return line. Next the control unit this is the control unit. Control unit is actually the valve. The first day we have seen that how this valve is functioning. But here I would like to say with this arrangement you can see this is a tandem time valve. That means in normal time this oil will go to the tank and these two will remain close. But if we actuate in this direction then oil will go to this and it will come back through this. Then say for this it is clock wise rotation and for this function it will rotate in the opposite directions. Now these are the two valves are used that is relief valve. That means oil is being relief from here to here. So, this is although open loop, but it can be said with this feature it is somewhat acting as a closed not loop closed circuit also. However, we can use this filtration line also other place that I will show. Now what if you would like to construct a closed circuit in that case the pump this is this arrow means variable displacement pump we are using and this pump is being driven by the prime mover and then these are directly connected to the motor two ends of this pump is connected to the two ends of the motor. Now depending on the direction of flow which again can be controlled by this control not changing the direction of rotation of the prime mover we can change the direction of the motor rotation. Now if we look into the circuit then we will find many things inside what these are we need there will be leakages in any hydraulic components we cannot avoid that. Now this leakage to be compensated for that we need a feed pump this feed pump means it is only compensating the leakage flow. So, capacity of this pump is both pressure wise and the flow wise is very small pump. So, and it is with is usually connected to the main pump also. So, through the same shaft it is connected. Now this is connected inlet is connected to the reservoir and from there oil is being pumped to this circuit to compensate the leakage and there is a relief valve the excess oil it is going back to the tank. In fact excess oil is coming to this casing in this diagram it can be directly coming out or through this casing it is coming out to the oil. Because for such components usually casing where the automatic leakage is being there is leakage and that always to be kept filled for the lubrication purpose. So, this arrangement is shown like this and then what we find the two non-return valve suppose the oil is going through this from the pump it is flowing like this that this means that this is a high pressure oil because it is rotating the motor. So, due to this high pressure this will remain closed and oil will go through this check valve or non-return valve to this side like this means that high pressure oil is directly sent to this motor for rotating and if there is any leakage that is being compensated here and then again it is being fed to the pump this means that there will be no shortage of oil in this circuit. If it move this oil moves in other directions then this side will remain closed and oil will be fed through this. So, this is to compensate leakage we need a feed pump. Next we this is called dual shock valve these are nothing but two relief valves this relief valve means if there is this pressure exceeds the need of the motor that means system pressure then oil will directly go back to this part of the circuit and it will go back to the tank and this motor will stall. Similarly when it is trying to rotate in the opposite what is the directions it will go to the other part of the pump. So, this would operate but time to time we need to leak the I mean bypass the oil to the tank and for that this system is there and this is again sent by the system pressure in that case what will happen oil will go back to the tank. So, minimum requirements for such a circuit should be like this. Unction of this part is that due to the high pressure this will operate and oil will go through this setting pressure this is set at the system pressure it will go back to the tank. So, for example, this is operating at 10 mega Pascal. Suppose, due to some reason due to high load it has it has exceeded that exceeded 10 mega Pascal then in that case oil will bypass through this may bypass through this otherwise it will go to the other side of the circuit. So, here the pump is also stalled oil has to pass through this. However it is possible that without this we can have this system, but if using this this is a full proof circuit means the pump and no components will be damaged oil will go back to the tank. Now this components are feed or charge pump this is called feed pump or charge pump then dual shock valve it is called dual shock valve protect the system from the damage in case of pressure override and over running conditions. To improve the performance and to fulfill other desired task many other appropriate components such as accumulator cooling system special purpose valves etcetera are included in this circuits. Say this is the minimum, but we can use say for example, for smooth performance we can add accumulator to cool the oil we can add the cooler this means that in that path on the return path there will be a cooler like that. Now we shall look into this circuits we have seen few circuits as well as we have seen that the motor open circuit closed circuit etcetera. Now depending on different types of loads the HST system employed may be of different types type of, but here we are discussing the type of closed circuit because this when we normally call hydrostatic transmission system for driving say earth moving equipment from driving a truck tractor from driving a for clip truck in that case we mean closed circuit may not be closed loop, but it is essentially a closed circuit. So, if we consider the closed circuit hydrostatic transmission system then the displacement of pump and motor we will consider the what type of displacement is there then transmission type and from there we will look into this what are the different types. Now first one is that pump is fixed displacement motor is also fixed displacement fixed displacement means it is having constant sway volume what is constant sway volume sway volume is the volume displacement by one revolution whether it is motor or whether it is pump. So, only one revolution whatever the geometric displacement that is called the sway volume without considering any leakage. Now if that remain fixed in that in this case we should call fixed displacement. Again with some mechanism it can be varied that means in a revolution that total displacement will vary we should call them variable displacement. So, here we understand now what is fixed displacement we have fixed displacement pump fixed displacement motor. So, power in that case will be constant torque will also be constant obviously this is for a constant pressure then output speed is also constant and commonly we call as a ordinary simple circuit. Next if we consider pump is variable and then motor is fixed then power will be also variable however the it will be usually for constant torque that means when the pressure is constant then torque is also in motor it is a constant, but we are varying this power. So, output speed will be variable in that case then we call it constant torque system. Next what we get fixed pump variable motor and in that case power remain constant with that constant power torque can be varied this is also variable and we should call it constant power system. You will find that this is a simple system first one second one is very widely used, but looking into some you should say that power saving system this is not suitable for where the torque is I mean very wide range it is may be controversial, but I would say this is power is varying, but range is not that high and we can go for such system this is also used, but in that way I would say we can make all variable. Now, all variable means then we can keep at a certain position. So, this will be fixed this will be fixed or it might be variable this is fixed this means that if you make this one variable variable then we can have all three preachers from out of this. Now this has no special name this can be made constant power system this can be made constant torque system or an ordinary system, but this will be definitely expensive. Otherwise I would suggest in every case we can go for such arrangement, but if it is not require not much variation in power and torque is there we need not go for such a system because this will be expensive. Now we shall look into the selection of such components through and work out a example. Now this let us see this what problem is there the drum of a concrete truck mixture is lined with spiral vanes this means you might have seen a big truck with a rotating drum it is moving say for a it is carrying cement you will find the cement what it is there the cement mixture that is done at one place and that is being carried to other place, but it should not that means it will if you do not rotate it then this may solidify I mean it will it will take the concrete shape to avoid that it is done also this is used for cement manufacturing while cement is being manufacture for that purpose of this might there might be something else also. So, there we use a drum which should be rotated and while it is being carried now this drum is rotated in one direction if it is rotated in one direction the vanes force the mixture downwards and mix it it is mixing. Now for unloading what it is it is rotated at high speed in other direction they lift the concrete mixture and discharge it it is like that at one place it is being mixed then it is being carried and then it is being mixed going up and down little arrangement I cannot explain here, but it is like that however while it is carrying in that case it should only just move. So, that they are they I mean some we are just mixing like this vanes are rotating like the inside and these are not allowed to being co-occulate it is like that. So, that is called agitating speed to prevent the concrete setting settling or is sorry setting while transported the drum is rotated at slow speed to agitate the mixture definitely we need not rotate at high speed neither we need that much power at that time. The drum drive is done through an HST system and gear reductions. The variable displacement pump we have a variable displacement pump of HST system is driven by the main engine of the truck characteristics of pump and motor are shown in figure there is a figure in next slides. Now, the drive system maintains the agitating speed range unless the engine is stopped this is important that means if you suppose you are not moving you have stopped the car not moving, but engine it is not stopped that speed that is usually you know for any car that is low speed not high speed at the speed the agitating operation should continue that means drum will rotate. So, this means that now data for the mixture drive system is that maximum drum speed is 15 rpm that means when it is mixing or discharging drum agitating speed is 5 rpm already one third of that overall gear reduction ratio is 1 is to 30 this means that from the motor output hydrostatic transmission motor output there is another gear reduction 1 is to 30. So, that we can have 15 rpm otherwise directly by the motor 15 rpm is very difficult performance of this motor will be then very poor that is why we use a gear box. So, 1 is to 30 gear ratio is there maximum running torque is 1200 deca Newton meter the value is given in deca Newton meter. Now, find out pressures different speeds of the engine pump motor etcetera and powers both running speeds of drum that means normal running speed as well as agitating speed assume 100 percent efficiency efficiencies in all units except the hydraulic motor. Now, I would say that every that rotating units or may be been ordinary units as having its own efficiencies say for example, this motor it cannot run at 100 percent efficiency that means there will be losses losses may be leakage losses mechanical losses that is the friction losses and also there is called hydraulic losses not in this lecture we shall discuss may be in other lectures that what are the losses. Now leakage loss you can understand what it is mechanical loss means there will be friction loss and such mainly friction loss we should say mechanical also thermal loss will be there in other form then there is a hydraulic loss hydraulic loss is usually that fluid is although we consider the hydraulic fluid is incompressible, but it will be compressed a little bit. So, there will be some loss also the body of the conduit say particularly flexible hose that will be also expand. So, there will be some loss so that normally put into hydraulic loss it is very difficult to calculate all such losses separately, but we can experimentally we can find out what are the total losses also we have to make a circuit for this. Now, here we have considered the variable displacement pump in that case we have considered the swash plate type pump which we can move and by that we can increase or reduce the sway to volume. Now the characteristics of this pump is shown here that means this chart is available we from the manufacturer and while we select a components we have to look into this. Say for example, here this flow output are given but that you can see against this rpm of the pump input and against the pressure say if it is a maximum pressure is 6000 pound per square inch in that case you will find that we have to follow this line. Now if the pressure is very low then definitely the that higher flow is available at lower speed. And these lines are the power say power will vary at different pressure following this lines at different rpm. So, this is the pump characteristics and motor what we have used this is called orbit motor which is low speed high torque that means this can give output of very high torque at low speed as you can see the maximum speed continuous speed only 500 rpm whereas, that pump you have seen 2000 rpm or more. And this you can see this torque is 60 decano Newton meter continuous and for intermittent it may be up to 625 rpm and output torque is 65. So, here a is continuous up to this point. So, we will normally follow this curve for continuous operations I mean this portion is for continuous operations. However, we can either increase this may be both cannot be increased we can increase the speed or we can increase the torque up to this limit that is for few seconds only may be at this starting or so 10 15 seconds it can run at high speed or at high torque. So, we are using this type of a motor. Now the solution will be like this the given data are maximum drum speed 15 rpm drum exiting speed is 5 rpm overall transmission ratio of the gear unit is 30 maximum output torque we need 1200 decano Newton meter 100 percent efficiencies for all components this is for the solution purpose we have considered like this actually we should consider efficiencies of all. However, we have considered that hydraulic motors we should consider its efficiency I will show that how the calculation is done. Now what we have to find that pressures different speeds of engine, pump, motor etcetera powers and also we have to draw the circuit. Now motor speed at maximum drum speed is we would say 15 into the transmission ratio 450 rpm that means we should motor output speed maximum that is while it is mix mixing or may be discharging definitely at the time of mixing the more power will be required look at this how the this is inclined it is arranged in such a way it is mixing the materials are moving normally downward directions because that time we need more force. So, gravity force helps for mixing while we are discharging it probably it is not mixing. So, some power optimization is there, but anyway we do not know maximum torque will be 1200 decano Newton meter. Now motor speed at a agitating drum speed is 5 into 30 150 rpm. Now maximum running torque 1200 decano Newton meter gives maximum motor torque. Now definitely if this is the output torque then input I mean output from the motor should be 1200 divided by the transmission ratio. So, 40 decano Newton meter assuming 100 percent transmission efficiency. Now here that gear box efficiency we have consider 100 percent. So, we would say if the motor can transmit 40 decano Newton meter it can output is 40 decano Newton meter then it is it will suffice the purpose. Now looking into this curve we will look into this motor curve motor characteristics curve then 450 rpm is here because we need 450 rpm. So, we will follow this line and then torque is 40 decano Newton meter. So, we will find that this is our operating point. Now at that operating point we will find the power etcetera we will look into this. So, from this graph what we find maximum power 18.85 kilowatt how I have done can you see this is 20 kilowatt and this is 15 kilowatt and we have to I mean estimate from these two curves it is to me it is around 18.85 kilowatt and what is the pressure this is 14 140 bar means 14 megapascal. So, therefore, it is around 14.8 megapascal we have estimated. So, this much this means that this line if you look into this at from low speed to high speed this slightly bending this line is isopressure lines. So, here we consider this is the pressure. Now this is again this is not the output pressure or so it is called a differential pressure that means when in a motor oil in and oil out when the oil out there is also some pressure because there is a filter and other components. So, oil in that pressure should be higher that means to know what is the actual pressure input to this motor we need to know output what is the pressure. In case of closed circuit it is it will be always there. So, it is estimated we have to calculate considering these two pressure in open circuit somewhat we may consider that outlet pressure is very low anyway this this remains unknown in this problem. However, we know this this is actual characteristics it is on experiments. So, we can say that this is the power output and the flow is 95 litre per minute how we can find out the flow this is 100 litre per minute and this is 80 litre per minute and we have estimated this is 95 litre per minute. Input power to motor pressure into flow we can say. So, what we find it is 23.43 kilowatt you can simply calculate like this pressure into flow will give you the power 60 is for per second to find calculate this power per second. This is megapascal we have written and this is litre per minute if you directly divide by that automatically you are going to how much kilowatt is there. Then from the chart what we find output of this motor is 14.8 which is directly can be found out from 450 rpm into the torque available available speed and available torque will give us this power. So, this means that definitely there is a efficiency matter of efficiency overall efficiency that efficiency what we calculate 80.5. Now, if we look into this say this is iso efficiency lines this is 80 percent and this is 85 percent that means if motor operates within this zone it is 85 percent. If it operates within this zone then we can say something between 80 to 85 percent and we can see this is 80.5. So, this is 80 line, but it is coming 80.5 may be some estimation it is slightly wrong, but we can say if this is 85 this is 80 this will be something in between. So, it is may be 81 or 82 percent. So, our calculation is going in the right directions and we can say that we have estimated more or less correctly. So, this motor can supply this maximum torque required. Now, if we consider that agitating this is an 150, but we have not said how much torque is required. Now, in that case the material is not moving this way or that way not going up nor down it is just simply may be that time drum is kept more or less horizontal and it is just rotating not to allowing setting it. In that case let us consider the half of the torque will be required we have assumed this one sorry. In that case what we find that it is the maximum efficiency zone. If you look into this you will find that one is the maximum efficiency zone will come into the other the slides later again. Now, again we are continuing now motor differential pressure is 14.8 mega Pascal and input flow to the motor is 95 LPM. It is clear that pump output flow must be 95 litre per minute that we have seen that we need 95 this is actual chart. So, 95 litre per minute that is fixed. However, to have motor differential pressure 14.8 mega Pascal it may need to pump deliver the flow at higher pressure which depends on different losses that is unknown. But we will consider let us consider as we have considered the efficiency of the pump is 100 percent. So, it is it will be 14.8. It is assumed that pressure at motor outlet is 0. If we assume in that way then as 100 percent efficiencies for all other components we will now consider that pressure output is 14.4 the pump is 14.8 mega Pascal itself now it is equivalent to 2114 PSI that is pound force per inch square. Now, how to calculate this roughly you can say 1000 PSI is equal to 7 mega Pascal 1000 PSI is equal to 7 mega Pascal. Then while delivering output flow is equal to 95.8 mega Pascal that is the litre per minute. Assuming this is an imperial gallons then we will consider divide by 4.5 we will give you gallon per minute. So, this we need this one pump flow output and pump pressure output. Now, we shall look into the pump chart first we will consider that the flow for that flow we have to assume that for 2114 PSI where may be the line. So, this blue line is there then we will consider the flow this is 20 this is 25. So, 21.1 gallon per minute then that intersection point is our this output point in terms of flow output at that pressure. Now, from there if we come down then we will find that RPM is around 2050 that is all I estimation we can one can calculate by measuring a scale and then calculating from my I estimation it is 2050 RPM of this pump. Then we shall consider the power how to estimate the power again we will consider this 2114 PSI this might be this line. Then this is the point where the power to estimate the power and we are getting this is 31 this is in horse power oh sorry this is 31 this is 31 horse power in horse power 30 horse power means what will be in kilowatt 1.6 horse power is equal to 1 kilowatt is it not 1.6. So, 30 divided by 1.6 around 18 what we have calculated there. So, I think this is made a mistake here. So, it is not 31.1 kilowatt it is will be 31 HP around 31 HP. So, this will be 18 or 20 kilowatt or like this, but actually if we carefully consider we will find it will be 23 kilowatt what we have calculated in terms of flow and pressure we as we have neglected the efficiency these results are coming in this way. Now, therefore, speed of the pump at maximum drum speed is 2500 RPM and it is 31 HP. So, this please note these corrections engine to be operated at same speed and power. So, that is we have selected the engine like that. Now, for agitating speed say this speed was as you see this is for motor specification for normal operations, but for agitating speed what we found that 150 RPM and this is the torque. Now, here I would say looking into this RPM is 150 and here RPM is 450. So, just it is three time less also output speed was 15 and 5. So, we may be tempted that in that case the flow will be just three times less and as the torque is half then maybe we can consider the power is totally six times less, but actually it is not because due to the efficiency factor we have to again reconsider this. We will find that therefore, at that speed loss is not much and again this agitating speed it is the normal say this is carrying for quite long distance that time we would try to utilize the power in such a way this is at the maximum efficiency zone. So, it is designed accordingly. So, this efficiency apparently it is close to the 100 percent, but it will never happen because this here it is this line is 87 percent and within this zone it may be at the most 90 percent efficiency, but never 100 percent. So, we would say this it is with 90 percent efficiency it is operating. So, again we have to find out the power in the same way what we did earlier. Now, the agitating torque is assumed this 20 degree Newton meter we have assumed from the graph then this is 31 liter per minute and pressure is 7 megapascal what we find that 70 bar means 7 megapascal and power we find it is 3.15 kilowatt, but hydraulic power is 3.6 kilowatt calculating from the flow and pressure term. Therefore, efficiency is around 87.5 percent. So, within this zone even the efficiency is showing like this not showing 100 percent and this is seems to be correct pump out for 31 liter per minute 8.89 gallon per minute and pressure is 7 megapascals. So, if I consider in the same way what we have calculated now this is the line for the flow term and on which this is the pressure term and we get this point there and then speed we find 600 rpm. If you have any idea about this engine industrial diesel engine or so you will find normally 600 to 700 there idle speed you will find that. So, 600 speed when even if the truck is not moving we can have that speed and we can have that power to for the purpose of agitating. Now, this is 600 rpm and again if we consider the 1000 pound per inch square and then we found this power is actually again this is not 3.6 kilowatt it is around you can find around 5 hp which is 5 divided by 1.6 is will be something like this of course, but this is a mistake by mistake I wrote like this actual may be slightly different from that. Now, we have to draw the diagram of circuit and now normally if you like to make an open circuit what you can do you can choose the same circuit what we have seen, but instead of using the relief valve here we can add one relief valve there. So, this is open circuit we have considered however instead of that whatever original was there we can use that one also. This circuit mind it this is only for rotating the drum this is not driving the truck for truck from engine there is a separate drive line it might be that ordinary speed gear box and there is differential etcetera not hydrostatic transmission hydrostatic transmission system is although the same engine is the power source, but this circuit is only for rotating the drum. Now, as well what we can do instead of this variable here the pump is variable displacement instead of variable displacement pump we can use a flow control valve is also there that is another possibility. Now you should keep in mind if there is a pressure setting say for example this pressure setting we have seen 7 megapascal. So, this pressure setting not 7 megapascal for exiting, but 14 point something for the maximum torque. So, it might be set at 15 megapascal. If you use this flow control valve your excess flow will always go through this relief valve by increasing blowing this relief valve that means pump to this point always pressure will be 15 megapascal in that case the loss will be more, but the advantage is that this oil is always ready with the pressure. So, performance of this part will be better. So, usually if we would like to rotate for a very short time output flow control valve will be better than this variable displacement pump. Variable displacement pump you have to make the pressure ready everything. So, there will be a sluggishness in the response. So, these are the differences anyway depending on the cost optimization we can select which one to be used. Now, again this while you are trying to answer such a questions you should name all the components like this. This is same as what we have discussed earlier. Now, also we can go for closed circuit mainly we may choose the closed circuit for this particular transmission because we have seen that this while it is mixing and while it is discharging it is having motion in both directions. You need clockwise and anti clockwise output and that might be not for longer time. I mean time period it is like that for a few minutes you are rotating in clockwise and few minutes in the opposite directions. So, looking into this may be closed circuit is the better option. In that case as I have told that this you may use or may not use, but it is better to use this for more safety. This is considering safety of whole circuit. So, while you are answering you may draw such a circuit that this will be for the drum drive and drum a gear box is connected here after that drum is connected there. So, if you come either this circuit or this circuit anything we will do you can answer if you answer both showing that and you can discuss. So, your answer will be better that is all. So, thank you very much for listening.