 Hello students, myself Siddhaswara B. Turzaapure, Associate Professor, Department of Mechanical Engineering, Walshan Institute of Technology, Soolapur. So today, we are going to deal with the counterbalancing circuit, the learning outcome. At the end of this session, students will be able to draw counterbalancing circuit and explain its working. The contents are firstly need of counterbalancing, then we will go for counterbalancing circuit and then we will go for the downward stroke of the piston, then upward stroke of piston and lastly we will have the references. See now, firstly we will go for the need of counterbalancing. So in case of counterbalancing word, we will have the say splitting of this particular word and we will firstly consider the balancing only, say balancing. So when the word balancing it comes, so it refers to the thing that unbalancing is already existing. So now unbalance of the force may exist due to the say different conditions. So one of them is say it is vertical position of the linear actuator that is the cylinder piston it is vertical and we are having the load attached at the end of the piston rod. And that load to some extent it is heavier, say drill head assembly etc., like that we can think of where the electric motor will be there and then we are going to have the gear box and then say we are going to have the output of that one to the spindle, then the drill and the drill holder etc., these things these are going to come. The whole thing it is going to be heavier. Then this unbalanced force needs to be resisted or it is to be countered. See this counter word it is now coming. So balancing we have seen, say unbalance it is existing due to the vertical position of the cylinder and the load attached at the end of the piston rod and say next to that one that vertical downward force which is unbalanced needs to be countered. So the wordings used are counterbalancing it is. If we are not doing that one see what is going to happen, say counterbalancing is not done we are going to come across the vertical downward motion of the piston either uncontrolled or in undesired way you can say. Now that unbalanced force now you can observe, say the vertical position of the cylinder we are having the load at the end of the piston rod, say drill head assembly or similar other you can have and then we are having the say supply to this cap end and the rod end by making use of the 4 by 3 direction control valve it is. Now you have to think of whether in the present condition the piston it is going to come vertically downward automatically due to the load at the end of the piston or it is not. See the question see the diagram carefully at the end of the piston rod we are having the load which is heavier and the cylinder it is vertical and we are having the connections like this 4 by 3 direction control valve is there. So the center position of spool is there and then we are going to have whether say the question is whether the piston will come automatically downward due to the load at the end of the piston or not in the present situation. See now in the present condition you have to check the spool position also so it is in the middle say if the piston has to come vertically downward the oil from this rod end side should be going to the tank but B port it is closed so the load it is not going to come vertically downward or piston it is not going to come vertically downward but it is exerting pressure to some extent presently so that is what the answer is. Now let us go to the counterbalance circuit so now the spool it is in the center position see that we have introduced to the counterbalance valve here counterbalance valve also belongs to pressure control group and it is also normally closed valve and going to open when a certain pressure it is reached where we are having the setting of that one say now the pressures we are considering. So now when the spool is having the center position no supply of oil is there say now we are to some extent the oil will be there in the pipelines they are having some pressure but say the pump supply it is not there presently and piston you can observe that piston is exerting the pressure on that oil or force on the oil which is on the rod end ball like structure it is coming first. Now this pressure say the pressure shown here in the pressure gauge it is only due to the say load which is attached at the end of the piston rod and weight of the piston etc. So it is say 15 bar now when we have to go for the setting of that counterbalance valve we should have the values which are higher than this one that is say the 25 bar we will take the value so the spring is there the setting of that one it is done and what we will have is we will have the setting at 25 bar unless and until the pressure reaches here 25 bar or it crosses the 25 bar value so the counterbalance valve it is not going to open so it is going to remain closed. Now let us see the say further position when we are going to shift the spool in the present condition now you can observe 15 bar is the only pressure say it is only due to the load which is attached here and piston rod and piston say weight so these are the contributing factors to that pressure and the oil it has come up to the counterbalance valve and it has remained there only no further flow through the counterbalance valve is there and the say load it is retained there only but now we are shifting the spool see now when the spool is shifted towards the say this position it is going to occur and P is now we are having connection to the A P connected to the A so the pressurized oil goes to the cap end of the cylinder so in case of this one the pressure it will be exerted or force it will be exerted on the piston now the total pressure you can consider and the total pressure now it is having the contribution of the two different say components one it is pressure due to the say load and the piston rod and the piston disc etc or the piston it is so that is already existing but additionally we have come across the oil on the cap inside which has been received from the pump itself and it is also the pressurized oil so this pressure and plus the pressure due to the load so together it is going to increase now and the value which is obtained is equal to its 60 bar 60 bar it is now suppose as it is say larger than the setting of the counterbalance valve it is 25 bar so the wall spool it has been shifted and the inlet is connected to the now outlet and we are having say the flow through the counterbalance valve and it is going to the port B and B is connected to the T so what should happen is say the pressure it should be more than that of the counterbalance valve set pressure so if it is like that then and then only the wall it is going to open and allow the flow through that one then we are going to come across the upward stroke so in case of the upward stroke again the shifting of the spool it is going to occur see now earlier we are having the first position of the spool it is so it is now in that case P it was connected to A B it was connected to T whereas in the exactly the first condition you can observe so where the question was raised so at that time so this A and B these are closed and this P it was connected to T directly now in the present condition what we are having is P is connected to B and A is connected to T so the green colored forward line you can observe and red colored return line is there so P is connected to A now see where it is going it is going to the say check wall and here this funnel like structure it is coming first and the ball it will be pushed ahead against the spring behind that one and the oil it is capable of easily flowing through this check wall it will go to the say rod end of the cylinder and the piston will be raised vertically upwards and we are going to have the oil returning from the cap end it will come to the say port it is A and A is connected to T at that time now the importance of the check wall you can observe in the earlier situation when the piston it was coming downwards at that time say the no use of the check wall was there but in case of the return stroke you can observe that we are having the use of the check wall so now it is P is connected to here it is B and from here the oil it is going to the cylinder through the check wall only it will not pass through the counterbalance wall but is it is going to pass through the check wall and it will go to the rod end and the piston will be raised vertically upwards the oil returning from the cap end it will go to the port A and A is connected to T at that time so like that what we are having is we are having the use of the counterbalance wall here and in case of the vertical downward motion we are going to have say uniform and say you can consider the situation when we are not having the counterbalance wall and we are having the spool position as one number so I have asked you the question with reference to the spool position second but if the spool position one is there so in case of that one say the combination of this total that is the pressure from the pump and the pressure due to the load will take place that is going to happen even if the pump pressure is lesser and if the load is heavier the load it is going to come automatically downward so suppose in this position we are having the say instead of three position if we are having only two position of the spool in case of that say even the oil supply is not there piston may come vertically downwards due to the load only if that is sufficiently heavy so like that we are going to have the use of the counterbalancing wall these are the references thank you