 Welcome to today's lecture on application and selection of accumulators. This is part one. Today, we shall learn very fundamentals of accumulators. Now in case of hydraulic circuits, where a large flow rate is required for a short period alternating with a low or no flow condition, the use of an accumulator allows smaller pumps and motors to be used thus reducing both installation and operating cost. So, basically we store the energy when the full energy is not required for the operations and it is kept in store and utilize when the more power is required, more pressure is required and flow is required. Now if we look into the cycle operation cycle of a any system which would require a pump having capacity of q 2, then what we can do say initially it needs V 1 and then V 3, then volume V 2 and then V 4 and so on. It goes on like this. This is one cycle, the next cycle is similar. In that case also we consider V 1 plus V 2 is less than V 3 and V 4. Here V 4 apparently it is 0 and this is the duration of such volume. Then what we can do? We can use a pump of this capacity and an accumulator. Obviously, this period should not be very long, these two periods then the fluids which will be stored in the accumulator during this period and this period can be utilized to have V 1 and V 2. If an oil pneumatic accumulator used, why this is oil and pneumatic accumulator? Because this oil is stored in the accumulator. Accumulator is nothing but some sort of a vessel, small vessel and within that the oil, in this case oil we are considering oil or liquid. It is stored whereas some part of this accumulator or initially accumulator is filled with say air and then air is compressed inside and oil is stored. This there might have one separator. That means inside this accumulator there might have another bladder in which the pneumatic or air pressure may be there or it might be open. That means oil can have direct contact with the air. Anyway, if we consider if an oil pneumatic accumulator is used, it is possible to store oil during the time T 2 minus T 1. Sorry this will be T 1, T 2 etc., not L 1. Say T 2 to T 1 and T 4 to T 3. These are not L T. As I have already explained, when the requirement is very low or 0 and to reuse it during this period T 1 and T 3, T 2, when the required flow rate is higher than the plumb-pump capacity Q 1. This pump must be selected to have the volumes V 1 plus V 2 which is again less than V 3 plus V 4. So, average capacity is calculated in this way. There are many potential applications including thermoplastic extruders, transfer lines in steel mills, rolling mills, machine tools, hydraulic sprays etc., these are only few to mention. By virtue of their design, both piston and diaphragm pumps create pulsation or pressure peaks during operation. This being undesirable and detrimental to both the smooth operations and operational life of the components. This we have learned that if there is a pulsation, there is a ripple, then that is performance wise it is not desired as well as it will affect the life of the components also. The fitting of a bladder type accumulator adjacent to and downstream of the pump will dampen the pulsation to an acceptable level. We have not yet seen what is a accumulator, but as I told that there will be a vessel usually that is made of steel metal body and inside there will be a bladder say for example, inside the bladder there will be air or some gas and the waste portion will be occupied by the oil. In fact, bladder is initially will remain inflated and then gradually it will the size of its will reduce and the oil will be stored inside. However, there is also possible that gas and oil they are in contact, the no bladder is used. How in any case the fitting of bladder type accumulator adjacent to downstream of the pump usually dampen, why usually it will dampen the pulsation to an acceptable level. Stable application are dosing pumps, pumps with small number of pistons etcetera. As we have learnt earlier the small pistons is having higher ripple small number of pistons and in most of the cases particularly in cylindrical pistons you will find that this numbers are odd to reduce the ripple and may be very common is 5, 7 and 9. So, 5 will have more ripple and if we use with that 5 pistons an accumulator in all applications then it is always better and dosing pump you understand it is some sort of feeding the oil may not be the main system. Now, improvement in performance can be realized from here what we have done that as if this oil is being pumped in from here then without this accumulator we may have ripple like this. And if we use an accumulator this ripple will reduce this is an accumulator this one very schematic diameter this better sorry this very schematic diagram that how it look like that we will see later. Now, another applications it shown here in the case of a sudden power loss that is pipe for joint failure pump breakdown the accumulator can provide sufficient energy to complete an operational cycle or to allow actuators valves etcetera to reset a safe position and therefore prevent damage to equipment or product. Now, what it is in this circuit what we find that there is the pump this is of course the filter and this is the reservoir from where the oil is being pumped through a non written valve or check valve this is very schematic it might be spring without spring. And then what we find in that line an accumulator is fitted in that accumulator as you see that this is as if a vessel inside there will be some gas is actually this is a gas pre charged or sometimes you will find a bladder with a charged gas or air is there. Now, this is a stock cock because sometimes we may not need to use the accumulator we can separate it. Now, what we find from here it is connected this line this is a joint junction point this is not crossing each other this is junction point that means this oil can first of all go through the relief valve then it will it can go to a two position valve this is or you can say some sort of switch on and off. And then there is four by two valve directional valve and through which it is going to a cylinder. And then from in the written line what we find that say this is a head side written line it can go to the tank again through this junction point or else the oil coming over here this can flow through this flow control valve and it also can go to the tank. Now, what will be the operations if we consider these connections then oil is going to the rod end side of the piston and oil from this head side is going back to tank. Now, in any case if the pressure is increased then oil will be relieved to the tank. However, when the full amount is not required in that case this is being stored and it is not being operated. Now, in case of any failure here then this oil can go this side and through this this is a passage through this oil will flow to the tank in a controlled manner and this piston although it will collapse to its position, but it will it will go very slowly. So, in that case this accumulator is helping to prevent this sudden collapse of this cylinder. And if it is connected like this in that case what we find that this oil is going to the accumulator. Of course, within the pressure setting of the relief valve and this oil this side oil is going perhaps this arrow could be in this directions is going back to the tank. So, this is just to prevent a system in case it fails. So, this is one application of such accumulator. Now, in a closed hydrostatic circuit the rise in temperature can cause an increase in pressure due to thermal expansion. In that case how this accumulator can help then title here it is written as volume compensator, but it will do an accumulator installed in the line will protect the valves gaskets and pressure gauges etcetera how common applications are found in refineries and pipelines where the temperature variations are there. So, in that case what actually happens this if there is rise in temperature there will be volume increase in the oil. So, excess volume will generate a pressure due to this pressure this oil can be stored in the accumulator and when temperatures comes down again that will be filled. So, very large pipelines and others where actually may not be hydrostatic transmission, but the oil is being transferred with full volume is filled in that case such accumulators will be very helpful. So, that is volume compensator. Now, we will think of the pressure compensator when a constant static pressure is required for a long period and accumulator is indispensable as it will compensate for pressure loss due to seepage through joints, seals etcetera as well as balancing pressure peak which may occur during the operating cycle. So, this means that we have to first keep in mind that oil is being when the pump is running then excess oil is being accumulated in the accumulator. Now, then if there is a loss suppose the system is stored that means a weight is lifted and then it is stored then what is happening there will be leakage and etcetera that leakage can be filled by the oil from such accumulator. Now, this is an system this is apparently some sort of press sort of things where this is being pressed with a pressure for a it is not very long time, but this operation is being done for a substantial time. And in that case what is the system this is a pump with non-returned valve and there is a direct relief valve here it is after the pump and then the non-returned valve this is the accumulator and then with this there perhaps is another relief valve is there and then oil is going like this and it is being used for for pressing this one. This is here written typical application are found in closing systems closing means in that case is pressing something closing something loading platforms curing presses machine tools lubrication system etcetera. In that case this accumulator whenever they excess flow and pressure will be required that will help. Now, for counter balancing earlier we have learned that counter balancing can systems can be designed using the pressure control valves. However, to some extent if we use an accumulator then the similar performance is also available and this is not for very large load small load and may be for small stroke it will be suitable. Now, how it works the balancing of a force or weight can be achieved by using hydraulic pistons driven by an accumulator thus avoiding the use of counter weights with attendant dimensional and weight savings. Now, this system looks like this typical application is machine tools hoist I would say small hoist not big hoist. Now, in that case what we find the pump is not shown but there is one stop cov not non-return valve stop cov is there. This is just to show the schematic diagram it can be replaced by non-return valve also we find the relief valve is here from the accumulator side and then it is connected to this side then how it operates that either we can run the pump but when the pump is not running then this oil will prevent the load for falling. So, in many cases you will find that machine tools particularly say let us consider the drill hole sorry drill head it is coming down when you just leave it that means when it the downward pressure is off then gradually it goes off. So, or we would like to maintain that positions in that case we can call it counter balancing and that can be done by an accumulator. Now, it can be used as a hydraulic line shock damper rapid valve closure can produce shock waves water hammer resulting in over pressurization of pipes joints valve etcetera and even it can damage the system. You see this water hammer is it is name is water hammer because this is may be first it observed with water flowing water storage system. But it can be it can happen in any liquid and if we close the valve suddenly what happens the say pressurized flow but it is blocked there will be very sharp rise of the pressure there that will generate a wave inside the oil and that wave propagates very rapidly and it oscillates it generate a dynamic condition inside the storage and that may even cause the bursting of the system pipelines etcetera. Now, let us see what happens the use of a suitable accumulator can neutralize or significantly reduce the shock. Now, this is an water storage system this is the pump from the reservoir and water is being pumped here then let us consider there is no accumulator without accumulator then suddenly if we close this valve then what will happen this water this side will be disconnected and there will be an water hammer inside and this will be large pulsation of this liquid. Now, if we use an accumulator then when we close this one then this shock will reduce and it even if it is not 0 amplitude is not 0 but this will low amplitude. So, this can be controlled by using this one definitely there will be a vibration sort of things or you can see this is acting as a damper in case of damper of course, there is a orifice and other system in that case it is nothing is there oil is going in and it is giving pressure on the bladder if it is inside or if the gas or pressure is air is there it is just knocking that air or gas and in that way the shock wave here is reduced. Now, typical application are water, fuel or oil distribution circuits, washing equipment etcetera. Now, definitely as you have explained for reduce the water hammer or shock there. So, definitely this such an accumulator can be used as a shock absorber also. Mechanical shocks in hydraulically driven equipment can be absorbed by accumulators. So, in this case what we have shown a some sort of carriage or this may be two wheels of a some earth moving equipment in that case what we find that this axle is on a damper this is damper and in that damper there is another accumulator is fitted but look into this there is no pump the oil is stored. So, there will be we have to pre-charge the system and then when any shock is coming over here then the oil is going inside and but this cannot be in here. So, while it is going back to the cylinder then it is going through this path. So, it acts as a something you can say that hydraulic spring sort of things also. So, instead of mechanical spring one accumulator or along with mechanical spring accumulator and a damper will have better vibration reduction than without accumulator. So, here the typical applications are forklift trucks, mobile trains, agriculture, civil engineering machinery etcetera. But these are usually used for large system not for the very small system. However, you may find that similar accumulator or very small accumulator also can be used for vibration isolations for small vehicles also. Now, I have just mentioned the hydraulic spring in that case again we will find that this can be used as an hydraulic spring. Now, the accumulator can be used with a advantage as an alternative to mechanical spring. Instead of mechanical spring we use some hydraulic spring. In that case if you look into these operations there is an accumulator fitted over this system and in that case this acts as an hydraulic spring. Probably this is an say hammering machines or forging machines. In that case we can use such hydraulic spring instead of mechanical spring. The thrust can be easily controlled to great accuracy over a wide range of pressures by oil pressure control without the need for springs or supports. This means in case of mechanical spring you cannot change the spring constant. Only say it can take certain amount load depending on the how much compression is possible up to the failure of course. In this case you can change the stiffness of the spring constant because you can increase the pressure of the system by regulating the pressure and your accumulator is selected accordingly. Now this is fluid separator and transfer barrier. This is another application of such an accumulator. In that case what is there and two sides of the system there are two different fluid in between there is an accumulator. The fundamentally the accumulator separates two fluids in the case of hydraulic applications say we can say nitrogen and oil. However, the accumulator can be used when pressure has to be transferred between two incompatible fluids hence the name is transferred. Now this is a very simple system. It is shown suppose what we consider that in figure simplified diagram for a fatigue test of a vessel is using water. In that case what we can do that we are testing fatigue testing of this cylinder and here we are creating this pressure by the oil, but inside there is water and this is separated by an accumulator. So, we are creating pressure here through this accumulator bladder the water inside is being pressurized and by oscillating this one we are applying the fatigue load to this vessel. So, this is one application of this accumulator which is called transfer. Then initial pressure pulse is generated by piston pump P this is the piston pump P using oil and equal volume and pressure is transferred to the water in the vessel by the accumulator. Many similar applications are found in petrochemical industries. Now another example of the transfer barrier is that in that case what we find that typical application of transfer between liquid and the gas this is a nitrogen by using an accumulator with additional gas bottles. So, here as if two accumulators and oil is being pumped here. So, this oil can go this way, but when we open it then this will be pressurized and then this nitrogen in this case nitrogen cylinder that will be filled or equalized something will be there. This is a very schematic applications of accumulator, but this is the transfer process these are usually used in industries say chemical industries and similar big industries. This application is especially convenient in those cases where the amount of liquid required is quite large compared to the small difference between the operating pressure. This is in the systems actually we need very large amount of oil with a very small pressure difference and then this accumulator helps is doing to meeting such requirements. To reduce the total capacity therefore, the number of accumulator requires the volume of available gas is increased by connecting the accumulators to additional gas bottles I see. So, we can add more bottles and by this we can reduce the number of accumulators. Now, this is another application where we can use the accumulator. This is fluid separator is same transfer barrier, but this application is steering unit. What we find that this is the steering and this is in steering valve and this is the accumulator and this is and we find that steering pump is here and steering pressure switch is here, manifold relief valve is here, steering hydraulic tank is there. Now, this is a circuit it is not very clear, but in, out, left and right that means there are this is some separate operation left, right motion and in and out motion. Now, these are two steering cylinders and double pressure relief valve is used here. Now, this actually if we think of the steering then in that case normally what we do suppose we are trying to turn the car or any vehicles in that case we move this one, then there the steering system which is fitted to the wheel hub of the steering wheels that is rotating the wheels to a position. Now, actual force is required much more than what the force we are applying. Then what happens in sometimes we suppose we are trying to negotiate these wheels, but we are turning this wheel we have to turn more and more to get the required action at these wheels. Now, in that case the accumulator is there that will help in help further to move these wheels. So, this is not very it will not be very clear from looking in the system, but this is just a system shown how it looks like. So, you will find usually these are not the ordinary car these are usually off highway vehicles where in the steering wheel you will find the huge load is required you will find and accumulator is fitted to the system. Without this accumulator this will also operate, but you in that case you will find you have to not only give more effort more load as well as you have to give the more motion to get such action, so get steering action. Accumulator will reduce such additional effort. Many parameters are involved in selection of an accumulator. Now, we will think of how this accumulator can be selected. We have seen just the very preliminary applications of accumulator. Now, we will look into how it can be selected. Now, the most important parts are in the process of selection. First of all we have to think of what will be the minimum working pressure P 1 and what is the maximum working pressure P 2. The value of P 2 must be lower or equal to the maximum authorized working pressure of the accumulator to be chosen for safety reasons. Now, in an accumulator whether it is with the bladder or simple the gas and oil accumulation, first of all we have to look into the capacity of such an accumulator. That accumulator can store say it is it can store a 10 megapascal. Then maximum pressure of the system should be below 10 megapascal. We cannot regulate that. That means accumulator pressure accumulator capacity is not regulated. It is always pre-charged. The value of P 1 is found in the ratio P 2 by P 0 is less than 4 normally. That P 0 is the charge pressure. P 1, P 2 is the working pressure of the system minimum and maximum. P 1 is the minimum, P 2 is the maximum, where P 0 is the charge pressure and usually P 2 by P 0 is less than 4. You see look into this value. Now, you as I told that it is less than 1 may think that P 0 should be that is charge pressure should be closed to this one. But actually what it means that if you measure the pressure of the bladder after charging you may find that pressure is some P 0 value. It will be less than the working pressure, but when this work pressure will work on that bladder or the gas or whatever is there that pressure will rise and that pressure will rise may rise a little above the P 2. It is design is in that way which will give optimum efficiency and operating life for life for calculation of pre-loading pressure P 0. This is called pre-loading pressure P 0. Volume of liquid to be stored or utilized that we have to consider. We are looking into the accumulator selections. First of all we will look into the pressures in that way then volume of liquid to be stored or utilized. That means in that case what may be the shortfall of the volume in the process. Accordingly we have to select the accumulator size. Sometimes we may find that one accumulator may not be sufficient. We have to go for one more accumulator. This information is required in addition to the maximum minimum pressure values for correct sizing the accumulator. Now we have to look into the method and application. It is important to establish if the gas during operation is subjected to isothermal or adiabatic condition. Now this is some thermal consideration we must do for accumulator selections. If compression or expansion is slow more than 3 minutes so that the gas maintains approximately constant temperature the condition is isothermal. Examples pressure stabilization volume compression compensation counter balancing lubrication circuit in that case this is isothermal condition. In other cases energy accumulator pulsation damper shock wave damper etcetera wind to high speed transfer heat interchange is negligible and therefore the condition is adiabatic. As a guide the adiabatic condition will exist when the compression or expansion period is less than 3 minutes. This guide means just thumb rule. If it is a 3 minutes then less than 3 minutes then you may consider the condition is adiabatic. So these adiabatic or isothermal is important for the what the gas we are using inside the accumulator. Operating temperature the operating temperature will determine the choice of materials for the bladder and steel cell and will have also have an influence on the pre loading pressures and consequently the accumulator volume type of liquid. This will determine the choice of accumulator body materials say what liquid we are using. Now maximum required flow rate is another factor the volume V 0 and or the size of the connection is influenced by the speed of response. Location it is important to know the eventual destination of the accumulator in order that the design can meet local design and test parameters. This is to I mean the position location selection of accumulator. Based on the foregoing it is possible to choose a suitable accumulator for the specific application required. There are other factors also which are not discussed but these are the main major factors we have to consider. Now we will look into the gas pre charge pressure. The accurate choice of pre charge pressure is fundamental in obtaining the optimum efficiency and maximum life from the accumulator and its components. So we have to look into this pre charge pressures which actually control the accumulator performance as well as the life of the components. The maximum storage or release of liquid is obtained theoretically when the gas pre charge pressure P 0 is as close as possible to the minimum working pressure. Now for practical purposes to give a safety margin and to avoid all sort of operation the value unless otherwise stated is P 0 is equal to 0.9 P 1. That means if you know the minimum system working pressure is P 1 then we can as a thumb rule we can select P 0 will be 0.9 of that. That means if P 1 is 1 megapascal then you can have the charge gas pressure without loading I mean no fluid is coming in may be 0.9 megapascal. The limit values of P 0 that is P 0 mean is equal to 0.25 into P 2. P 2 is the maximum pressure mind it or P 0 max is 0.9 of P 1. So P 0 should be 0.25 into P 2 one at one point we have shown P 2 P 0 P 2 by P 0 is equal to 4. So from there this relation and from this above relation we can have. So looking into this working pressure we can have that what should be the P 0 which will be in between this and this. Then special values as follows are used for pulsation damper and shock absorber. The P 0 is 0.6 plus 0.75 of P m. I think this relations we should look into again because this value is there without bracket. So if it is an additional part this is definitely the unit sensitive. So we have to look into this relation is whether it is correct or not or it is simply P 0 is equal to 0.8 into P 1 pulsation damper and shock absorber where P m average working pressure with free flow. Now this free flow means that when the there is no restriction over the flow from the accumulator. For hydraulic line shock damper it is again taken P 0 is equal to 0.6 plus 0.9 P m again it is the unit sensitive. So we have to look into this where P m average working pressure with free flow the same. But these two relations are different for two applications. For accumulator plus additional gas bottles it is 0.95 into 0.97 P 1 where P 0 is valid for maximum operating temperature required by the user. Checking of pre loading of accumulator takes place generally at a different temperature to the operational one. So that the value P 0 at the checking temperature becomes P 0 some critical value P 0 into theta c plus 273 theta 2 plus 273. This must be temperature in Celsius. Preachers pressure of accumulators directly supplied from the factory is referred to a temperature of 20 degree centigrade. Now this lecture will be continued further. We shall continue over the accumulator selections and then we will solve a problem also and we will learn more about the accumulator. Now the reference for this one is very old tutorial note in a fluid power. It is not journal you can say this magazine. It was in 1992 when this accumulator was still in development stage or it was finding its application and then this topic was found very interesting. So this is from that topic but next time we will also consult some book. Thank you for listening.