FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an improvement on U.S. Pat. No. 4,801,126 “Hydraulically operated lift mechanism”. This patent includes a three chamber cylinder that allows for the use of one chamber as a gas accumulator acting as a phantom counterweight for vertical Industrial hoisting and artificial lift pumping applications. 
     This mentioned patented invention has been successfully applied for artificial lift on the oil and water pumping industries, among others. It has done so with 10% of the weight of the classic equivalent Beam pump, and less than 50% energy consumption per barrel of fluid extracted. 
     However, when applications of the mentioned patent use the triple cylinder with the plunger pointing up, which is the case for artificial lift, the gas chamber ends being situated at the lower part of mentioned cylinder. It is very difficult to stop a migration of gas to the up chamber, not having the possibility to bleed the gas from the hydraulic oil, creating a much lower life for the cylinder and several maintenance issues. This use is a 24/7 application, totaling 8760 hours a year, a major engineering challenge. 
     This application entails the conversion of the triple cylinder gas chamber to contain now oil instead of gas. That former gas chamber will now be connected to an independent accumulator (gas over oil), whereas now the gas is above the oil instead of below, avoiding in this manner any migration of gas to the oil. A small third pump is now able to replenish the oil lost or the system can bleed this new oil chamber that no longer contains gas. 
     This new arrangement creates other major improvements:
         When a loss of load occurs (wire rope broken, rod parted) the present solution closes a ball valve that connects the large accumulator to the triple cylinder. No matter how fast this ball valve closes, a volume of pressurized gas stays in the cylinder launching the plunger at a very high speed to the end stop. On the new arrangement, when the load is lost, a check valve closes the oil connection to the triple cylinder, with a minimum energy left, hence avoiding the launching of the plunger.   In artificial lift, when a pump stops, normally the rod load will change as time passes. In the older design of the triple cylinder, when that occurs, the position of the plunger changes due to the gas still in the cylinder, this gas will force a changed position when the load changes. This new arrangement will maintain the same position of the rod, no matters what occurs with the load.   When, during servicing the unit, it is necessary to descend the plunger, the present technology makes this task difficult due to the rebounding of the plunger containing gas. As the new design has no gas, the annoying rebounding disappears.   All seals of the triple cylinder are now under oil, making a leak far less important and increasing the life of the cylinder many times over, and at the same time eliminating many maintenance problems.       

     In one of the preferred designs, one or more matrix variable frequency drive (MVFD) designed for real four quadrant applications is used, able to return power to the grid with very high efficiency. This feature is indispensable as a vertical pumping movement has always energy generating parts of a cycle which is, with today&#39;s technology, energy lost. This device new MVFD has the added advantage to eliminate the harmonics on the power lines, a major problem with a standard VFD for the power companies. 
     In another design version, the prime mover, instead of an electric motor uses an engine propelled by the casing gas of the well itself. This application is very well suited to this design as a triple cylinder has a very low kinetic energy content, compared with a typical Beam pump, and the engine does no longer have the heavy kinetic load of the old design. 
     In another design version, a fixed speed electrical motor is attached to an over center swash plate pump/motor. The pump controls now the direction of the flow, the accelerations and decelerations as well as the speed. This set up eliminates the nasty frequencies created by variable frequency drives, and is also able to motor as well as generate power back to the grid. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided, as an add-on to the three chamber cylinder and structure of the present solution, a gas over oil accumulator, the oil port connected to the former gas chamber via a very large pilot operated check valve. The gas side of said accumulator is now connected to the large gas containers of the structure itself. 
     In one version, the hydraulic power system consist in one or more fixed delivery hydraulic motor-pumps with reversal operation via one or more electrical motors controlled by a variable frequency drive (VFD). This VFD could be a standard one with resistors to dissipate the generating energy, or better a Matrix VFD (MVFD), which automatically discharges to the grid the excess energy generated by the pumping system. Efficiency is enhanced and maintenance is lowered. 
     In another hydraulic power system version, one or more “over the center hydraulic pumps” moved by a fixed speed unidirectional electric motor or motors, or a natural casing gas or diesel engine as a prime mover, whereas the flow reversal, speed, accelerations and decelerations are realized by the “over the center hydraulic pump or pumps”. 
     The hydraulic system will incorporate a low pressure charge pump to maintain a minimum pressure on the system, cool, take air out and filter the oil. A small accumulator will be used to help maintain the pressure when an over the center pump is used; another option is a VFD for the charge motor and used to maintain a constant pressure with a variable flow. 
     The hydraulic system will incorporate a medium pressure very low flow pump to refill the accumulator oil if there is a loss to the upper and/or lower chambers of the triple cylinder in all the versions for the system. 
     An electric system, containing a PC or PLC as the automatic interface to control this machinery. A screen will be available to control, set parameters, get feedback and diagnose failures. Moreover wireless control will also be available. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a large side view of the extra oil/gas accumulator positioning. 
         FIG. 2  is a schematic illustration of hydraulic schematics in accordance with one aspect of the invention. 
         FIG. 3  is an illustration of a large flow pilot operated check valve. 
         FIG. 4  is an illustration of the mechanical connection between the check valve and the bottom of the accumulator and the triple cylinder. 
         FIG. 5  is a top view of the mechanical connection of  FIG. 3 . 
         FIG. 6  is a schematic illustration of the hydraulic schematics using over the center hydraulic pumps. 
       
         
           
                 
               
                 
                 
               
             
                 
                     
                 
                 
                   Part Name 
                 
                 
                     
                 
               
               
                 
                     
                 
               
            
             
                 
                   10 
                   Gas accumulator 
                 
                 
                   12 
                   oil/gas accumulator 
                 
                 
                   13 
                   Structural base 
                 
                 
                   14 
                   Service ball valve 
                 
                 
                   16 
                   Piston separator/oil/gas 
                 
                 
                   18 
                   Plunger of triple cylinder 
                 
                 
                   19 
                   (Matrix) Variable frequency drive 
                 
                 
                   20 
                   Variable speed reversible motor 
                 
                 
                   22 
                   Reversible hydraulic pump fixed delivery 
                 
                 
                   24 
                   Leakage flow meter with switch 
                 
                 
                   26 
                   Pressurized reservoir 
                 
                 
                   28 
                   Safety relief valve down flow 
                 
                 
                   30 
                   Safety relief valve up flow 
                 
                 
                   32 
                   Compensation valve 
                 
                 
                   34 
                   Check valve down flow 
                 
                 
                   36 
                   Check valve up flow 
                 
                 
                   38 
                   Compensation accumulator 
                 
                 
                   40 
                   Oil down chamber 
                 
                 
                   41 
                   Pressure gage 
                 
                 
                   42 
                   Oil up chamber 
                 
                 
                   43 
                   Triple cylinder 
                 
                 
                   44 
                   Oil counterweight chamber 
                 
                 
                   46 
                   Replenishing check valve 
                 
                 
                   47 
                   Accumulator relief valve 
                 
                 
                   48 
                   Relief valve charge system 
                 
                 
                   49 
                   Check valve 
                 
                 
                   50 
                   Air oil cooler 
                 
                 
                   52 
                   Large flow piloted safety Check valve 
                 
                 
                   53 
                   Ball valve accumulator discharge 
                 
                 
                   54 
                   Opening valve three way, two position 
                 
                 
                     
                   Pilot operated with manual control 
                 
                 
                   56 
                   unidirectional flow control 
                 
                 
                   58 
                   solenoid valve three way, two position 
                 
                 
                   60 
                   Check valve 
                 
                 
                   62 
                   Low pressure filter 
                 
                 
                   63 
                   Medium pressure filter 
                 
                 
                   64 
                   Pressure drop switch 
                 
                 
                   66 
                   Make up low pressure charge pump 
                 
                 
                   68 
                   Prime mover of 66 and 70 pumps 
                 
                 
                   70 
                   Refill accumulator pump 
                 
                 
                   72 
                   Solenoid valve two way, two position, N.O. 
                 
                 
                   74 
                   Solenoid valve two way, two position, N.C. 
                 
                 
                   76 
                   Linear transducer, accumulator 
                 
                 
                   78 
                   Linear transducer, three chamber cylinder 
                 
                 
                   80 
                   Variable frequency drive 
                 
                 
                   82 
                   Oil/gas accumulator bottom 
                 
                 
                   84 
                   Bottom of triple cylinder 
                 
                 
                   86 
                   Bias spring 
                 
                 
                   88 
                   Pilot opening piston 
                 
                 
                   90 
                   Check valve body 
                 
                 
                   92 
                   Over center swash plate pump 
                 
                 
                   94 
                   Natural Gas Engine/or electric motor 
                 
                 
                   96 
                     
                 
                 
                   PT1 
                   Pressure transducer cylinder down 
                 
                 
                     
                   chamber 
                 
                 
                   PT2 
                   Pressure transducer cylinder up chamber 
                 
                 
                   PT3 
                   Pressure transducer cylinder acc. chamber 
                 
                 
                   PT4 
                   Pressure transducer accumulator chamber 
                 
                 
                     
                 
               
            
           
         
       
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  represents one arrangement-of many-for the add-on oil over gas accumulator reference  12 , with the large pilot operated check valve No  52 . Pos  10  is the structural gas accumulator, pos  43  is the triple cylinder and pos  13  is the mechanical base structure. 
     One preferred embodiment of the present invention is illustrated on  FIG. 2  of the drawings. It should be appreciated that the embodiment shown in  FIG. 2  of the drawing is representative of a hydraulic schematics and variations and modifications may be made in accordance with the application. 
     With reference to  FIG. 2  of the drawings, there is shown a preferred embodiment of one hydraulic circuit which falls within the scope of the Invention.  FIG. 2  of the drawings shows schematically a triple cylinder  43 , a gas over oil accumulator pos  12 , and a pressured gas accumulator  10 , connected to the gas side of the “gas over oil accumulator” pos  12 . The pilot operated check valve pos  52 , connects the oil side of the gas over oil accumulator with the third chamber of the triple cylinder, pos  44 .
         On the same reference  FIG. 2 , the operation of the unit is as follows: Matrix variable frequency drive (or MVFD) pos  19 , controls speed, acceleration, deceleration and direction of electrical motor  20  which commands a reversible fixed flow hydraulic pump-motor pos  22 . A matrix VFD allows for the use of a four quadrant real operating drive, generating power back to the grid in a very efficient way. In another version it is used a VFD with resistors to dissipate the generated energy. Pump-motor  22  flow oil to chamber  40  of triple cylinder  43  when going down, and will flow through internal rod  42  to go up.   In order for the system to operate, the check valve  52  has to be piloted open by pilot operated three way two position valve  54 , which receives a pressure signal from solenoid valve three way, two position  58 . The pressure signal originates from charge pump  66 , propelled by electrical motor  68 . So, to be able to operate check valve  52 , it is required for the charge system to be pressurized, and an electrical signal to be received by the solenoid valve  58 .   Charge pump  66  sends pressure to solenoid valve  58  and keeps a steady pressure on the low pressure side of the cylinder. The steady pressure is either maintained by an accumulator  38  or by a VFD controlling motor  68  speed with feed back by pressure transducer PT 5 . The charge pump flow goes trough filter  62 -with pressure drop indicator  64 -via check valve  60 . Gage  82  indicates the visual charge pump pressure.   Charge pump  66  flow goes through relief valve  48  and cooler  60  ending back into reservoir  26 . Replenish valve  46  allows the accumulator side of triple cylinder to avoid any vacuum. Safety relief valve  47  limits the accumulator pressure  44 . Relief valves  28  and  30  limits the maximum pressure and valve  32  connects the low pressure side of the triple cylinder with the charge line.   Charge pump  66  goes through low pressure filter  62  and pressure drop indicator  64  and check valve  60 .   Replenish pump  70  allows the refill of the oil of the accumulator oil side, in case some oil is lost to the other chambers of the triple cylinder. Pump  70  flows through medium pressure filter  63  all the time. This pump flow is normally going back to tank through cooler  50  under null pressure via solenoid valve  72 . To operate this function, solenoid valve  72  is activated-closed, and solenoid valve  74  is also activated to open, leaving the charge pump flow  66  to go to tank. The ratio of flow among pump  66  and  70  will be around 10 to 1. This operation could be done manually or automatically. Relief valve  47  adjustment allows the reduction of the oil volume in the accumulator if a leak occurs from the triple cylinder to the accumulator. There will be no nitrogen gas lost.   The system is completed by pressure transducers PT 1  to PT 4  and linear transducers  78 -rod positioning, and  76 , piston  16  position. Flow switch or pressure transducer  24  controls the status of the leakage of pump-motor  22  for service purposes.     FIG. 3  is a cutaway of pilot operated check valve  52 , which has to handle very large flows, starting above 100 GPM. Port a has the accumulator pressure that is used to open the check valve via port C. Piston  88  diameter should be higher than 10% than check piston  90  diameter. Spring  86  guaranteed than, absent pressure pilot at port C, the check valve is closed by check valve body, stopping any transmission of flow and pressure to the triple cylinder.     FIG. 4  is a side view one version of the bottom arrangement of the mechanical/hydraulic arrangement. Pos  2  is the bottom of the oil over gas accumulator, Pos  52  is the large flow pilot operated check valve and  84  is the bottom of the triple cylinder.     FIG. 5  is a top view of the bottom gas over oil accumulator  82 , the large check valve  52  and the bottom of the three chamber cylinder  84 .     FIG. 6  is very similar to  FIG. 2  with the propelling differences as follows:   Oil flow comes now though a over center swash plate pump  92 , motored by a constant speed natural gas or diesel engine  94 , or a standard squirrel cage fixed speed electrical motor. Now the pump creates the speed, accelerations, decelerations and direction of the oil flow instead of a matrix VFD  19  in  FIG. 2 .   In  FIGS. 2 and 6  a flow switch or transducer  24  allows for the direct feedback of the pump/motor leakage, facilitating troubleshooting and maintenance. Also a Pressure gage  41  is installed.
A hydraulic lift system for artificial lift pumping or industrial hoisting comprises a three chamber cylinder, a gas over oil accumulator, a large structural gas accumulator and a large flow pilot operated check valve. A matrix variable frequency drive, a standard variable frequency drive, an electrical squirrel cage motor or a natural gas engines are part of the main prime mover alternatives.