Patent Publication Number: US-9890622-B2

Title: Progressive cavity pump holdback apparatus and system

Description:
TECHNICAL FIELD 
     The present invention relates to progressive cavity pump systems, and more particularly to a holdback apparatus and system that prevents reverse rotation of the polish rod that drives a progressive cavity pump. 
     BACKGROUND ART 
     Progressive cavity pump systems used for pumping liquids, such as crude oil, from wells generally have a drive head above ground with a motor that drives a polish rod. The polish rod extends downwardly through a stuffing box at the top of the well casing and connects with the top of a sucker rod that drives the progressive cavity pump at the bottom of the well. 
     The sucker rod can extend downwardly several thousand feet. During operation of the pump, the sucker rod twists in response to the torque applied by the motor. The sucker rod can have several hundred revolutions of twist. When the motor is shut down or loses power, the torsional energy in the sucker rod can backspin the polish rod and motor at a high speed, potentially causing damage to the drive head and motor, and injuring personnel. 
     Several prior known devices controlled the rate of backspin while releasing the torsional energy stored in the sucker rod. These devices include hydraulic or viscous brakes, and mechanical brakes actuated by hydraulic or centrifugal force. Generally these devices are relatively complex. These devices release the torsional energy and the twist in the sucker rod, so that when the motor is restarted, the motor rotates the polish rod several hundred revolutions before the pump starts to pump again, wasting time and energy. 
     DISCLOSURE OF THE INVENTION 
     A progressive cavity pump system has a drive head, a polish rod, a motor, a sucker rod, a pump, and a holdback apparatus. The drive head is mounted on the well head on top of the casing for a well. The polish rod is rotatably mounted in the drive head. The motor drives the polish rod. The sucker rod is connected to and extends downwardly from the polish rod to the pump. The holdback apparatus includes a holdback housing and a one-way bearing. The holdback housing is rigidly attached to the drive head. The one-way bearing has an outer race that is pressed into the holdback housing and an inner race that connects to the polish rod. The inner race rotates in only one direction relative to the outer race and prevents reverse rotation of the polish rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Details of this invention are described in connection with the accompanying drawings that bear similar reference numerals in which: 
         FIG. 1  is a schematic front elevation view of a progressive cavity pump system embodying features of the present invention. 
         FIG. 2  is a perspective view of the holdback apparatus of the system of  FIG. 1 . 
         FIG. 3  is a front elevation view of the holdback apparatus of  FIG. 2 . 
         FIG. 4  is a sectional view of the holdback apparatus taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  is an exploded perspective view of the holdback apparatus of  FIG. 2 . 
         FIG. 6  is a cut-away top plan view of a one-way bearing of the holdback apparatus of  FIG. 2 . 
         FIG. 7  is a partial cut-away top plan view of an alternative one-way bearing of the holdback apparatus of  FIG. 2 . 
         FIG. 8  is a schematic front elevation view of the system of  FIG. 1  with an alternative mounting location for the holdback apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a progressive cavity pump system  11 , embodying features of the present invention, includes a drive head  14 , a polish rod  15 , a motor  16 , a sucker rod  17 , a progressive cavity pump  18  and a holdback apparatus  19 . The drive head  14  mounts on top of a well head  22  at the top of the casing  23  that extends down into the well  24 . The polish rod  15  is rotatably mounted in the drive head  14  and extends downwardly through the well head  22 . 
     The motor  16  shown is mounted on the side of the drive head  14 . The motor  16  is connected to the polish rod  15  to rotationally drive the polish rod  15 . Generally the motor  16  drives the polish rod  15  through a system of belts and sheaves or pulleys, but other drive systems can be used. The sucker rod  17  connects to the lower end of the polish rod  15 , extending downwardly, and is rotated by the polish rod  15 . 
     The pump  18  has a stator  26  and a rotor  27  that fits inside the stator  26 . The stator  26  is connected to the lower end of the casing  23 . The rotor is connected to the lower end of the sucker rod  17  and rotated by the sucker rod  17 . The holdback apparatus  19  mounts on the top of the drive head  14 , and includes a holdback housing  30  and an elongated retaining arm  31 . The retaining arm  31  attaches to the holdback housing  30  at one end, extends radially outwardly, and attaches to the drive head  14  at the other end. 
     As shown in  FIGS. 2-5 , the holdback apparatus  19  also includes a one-way bearing  34  and a holdback shaft  35 . The holdback housing  30  includes an elongated, substantially cylindrical, hollow body  37 , a flange  38 , a lower end cap  39 , an upper end cap  40  and a seal  41 . The flange  38  projects radially outwardly from the body  37  for attachment of the retaining arm  31 . The body  37  defines an interior cavity  43 . 
     The one-way bearing  34  has an outer race  45  and an inwardly spaced inner race  46 . The inner race  46  is mounted in the outer race  45  and rotatable in the outer race  45  in one direction only. The outer race  45  is sized to be pressed into the interior cavity  43 . 
     The holdback shaft  35  is a cylindrical shaft, preferably of the about the same diameter as the polish rod  15 . The inner race  46  is sized to be pressed onto the holdback shaft  35 . An internally threaded cavity  48  extends inwardly from each end of the holdback shaft  35 . The threaded cavities  48  are sized and threaded to thread onto an externally threaded upper end of the polish rod  15 . 
     The lower end cap  39  has a shaft aperture  50  that the holdback shaft  35  extends through, and a plurality of circumferentially spaced fastener apertures  51  that threaded fasteners (not shown) extend through to fasten the lower end cap  39  to the body  37 . The upper end cap  40  has a shaft aperture  53  that the holdback shaft  35  extends through, a plurality of circumferentially ventilation apertures  54  that extend vertically through the upper end cap  40 , and external threads  55  that are sized to thread into internal threads  56  at the upper end of the interior cavity  43  to fasten the upper end cap  40  to the body  37 . 
     The seal  41  includes a lower seal race  58 , an upper seal race  59 , a spring  60 , and a seal washer  61 . The lower and upper seal races  58  and  59  are generally flat, hollow rings that fit snugly around the holdback shaft  35 . The interior cavity  45  in the body  37  has an inwardly projecting lip  62  below the outer race  45 . The seal washer  61  is a flat, hollow ring that fits around the holdback shaft  35 . The spring  60  is a spiral compression spring that fits around the holdback shaft  35  between the upper seal race  59  and the seal washer  61  to bias the lower and upper seal races  58  and  59  against the lower end cap  39 . Oil in the interior cavity  45  cools and lubricates the one-way bearing  34 , and the seal  41  prevents leakage of the oil. 
     The one-way bearing  34  can be a ramp and roller clutch  64  as shown in  FIG. 6 . The ramp and roller clutch  64  shown has a plurality of circumferentially spaced ramps  65  on the inside of the outer race  45  and a plurality of circumferentially spaced rollers  66  between the outer and inner races  45  and  46 . The rollers  66  allow the inner race  46  to rotate freely in the clockwise direction and prevent the inner race  46  from rotating in the counterclockwise direction by wedging between the ramps  65  and the inner race  46 . 
     The one-way bearing  34  can alternatively be a sprag clutch  68  as shown in  FIG. 7 . The sprag clutch  68  shown has a plurality of circumferentially spaced, generally hourglass shaped sprags  69  between the outer and inner races  45  and  46 . The sprags  69  allow the inner race  46  to rotate freely in the clockwise direction and prevent the inner race  46  from rotating in the counterclockwise direction by wedging between the outer race  45  and the inner race  46 . Other types of one-way clutches and bearings can be used. 
     If the progressive cavity pump system  11  has a failure below the well head  22 , such that the sucker rod  17  needs to be unwound, a rod pin can be threaded into the threaded cavity  48  at the top of the holdback shaft  35 . A rod wrench can be applied to the rod pin, the retaining arm  31  can be released, and the sucker rod  17  can be manually unwound. 
       FIG. 8  shows the progressive cavity pump system  11  with the holdback apparatus  19  located below the drive head  14 . The holdback housing  30  is integrated with the drive head  14 , being either manufactured as part of the drive head  14  or attached to the drive head  14  before the drive head  14  is mounted on the well head  22 . Also, the holdback housing  30  can be a part of an existing drive head  14  with the one-way bearing  34  replacing or supplementing an existing bearing. 
     The progressive cavity pump system  11  prevents the sucker rod  17  from unwinding when the motor  16  loses power and further prevent reverse rotation of the rotor  27 , which would allow fluid in the casing  23  above the pump  18  to drain out. The holdback apparatus  19  eliminates rewinding the sucker rod  17  and repumping the fluid when the motor  16  is restarted. 
     Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example and that changes in details of structure may be made without departing from the spirit thereof.