Abstract:
Apparatus and method of utilizing differential pressure to seat an almost-closed valve ball. Included are apparatus and means to protect valve ball from excessive closing force. Also included is a multiple valve arrangement to relieve excessive differential pressure.

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part application of application Ser. No. 832,445, filed Feb. 24, 1986, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     Gas and oil well swabs, particularly internal valving of pneumatically-operated valving in swabs as described in the teachings of U.S. Pat. No. 4,070,134, the valve being closed solely by the movement of a piston sliding inside a cylinder. No auxiliary actuating apparatus is utilized. In the event the valve ball is seated and pressure surrounding the pneumatic cylinder continues to build, the piston exerts excessive force on the valve ball, damaging the ball. 
     SUMMARY OF THE INVENTION 
     Apparatus and method for closing an almost-closed valve ball by providing a resilient coupling between the ball and the actuating rod. The increased pressure caused by the restriction of the flow of liquids through the almost-closed valve acts on the bottom of the valve ball, seating it onto the valve seat against the resiliency of the coupling. If the valve is fully closed but pressure continues to build around the pneumatic closing device, the resiliency of the coupling allows the piston rod to separate from the ball, relieving damaging pressure on the ball. Apparatus and method for relieving excessive pressure under the valve ball. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the pneumatically-operated swab for oil and gas wells. 
     FIG. 2 is the valve ball in an almost-closed position, before the differential pressure seats it. 
     FIG. 3 illustrates the present invention after the differential pressure has seated the valve ball. 
     FIG. 4 represents the addition of the relaxed valve ball tension relief mechanism, and 
     FIG. 5 is the relief mechanism in the actuated mode. 
     FIG. 6 shows the configuration of an additional small valve ball and seat mounted onto the primary valve ball. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The basic automatic swab, described in U.S. Pat. No. 4,070,134 and basically illustrated in FIG. 1, uses a pneumatic tube 2 and piston 4 actuated by changes in head pressure as the device sinks deeper in the oil, pulls a valve ball 8 hard-coupled to a piston rod 6 against a valve seat 10. The seating of the valve ball effectively shuts off the flow of natural gas through the swab. Consequently, the increasing gas pressure under the swab lifts it and its oil load to the surface. 
     This arrangement worked satisfactorily for the most part. However, a condition arises when the valve ball is almost closed, being about 1/8 inch from the seat. This restriction builds a slight pressure under the swab. This three or four pounds of pressure is sufficient to suspend the swab, stopping its descent. Since no more oil passes upward through the swab, the head pressure remains constant, the valve ball 8 never seats, and the swab stops indefinitely. 
     The first portion of the present invention as presented in FIG. 2 connects the valve ball 8 to the piston rod 6 through a mechanism comprising a piston 17, slideable in a cylinder enclosure 19 and lightly held downward by a compression spring 21. The arrows under the ball valve indicate pressure building from the restriction of the flow of gas. In FIG. 3, the pressure has risen to a point where it has pushed the ball valve 8 against the valve seat 10 compressing the spring 21. The swab is now effectively sealed. 
     Another situation can occur wherein the swab valve has closed but, due to a torn external seal or the shutting in of the well, pressure acting on the pneumatic tube continues to rise. The piston rod pulls increasingly harder on the valve ball and eventually the ball becomes distorted and useless. In FIG. 4, the valve ball 8 is coupled to the piston rod 6 by the mechanism shown in FIGS. 2 and 3, and additionally through an expansion spring 30 connected to the cylindrical enclosure 31 and the bottom of the piston rod 6. FIG. 4 shows the connection in a normal, relaxed state. In FIG. 5, the piston rod 6 is being pulled upward by the pneumatic cylinder by excessive head pressure. Since the valve ball 8 is seated and cannot move, the strain is relieved by the expansion of the spring 30. When the head pressure returns to normal, the piston rod 6 moves downward, relaxing the spring 30 to its normal state shown in FIG. 4. 
     A condition arises wherein excessive gas pressure builds under the valve ball. When this happens, the pneumatic tube 2 and piston 4, in FIG. 1, pushing on rod 6 is unable to unseat the valve ball 8. The pressure continues to build, stopping the operation of the swab and creating a dangerous condition. Referring to FIG. 6, a passageway is placed through the primary valve ball 14. A smaller secondary valve ball 15 is mounted beneath the primary valve ball 14 and is held against the bottom end of the passageway by the spring 17 contained in the cage 19. 
     When the actuating rod 6 moves downward to unseat the primary valve ball 14, the pin 12 first contacts the secondary valve ball 15 and unseats it. The pressure is then exhausted upward through the passageway in the primary valve ball 14. When the pressure is sufficiently reduced, the rod 6 can then unseat the primary valve ball 14. 
     The ball assembly hands on the flange of the pin 12 contacting the shoulders on the upper part of the passageway. The space between the pin 12 and the valve ball 15 allows the primary valve ball 14 to move upward from an almost-closed to a closed position as described earlier.