Abstract:
This invention relates to a hydraulic pig advance system comprising a control volume chamber containing hydraulic fluid and a force transmitting member. The system further comprises two directional control valves which can be selectively repositioned to cause hydraulic fluid to cycle the force transmitting member back and force such that in each cycle, a metered amount of hydraulic is transmitted into a pig housing where it causes a pig to move a predetermined distance.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a hydraulic pig advance system comprising a control volume chamber containing hydraulic fluid and a force transmitting member. The system further comprises two directional control valves which can be selectively repositioned to cause hydraulic fluid to cycle the force transmitting member back and force such that in each cycle, a metered amount of hydraulic is transmitted into a pig housing where it causes a pig to move a predetermined distance. 
   2. Description of the Prior Art 
   Pressurized accumulators have been used to use an injection burst of pressurized fluid to advance a pig in a process fluid line. The use of only a pressurized accumulators does not provide for precise control of the distance that the pig is advanced. 
   SUMMARY OF THE INVENTION 
   An apparatus embodiment of the present invention is directed toward a hydraulic pig advanced system comprising a control volume chamber having a first region and a second region. The chamber comprises hydraulic fluid. A first force transmitting member is moveably mounted in the chamber. 
   The invention further comprises a control volume chamber comprising a first region and a second region. The invention further comprises a first fluid line having a first end in communication with the first region of the chamber and a second end in fluid communication with the reservoir. The invention further comprises a second fluid line having a first end in fluid communication with the second region of the chamber and second end in fluid communication with the reservoir. 
   The invention further comprises a pig housing. The pig housing may also comprise a pig movably mounted in the housing. The invention further comprises a downstream flow path having first end in fluid communication with the housing, a second end in fluid communication with the first region of the chamber, and a third end in fluid communication with the second region of the chamber. 
   The invention further comprises a flow control device installed in the downstream flow path to selectively permit fluid flow from one of the first or second regions to the housing. 
   The present invention is also directed toward a method of advancing a pig in a pig housing. In the method of the present invention, hydraulic fluid is used to move a force transmitting member in a control volume from a first region of the control volume to a second region of the control volume. This movement of the force transmitting member causes a predetermined volume of hydraulic fluid to enter a pig housing, thereby causing a pig in the housing to move a predetermined distance. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a flow diagram of the present invention depicting flow through the first fluid line and first loop section. 
       FIG. 1   b  is a flow diagram of the present invention depicting flow through the second fluid line and second loop section. 
       FIG. 2  is a block diagram of a first method embodiment of the present invention. 
       FIG. 3  is a block diagram of a second method embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred apparatus embodiment of the present invention comprises a control volume chamber  10  having a first region  12  and a second region  14 , as shown in  FIGS. 1   a  and  1   b . The chamber comprises hydraulic fluid. A first force transmitting member  16  is moveably mounted in the chamber, as shown in  FIGS. 1   a  and  1   b . In a preferred embodiment, the control volume chamber is cylindrical and the first force transmitting member is round. 
   The invention further comprises a first fluid line  18  having a first end  20  in fluid communication with the first region of the chamber and a second end  22 , as shown in  FIG. 1   a . Additionally, the invention comprises a second fluid line  24  having a first end  26  in fluid communication with the second region of the chamber and a second end  28 , as shown in  FIG. 1   b.    
   The invention further comprises a fluid control loop  30  having a first loop section  32  in fluid communication with the second end of the first fluid line and a second loop section  34  in fluid communication with the second end of the second fluid line. The first loop section is that portion of control loop  30  extending from point A to point B as shown in  FIG. 1   a . The second loop section is that section of control loop  30  extending from point C to point D, as shown in  FIG. 1   b.    
   A first directional flow control device  36  is installed or positioned in the fluid receiving section so as to be capable of permitting fluid flow through the device  36  to the first loop section and the first fluid line or to the second loop section and second fluid line, depending upon the selective positioning of the first directional flow control device, as shown in  FIGS. 1   a  and  1   b.    
   A second directional flow control device  40  is installed or positioned in the fluid discharge section so as to be capable of permitting fluid through the device  40  from the first loop section and the first fluid line or from the second loop section and the second fluid line, depending upon the selective positioning of the second directional flow control device, as shown in  FIGS. 1   a  and  1   b . In one preferred embodiment, the first and second directional flow control devices are three way valves, each comprising three moveable valve members. In another preferred embodiment, the first and second directional control valves are hydraulically operated. 
   The invention further comprises a pig housing  44  having a first end  46  in fluid communication with the second directional flow control device such that fluid can flow from the control volume through the control loop and the second directional flow control device into the housing, as shown in  FIGS. 1   a  and  1   b.    
   In a preferred embodiment, the invention further comprises a second force transmitting member  48  which is moveably mounted in the housing such that the injection of fluid through the second directional flow control device into the housing will cause the second force transmitting member to move away from the first end of the housing, as shown in  FIGS. 1   a  and  1   b . The will result in displacement of the pig. In another preferred embodiment, the invention further comprises a pig  45  mounted in the pig housing, downstream of, and in fluid communication with, the second force transmitting member. In another preferred embodiment, the pressure resulting from the ejection of fluid into the pig housing can cause the pig to move a preselected distance. 
   In a preferred embodiment, the invention further comprises a fluid injection line  50  having a first end  52  and fluid communication with the first direction control valve. The fluid injection line further comprises a second end  54 , as shown in  FIG. 1   b . In this preferred embodiment, the invention further comprises a pressurized source of hydraulic fluid, such as an accumulator  56  comprising hydraulic fluid, as shown in  FIGS. 1   a  and  1   b . The accumulator is in fluid communication with the second end of the fluid injection line. 
   The present invention is also directed toward a method of advancing a pig in a pig housing. A first preferred embodiment of this method comprises selectively positioning a first directional flow control device and second directional flow control device to form a first flow path from the first directional control device, through a first loop section of a fluid control loop to a second fluid line, into a first region of a control volume, as shown in  FIG. 1   a . In a preferred embodiment, the positioning is performed with a control valve. 
   This preferred method embodiment of the present invention further comprises injecting a metered volume of hydraulic fluid through the first flow path to cause a first force transmitting member located in a first location in the control volume to move to a second location in the control volume, as shown by the arrow in control volume  10  in  FIG. 1   a . The movement of the first force transmitting member results in an ejection of a metered volume of fluid from the control volume into a flow path comprising a first downstream loop section  31  of the control loop, the second directional flow control device, and then into a pig housing. This fluid movement causes a second force transmitting member located in the housing to advance a preselected distance in said housing thereby causing a pig located in the housing downstream of the second force transmitting member to advance a preselected distance, as shown in  FIG. 1   a.    
   Another preferred method embodiment of the present invention provides for repositioning the directional flow control devices to permit reverse flow that also results in displacement of the pig located in the pig housing. In this preferred embodiment, the method of the present invention further comprises selectively positioning the first directional flow control device and the second directional flow control device to form a second flow path from the first directional flow control device through a second loop of the fluid control loop to a second fluid line and into a second region of the control volume, as shown in  FIG. 1   b.    
   This preferred method embodiment of the invention further comprises injecting a metered volume of hydraulic fluid through the second flow path to cause the first force transmitting member located in the second location of the control volume to move back into the first location of the control volume, thereby ejecting the metered volume of fluid from the control volume into a flow path comprising a second downstream loop section  33  of the control loop, the second directional flow control device, and then into a pig housing to cause the second force transmitting member located in the housing to advance a preselected distance in the housing. This movement of the second face transmitting member causes the pig located in the housing downstream of the second force transmitting member to advance a preselected distance. 
   In a preferred embodiment, the selective positioning of the present method invention involves the selective positioning of three way valves. In a preferred embodiment, this selective positioning is accomplished by actuating a hydraulically operated first directional control valve. 
   Another method embodiment of the present invention is depicted in the block diagram shown in  FIG. 2 . This embodiment comprises positioning at least one component of a flow system to form a first flow path comprising a control volume containing a force transmitting member, as shown in block  50  of  FIG. 2 . This method further comprises injecting a metered volume of hydraulic fluid through the first flow path to cause the force transmitting member located in a first location in the control volume to move into a second location in the control volume as shown in block  52  of  FIG. 2 . This method further comprises ejecting a metered volume of fluid from the control volume into a downstream flow path and then into a pig housing to cause a second force transmitting member located in the housing to advance a preselected distance in the housing, as shown in block  54  of  FIG. 2 . This method further comprises causing a pig located in the housing downstream of the second force transmitting member to advance a preselected distance, as shown in block  56  of  FIG. 2 . 
   Another preferred method embodiment of the present invention comprises all the steps shown in  FIG. 2 , plus the additional step of positioning at least one component of a flow system to form a second flow path comprising a control volume containing a force transmitting member as shown in block  60  of  FIG. 3 . This preferred method embodiment further comprises injecting a metered volume of hydraulic fluid through the second flow path to cause the first force transmitting member located in the second location in the control volume to move back into the first location in the control volume, as shown in block  62  of  FIG. 3 . This preferred method embodiment further comprises ejecting a metered volume of fluid from the control volume into a downstream flowpath and then into the pig housing to cause the second force transmitting member located in the housing to advance a preselected distance in the housing, as shown in block  64  of  FIG. 3 . This preferred method embodiment further comprises causing the pig located in the housing downstream of the second force transmitting member to advance a preselected distance, as shown in block  66  of  FIG. 3 . 
   The foregoing disclosure and description of the invention are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction may be made without departing from the spirit of the invention.