Hydraulically Operated Polished Rod Clamp

Abstract

A polished rod clamp includes a clamp housing having a central passage passing through a tapered bore. A wedge lock is arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock grips a rod in the central passage in a lock position. A first reciprocating piston is arranged to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to the lock direction of the wedge lock. A second reciprocating piston is arranged to apply a second force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a second direction that is opposite to the first direction.

What is claimed is: 
     
         1 . A polished rod clamp, comprising:
 a clamp housing having a central passage and a tapered bore, wherein the central passage passes through the tapered bore;   a wedge lock arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock circumscribes the central passage, the second surface being adapted for gripping a rod extending through the central passage in a lock position of the wedge lock; and   a first piston arranged in a first cavity within the clamp housing to reciprocate within the first cavity in response to hydraulic pressure and to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to a lock direction of the wedge lock.   
     
     
         2 . The polished rod of  claim 1 , further comprising a second piston arranged within a second cavity in the clamp housing to reciprocate within the second cavity in response to hydraulic pressure and to apply a second force to the wedge lock that effects a relative motion between the wedge lock and the tapered surface in a second direction opposite to the first direction. 
     
     
         3 . The polished rod clamp of  claim 1 , wherein the wedge lock comprises a wedge body terminating in a flange. 
     
     
         4 . The polished rod clamp of  claim 3 , wherein a longitudinal slot is integrally formed with the wedge body and flange such that the wedge lock is flexible to expand or contract. 
     
     
         5 . The polished rod clamp of  claim 3 , wherein a plurality of circumferentially spaced longitudinal grooves is formed in the wedge body and a plurality of circumferentially spaced radial slots is formed in the flange to facilitate distribution of force along a circumference of the wedge lock. 
     
     
         6 . The polished rod clamp of  claim 2 , wherein the first piston and second piston are arranged in opposing relation within the clamp housing. 
     
     
         7 . The polished rod clamp of  claim 6 , wherein the wedge lock has a flange received in between the first piston and the second piston such that the first piston and the second piston are configured to apply the first force and the second force, respectively, to the flange. 
     
     
         8 . The polished rod clamp of  claim 1 , further comprising at least a first port formed in the clamp housing for communication of hydraulic fluid to the first cavity. 
     
     
         9 . The polished rod clamp of  claim 8 , further comprising a first fitting removably mounted in the at least a first port, wherein the first fitting is selected from the group consisting of grease fitting, plug, and valve. 
     
     
         10 . The polished rod clamp of  claim 8 , further comprising at least a second port formed in the clamp housing for communication of hydraulic fluid to the second cavity. 
     
     
         11 . The polished rod claim of  claim 10 , further comprising a second fitting removably mounted in the at least a second port, wherein the at least a second fitting is selected from the group consisting of grease fitting, plug, and valve. 
     
     
         12 . A drive system for a rod pump, comprising:
 a rod pump driver;   a clamp housing coupled to the rod pump driver, the clamp housing having a central passage and a tapered bore, wherein the central passage passes through the tapered bore;   a wedge lock arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock circumscribes the central passage, the second surface being adapted for gripping a rod extending through the central passage; and   a first piston arranged to reciprocate in a first cavity within the clamp housing in response to hydraulic pressure and to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to a lock direction of the clamp.   
     
     
         13 . The drive system of  claim 12 , further comprising a second piston arranged to reciprocate in a second cavity within the clamp housing in response to hydraulic pressure and to apply a second force to the wedge lock that effects a relative motion between the wedge lock and the tapered surface in a second direction corresponding to an unlock direction of the clamp. 
     
     
         14 . The drive system of  claim 12 , wherein the rod pump is a rotary pump and the rod pump driver comprises a rotary drive having a drive shaft with a central bore, wherein the clamp housing is mounted on the drive shaft such that the central passage is aligned with the central bore. 
     
     
         15 . The drive system of  claim 12 , wherein the rod pump is an axially reciprocating pump and the rod pump driver is a mechanism for providing axial reciprocating motion to a rod string. 
     
     
         16 . A method of coupling a rotary drive to a rod string, comprising:
 mounting a polished rod clamp on a drive shaft of a rotary drive such that a central passage of the polished rod clamp is aligned with a central bore of the drive shaft;   receiving the rod string in the aligned central bore and central passage; and   applying hydraulic pressure to a first piston in the polished rod clamp to drive a wedge lock in the polished rod clamp to a lock position in which the wedge lock grips the rod string in the central passage.   
     
     
         17 . The method of  claim 16 , further comprising applying hydraulic pressure to a second piston in the polished rod clamp to drive the wedge lock to an unlock position in which the wedge lock releases the rod string in the central passage. 
     
     
         18 . The method of  claim 17 , wherein applying hydraulic pressure to the first piston results in sliding of a surface of the wedge lock along a tapered surface in the polished rod clamp in a first direction. 
     
     
         19 . The method of  claim 18 , wherein applying hydraulic pressure to the second piston results in sliding of the surface of the wedge lock along the tapered surface in the polished rod clamp in a second direction opposite to the first direction. 
     
     
         20 . The method of  claim 19 , wherein the first piston is arranged to reciprocate in a first cavity in the polished rod clamp, and wherein applying hydraulic pressure to the first piston comprises injecting grease into the first cavity to pressurize the first cavity. 
     
     
         21 . The method of  claim 20 , wherein the second piston is arranged to reciprocate in a second cavity in the polished rod clamp, and wherein applying hydraulic pressurize to the second piston comprises injecting grease into the second cavity to pressurize the second cavity.