Multi-Cylinder Hydraulically-Driven Pump System

Abstract

A hydraulically-driven pumping unit for pumping a working fluid includes a pair of double-acting hydraulic piston-cylinder (HPC) assemblies, each having a central axis, a hydraulic cylinder, a piston, and a rod coupled to the piston for axial movement relative to the first hydraulic cylinder. The pumping unit also includes a hydraulic fluid source and an exhaust path for hydraulic fluid. The two hydraulic cylinders are coupled to the hydraulic fluid source and the exhaust path such that the movements of the two pistons are synchronized. The two HPC assemblies are configured for phase-shifted operation such that when pumping unit is reciprocating the two pistons and rods, the a first pair of the pistons and rods always has a different combination of axial position and direction of travel than does a other pair of the pistons and rods. During phase-shifted operation, at least one of the two rods is moving to extend further beyond the corresponding hydraulic cylinder at all times.

What is claimed is: 
     
         1 . A hydraulically-driven pumping unit for pumping a working fluid, the pumping unit comprising:
 a first double-acting hydraulic piston-cylinder (HPC) assembly comprising a first central axis, a first hydraulic cylinder, a first piston, and a first rod coupled to the first piston for axial movement relative to the first hydraulic cylinder;   a second double-acting hydraulic piston-cylinder (HPC) assembly comprising a second central axis, a second hydraulic cylinder, a second piston, and a second rod coupled to the second piston for axial movement relative to the second hydraulic cylinder;   a hydraulic fluid source; and   an exhaust path for hydraulic fluid;   wherein the first and second hydraulic cylinders are coupled to the hydraulic fluid source and the exhaust path such that movements of the first and second pistons are synchronized;   wherein the first and second HPC assemblies are configured for phase-shifted operation such that when pumping unit is reciprocating the two pistons and rods, the second piston and rod always have a different combination of axial position and direction of travel than do the first piston and rod, and such that at least one of the two rods is moving to extend further beyond the corresponding hydraulic cylinder at all times.   
     
     
         2 . The hydraulically-driven pumping unit of  claim 1 :
 wherein the first piston defines a first extension-chamber and a first retraction-chamber in the first hydraulic cylinder;   wherein the second piston defines a second extension-chamber and a second retraction-chamber in the second hydraulic cylinder;   wherein the first piston is configured to move axially within the first hydraulic cylinder to a first far-extended position, to a first retracted position, and to a first extended position disposed between the first far-extended position and the first retracted position;   wherein the second piston is configured to move axially within the second hydraulic cylinder to a second far-extended position, to a second retracted position, and to a second extended position disposed between the first far-extended position and the first retracted position;   wherein the pumping unit is configured with at least these following operational states for the first HPC assembly:
 a first state in which the first extension-chamber is in fluid communication with the hydraulic fluid source; and 
 a second state in which the first extension-chamber is in fluid communication with the exhaust path; 
   wherein the pumping unit is configured with at least these following operational states for the second HPC assembly:
 a third state in which the second extension-chamber is in fluid communication with the hydraulic fluid source; 
 a fourth state in which hydraulic fluid is exhausted from the second extension-chamber is in fluid communication with the exhaust path; 
   wherein the pumping unit is configured to perform a first transition, transitioning the second HPC assembly from the fourth state to the third state when the first piston reaches the first extended position while the first rod moves to extend further beyond the first hydraulic cylinder, or when the second piston reaches the second retracted position while the second rod retracts;   wherein the pumping unit is configured to perform a second transition, transitioning the first HPC assembly from first state to the second state when the first piston reaches the first far-extended position while the first rod moves to extend further beyond the first hydraulic cylinder;   wherein the pumping unit is configured to perform a third transition, transitioning the first HPC assembly from the second state to first state when the second piston reaches the second extended position while the second rod moves to extend further beyond the second hydraulic cylinder, or when the first piston reaches the first retracted position while the first rod retracts; and   wherein the pumping unit is configured to perform a fourth transition, transitioning the second HPC assembly from the third state to the fourth state when the second piston reaches the second far-extended position while the second rod moves to extend further beyond the second hydraulic cylinder.   
     
     
         3 . The hydraulically-driven pumping unit of  claim 2  further comprising a rod-end fluid circuit configured to provide fluid communication between the first retraction-chamber in the first hydraulic cylinder and a second retraction-chamber in the second hydraulic cylinder;
 wherein the rod-end fluid circuit is fluidically-isolated from the hydraulic fluid source in at least one mode of operation. 
 
     
     
         4 . The hydraulically-driven pumping unit of  claim 2 :
 wherein the first HPC assembly is in the first state during the first transition;   wherein the second HPC assembly is in the third state during the second transition;   wherein the second HPC assembly is in the third state during the third transition; and   wherein the first HPC assembly is in the first state during the fourth transition.   
     
     
         5 . The hydraulically-driven pumping unit of  claim 2 :
 wherein the first state and the second state are mutually exclusive; and   wherein the third state and the fourth state are mutually exclusive.   
     
     
         6 . The hydraulically-driven pumping unit of  claim 5  further comprising:
 a first control valve fluidically coupled between the first extension-chamber and the hydraulic fluid source and configured to activate and deactivate the first state; and 
 a second control valve fluidically coupled between the second extension-chamber and the hydraulic fluid source and configured to activate and deactivate the third state. 
 
     
     
         7 . The hydraulically-driven pumping unit of  claim 6  further comprising:
 a first exhaust valve fluidically coupled between the first extension-chamber and the exhaust path and configured to activate and deactivate the second state; and 
 a second exhaust valve fluidically coupled between the second extension-chamber and the exhaust path and configured to activate and deactivate the fourth state. 
 
     
     
         8 . The hydraulically-driven pumping unit of  claim 6   wherein the first control valve is also fluidically coupled between the first extension-chamber and the exhaust path and is further configured to activate and deactivate the second state; and   wherein the second control valve is also fluidically coupled between the second extension-chamber and the exhaust path and is further configured to activate and deactivate the fourth state.   
     
     
         9 . The hydraulically-driven pumping unit of  claim 1  further comprising:
 a first pump driven by the first rod of the first HPC assembly and having a first discharge port; 
 a second pump driven by the second rod of the second HPC assembly and having a second discharge port; and 
 a discharge manifold coupled for fluid communication with the first and second discharge ports. 
 wherein the first and second pump are configured to receive and to pump a working fluid through the discharge manifold. 
 
     
     
         10 . The hydraulically-driven pumping unit of  claim 2 :
 wherein the pumping unit is configured with the following operational states:
 a fifth state in which the first extension-chamber chamber of the first HPC assembly is not in fluid communication with the hydraulic fluid source and is not in fluid communication with the exhaust path; and 
 a sixth state in which the second extension-chamber of the second HPC assembly is not in fluid communication with the hydraulic fluid source and is not in fluid communication with the exhaust path; 
   wherein the first HPC assembly is in the fifth state between the first state and the second state during the second transition; and   wherein the second HPC assembly is in the sixth state between the third state and the fourth state during the fourth transition.   
     
     
         11 . A method for operating a fluid-driven pumping unit, the method comprising:
 supplying a flow rate of a driving fluid during an operation period;   dividing the flow rate of the driving fluid between members of a plurality of double-acting hydraulic piston-cylinder (HPC) assemblies, each assembly having a movable rod;   operating at least two of the HPC assemblies using synchronized, phase-shifted cycles, wherein the corresponding two movable rods extend and retract periodically, such that the two rods always have a different combination of axial position and direction of travel and such that at least one of the two rods is extending at all times;   providing a plurality of pumps configured to deliver a working fluid, each pump driven by a rod of the plurality of rods; and   pumping a working fluid using the plurality of pumps.   
     
     
         12 . The method of  claim 11  further including:
 interconnecting the plurality of HPC assemblies so the extension of a first actuator causes the refraction of a second actuator and the extension of the second actuator causes retraction of the first actuator. 
 
     
     
         13 . The method of  claim 12  further including:
 operating the HPC assemblies such that the pistons perform smooth reversals, not reaching the maximum extent of their strokes.