US20090041588A1 - Active valve system for positive displacement pump - Google Patents

Active valve system for positive displacement pump Download PDF

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Publication number
US20090041588A1
US20090041588A1 US11/835,523 US83552307A US2009041588A1 US 20090041588 A1 US20090041588 A1 US 20090041588A1 US 83552307 A US83552307 A US 83552307A US 2009041588 A1 US2009041588 A1 US 2009041588A1
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Prior art keywords
suction
stroke
valve
pump
suction valve
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Abandoned
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US11/835,523
Inventor
Timothy Hunter
Stanley Stephenson
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Halliburton Energy Services Inc
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Halliburton Energy Services Inc
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Priority to US11/835,523 priority Critical patent/US20090041588A1/en
Assigned to HALLIBURTON ENERGY SERVICES, INC. reassignment HALLIBURTON ENERGY SERVICES, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: STEPHENSON, STANLEY, HUNTER, TIMOTHY H.
Publication of US20090041588A1 publication Critical patent/US20090041588A1/en
Abandoned legal-status Critical Current

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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/02Stopping, starting, unloading or idling control
    • F04B49/03Stopping, starting, unloading or idling control by means of valves
    • F04B49/035Bypassing
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/22Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00 by means of valves
    • F04B49/24Bypassing
    • F04B49/243Bypassing by keeping open the inlet valve
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B7/00Piston machines or pumps characterised by having positively-driven valving
    • F04B7/0076Piston machines or pumps characterised by having positively-driven valving the members being actuated by electro-magnetic means
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B7/00Piston machines or pumps characterised by having positively-driven valving
    • F04B7/02Piston machines or pumps characterised by having positively-driven valving the valving being fluid-actuated
    • F04B7/0266Piston machines or pumps characterised by having positively-driven valving the valving being fluid-actuated the inlet and discharge means being separate members
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B2201/00Pump parameters
    • F04B2201/02Piston parameters
    • F04B2201/0201Position of the piston
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04BPOSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B2201/00Pump parameters
    • F04B2201/12Parameters of driving or driven means
    • F04B2201/1208Angular position of the shaft

Abstract

An active valve system may be used to improve operation of the suction valve(s) of a positive displacement pump. As appropriate, the active valve system may apply a force to the suction valve directed to open and/or close the suction valve. By quickening the opening and/or closing of the suction valve, the pump may run at a higher speed and operate with less wear. Additionally, the active valve system may allow all suction valves of a pump to be held open for various purposes.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • Not applicable
  • STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
  • Not applicable.
  • REFERENCE TO A MICROFICHE APPENDIX
  • Not applicable.
  • FIELD OF THE INVENTION
  • Embodiments described herein relate to positive displacement pumps, and more specifically to devices and methods to improve the efficiency, durability, performance, and operating characteristics of reciprocating positive displacement pumps (of the sort that might be used in pumping wellbore servicing fluids) by actively operating the suction valve(s) of the pump.
  • BACKGROUND
  • Positive displacement pumps, and specifically reciprocating pumps, are used in all phases of oilfield operation to pump water, cement, fracturing fluids, and other stimulation or servicing fluids. Pumps in oil field operations often endure harsh conditions, especially when pumping abrasive fluids (such as fracturing fluids). Thus, there is an ongoing need for improved pumps and methods of operation for pumps, allowing for more effective oil field pumping operations in the face of such harsh operating conditions.
  • SUMMARY
  • In one aspect, the present disclosure is directed to a device comprising a reciprocating pump having a suction valve through which fluid is drawn into a chamber during a suction stroke in order to be discharged from the pump during a discharge stroke; and an active valve system (typically including an active valve train and often also including a sensor for pump stroke position and a controller) operable to provide force to operate the suction valve. The device may further comprise a timing marker indicative of pump stroke, a sensor operable to detect the timing marker, and a controller operable to activate the active valve train based on the sensed pump stroke. Further, the active valve train may comprise a cylinder with a rod, with the rod connected to or in contact with the suction valve. The active valve train may provide a force directed to open the suction valve prior to or shortly after the suction stroke begins. Alternatively, in embodiments that pre-load the suction valve to open, the active valve train may provide a force directed to open the suction valve during the discharge stroke. Typically, the reciprocating pump further comprises a suction valve spring (closure member) operable to provide force to close the suction valve. The suction valve spring (closure member) may close the suction valve prior to the discharge stroke.
  • In one embodiment, the suction valve spring (closure member) is sufficiently stiff to minimize valve float as the suction valve closes. The force provided by the active valve train may be greater than the closing force exerted by the suction valve spring (closure member). Additionally, as pressure in the chamber varies during the suction and discharge strokes, the force provided by the active valve train may be less than the closing force exerted by the suction valve spring (closure member) in conjunction with the pressure in the chamber during the discharge stroke. Alternatively, as pressure in the chamber varies during the suction and discharge strokes, the force provided by the active valve train may be less than the force exerted by the suction valve spring (closure member), but sufficient in conjunction with the pressure in the chamber during the suction stroke (such as the pressure differential between the high pressure suction header and the low pressure chamber, for example) to open the suction valve quickly enough to minimize cavitation. The active valve train may release the opening force prior to the discharge stroke. Thus, the active valve train may provide a force directed to open the suction valve during the discharge stroke, and may then release the opening force prior to the discharge stroke.
  • In an alternative embodiment of the device, the suction valve spring (closure member) may be insufficiently stiff to close the suction valve quickly enough to minimize valve float on its own, and the active valve train may provide a force directed to assist in opening the suction valve and a force directed to assist in closing the suction valve. Then, the force of the suction valve spring (closure member) in conjunction with the closing force provided by the active valve train would typically be sufficient to close the suction valve quickly enough to minimize valve float. Often, the suction valve connects to a fluid header operable to deliver fracturing fluid and the like to the pump for discharge into a well bore. The pump may also be mobile, with the pump being transported via a motorized vehicle, and the pump possibly being powered by the engine of the motor vehicle. In another embodiment in which there is no suction valve spring (closure member), the active valve train may provide a force directed to open the suction valve and a force directed to close the suction valve (actively operating the opening and closing of the suction valve entirely on its own).
  • In another aspect, the present disclosure is directed to a method for bringing online a reciprocating pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke by a common crankshaft, the method comprising actively opening the suction valves of all cylinders and holding the suction valves open; bringing the crankshaft up to operating speed; and releasing the suction valves to bring the pump online. The suction valves may be released sequentially (such as one at a time, for example). Additionally, the suction valves may each be released at or near the end of the discharge stroke (when the plunger is fully extended and there is maximum mechanical advantage). The suction valves typically would be released when the crankshaft speed is sufficiently high to provide adequate torque from the engine, motor, or other prime mover to start the pump (as the pump can only start operating once the engine's torque is sufficient to overcome the discharge pressure).
  • In one embodiment, the method may further comprise priming the pump (before normal operation), which may further include actively holding the suction valves open during suction stroke to minimize the pressure drop across the suction valve until each chamber fills completely during the suction stroke. Additionally, the method may further comprise actively opening each suction valve prior to its chamber's suction stroke, and releasing each suction valve prior to its chamber's discharge stroke (once the pump is functioning normally at operating speed). This may require sensing the timing for each suction stroke and discharge stroke. The method may further comprise charging the cylinder during the suction stroke; closing the suction valve prior to the discharge stroke; and discharging the cylinder during the discharge stroke. The suction valve may automatically be closed at or near the end of the suction stroke (prior to the discharge stroke) by a suction valve spring sufficiently stiff to minimize valve float. Alternatively, when the closing of the suction valve operates by a suction valve spring, the method may further comprise actively assisting the closing of the suction valve at or near the end of the suction stroke in order to minimize valve float. In one embodiment, the method further comprises connecting the suction valve to a source of fracturing fluid and/or pumping fracturing fluid into a well bore.
  • In yet another aspect, the present disclosure is directed to a method for actively assisting the opening of a suction valve in a reciprocating pump having a suction stroke and a discharge stroke, the method comprising providing a spring operable to close the suction valve prior to each discharge stroke; actively applying an opening force to the suction valve during each discharge stroke (and actively holding the suction valve open during the suction stroke by maintaining the opening force on the suction valve); and releasing the opening force prior to each discharge stroke. In one embodiment, the method further comprises sensing the timing of the pump stroke. The spring may provide a closing force sufficient to close the suction valve fast enough to minimize valve float. The pump may further comprise a chamber in which the pressure varies during suction and discharge strokes; and the opening force actively applied may be greater then the spring closing force, but less than the spring closing force in conjunction with the pressure in the chamber during the discharge stroke.
  • In still another aspect, the present disclosure is directed to a method of servicing a wellbore with a servicing fluid (e.g., a fracture fluid) using a reciprocating pump having multiple chambers each with a suction valve and a discharge valve and operable to provide a suction stroke and a discharge stroke, the method comprising connecting each suction valve to a source of wellbore servicing fluid; connecting each discharge valve to the wellbore; providing a force to actively open each suction valve prior to the suction stroke of its chamber; charging each chamber with wellbore servicing fluid during its suction stroke; releasing the opening force on each suction valve prior to the discharge stroke of its chamber; and discharging wellbore servicing fluid from each chamber during its discharge stroke and into the wellbore. When the suction stroke and discharge stroke of each chamber is driven by a common crankshaft, the method may further comprise sensing the timing of the suction stroke and the discharge stroke based on rotation of the crankshaft. Each suction valve may also be opened sufficiently fast to minimize cavitation.
  • In an embodiment, the method may further comprise providing a force for closing the suction valve of each chamber prior to its discharge stroke. Each suction valve may then be closed sufficiently fast to minimize valve float. The method may further comprise providing one or more springs operable to close the suction valve of each chamber prior to its discharge stroke (with the springs providing the closing force). In one embodiment, the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is greater than the closing force provided to close the suction valve of each chamber prior to its discharge stroke. In another embodiment, the pressure in the chamber varies during the suction and discharge strokes; and the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is less than the closing force provided to close the suction valve of each chamber prior to its discharge stroke, but is sufficient in conjunction with the pressure in the chamber during the suction stroke to open the suction valve quickly enough to minimize cavitation.
  • In still another embodiment, the method may further comprise actively holding all suction valves open to prime the pump. Alternatively, the method may further comprise actively holding all suction valves open during start-up; bringing the pump up to operating speed; and releasing one or more suction valves to bring the pump online. The suction valves may be released sequentially. Further, the engine may have sufficient torque at operating speed for start-up (so that the engine may be brought up to operating speed to have sufficient torque to bring the pump online during start-up). The suction valves also may be released at or near the end of the discharge stroke to take advantage of maximum mechanical advantage.
  • In another embodiment, a method of pumping wellbore servicing fluid comprises sensing the position of a reciprocating pump stroke and actively assisting the opening, closing or both of a suction valve in response to the sensed position of the pump stroke. In an embodiment, the active assistance applies a force to overcome a static or passive force applied to the suction valve, for example a static or passive force applied by a biasing spring or other closure device.
  • In still another aspect, the present disclosure is directed to a method for draining a pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke, the method comprising actively opening the suction valves of all cylinders (all suction valves); holding all suction valves open as the pump runs/is driven (or as the plunger cycle through suction and discharge strokes); and running/driving the pump so that each plunger goes through multiple suction and discharge strokes. In one embodiment, the method may further comprise flushing fluid out of the pump (specifically the chambers and the suction valves). In another embodiment, the method may further comprise sucking air in and out of each chamber through the open suction valves in order to dry the pump. Typically this draining, cleaning, and drying technique would be used at the end of a pumping process/job, after fluid pumping is completed. In yet another embodiment, the method further comprises closing all suction valves and stopping running/driving the pump.
  • In yet another aspect, the present disclosure is directed to a method for varying the available displacement of a pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke, the method comprising running/driving the pump so that each plunger cycles through suction and discharge strokes; actively opening one or more suction valves and holding the one or more opened suction valves open (throughout both suction and discharge strokes); and continuing to run/drive the pump (with the plungers cycling through suction and discharge strokes). When running the pump while one or more suction valves are held open, only the cylinders whose suction valves are not being held open will actually pump fluid (be on line). Actively opening and holding one or more suction valves open serves to drop the cylinders associated with the one or more opened suction valves out of active pumping/pumping operation (so that the pump acts as a pump having fewer cylinders/less fluid displacement). This allows the pump to pump fluid at a rate less than possible if all cylinders are pumping (with suction valves opening and closing in time with the suction and discharge strokes). In fact, dropping cylinders out of use allows the pump to pump fluid at a rate less than it would be able to even if the engine driving the pump were operating at its lowest speed (in first gear) with all cylinders operating/pumping. It may also provide more precise control of the pump/flow rate (by offering smaller intervals of available displacement).
  • In another aspect, the present disclosure is directed to a method for quickly stopping fluid pumping by/fluid flow through a pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke, the method comprising running/driving the pump so that each plunger cycles through suction and discharge strokes; actively opening all suction valves (the suction valves of all chambers) and holding the suction valves open as the plungers continue to cycle through suction and discharge strokes. In one embodiment, the method further comprises stopping the pump (stopping driving the plungers). By holding all suction valves open (even as the plungers continue to move), the fluid flow rate through the pump drops nearly instantaneously to zero (fluid ceases to be pumped nearly instantaneously). This provides the possibility of a fast/emergency/safety stop of fluid pumping, despite the inertia of the pump elements (such as the plungers). In effect, opening all of the suction valves serves as a safety stop/quick kill. In an embodiment, the method further comprises holding the suction valves open until the pump stops running (i.e. the plungers stop moving/cycling).
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • For a more complete understanding of the present disclosure, and for further details and advantages thereof, reference is now made to the accompanying drawings, wherein:
  • FIG. 1A is a side view of an exemplary pump with active suction valve activation;
  • FIG. 1B is a front view of an exemplary pump with active suction valve activation;
  • FIG. 1C is a top view of an exemplary pump with active suction valve activation;
  • FIG. 1D is a cut-away cross-sectional view of the exemplary pump as shown in FIG. 1A, illustrating the internal components of the pump; and
  • FIG. 2 is a cut-away cross-sectional side view schematic diagram of one chamber of an exemplary reciprocating positive displacement pump with active suction valve activation via the mechanical linkage of an active valve train.
  • DETAILED DESCRIPTION OF THE INVENTION
  • Disclosed embodiments demonstrate an active valve system for assisting or providing the operation of the suction valve(s) of a positive displacement pump. In the disclosed embodiments shown in the figures, the active valve system provides active operation of the suction valve(s) of a reciprocating positive displacement pump (providing a force directed to open and/or close the suction valve). The active valve system may often be configured to provide a force directed to open the suction valve(s) in a controlled manner, so that the opening force is applied to the suction valve(s) at the appropriate time in the pump stroke cycle for opening of the suction valve(s), with the opening force then released/removed from the suction valve(s) at the appropriate time in the pump stroke cycle to allow for closing of the suction valve(s). While the active valve system may provide the sole means for opening and/or closing the suction valve(s), often it would be used in conjunction with other forces (such as pressure differentials and/or springs, by way of non-exclusive example) to assist in opening and/or closing the suction valve(s) of a reciprocating pump.
  • Using an active valve system, it may be possible to both quickly open and quickly close the suction valves(s). For instance, a stiff suction valve spring (providing a strong closing force to quickly close the suction valve) may be used, while the active valve system may apply an opening force at the appropriate time to quickly open the suction valves(s) (despite the stiff suction valve spring). As another possible alternative, a weak suction valve spring (allowing for quick opening of the suction valve) may be used, while the active valve system may apply a closing force at the appropriate time to assist in quickly closing the suction valve. By improving the opening and/or closing of the suction valve(s), the active valve system may improve the operating efficiency and lifespan of reciprocating pumps. Additionally, the active valve system may be used for other purposes. By way of example, the active valve system may aid in bringing a pump online (especially if it is facing back pressure), in priming the pump, in making transmission shifts (by selectively disabling chambers during a shift sequence), and in draining the pump.
  • FIGS. 1A, 1B, 1C, and 1D illustrate an exemplary embodiment of a reciprocating positive displacement pump 100 with an active valve system 150. As shown in FIGS. 1A-1C, each pump often comprises multiple chambers with plungers driven by a single crankshaft. In the example of FIGS. 1A-1C, by way of example, three chambers 130 are connected to a common crankshaft 110. FIG. 1D provides a fairly detailed illustration of the internal components of pump 100, which is comprised of a power end 103 and a fluid end 105. For each chamber 130 of pump 100, the crankshaft 110 drives a plunger 120 located within the chamber 130. The chamber 130 includes a suction valve 137 (biased closed by spring 135 in this example) and a discharge valve 139 (biased closed by spring 143 in this example). The suction valve 137 of FIGS. 1A-1D connects a fluid source 160 (such as a suction header with fluid to be pumped) to pump 100. And as best seen in the example of FIG. 1D, an active valve system 150 may act upon the suction valve 137 (with a rod passing through the fluid source 160 in a sealed manner so as to be operable to engage the suction valve 137). Typically, the power end 103 of the pump 100 is coupled to an engine, motor, or other prime mover (not shown) in a known manner, driving the crankshaft 110 and powering the pump. Hereinafter, the term “engine” will be used for convenience to mean any prime mover (such as an engine or motor); it should be understood that any reference to engine is not limiting, but includes any prime mover and its equivalents.
  • While FIGS. 1A-1D illustrate a particular multi-chamber pump having a specific active valve activation system in detailed operational configuration, FIG. 2 provides a simplified cross-sectional diagram of one representative chamber of an embodiment of reciprocating pump 200, shown in relation to a more fully detailed representative schematic diagram of an active valve system. By focusing on the core components of the chamber 230, FIG. 2 may aid in visualizing the operation of the pump 200 using the component elements of an exemplary active valve system (and it is to be understood that the exemplary description of FIG. 2 could apply to operation of each chamber of a multi-chambered pump, such as shown in FIGS. 1A-1D). Thus for illustrative purposes, the following discussion will specifically relate to the example of FIG. 2.
  • The pump 200 of FIG. 2 comprises a power end 203, including a crankshaft 210 that drives the plunger 220, and a fluid end 205, including a compression chamber 230 into which fluid flows (through the suction valve 237) in order to be pumped out through the discharge valve 239 under pressure as the plunger 220 extends into the chamber 230. In the embodiment of FIG. 2, the active valve system employs a mechanical mechanism for actively assisting in the opening of the suction valve 237. Specifically, in FIG. 2 the active valve system comprises an active valve train 250 operable to provide a force directed to open the suction valve 237, a sensor 257 for detecting pump stroke position (and/or velocity) possibly based on the location of a timing marker 258 (typically attached to the crankshaft 210 of the pump 200, but shown for purposes of illustration in FIG. 2 as a radial marker on the crankshaft 210), and a controller 259 that uses the sensed pump stroke information to determine when to activate/deactivate the active valve train 250. It should be understood that for a multi-chamber pump, a single sensor 257 and a single controller 259 could operate an active valve train 250 for each chamber 230, or alternatively, each chamber 230 could employ its own sensor 257 and controller 259; FIG. 2 is merely an illustrative example of a single chamber.
  • Rather than using a sensor 257 with a controller 259 to determine activation of the active valve train 250, the active valve system could alternatively employ a mechanical, electrohydraulic, pneumatic, electric, or other linkage coupling the movement of the active valve train 250 directly to the movement of the crankshaft 210. In such an embodiment, the active valve train 250 would act on the suction valve 237 based directly on the position of the plunger 220. While such alternative active valve systems are feasible, using a mechanical linkage may restrict alternative uses of the active valve system, for example embodiments requiring the ability to hold suction valves open throughout both suction and discharge strokes.
  • In FIG. 2, the active valve train 250 comprises a cylinder 253 with a rod 255 interacting with the suction valve 237 of the pump 200. The cylinder 253 that drives the rod 255 to operate the suction valve 237 in this example is often hydraulic, but it could be pneumatic (or powered by some other gas) or electric, by way of non-exclusive example. When the rod 255 extends, it provides a force on the suction valve directed to open the suction valve (by way of pushing the suction valve from its seat).
  • In FIG. 2, as the active valve train 250 provides an opening force directed to the open suction valve 237, the active valve train 250 is opposed by a closure member (that provides a force directed to close the suction valve). In FIG. 2, the closure member continuously provides a closing force while the suction valve is open. The closure member embodiment shown in FIG. 2 is a suction valve spring 235 that is compressed as the suction valve 237 opens, providing a closing force on the suction valve 237. It should be understood that other types of closure members could be used in place of a suction valve spring, including by way of non-exclusive example a compressed gas (air) cylinder and/or a hydraulic system with gas-filled accumulator. Alternatively, a gravity or buoyancy based closure system could be employed, either alone or in conjunction with other closure means. The term “suction valve spring” will be used hereinafter for convenience to mean any closure member; it should be understood that any reference to the suction valve spring 235 is not limiting, but explicitly includes any closure member (such as a compressed gas (air) cylinder and/or a hydraulic system with gas-filled accumulator, as well as any equivalents). So in FIG. 2, as the rod 255 extends (when the active valve train 250 provides an opening force to the suction valve 237), the suction valve spring 235 resists in compression (since the suction valve is biased closed by the suction valve spring). When the active valve train 250 releases the opening force (by the rod 255 retracting, for example), the suction valve spring 235 and/or chamber pressure during the discharge stroke provide a force directed to close the suction valve 237 (a closing force).
  • In the example set forth in FIG. 2, the cylinder 253 is mounted to the fluid header 260 which brings fluid to be pumped by the pump 200 from a fluid source to the suction valve 237, and the rod 255 extends through an appropriately sealed opening in the fluid header 260 to interact mechanically with the suction valve 237. In this way, the active valve train 250 of FIG. 2 is operable to act on/operate the suction valve 237. As the rod 255 extends, it provides a force to open the suction valve 237, and when it later releases the opening force, it allows the suction valve 237 to close under the influence of the suction valve spring 235 and/or chamber pressure during the discharge stroke.
  • In operation, sensor 257 of FIG. 2 detects the pump stroke, allowing the controller 259 to determine when the plunger 220 has completed a suction stroke, when it has completed a discharge stroke, or when it has sensed other positions as appropriate in order to properly time the activation of the active valve train 250 in order to open and/or close the suction valve 237 appropriately. During the suction stroke, the suction valve 237 should be open (with the suction valve 237 away from its seat), allowing fluid from the fluid header 260 to enter the chamber 230 through the suction valve 237. The discharge valve 239 of pump 200 would be closed under the influence of discharge valve spring 243 and line pressure during the suction stroke. Pressure in the chamber 230 will vary during suction and discharge strokes depending upon the position of the plunger 220 in the chamber 230 and the amount and type of fluid (and/or other material) in the chamber 230. During the discharge stroke, the suction valve 237 should generally be closed, preventing fluid in the chamber 230 from exiting via the suction valve 237 so that as pressure in the chamber 230 builds (due to compression by the plunger 220), the discharge valve 239 opens (as the discharge valve spring 243 is compressed away from its seat), and fluid in the chamber 230 is pumped under pressure out the discharge valve 239.
  • So in operation, the suction stroke of the pump 200 in FIG. 2 would begin with the fully extended plunger 220 starting to retract back through the chamber 230. Before the suction stroke begins, the suction valve 237 would be closed (with the suction valve spring 235 and the pressure in the chamber 230 providing closing force on the suction valve 237). As the suction stroke begins and the plunger 220 retracts, a low pressure area is created in the chamber 230. Thus, the fluid pressure in the fluid header 260 connected to the outside of the suction valve 237 would be greater than the pressure within the chamber 230. This provides a net opening force on the suction valve 237 due to the pressure differential between the chamber 230 (at a low pressure) and the fluid header 260 (with fluid under some pressure) on either side of the suction valve 237, such that the suction valve 237 would experience a force pressing in opposition to the suction valve spring 235 to open the suction valve 237.
  • Additionally, however, as the sensor 257 detects the end of a discharge stroke and the beginning of a suction stroke, the controller 259 activates the active valve train 250, providing an additional force directed to open the suction valve 237. In FIG. 2, the rod 255 of the active valve train 250 extends to push the suction valve 237 open. Use of the active valve train 250 provides greater opening force upon the suction valve 237 (instead of relying solely on passive activation by the chamber pressure (in this case, the pressure differential between the high pressure in the suction/fluid header and the low pressure in the chamber)), overcoming the suction valve spring's 235 closing force and compressing the suction valve spring 235 more easily, thereby allowing the suction valve 237 to open more quickly and/or fully. This reduces wear (since the larger flow area for the fluid through the suction valve 237 reduces fluid flow speed through the suction valve 237, decreasing erosion) and minimizes cavitation (since the larger flow area and the lower fluid speed reduce opportunities for formation of a gas pocket in the chamber). Wear can be a major concern for pump valves, especially when pumping abrasive fluid, since it may reduce the service life of the pump 200. Additionally, cavitation (which typically occurs if a valve opens too slowly so that high fluid velocity through the valve reduces the fluid pressure below the vapor pressure and forms a gas pocket in the chamber, resulting in a water-hammer effect as the gas pocket cannot adequately resist the force of the plunger during the discharge stroke, and the plunger generates an impact force on the internal components of the pump 200) can be a problem for pump valves, since it may damage internal components. So in FIG. 2, the active valve system provides an additional opening force on the suction valve 237, allowing the suction valve 237 to open more quickly, thereby reducing wear and minimizing cavitation, As the suction stroke continues, the pressure differential drops (as the chamber pressure increases) throughout the suction stroke. The pressure in the chamber 230, however, is still insufficient to overcome the discharge valve spring 243, discharge line pressure and open the discharge valve 239. For convenience, the terms “chamber pressure” and/or “pressure in the chamber” include both positive (high) and negative (low) chamber pressure, as well as any pressure differential between the chamber and the suction header/discharge line.
  • When the suction stroke ends and the discharge stroke is about to begin, pressure in the chamber 230 should be approximately the same as the pressure in the fluid chamber 260. Thus, the suction valve spring's 235 closing force on the suction valve 237 would only be resisted by the opening force applied by the active valve train 250. Before the discharge stroke begins, the controller 259 of FIG. 2 would deactivate the active valve train 250, causing the active valve train 250 to release the opening force on the suction valve 237. In the specific example of FIG. 2, the rod 255 would no longer have a force applied to it by the cylinder (such that the rod would retract under the force of the suction valve spring). When this occurs, the compressed suction valve spring 235, which has been applying a continuous closing force on the suction valve 237, will act to close the suction valve 237 (since the closing force applied to the suction valve 237 by the suction valve spring 235 would no longer be opposed by opening forces from the pressure differential and/or the active valve train 250).
  • In the example of FIG. 2, the suction valve spring 235 is stiff/strong, providing sufficient closure force so that the suction valve 237 closes quickly enough prior to the discharge stroke to minimize valve float (by closing the suction valve completely prior to the discharge stroke). Minimizing valve float can be important, because if the discharge stroke begins while the suction valve 237 is partially open, the force of the discharge stroke would slam the suction valve 237 down onto its seat, creating a water-hammer effect that could damage the suction valve 237. In addition to the wear/damage problem caused by valve float, having a suction valve 237 that closes too slowly (valve float) may reduce pump efficiency by limiting the pump speed (since the spring would be too weak to close properly at higher speeds). A stiffer spring 235 may effectively be used in the example of FIG. 2, since the active valve train 250 supplements the opening force of the pressure differential during the suction stroke, allowing the suction valve 237 to open quickly enough during the suction stroke (otherwise, a stiff spring would result in unwanted wear and cavitation). So when the sensor 257 detects that the discharge stroke is about to begin, the controller 259 causes the active valve train 250 to release the opening force, and the suction valve spring 235 quickly closes the suction valve 237.
  • During the discharge stroke, fluid pressure in the chamber 230 increases throughout the discharge stroke as the plunger 220 extends (since both the suction valve 237 and the discharge valve 239 are closed). Pressure now assists in keeping the suction valve 237 closed (although the suction valve spring 235 would generally be sufficiently strong on its own), and when the pressure becomes sufficiently high to overcome the closing force of discharge valve spring 243 and discharge line pressure, the discharge valve 239 opens and pumps fluid out of the chamber 230 under pressure. Once the discharge stroke has ended and the following suction stroke is about to begin, the cycle starts over and repeats, with the discharge valve 239 closing (since there is insufficient pressure in the chamber 230 to overcome the discharge valve spring 243 and discharge line pressure biasing the discharge valve 239 closed), the active valve train 250 applying a force directed to open the suction valve 237, the pressure (of the partial vacuum) in the chamber 230 applying an opening force on the suction valve 237, the suction valve spring 235 compressing, and the suction valve 237 opening as the suction stroke begins.
  • The amount of opening force applied by the active valve train 250 can vary depending on design factors and/or need. If the active valve train 250 is designed to merely assist the chamber pressure in opening the suction valve 237 by reducing the effective stiffness of the suction valve spring 235 during the suction stroke (so that the suction valve spring 235 acts as a stiff spring to close the suction valve 237 prior to the discharge stroke, but acts as a weak spring when the suction valve 237 is being opened prior to, after, or as the suction stroke due to the opening force applied by the active valve train), then the opening force of the active valve train 250 would be less than the closing force exerted by the suction valve spring 235. In such a case, the opening force provided by the active valve train 250 would only be sufficient to overcome the suction valve spring's 235 closing force and/or to open the suction valve 237 quickly enough to minimize cavitation and wear when it was used in conjunction with the chamber pressure (pressure differential) during the suction stroke.
  • Alternatively, the active valve train 250 could be designed to provide a powered opening. In such a case, the active valve train 250 would apply an opening force greater than the suction valve spring's 235 closing force to the suction valve 237, in an attempt to drive the suction valve 237 open quickly. It may be beneficial to cap the opening force provided by the active valve train 250, however, so that it does not exceed the closing force of the suction valve spring 235 plus the chamber pressure during the discharge stroke (with the high pressure in the chamber providing an additional closing force on the suction valve). This precaution would prevent early opening of the suction valve 237 in case the active valve train 250 was activated during the discharge stroke (as will be discussed below in one alternative embodiment). Alternatively, the active valve train 250 may apply an opening force greater than the suction valve spring's 235 closing force in conjunction with the chamber pressure force to the suction valve 237, allowing a powered opening at any time during the pump operation/cycle (even during the discharge stroke).
  • While the embodiment shown in FIG. 2 and described above has the active valve train 250 applying its opening force just prior to the beginning of the suction stroke (when the plunger 220 is approximately fully extended), the active valve train 250 could alternatively apply its opening force to the suction valve 237 sometime during the discharge stroke. Such modified timing of the application of the opening force from the active valve train 250 on the suction valve 237 would essentially pre-load the suction valve 237 to further improve opening for the suction stroke. This sort of early application of opening force during the discharge stroke will not provide sufficient force to open the suction valve 237 during the discharge stroke (and prior to the beginning of the suction stroke), so long as the opening force provided by the active valve train 250 is less than the closing force of the suction valve spring 235 in conjunction with the chamber pressure during the discharge stroke (as discussed above). Such pre-loading of the suction valve 237 with an opening force will not affect the discharge stroke characteristics and performance of the pump 200, but may further improve opening of the suction valve 237 during the suction stroke (by further speeding opening to minimize wear and cavitation).
  • In another alternative embodiment, the active valve train 250 could operate to provide both an opening force and a closing force on the suction valve 237. In such an instance, the active valve train 250 would apply an opening force prior to the suction stroke (and as described above, this could include application during the discharge stroke), and would apply an active closing force to the suction valve 237 prior to the discharge stroke (rather than simply releasing the opening force). This type of two-way active valve operation might also allow the use of a weak suction valve spring 235 (since the suction valve spring 235 would be assisted in closing the suction valve 237 quickly). Thus, while a weak suction valve spring 235 might be insufficiently stiff/strong to close the suction valve 237 quickly enough to minimize valve float on its own, when used in conjunction with a closing force applied prior to the discharge stroke by the active valve train 250, valve float could still be minimized.
  • Alternatively, such two-way active valve operation could allow the suction valve spring 235 to be completely eliminated (with the active valve train 250 then providing both the opening and the closing force on the suction valve 237). In such a case, the closing force would need to be sufficient alone to close the suction valve 237 quickly enough to minimize valve float. This variant may be disfavored, however, since it would not provide fail-safe operation of the pump 200 in case of failure of the active valve train 250. Rather, it is preferred to use a stiff suction valve spring 235 with an active valve train 250, so that the suction valve spring 235 may act as a fail-safe (allowing the pump 200 to continue operation, although less efficiently, even if the active valve train is unavailable).
  • The pump 200 of FIG. 2 is often used for well servicing (as for pumping fluids into the wellbore of an oil well). Thus, it may be beneficial if the pump 200 is mobile, so that it can be transported and positioned for a job in relation to a well to be serviced and then transported to the next job site. For example, the pump 200 may be mounted on and/or transported by a motorized vehicle such as a truck and/or a trailer or skid. This would also allow the pump 200 to be powered by the engine of the motorized vehicle. Alternatively, the pump may be powered by a separate hydraulic or electric power system, for example. The active valve system may also be jointly powered by the engine of the vehicle and/or a separate power system, or it may have its own separate power system.
  • When used for wellbore servicing, the pump 200 is often used to pump an abrasive fluid, such as fracture fluid that may contain sand or other proppants/abrasives. This tends to increase wear concerns for pump components, making the benefits of the active valve system even more important. Typically, the discharge valve 239 of the pump 200 would be attached in fluid communication to the wellbore, so that fracture fluid supplied to the pump 200 via a fluid header 260 (leading to a fluid source, such as a tank) may be pumped into the wellbore under pressure. The fracture fluid from the fluid header 260 enters the pump 200 through the suction valve 237 during the suction stroke, and is discharged out the discharge valve 239 during the discharge stroke. As discussed above, the active valve system allows for quick opening and closing of the suction valve 237, such that fracturing fluid may be pumped into the wellbore without substantial wear on the pump 200. In addition to increasing the service life of the pump 200, the active valve system may allow the pump 200 to operate effectively at higher speeds (by allowing the suction valve 237 to open and close more quickly, so that the pump stroke speed may be increased). Thus pump efficiency and output may also be improved.
  • Additionally, the chamber 230 of a pump 200 used for wellbore servicing could be susceptible to damage due to compression of incompressible materials. This could be a problem, especially when pumping fracture fluid, since the fluid may include solids (such as proppant). To address this concern, the chamber 230 may be sealed at one end (opposite the plunger 220) with an end cap 275. The end cap 275 generally closes the chamber, but it is designed as a plug that may shear off and open the chamber if too much incompressible material fills the chamber (preventing damage to the pump from extreme pressure buildup).
  • In addition to improving pump efficiency and reducing pump wear, an active valve system may also provide other benefits, by allowing for control of suction valve(s) independent of the pump stroke. By way of example, the active valve system could also be used to assist in bringing a pump online during start-up. It can be challenging to bring a pump online against high pressure, due to the torque curve characteristics typical of an engine. More specifically, engines tend to provide very low torque at low speeds (RPMs), and only provide significant torque levels above a certain speed. So during start-up, as the pump begins to slowly operate, it can be difficult for the engine to generate sufficient torque to overcome resistance. An active valve system may be used to help bring pumps online in such challenging circumstances.
  • Recall that while the discussion above regarding FIG. 2 focused on only a single exemplary chamber 230 of a pump 200, typically in operation, a pump would actually have multiple chambers, each with its own plunger, all driven by a single, common crankshaft (as shown in FIGS. 1B and 1C). Alternatively, there could be multiple crankshafts (typically coupled together), each driving the plunger for one or more chambers. The discussion above regarding use of an active valve system to reduce wear applies equal well to a pump with multiple chambers/plungers (with each chamber's suction valve being operated on by an active valve system as discussed in detail above). Such pumps can be difficult to bring online, especially when start-up conditions include substantial back pressure (as when the discharge valve is under pressure), high altitudes, or worn components. At low speeds, the engine does not generate enough torque to overcome pressure and/or internal resistance; the torque necessary to start the pump can often only be achieved once the engine reaches a certain, minimum speed (as may be seen by considering a typical torque curve diagram for an internal combustion engine).
  • So during start-up, it may be difficult to get an engine driving the pump up to operating speed. Using an active valve system, however, the suction valves of all cylinders of the pump may be held open during start-up, reducing start-up torque resistance. This basically allows the engine and/or pump to be brought up to operating speed without any load acting as resistance, and then once the pump's inertial mass is in motion at operating speed, such that the engine is capable of generating sufficient torque to overcome resistance, the suction valves may be released to bring the pump online (so that it begins actual pumping of fluid). By bringing the crankshaft up to speed without a load, the pump can be brought online once the engine is operating at a speed capable of generating sustainable torque.
  • Thus, a pump may be brought online using an active valve system by first opening all of the pump's suction valves, and then starting to cycle the pump (through suction strokes and discharge strokes) while the suction valves are actively held open. In other words, the crankshaft is brought up to operating speed (often by starting and engaging an engine or motor for powering the crankshaft) while the suction valves are actively held open (so that the pump experiences no load/resistance). Fluid is sucked into each chamber through the suction valve during its suction stroke, and forced out of each chamber through the suction valve during its discharge stroke (since the suction valve for the chamber is being held open and the discharge valve is closed, since the chamber pressure would be too low to overcome the discharge valve spring while the suction valve is open). Thus, during start-up, fluid would basically slosh back and forth across the suction valve(s). The effect of holding the suction valves open is akin to placing the pump in neutral (since the pump does not have to generate pumping pressure to discharge fluid through the discharge valve). This lowers the resistance that the pump experiences during start-up, allowing the engine and/or pump to be brought up to operating speed. Once at operating speed, the engine is capable of generating sufficient torque to begin actually pumping fluid (overcoming the pressure/resistance), and the suction valve(s) may be released to bring the pump online.
  • Furthermore, the suction valves may be sequentially released, allowing for example one chamber of the pump to come online at a time in order to provide a soft-start for the pump. The process of bringing a pump online with the assistance of an active valve system may be further improved by releasing the suction valves when their plungers are at full extension (approximately at the end of a discharge stroke), in order to take advantage of the maximum mechanical advantage. So again, all the suction valves would be held open as the pump is brought up to speed. Once the engine reaches an operating speed where it can achieve full torque (or at least sufficient torque to overcome pressure/resistance), the suction valves that are being held open could then be released as their corresponding plungers reach full extension (late in the displacement stroke), and the suction valves would operate as normally (opening for the suction stroke, with the active valve system perhaps providing an opening force, and closing for the displacement stroke, with the active valve system perhaps providing a closing force as well).
  • The active valve system could also be used to aid in priming the pump. Actively holding the suction valves wide open during the suction stroke reduces pressure drop across the suction valve and allows the pump to take on fluid while minimizing the expansion of any gas in the chamber. This minimizes the chance of vapor locking.
  • Additionally, an active valve system may be used to float suction valves during transmission shifts, as a way to reduce the load on the pump. During transmission shifts (of the motor or engine used to power the crankshaft of the pump, for instance), available torque may drop significantly. Thus, it might be useful to reduce the effective load/resistance experienced by the pump's crankshaft during transmission shifts. By floating one or more suction valves (by actively opening the suction valves using an active valve system), the effective load can be reduced while transmission shifts are being made. Thus, one or more suction valves could be actively held open whenever a transmission shift is to occur, and then released once the transmission shift is completed (returning to normal operation). The number of suction valves floated could be determined based on the amount of torque that the engine and/or pump can generate during a transmission shift, and the amount of load that floating each suction valve takes from the overall resistance load, with at least the appropriate number of suction valves being floated to allow the engine to provide adequate torque (preventing stalling). This may improve the efficiency of the pump during transmission shifts, as the engine can continue to operate at whatever level it can sustain until the transmission shift is completed and the new gear is brought up to operating speed.
  • An active valve system may also be used to aid in cleaning out/draining the pump (for example, when a pump job is completed). Once all of the fluid for a job has been appropriately pumped, it may be useful to flush any remaining fluid out of the pump (draining the pump) and/or to dry the pump. This can be especially important in cold environments, since any fluid remaining in the pump could freeze and prevent the pump from operating properly. By actively holding all of the suction valves open as the pump is run/driven (with the plunger cycling through suction and discharge strokes), any fluid remaining in the chamber(s) and/or suction valve(s) may be discharged and/or evaporated. Additionally, air is sucked in and out of the suction valves, serving to air dry the pump. So by continuing to run the pump (after pumping of fluid for the job is complete) while holding all of the suction valves open, the pump may be drained and dried.
  • Additionally, an active valve system may be used to selectively drop one or more chamber of a pump out of action. By selectively holding one or more suction valves open during operation of the pump, the chambers associated with the one or more suction valves being held open may be deactivated (so that they do not aid in pumping fluid). In essence, this provides for a variable displacement pump. So for example, if a pump has five cylinders, it may be made to effectively operate as a pump having one to five cylinders, depending on the number of suction valves held open per revolution. If the suction valve for one cylinder is held open during pump operation, then the pump would effectively act as a four cylinder pump, while holding two suction valves open per revolution would allow the pump to act as a three cylinder pump. This may be useful in providing finer control over the flow rate of the pump. By taking cylinders out of line (so that one or more cylinders do not pump fluid when the pump is run), it is possible to operate the pump at a slower speed than would otherwise be available (even at the engine's slowest speed in its lowest gear). While deactivating cylinders (by holding suction valve(s) open during pump operation) may reduce the smoothness at which the pump operates, it allows the pump's flow rate range to be expanded (by reducing the minimum available pump flow rate, and by providing for additional intermediate flow rates).
  • Similarly, if all of the suction valves (associated with all of the cylinders of a pump) are held open (so that all of the cylinders are effectively taken off line and will not pump fluid), then the pump's fluid flow rate may be quickly reduced to zero (even if the pump is still running/the pump components are still moving and/or cycling). In other words, fluid flow may be stopped more quickly by opening and holding all of the suction valves open even as the plunger continues to cycle through suction and discharge strokes. Ceasing to drive/power the pump may not be sufficient for a quick stop (due to inertia). Rather, the suction valves may all be held open until the plunger stops moving. This may serve as a way to more quickly stop pumping (even if the pump components, such as the plunger, are still in motion). Conventionally, a pump cannot be stopped too quickly since the inertia of the pump components/element (such as the plunger) would have to be overcome by the friction forces, etc. before the pump stopped. By holding all of the suction valves open even as the pump components continue to move (for example, as they slow to an eventual stop), it is possible to nearly instantaneously stop actual pumping of fluid. Thus, an active valve system may provide for a safety stop, improving job safety by allowing for fluid pumping to be nearly instantaneously stopped (even if the pump's physical components, such as the plunger, must slow to a stop due to inertia). Persons skilled in the art field will understand these and other uses of such an active valve system.
  • While various embodiments in accordance with the principles disclosed herein have been shown and described above, modifications thereof may be made by one skilled in the art without departing from the spirit and the teachings of the disclosure. The embodiments described herein are representative only and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow, that scope including all equivalents of the subject matter of the claims. Furthermore, any advantages and features described above may relate to specific embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages or having any or all of the above features.
  • Additionally, the section headings used herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or to otherwise provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Field of the Invention,” the claims should not be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the “Background” is not to be construed as an admission that certain technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a limiting characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. The term “comprising” as used herein is to be construed broadly to mean including but not limited to, and in accordance with its typical usage in the patent context, is indicative of inclusion rather than limitation (such that other elements may also be present). In all instances, the scope of the claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

Claims (20)

1. A device comprising:
a reciprocating pump having a suction valve through which fluid is drawn into a chamber during a suction stroke in order to be discharged from the pump during a discharge stroke; and
an active valve train providing force to the suction valve.
2. A device as in claim 1 further comprising a timing marker indicative of pump stroke, a sensor operable to detect the timing marker and thereby sense a pump stroke, and a controller coupled to the sensor and the active valve train and activating the active valve train based on the sensed pump stroke.
3. A device as in claim 1 wherein the reciprocating pump further comprises a suction valve spring providing force to close the suction valve.
4. A device as in claim 3 wherein the suction valve spring is sufficiently stiff to minimize valve float as the suction valve closes.
5. A device as in claim 3 wherein the active valve train provides a force directed to open the suction valve prior to, after, or as the suction stroke begins.
6. A device as in claim 5 wherein the opening force is provided by the active valve train during the discharge stroke, and the force provided by the active valve train is greater than the closing force exerted by the suction valve spring.
7. A device as in claim 6 wherein pressure in the chamber varies during the suction and discharge strokes, and the force provided by the active valve train is less than the closing force exerted by the suction valve spring in conjunction with the pressure in the chamber during the discharge stroke.
8. A device as in claim 5 wherein pressure in the chamber varies during the suction and discharge strokes, and the force provided by the active valve train is less than the force exerted by the suction valve spring, but is sufficient in conjunction with the pressure in the chamber during the suction stroke to open the suction valve quickly enough to minimize cavitation.
9. A device as in claim 5 wherein the active valve train releases the opening force prior to the discharge stroke.
10. A method for bringing online a reciprocating pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke by a common crankshaft, the method comprising:
actively opening the suction valves of one or more cylinders and holding the suction valves open;
bringing the crankshaft up to operating speed; and
releasing the suction valves to bring the pump online.
11. A method as in claim 10 wherein the suction valves are released sequentially one or more at a time.
12. A method as in claim 10 wherein the suction valves are each released at or near the end of the discharge stroke.
13. A method as in claim 10 wherein the suction valves are released when the crankshaft speed is sufficiently high to provide adequate torque to bring the pump online.
14. A method as in claim 10 further comprising actively opening each suction valve prior to its chamber's suction stroke, and releasing each suction valve prior to its chamber's discharge stroke.
15. A method as in claim 14 further comprising sensing the timing for each pump stroke.
16. A method of servicing a wellbore with servicing fluid using a reciprocating pump having multiple chambers each with a suction valve and a discharge valve and operable to provide a suction stroke and a discharge stroke, the method comprising:
connecting each suction valve to a source of servicing fluid;
connecting each discharge valve to the wellbore;
providing a force to actively open each suction valve prior to, after, or at the start of the suction stroke of its chamber;
charging each chamber with servicing fluid during its suction stroke;
releasing the opening force on each suction valve prior to the discharge stroke of its chamber; and
discharging servicing fluid from each chamber during its discharge stroke and into the wellbore.
17. A method as in claim 16 wherein the suction stroke and discharge stroke of each chamber is driven by a common crankshaft; and the method further comprises sensing the timing of the suction stroke and the discharge stroke based on rotation of the crankshaft.
18. A method as in claim 16 further comprising providing a force for closing the suction valve of each chamber prior to its discharge stroke.
19. A method as in claim 18 wherein the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is greater than the closing force provided to close the suction valve of each chamber prior to its discharge stroke.
20. A method as in claim 18 wherein pressure in the chamber varies during the suction and discharge strokes; and the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is less than the closing force provided to close the suction valve of each chamber prior to its discharge stroke, but is sufficient in conjunction with the pressure in the chamber during the suction stroke to open the suction valve quickly enough to minimize cavitation.
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