what is reciprocating mud pump free sample

A plunger pump operates using the reciprocating motion of plungers or pistons. Depending on the design of the pump, the use of a single or multiple plungers may be used.

Action 1: The plunger or piston is pulled back. The action increases the volume of the cavity. As the cavity volume expands, fluid is drawn in through the inlet to fill the expanding cavity.

Action 2: The piston has reached it’s maximum displacement. Since it is not moving into or out of the cavity, fluid is not flowing through the inlet or the outlet.

Action 3: After reaching it’s maximum position, it is then pushed back into the cavity. During this process, the piston applies enough pressure to the fluid to overcome the pressure in the outlet of the pump. This pressure differential pushes the fluid from inside the cavity through the outlet of the pump.

Action 4: The piston reaches its maximum extension into the cavity. Here the volume of the cavity is at a minimum and fluid is not flowing through the inlet or the outlet. The next action repeats the process, starting again with action 1.

All these parts have the basic functionality of moving the liquid inside the cylinder. The piston is a lubricated sliding shaft that moves inside the cylinder and pushes the liquid in a forward and backward motion, creating a cavity and a high volume pressure at the outlet. In a diaphragm pump, the diaphragm is used to avoid leaking of the liquid since it completely seals the liquid to penetrate outside, and hence they are especially useful when the liquids are dangerous or toxic. In a plunger pump, there is a high-pressure seal that is stationary and a smooth cylindrical plunger slides through the seal.

Crank and Connecting rod: Crank is a circular disk attached to the motor and used to transfer the rotary motion of the motor to the piston. Piston, in turn, moves in a reciprocating motion with help of a connecting rod.

Suction pipe: Liquid flows from this pipe into the cylinder. One side of the pipe is immersed in the liquid and the other end is connected to the cylinder.

Reciprocating pumps are different from Centrifugal pumps on basis of its working, features, applications etc. The main difference is that Impellers are used in Centrifugal pumps whereas in reciprocating pumps piston is used to move the liquid. Centrifugal pumps continuously discharge the liquid, unlike reciprocating pumps. They are used for high viscous fluid and are lighter in weight, less expensive as compared to reciprocating pumps.

The basic Quality standards of reciprocating pumps include ISO13710, API (American Petroleum Institute) standard 674, API standard 675 “Positive Displacement Pumps- Reciprocating”  and Reciprocating Pump Standards, Hydraulic Institute.

High Pressure, Low Flow Applications: Reciprocating pumps are generally designed to pump in low flow, high head applications. One of the most extreme of these applications is water jet cutting, where only a few gallons pass through the pump per minute but exceed pressures of 10,000 PSI.

Proven, Common Technology: Reciprocating pumps are one of the oldest, most proven pump types. Today, a wide variety of reciprocating pumps can be found in many different materials, types, and sizes. Reciprocating pumps range from less than 1 horsepower to over 3,000 horsepower.

Durability: Reciprocating pumps are used in some of the most abrasive and corrosive applications. Fluid ends and fluid end parts can be made of many different materials such as stainless steel, aluminum bronze, tungsten carbide, ceramic, and more. A wide selection of valve types is used in abrasive applications such as pumping cement, sand slurry, mud, etc.

Efficiency: Reciprocating pumps operate at high a higher efficiency compared to other pump designs. In most cases, at any setpoint, reciprocating pumps operate around 90%.

There are several performance indicators of a reciprocating pump which determine how effectively it works. Following are some of the key performance indicators:

High Maintenance / Short Life:The main disadvantage of a reciprocating pump is high maintenance and short life. There are many parts in the pump works, all constantly changing directions. Unless careful maintenance takes place, the lifespan of the pump is greatly reduced. While pumps such as centrifugal pumps can last 15 to 20 years with little maintenance, a reciprocating pump requires higher levels of attention and rebuilding several times within the same time frame. The cost of a reciprocating pump rebuild is usually inexpensive which still makes them cost-competitive compared to longer-lasting, higher-priced pump designs.

Pulsations:A characteristic of reciprocating pumps is the production of pressure pulsations through the pump inlet and outlets. The reciprocating motion of the pump produces these pulsations. Increasing the number of pump chambers can greatly reduce the pulsations produced, but it does not remove them completely. To negate damage to piping and surrounding systems or the pump itself, pulsation dampeners must be installed. Further system design can further decrease pulsations to nearly zero. In all cases, overall system design is important when using reciprocating pumps.

Plunger pumps come in a variety of styles, shapes, and sizes. The specific type of pump chosen for an application takes into account the pressures encountered, the flow rates needed, measurement and control systems, fluid viscosity and corrosivity, pipe material, etc. Careful attention should be given to the application before selecting a pump. Selecting the wrong pump for a job can result in damage to equipment, piping, systems, and possibly endanger personnel.

Simplex, Duplex, Triplex, Quintuplex Pumps: Many reciprocating type pumps are simplex(one), duplex (two), or triplex (three) cylinder. Duplex pumps are usually used where the two pumps can be used alternatively. Such pumps are commonly used in oil-line pumping, mine de-watering, and chemical and petroleum products transfer, but has many more applications. A triplex pump consists of three plungers, with the aim of reducing the pulsation of a single reciprocating pump. Quintuplex pumps are designed with a gear case that assists in a high-pressure task. Common applications of which are in cement slurries, sand-laden fluids, crude oil, acids, mud, and other oil well-servicing fluids. Well known manufacturers for these types of pumps are National, Gardner Denver, FMC, SPM, Oilwell, Kerr, Union, Gaso, Emsco, Aplex, and Wheatley.

Metering Pumps: A metering pump is usually used where the rate of flow of the liquid needs to be adjusted in a specific time period. Most of the metering pumps are piston-driven and are called Piston pumps. Piston pumps can pump at a constant flow rate against any kind of discharge pressure. Both Piston pumps and Plunger pumps are reciprocating positive displacement pumps that use a plunger or piston to move fluid/substance through a cylindrical chamber. Manufacturers such as

Reciprocating Pumps can also be classified according to the number of cylinders: Single cylinder and double cylinder pump. They are also sometimes classified according to their operation, known as simple hand-operated reciprocating pump & power-operated deep well reciprocating pump.

Reciprocating positive displacement pumps are highly effective, where a high degree of accuracy and reliability under different ranges of conditions that are required. Reciprocating pumps with very high efficiency are often available in a wide range of hydraulic, mechanical, and material options. They are widely used across industries such as chemical, petrochemical, refinery, pharmaceutical, cosmetic and water treatment. Typically, these types of pumps are used for applications such as Salt Water Disposal, Well Services, Descaling, Hydraulic Fracturing, and Oil & Gas Pipelines. All types of reciprocating pumps are easily available in the market to meet the diverse demands, as per different processes and applications. Piston pumps are widely used in applications such as Energy Recovery, Steam Recovery and hazardous area pumping and are available with manufacturers such as

Diaphragm Pumps are commonly used for Sludge Transfer, Acid Pumping, and Chemical Fluid Transfer and are easily available with manufacturers such as Wilden, Sandpiper, ARO, Roughneck, and Graco.

All the mentioned manufacturers in this article, offering various kinds of pumps hold a good reputation with respect to quality, price, revenue (value), and market share and are preferred by many consumers. However, a thorough check of all its features, specific to your process application, should be ideally done to buy the most suitable reciprocating pump, which can be used for a longer period of time requiring low maintenance, ease of operation, and easy availability of its spare parts.

Reciprocating pump terms are based on how the fluid is pumped (action) and the number of plungers or pistons (arrangement). For example, a Union TX-200 is a “single-acting triplex plunger pump”, a Gaso 1849 is a “double-acting duplex plunger pump”, and an Oilwell B-558 is a “single-acting quintuplex plunger pump”.

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I’ve run into several instances of insufficient suction stabilization on rigs where a “standpipe” is installed off the suction manifold. The thought behind this design was to create a gas-over-fluid column for the reciprocating pump and eliminate cavitation.

When the standpipe is installed on the suction manifold’s deadhead side, there’s little opportunity to get fluid into all the cylinders to prevent cavitation. Also, the reciprocating pump and charge pump are not isolated.

The gas over fluid internal systems has limitations too. The standpipe loses compression due to gas being consumed by the drilling fluid. In the absence of gas, the standpipe becomes virtually defunct because gravity (14.7 psi) is the only force driving the cylinders’ fluid. Also, gas is rarely replenished or charged in the standpipe.

Another benefit of installing a suction stabilizer is eliminating the negative energies in fluids caused by the water hammer effect from valves quickly closing and opening.

The suction stabilizer’s compressible feature is designed to absorb the negative energies and promote smooth fluid flow. As a result, pump isolation is achieved between the charge pump and the reciprocating pump.

The isolation eliminates pump chatter, and because the reciprocating pump’s negative energies never reach the charge pump, the pump’s expendable life is extended.

Investing in suction stabilizers will ensure your pumps operate consistently and efficiently. They can also prevent most challenges related to pressure surges or pulsations in the most difficult piping environments.

Sigma Drilling Technologies’ Charge Free Suction Stabilizer is recommended for installation. If rigs have gas-charged cartridges installed in the suction stabilizers on the rig, another suggested upgrade is the Charge Free Conversion Kits.

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The 2,200-hp mud pump for offshore applications is a single-acting reciprocating triplex mud pump designed for high fluid flow rates, even at low operating speeds, and with a long stroke design. These features reduce the number of load reversals in critical components and increase the life of fluid end parts.

The pump’s critical components are strategically placed to make maintenance and inspection far easier and safer. The two-piece, quick-release piston rod lets you remove the piston without disturbing the liner, minimizing downtime when you’re replacing fluid parts.

A mud pump (sometimes referred to as a mud drilling pump or drilling mud pump), is a reciprocating piston/plunger pump designed to circulate drilling fluid under high pressure (up to 7,500 psi or 52,000 kPa) down the drill string and back up the annulus. A mud pump is an important part of the equipment used for oil well drilling.

Mud pumps can be divided into single-acting pump and double-acting pump according to the completion times of the suction and drainage acting in one cycle of the piston"s reciprocating motion.

Mud pumps come in a variety of sizes and configurations but for the typical petroleum drilling rig, the triplex (three piston/plunger) mud pump is used. Duplex mud pumps (two piston/plungers) have generally been replaced by the triplex pump, but are still common in developing countries. Two later developments are the hex pump with six vertical pistons/plungers, and various quintuplexes with five horizontal piston/plungers. The advantages that these new pumps have over convention triplex pumps is a lower mud noise which assists with better measurement while drilling (MWD) and logging while drilling (LWD) decoding.

The fluid end produces the pumping process with valves, pistons, and liners. Because these components are high-wear items, modern pumps are designed to allow quick replacement of these parts.

To reduce severe vibration caused by the pumping process, these pumps incorporate both a suction and discharge pulsation dampener. These are connected to the inlet and outlet of the fluid end.

The power end converts the rotation of the drive shaft to the reciprocating motion of the pistons. In most cases a crosshead crank gear is used for this.

Displacement is calculated as discharged liters per minute. It is related to the drilling hole diameter and the return speed of drilling fluid from the bottom of the hole, i.e. the larger the diameter of drilling hole, the larger the desired displacement. The return speed of drilling fluid should wash away the debris and rock powder cut by the drill from the bottom of the hole in a timely manner, and reliably carry them to the earth"s surface. When drilling geological core, the speed is generally in range of 0.4 to 1.0 m^3/min.

The pressure of the pump depends on the depth of the drilling hole, the resistance of flushing fluid (drilling fluid) through the channel, as well as the nature of the conveying drilling fluid. The deeper the drilling hole and the greater the pipeline resistance, the higher the pressure needed.

With the changes of drilling hole diameter and depth, the displacement of the pump can be adjusted accordingly. In the mud pump mechanism, the gearbox or hydraulic motor is equipped to adjust its speed and displacement. In order to accurately measure the changes in pressure and displacement, a flow meter and pressure gauge are installed in the mud pump.

The construction department should have a special maintenance worker that is responsible for the maintenance and repair of the machine. Mud pumps and other mechanical equipment should be inspected and maintained on a scheduled and timely basis to find and address problems ahead of time, in order to avoid unscheduled shutdown. The worker should attend to the size of the sediment particles; if large particles are found, the mud pump parts should be checked frequently for wear, to see if they need to be repaired or replaced. The wearing parts for mud pumps include pump casing, bearings, impeller, piston, liner, etc. Advanced anti-wear measures should be adopted to increase the service life of the wearing parts, which can reduce the investment cost of the project, and improve production efficiency. At the same time, wearing parts and other mud pump parts should be repaired rather than replaced when possible.

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When choosing a size and type of mud pump for your drilling project, there are several factors to consider. These would include not only cost and size of pump that best fits your drilling rig, but also the diameter, depth and hole conditions you are drilling through. I know that this sounds like a lot to consider, but if you are set up the right way before the job starts, you will thank me later.

Recommended practice is to maintain a minimum of 100 to 150 feet per minute of uphole velocity for drill cuttings. Larger diameter wells for irrigation, agriculture or municipalities may violate this rule, because it may not be economically feasible to pump this much mud for the job. Uphole velocity is determined by the flow rate of the mud system, diameter of the borehole and the diameter of the drill pipe. There are many tools, including handbooks, rule of thumb, slide rule calculators and now apps on your handheld device, to calculate velocity. It is always good to remember the time it takes to get the cuttings off the bottom of the well. If you are drilling at 200 feet, then a 100-foot-per-minute velocity means that it would take two minutes to get the cuttings out of the hole. This is always a good reminder of what you are drilling through and how long ago it was that you drilled it. Ground conditions and rock formations are ever changing as you go deeper. Wouldn’t it be nice if they all remained the same?

Centrifugal-style mud pumps are very popular in our industry due to their size and weight, as well as flow rate capacity for an affordable price. There are many models and brands out there, and most of them are very good value. How does a centrifugal mud pump work? The rotation of the impeller accelerates the fluid into the volute or diffuser chamber. The added energy from the acceleration increases the velocity and pressure of the fluid. These pumps are known to be very inefficient. This means that it takes more energy to increase the flow and pressure of the fluid when compared to a piston-style pump. However, you have a significant advantage in flow rates from a centrifugal pump versus a piston pump. If you are drilling deeper wells with heavier cuttings, you will be forced at some point to use a piston-style mud pump. They have much higher efficiencies in transferring the input energy into flow and pressure, therefore resulting in much higher pressure capabilities.

Piston-style mud pumps utilize a piston or plunger that travels back and forth in a chamber known as a cylinder. These pumps are also called “positive displacement” pumps because they literally push the fluid forward. This fluid builds up pressure and forces a spring-loaded valve to open and allow the fluid to escape into the discharge piping of the pump and then down the borehole. Since the expansion process is much smaller (almost insignificant) compared to a centrifugal pump, there is much lower energy loss. Plunger-style pumps can develop upwards of 15,000 psi for well treatments and hydraulic fracturing. Centrifugal pumps, in comparison, usually operate below 300 psi. If you are comparing most drilling pumps, centrifugal pumps operate from 60 to 125 psi and piston pumps operate around 150 to 300 psi. There are many exceptions and special applications for drilling, but these numbers should cover 80 percent of all equipment operating out there.

The restriction of putting a piston-style mud pump onto drilling rigs has always been the physical size and weight to provide adequate flow and pressure to your drilling fluid. Because of this, the industry needed a new solution to this age-old issue.

As the senior design engineer for Ingersoll-Rand’s Deephole Drilling Business Unit, I had the distinct pleasure of working with him and incorporating his Centerline Mud Pump into our drilling rig platforms.

In the late ’90s — and perhaps even earlier —  Ingersoll-Rand had tried several times to develop a hydraulic-driven mud pump that would last an acceptable life- and duty-cycle for a well drilling contractor. With all of our resources and design wisdom, we were unable to solve this problem. Not only did Miller provide a solution, thus saving the size and weight of a typical gear-driven mud pump, he also provided a new offering — a mono-cylinder mud pump. This double-acting piston pump provided as much mud flow and pressure as a standard 5 X 6 duplex pump with incredible size and weight savings.

The true innovation was providing the well driller a solution for their mud pump requirements that was the right size and weight to integrate into both existing and new drilling rigs. Regardless of drill rig manufacturer and hydraulic system design, Centerline has provided a mud pump integration on hundreds of customer’s drilling rigs. Both mono-cylinder and duplex-cylinder pumps can fit nicely on the deck, across the frame or even be configured for under-deck mounting. This would not be possible with conventional mud pump designs.

Centerline stuck with their original design through all of the typical trials and tribulations that come with a new product integration. Over the course of the first several years, Miller found out that even the best of the highest quality hydraulic cylinders, valves and seals were not truly what they were represented to be. He then set off on an endeavor to bring everything in-house and began manufacturing all of his own components, including hydraulic valves. This gave him complete control over the quality of components that go into the finished product.

The second generation design for the Centerline Mud Pump is expected later this year, and I believe it will be a true game changer for this industry. It also will open up the application to many other industries that require a heavier-duty cycle for a piston pump application.

A ship consists of various types of fluids moving inside different machinery and systems for the purpose of cooling, heating, lubrication, and as fuels. These liquids are circulated by different types of pumps, which can be independently driven by ship power supply or attached to the machinery itself. All the systems on board ship require proper operational and compatible pump and pumping system so that ship can run on its voyage smoothly.

The selection of a type of pump for a system depends on the characteristics of the fluid to be pumped or circulated. Characteristics such as viscosity, density, surface tension and compressibility, along with characteristics of the system such as require rate of fluid, head to which the fluid is to be pumped, temperature encountered in the system, and pressure tackled by the fluid in the system, are taken into account.

An ardent sailor and a techie, Anish Wankhede has voyaged on a number of ships as a marine engineer officer. He loves multitasking, networking, and troubleshooting. He is the one behind the unique creativity and aesthetics at Marine Insight.

The disclosure relates generally to a reciprocating pump. More particularly, the disclosure relates to a hydraulically actuated reciprocating pump having a piston driven to reciprocate within a cylinder by fluid pressure. The disclosure also relates to systems and methods for reducing pressure pulsations created within the pump by reciprocation of the piston within the cylinder.

To form an oil or gas well, a bottom hole assembly (BHA), including a drill bit, is coupled to a length of drill pipe to form a drill string. The drill string is then inserted downhole, where drilling commences. During drilling, fluid, or “drilling mud,” is circulated down through the drill string to lubricate and cool the drill bit, to pressurize the borehole, and to provide a vehicle for removal of drill cuttings from the borehole. After exiting the bit, the drilling fluid returns to the surface through the annulus formed between the drill string and the surrounding borehole wall. Instrumentation for taking various downhole measurements and communication devices are commonly mounted within the drill string. Many such instrumentation and communication devices operate by sending and receiving pressure pulses through the annular column of drilling fluid maintained in the borehole.

Mud pumps are commonly used to deliver drilling fluid to the drill string during drilling operations. Many conventional mud pumps are reciprocating pumps, having at least one piston-cylinder assembly driven by a crankshaft and hydraulically coupled between a suction manifold and a discharge manifold. During operation of the mud pump, the piston is mechanically drive to reciprocate within the cylinder. As the piston moves to expand the volume within the cylinder, drilling fluid is drawn from the suction manifold into the cylinder. After the piston reverses direction, the volume within the cylinder decreases and the pressure of drilling fluid contained with the cylinder increases. When the piston reaches the end of its stroke, pressurized drilling fluid is exhausted from the cylinder into the discharge manifold. While the mud pump is operational, this cycle repeats, often at a high cyclic rate, and pressurized drilling fluid is continuously fed to the drill string at a substantially constant rate.

Because the piston directly contacts drilling fluid within the cylinder, loads are transmitted from the piston to the drilling fluid. Due to the reciprocating motion of the piston, the transmitted loads are cyclic, resulting in the creation of pressure pulsations in the drilling fluid. The pressure pulsations may disturb the downhole communication devices and instrumentation by degrading the accuracy of measurements taken by the instrumentation and hampering communications between downhole devices and control systems at the surface. Over time, the pressure pulsations may also cause fatigue damage to the drill string pipe and other downhole components.

Accordingly, there is a need for an apparatus or system and associated method that reduces pressure pulsations created within fluid pressurized by a reciprocating pump due to contact between the pump piston and the fluid.

A hydraulically driven pump is disclosed. In some embodiments, the pump includes a housing having a hydraulic chamber, a piston assembly separating the hydraulic chamber into at least a first subchamber and a second subchamber and disposed for reciprocal motion within the housing, and a hydraulic system fluidicly coupled with the first subchamber and the second subchamber. The hydraulic system is actuatable to deliver hydraulic fluid to the first subchamber, whereby the first subchamber is pressurized and the piston assembly translates in a first direction from a stroked back position toward a stroked out position, and to deliver hydraulic fluid to the second subchamber, whereby the second subchamber is pressurized and the piston translates in a second direction opposite the first direction from the stroked out position toward the stroked back position.

In some embodiments, the pump includes a housing including a hydraulic chamber, a cylinder coupled to the housing, a piston assembly adapted for reciprocal motion within the housing and the cylinder, the piston assembly separating the hydraulic chamber into three subchambers, and a hydraulic system fluidicly coupled to each of the subchambers. The hydraulic system is actuatable to deliver hydraulic fluid to a first of the subchambers, whereby the piston assembly strokes back and a working fluid is drawn into the cylinder, to deliver hydraulic fluid to a second of the subchambers, whereby the piston assembly strokes out and the working fluid is exhausted from the cylinder, and to adjust a volume of hydraulic fluid within a third of the subchambers, whereby the piston assembly translates to bring a pressure of the working fluid in the cylinder to within a pre-selected range.

In some embodiments, the pump includes a housing and a piston assembly disposed within the housing. The piston assembly has a piston body translatable relative to the housing and a bladder coupled between the piston body and the housing. The bladder separates a first hydraulic chamber and a second hydraulic chamber. The pump further includes a hydraulic system fluidicly coupled to the first hydraulic chamber and the second hydraulic chamber. The hydraulic system is actuatable to deliver hydraulic fluid to the first hydraulic chamber, whereby the bladder flexes and the piston body translates in a first direction, and to deliver hydraulic fluid to the second hydraulic chamber, whereby the bladder flexes and the piston body translates in a second direction opposite the first direction.

Thus, embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with conventional mechanically driven reciprocating pumps. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings.

FIG. 2 is a cross-sectional view of one piston-cylinder assembly of FIG. 1 fluidicly coupled with the hydraulic system and electrically coupled the control system, the hydraulic system and the control system both schematically represented;

FIG. 6 is an enlarged, cross-sectional view of the piston-cylinder assembly of FIG. 3, better illustrating the stepped piston, piston cover, and linear displacement transducer;

FIG. 7 is an enlarged, cross-sectional view of the opposite end of the piston-cylinder assembly of FIG. 3, better illustrating the piston seal and backup seal;

FIG. 13 is a cross-sectional, lengthwise view of one piston-cylinder assembly of FIG. 12 fluidicly coupled with the hydraulic system and electrically coupled the control system, the hydraulic system and the control system both schematically represented;

The following description is directed to exemplary embodiments of a hydraulically driven reciprocating pump system. The embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and that the discussion is meant only to be exemplary of the described embodiments, and not intended to suggest that the scope of the disclosure, including the claims, is limited only to those embodiments. For example, the pump described herein may be employed in any fluid conveyance system where it is desirable to reduce the turbulence of fluid contained within or moving through the system.

Certain terms are used throughout the following description and the claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. Moreover, the drawing figures are not necessarily to scale. Certain features and components described herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, the connection between the first device and the second device may be through a direct connection, or through an indirect connection via other intermediate devices and connections. Further, the terms “axial” and “axially” generally mean along or parallel to a central or longitudinal axis. The terms “radial” and “radially” generally mean perpendicular to the central or longitudinal axis, while the terms “circumferential” and “circumferentially” generally mean disposed about the circumference, and as such, perpendicular to both the central or longitudinal axis and a radial axis normal to the central longitudinal axis. As used herein, these terms are consistent with their commonly understood meanings with regard to a cylindrical coordinate system.

Referring now to FIG. 1, there is shown a hydraulically driven reciprocating pump 100 for pressurizing a working fluid, such as but not limited to drilling mud. Reciprocating pump 100 includes three substantially identical piston-cylinder assemblies 105. Each piston-cylinder assembly 105 includes a piston assembly (not visible in FIG. 1, but identified in FIG. 2 by reference number 145) translatably disposed within a cylinder 110, meaning the piston assembly is translatable within and relative to cylinder 110. The piston assemblies are driven out of phase with each other, meaning the position of each relative to its associated cylinder 110 is different than that of the other piston assemblies at any given instant. In certain embodiments, piston-cylinder assemblies 105 are operated 120 degrees out of phase with each other. Even so, other phase relationships may also be employed. As will be described, the piston assemblies are driven by a hydraulic system 115 that is, in turn, governed by a control system. For simplicity, hydraulic system 115 is only partially depicted in FIG. 1 whereas the control system is not shown at all. These systems are, however, shown in other figures of this disclosure and described below.

Each piston-cylinder assembly 105 is coupled between a suction manifold 120 and a discharge manifold 125. Referring to FIG. 2, which, for simplicity, illustrates only one piston-cylinder assembly 105, drilling mud is delivered from a source 130 via a pump 135 driven by a motor 140 through suction manifold 120 to cylinder 110. As piston assembly 145 is stroked back within cylinder 110, meaning translated within cylinder 110 to the right as viewed in FIG. 2, drilling mud is drawn through a suction valve 150 into a compression chamber 160 within cylinder 110. After piston assembly 145 reverses direction and begins to translate within cylinder 110 to the left as viewed in FIG. 2, or stroke out, drilling mud contained within compression chamber 160 is pressurized by piston assembly 145. As piston assembly 145 approaches the end of its stroke, the pressurized drilling mud is exhausted from cylinder 110 through a discharge valve 155 into discharge manifold 125. Thus, as piston assembly 145 reciprocates within cylinder 110, piston-cylinder 105 repeatedly receives drilling mud from suction manifold 120, pressurizes the drilling mud received, and delivers the pressurized drilling mud to discharge manifold 125.

Piston-cylinder assembly 105 further includes a two flanges 165, 170, a composite housing 175 disposed therebetween, and a circular plate 180. Cylinder 110 is coupled to flange 170 with plate 180 disposed therebetween. Circular plate 180 is a cover plate for sealing elements disposed along the bore of flange 170, as shown in FIG. 2 and discussed further below. Flanges 165, 170 and composite housing 175 form a hydraulic chamber 200. Also, each of flange 165, composite housing 175, and flange 170 have a hydraulic fluid port 185, 190, 195, respectively, fluidicly coupled, meaning in fluid communication, with hydraulic chamber 200.

Piston assembly 145 is disposed within hydraulic chamber 200 and compression chamber 160 of cylinder 110, and reciprocates within chambers 160, 200 to draw drilling fluid into compression chamber 160, pressurize the drilling fluid, and exhaust the pressurized drilling fluid from compression chamber 160, as previously described. Piston-cylinder assembly 105 further includes a stepped piston 365 and a piston cover 370 disposed within hydraulic chamber 200 between piston assembly 145 and flange 165. Stepped piston 365 and piston cover 370 are rigidly coupled such that there is no relative movement between the two. Further, stepped piston 365 and piston cover 370 coupled thereto are axially translatable relative to piston assembly 145 within composite housing 175.

Each of piston assembly 145 and stepped piston 365 sealingly engages the inner surface 205 of composite housing 175. Thus, hydraulic chamber 200 is divided by piston assembly 145 and stepped piston 365 into three subchambers 210, 215, 220. Subchamber 210 is disposed between stepped piston 365 and flange 165. Subchamber 220 is disposed adjacent flange 170, and subchamber 215 is disposed between subchambers 210, 220. Hydraulic fluid ports 185, 190, 195 are fluidicly coupled with subchambers 210, 215, 220, respectively.

Hydraulic system 115 drives piston assembly 145, meaning hydraulic system 115 causes piston assembly 145 to reciprocate. Hydraulic system 115 includes three valves 225, 230, 235, three pressure sensors 240, 245, 250, a hydraulic fluid supply unit 255, a hydraulic fluid supply piping network 260, a hydraulic fluid return piping network 265, and three flowlines or jumpers 270, 275, 280. Valves 225, 230, 235 are fluidicly coupled to ports 185, 190, 195, respectively, via flowlines 270, 275, 280. Valves 225, 230, 235 are also fluidicly coupled to hydraulic fluid supply unit 255 via supply piping network 260 and return piping network 265. In the illustrated embodiment of FIG. 2, valves 225, 230, 235 are electro-proportional reducing/relieving pressure control valves, such as those having model number EHPR98-T38 and manufactured by HydraForce, Inc., headquartered at 500 Barclay Blvd., Lincolnshire, Ill. 60069. In certain embodiments, the valve 225 (and also the valve 230 and the valve 235) is a valve system or composite valve. For example, the valve system 225 can include a pneumatic or hydraulically actuated valve via a solenoid or electrically driven pilot valve, as is known in the industry. In another example, the valve system 225 can include other valves as disclosed herein such as the valve 230, the valve 235, a relief valve 300 (discussed below), the valve 150, the valve 155, or a combination thereof. Also, sensors 240, 245, 250 are high pressure sensors, such those having model number P5000-500-1G3S and manufactured by Kavlico, Inc., headquartered at 14501 Princeton Avenue, Moorpark, Calif. 93021.

Hydraulic fluid supply unit 255 includes a hydraulic fluid source 285, a pump 290 driven by a motor 295, a relief valve 300 and gauge 305, and an accumulator 310, all fluidicly coupled. When motor 295 is operating, source pump 290 delivers hydraulic fluid from source 285 through a flowline 315 to supply piping network 260. Supply piping network 260, in turn, conveys the hydraulic fluid to valves 225, 230, 235, which are operable, as will be described, to allow the hydraulic fluid to pass through flowlines 270, 275, 280 and ports 185, 195, 190 to subchambers 210, 215, 220, respectively, of piston-cylinder assembly 105. Valves 225, 230, 235 are also operable to relieve hydraulic fluid from subchambers 210, 220, 215, respectively. Hydraulic fluid relieved from subchambers 210, 215, 220 is returned through return piping network 265 to hydraulic fluid source 285.

Gauge 305 is operable to sense the pressure of hydraulic fluid provided by source 285 to flowline 315. The sensed pressure is then communicated to relief valve 300 by an electrical conductor 320. For clarity, all electrical conductors, including line 320, shown in the figures are represented by dashed lines, whereas all flowlines, piping networks, or manifolds through which hydraulic fluid and drilling mud flows are represented by solid lines. Referring still to FIG. 2, if the pressure sensed by gauge 305 exceeds a pre-selected pressure setting, relief valve 300 is actuated to divert hydraulic fluid from flowline 315 into a bypass flowline 325. The diverted hydraulic fluid is then returned to hydraulic fluid source 285. Diverting hydraulic fluid from flowline 315 into bypass flowline 325 in this manner prevents overpressuring of supply piping network 260 and other components of hydraulic system 115 downstream of network 260 beyond the pre-selected pressure setting.

Pressure sensor 245 is disposed on flowline 275 proximate port 190. Sensor 245 is operable to sense the pressure of hydraulic fluid in flowline 275, and thus subchamber 215. Similarly, pressure sensor 250 is disposed on flowline 280 proximate port 195. Sensor 250 is operable to sense the pressure of hydraulic fluid in flowline 280, and thus subchamber 220. Pressure sensor 240 is disposed downstream of discharge valve 155 of piston-cylinder assembly 105. Sensor 240 is operable to sense the pressure of drilling mud exhausted from piston-cylinder assembly 105.

Pump 100 further includes a control system 345. Control system 345 is electrically coupled to PPC valves 225, 230, 235 via electrical conductors 347, 350, 355, respectively, and to pressure sensors 240, 245, 250 via electrical conductors 330, 335, 340, respectively. As will be described, control system 345 governs the opening and closing of valves 230, 235 dependent upon pressures sensed by sensors 240, 245, 250 to supply hydraulic fluid in an alternating fashion to subchamber 215 while relieving hydraulic fluid from subchamber 220 and to subchamber 220 while relieving hydraulic fluid from subchamber 215. When subchamber 215 is supplied with hydraulic fluid, or pressurized, subchamber 220 is relieved of hydraulic fluid, or de-pressurized, and vice versa. Cyclic pressurization of subchambers 215, 220 and substantially simultaneous depressurization of chambers 220, 215 enables piston assembly 145 to be driven by fluid pressure. When subchamber 215 is pressurized, piston assembly 145 strokes out, moving from right to left as viewed in FIG. 2 and pushing hydraulic fluid from subchamber 220 through port 195. When subchamber 220 is subsequently pressurized, piston assembly 145 strokes back, moving from left to right as viewed in FIG. 2 and pushing hydraulic fluid from subchamber 215 through port 190. At the same time, control system 345 governs the opening and closing of valve 225 to adjust the volume of hydraulic fluid in subchamber 210 to maintain the discharge pressure of pump 100 substantially constant, or within a range.

Turning to FIG. 3, piston assembly 145 includes an axially extending body 360. Body 360 is a generally cylindrical member with two opposing ends 375, 380. Ends 375, 380 of body 360 have reduced diameters, meaning each has a diameter that is smaller than that of the remainder of body 360 extending therebetween. As will be described further below, body 360 receives a coupling 385 disposed about reduced diameter end 380. Referring now to FIG. 4, body 360 further includes a groove 390 extending circumferentially thereabout at end 375. An annular disc or ring 395 (not shown in FIG. 4 but shown in FIGS. 3 and 6) is seated in groove 390. Disc 395 prevents body 360 from disengaging stepped piston 365 when body 360 strokes out during operation of pump 100, as illustrated by FIG. 6.

Body 360 further includes a radially extending piston 400 and a radially extending flange 405. Piston 400 has an axially extending outer surface 410 defined by a substantially constant or uniform diameter. Uniform piston 400 includes a plurality of circumferentially extending grooves 415 formed in surface 410. A sealing element 420 is disposed within each groove 415. In some embodiments, sealing elements 420 are O-rings. Elements 420 enable sealing engagement between uniform piston 400 and inner surface 205 of composite housing 175, as illustrated by FIG. 3, thereby limiting or preventing the transfer of hydraulic fluid between subchambers 215, 220.

Referring to FIGS. 3 and 4, flange 405 has a radially extending annular surface 425 and an angled or frustoconical outer surface 430 extending therefrom. Surface 430 is defined by a diameter that increases in the axial direction moving away from surface 425. The angular nature of surface 430 enables gradual or increasing engagement between flange 405 and hydraulic fluid in subchamber 215 (FIG. 3) as body 360 strokes back and the displacement of hydraulic fluid from the bores of stepped piston 365 and piston cover 370, to be described further below, as end 375 of body 360 is received therein. This minimizes, even eliminates, the application of a blunt load to body 360 due to engagement with the hydraulic fluid that may otherwise occur were surface 430 not frustoconical. Such blunt interaction between the hydraulic fluid and body 360 may create undesirable pressure fluctuations in the drilling mud within cylinder 110 and/or pressure fluctuations in the hydraulic fluid that may damage components of hydraulic system 115.

Referring now to FIGS. 5A and 5B, stepped piston 365 is an annular member with two opposing ends 435, 440 and a bore 445 extending therethrough. At end 435, best viewed in FIG. 5A, stepped piston 365 has a radially extending surface 450 with two circumferentially extending grooves 455 and an axially extending bore 460 (see also FIG. 3) formed therein. A sealing element 465 (not shown in FIG. 5A, but visible in FIGS. 3 and 6) is disposed within each groove 455. In some embodiments, sealing elements 465 are O-rings. Elements 465 enable sealing engagement between stepped piston 365 and piston cover 370, thereby limiting or preventing the transfer of hydraulic fluid between subchambers 210, 215.

At end 440, best viewed in FIG. 5B, stepped piston 365 has a radially extending surface 470 and a recess 475 formed therein. Recess 475 is bounded at its base by a radially extending surface 480 and along its side by a substantially axially extending surface 485. Recess 475 is configured to receive flange 405 (FIG. 3) therein such that surface 425 of flange 405 abuts surface 480. Stepped piston 365 further includes a substantially axially extending surface 490 extending from surface 480 and bounding bore 445. A plurality of circumferentially spaced grooves 495, 500 are formed in surfaces 485, 490, respectively.

Referring to FIG. 6, stepped piston 365 has a radially facing, circumferential outer surface 505 proximate end 440. Surface 505 is defined by a substantially constant diameter. Stepped piston 365 includes a plurality of circumferentially extending grooves 510 formed in surface 505. A sealing element 515 is disposed within each groove 510. In some embodiments, sealing elements 515 are O-rings. Elements 515 enable sealing engagement between stepped piston 365 and inner surface 205 of composite housing 175, thereby limiting or preventing the transfer of hydraulic fluid between sub chambers 210, 215.

Stepped piston 365 also has an angled or frustoconical outer surface 520. Surface 520 is defined by a diameter that increases moving in the axial direction away from end 435 of stepped piston 365. The angular nature of surface 520 enables gradual or increasing engagement between stepped piston 365 and hydraulic fluid in subchamber 210 as stepped piston 365 strokes back. This minimizes the application of a blunt load to stepped piston 365 due to engagement with the hydraulic fluid that may otherwise occur were surface 520 not frustoconical.

Bounding bore 445, stepped piston 365 has a radially extending surface 525 extending from surface 490 and an axially extending surface 530 extending from surface 525. Surface 530 is defined by a diameter exceeding that defining surface 490. Thus, a stop or shoulder 535 is formed at the intersection of surfaces 525, 530 within stepped piston 365. Shoulder 535 limits axial translation of body 360 relative to stepped piston 365. When body 360 strokes out relative to stepped piston 365, engagement between disc 395 seated in groove 390 of body 360 and shoulder 535 of stepped piston 365 prevents body 360 from disengaging stepped piston 365.

Referring still to FIG. 6, piston cover 370 is an annular member having two opposing ends 540, 545 and a bore 550. At end 540, piston cover 370 has a radially extending flange 555. Flange 555 enables coupling of piston cover 370 to end 435 of stepped piston 365. As previously described, elements 465 enable sealing engagement between piston cover 370 and stepped piston 365, limiting or preventing the exchange of hydraulic fluid between subchambers 210, 215. Bore 550 extends from end 540 of piston cover 370 and is substantially aligned with bore 445 of stepped piston 365. Alignment of bores 445, 550 enables end 375 of body 360 to be inserted through bore 445 of stepped piston 365 into bore 550 of piston cover 370. End 545 of piston cover 370 is closed. Due to the sealing engagement of stepped piston 365 with inner surface 205 of composite housing 175, the sealing engagement between stepped piston 365 and piston cover 370, and the closed end 545 of piston cover 370, together stepped piston 365 and piston cover 370 form a barrier that fluidicly isolates subchamber 210 from subchamber 215, and vice versa.

Piston cover 370 further includes an axially extending bore 560 and a recess 570 formed at end 545 of piston cover 370. Bore 560 extends through flange 555 and aligns with bore 460 of stepped piston 365. Support ring 565 is seated in a recess 570 formed at end 545 of piston cover 370 and coupled thereto. Piston-cylinder assembly 105 further includes a linear displacement transducer 575 and a magnetic marker 565. Linear displacement transducer 575 is coupled to flange 165 and extending through subchamber 210 and magnetic marker 565 into aligned bores 460, 560. Linear displacement transducer 575 is electrically coupled with control system 345 (FIG. 2) via an electrical conductor 580 (FIG. 2). Magnetic marker 565 produces a magnetic field thereabout, as does linear displacement transducer 575. Interaction between the two magnetic fields causes linear displacement transducer 575 to deform. Electronic signals generated by linear displacement transducer 575 in response to its deformation and delivered from linear displacement transducer 575 to control system 345 enable control system 345 to determine the axial position of marker 565, and thus stepped piston 365, relative to flange 165 and, in turn, the volume of subchamber 210 during operation of pump 100. In the illustrated embodiment, transducer 575 may be one of those manufactured by Novotechnik U.S., Inc., headquartered at 155 Northboro Road, Southborough, Mass. 01772, such as transducers having model number TIM 0200 302 821 201. Alternatively, transducer 575 may be manufactured by MTS Systems Corporation, headquartered at 14000 Technology Drive, Eden Prairie, Minn. 55344, and having model number GT2S 200M D60 1A0.

Referring again to FIG. 3, piston assembly 145 is axially translatable relative to stepped piston 365 and piston cover 370 coupled thereto, as previously described. When piston assembly 145 strokes back, end 375 of body 360 is inserted through bore 445 of stepped piston 365 and received within bore 550 of piston cover 370, as shown. Hydraulic fluid contained within bore 445 of stepped piston 365 and bore 550 of piston cover 370 is displaced therefrom through grooves 495, 500 (FIG. 5B) into subchamber 215. Thus, hydraulic fluid within bores 445, 550 does not remain trapped between flange 405 of body 360, stepped piston 365, and cover piston 370, exerting a force that resists translation of piston assembly 145.

Piston-cylinder assembly 105 further includes a piston seal 585 and a backup seal 590 disposed about recessed end 380 of piston assembly 145 translatably received within cylinder 110 and secured thereto by coupling 385. Seal 585 sealingly engages the inner surface 595 of cylinder 110 to prevent the loss of pressurized drilling mud from compression chamber 160 along these interfaces. Backup seal 590 rigidly supports piston seal 585. As best viewed in FIG. 7, backup seal 590 is annular or ring-shaped, similar to a washer. Piston seal 585 is also annular and has two opposing ends 600, 605. End 600 has a planar, radially extending surface 610 engaging backup seal 590. End 605 has a generally concave surface 615 facing compression chamber 160. The concave shape of surface 615 enables sealing engagement between piston seal 585 and cylinder 110. The pressure of drilling mud within cylinder 110 acts against surface 615, forcing the outer surface 617 of piston seal 585 into engagement with the inner surface 112 of cylinder 110.

Referring again to FIG. 3, piston assembly 145 extends through aligned bores 620, 625 in flange 170 and circular plate 180, respectively, between compression chamber 160 of cylinder 110 and hydraulic chamber 200 within composite housing 175. One or more grooves 630 are formed along the inner surface 635 of flange 170 bounding bore 620. A sealing element 640 is disposed within each groove 630. In some embodiments, sealing elements 640 are O-rings. Elements 640 enable sealing engagement between flange 170 and piston assembly 145, limiting or preventing the loss of hydraulic fluid from subchamber 220 at this interface.

To increase the life of sealing elements 640, pump 100 may optionally include a seal lubrication system 900, illustrated in FIG. 8. As shown, lubrication system 900 includes a lubrication fluid inlet port 905 and a lubrication fluid outlet port 910. Inlet port 905 extends radially between the outer surface of flange 170 and inner surface 635 of flange 170 proximate sealing elements 640. Outlet port 910 extends radially between the outer surface of circular plate 180 and bore 625 of plate 180. During operation of pump 100, a lubricating fluid or lubricant may be injected into port 905 to lubricate sealing elements 640. The injected lubricant flows from pump 100 through outlet port 910. Flushing sealing elements 640 with lubricant in this manner reduces wear to sealing elements 640 from friction and removes dirt and other particulates which may otherwise cause wear and abrasion to sealing elements 640 as piston assembly 145 reciprocates.

Referring to FIG. 9, composite housing 175 is a generally tubular member 645 formed by two concentric layers 650, 655 with an electrically resistive coil 660 embedded therebetween. Tubular member 645 is manufactured by Polygon Company, headquartered at 103 Industrial Park Drive, Walkerton, Ind. 46574, and referred to as the POLYSLIDE IST Smart Cylinder. Tubular member 645 has two opposing ends 665, 670, an electrical wire 675 extending radially from embedded coil 660 proximate end 665, and a bore 680 extending therethrough. In some embodiments, outer layer 655 comprises steel, and inner layer 650 is a composite liner. In other embodiments, the coil may be embedded directly into the inner layer, rather than exist as a separate component which is disposed between the concentric layers as illustrated. Bore 680 enables fluid communication between hydraulic fluid port 190 (FIG. 2) and subchamber 215 (FIG. 2), as previously described.

Wire 675 is electrically coupled between resistive coil 660 and control system 345 (FIG. 2) via an electrical conductor 685 extending therebetween. When piston assembly 145 translates within piston-cylinder assembly 105, as illustrated by FIG. 2, uniform piston 400 of piston assembly 145 engages inner surface 205 of composite housing 175, causing a localized pressure load on coil 660 and a change in the resistance of coil 660 in the region of compression. Control system 345 is operable to determine the axial position of uniform piston 400 within composite housing 175 relative to stepped piston 365 and to cylinder 110 using a signal from coil 660 delivered to control system 345 via wire 675 and electrical conductor 685 indicative of the localized change in the resistance of coil 660. Using the axial position of uniform piston 400 and the axial position of stepped piston 365, determined as previously described, control system 345 is also operable to determine the volumes of subchambers 215, 220.

As an alternative to resistive coil 660, piston-cylinder assembly 105 may comprise a linear displacement transducer and magnetic marker coupled to uniform piston 400, similar to transducer 575 and marker 565 coupled to piston cover 370. In such embodiments, the linear displacement transducer is operable to deliver electrical signals to control system 345. Using signals from the linear displacement transducer, control system 345 determines the axial position of uniform piston 400 and the volumes of subchambers 215, 220.

Returning to FIG. 3, composite housing 175 further includes a plurality of sealing elements 690 disposed between outer and inner layers 650, 655 proximate ends 665, 670 and around bore 680. Elements 690 prevent the seepage of hydraulic fluid between concentric layers 650, 655 which may otherwise tend to cause separation of layers 650, 655, damage to coil 660 (FIG. 9), and/or degradation of the coil"s performance.

During operation of pump 100, piston assembly 145 reciprocates between a fully stroked back position, illustrated by FIG. 10, and a fully stroked out position, illustrated by FIG. 11. Referring initially to FIG. 10, piston assembly 145 is fully stroked back. Control system 345 (FIG. 2) determines piston assembly 145 is fully stroked back based on the axial position of uniform piston 400 relative to stepped piston 365, the axial position of uniform piston 400 relative to cylinder 110, and the fluid pressures sensed by sensors 240, 245, 250. The axial position of uniform piston 400 stepped piston 365 and the axial position of uniform piston 400 relative to cylinder 110 are determined by control system 345 using signals transmitted from linear displacement sensor 575 and coil 660 (FIG. 9) of composite housing 175. When piston assembly 145 is fully stroked back, the pressure of drilling mud within compression chamber 160 and sensed by sensor 240 is approximately equal to the pressure of drilling mud at drilling mud source 130. The pressure of hydraulic fluid within subchamber 220 and sensed by sensor 250 is approximately equal to the pressure of hydraulic fluid in supply network 260. The pressure of hydraulic fluid within subchamber 215 and sensed by sensor 245 is approximately equal to the pressure of hydraulic fluid in return network 265.

Having determined piston assembly 145 is fully stroked back, control system 345 then actuates valve 230 (FIG. 2) to allow hydraulic fluid to pass from supply piping network 260 through valve 230 and port 190 into subchamber 215, actuates valve 235 to allow hydraulic fluid to be relieved from subchamber 220 through port 195 and valve 235 (FIG. 2) into return piping network 265, and actuates valve 225 such that no hydraulic fluid is allowed to enter or leave subchamber 210. As the volume of hydraulic fluid in subchamber 215 increases, the pressure of hydraulic fluid in subchamber 215 acts against piston assembly 145, causing piston assembly 145 to stroke out. As piston assembly 145 strokes out, hydraulic fluid is forced from subchamber 220 through valve 235 into return piping network 265. Also, drilling mud within compression chamber 160 is pressurized and forced therefrom through discharge valve 155 into discharge manifold 125.

When piston assembly 145 is fully stroked out, as illustrated by FIG. 11, control system 345 determines that is the case based on the axial position of uniform piston 400 relative to stepped piston 365, the axial position of uniform piston 400 relative to cylinder 110, and the fluid pressures sensed by sensors 240, 245, 250. The axial position of uniform piston 400 relative to stepped piston 365 and the axial position of uniform piston 400 relative to cylinder 110 are again determined by control system 345 using signals transmitted from linear displacement transducer 575 and coil 660. When piston assembly 145 is fully stroked out, the pressure of drilling mud within compression chamber 160 and sensed by sensor 240 is equal to the discharge pressure of pump 100. The pressure of hydraulic fluid within subchamber 220 and sensed by sensor 250 is approximately equal to the pressure of hydraulic fluid in return network 260. The pressure of hydraulic fluid within subchamber 215 and sensed by sensor 245 is approximately equal to the pressure of hydraulic fluid in supply network 265.

Having determined piston assembly 145 is fully stroked out, control system 345 then actuates valve 235 to allow hydraulic fluid to pass from supply piping network 260 through port 195 and valve 235 into subchamber 220, actuates valve 230 to allow hydraulic fluid to be relieved from subchamber 215 through port 190 and valve 230 into return piping network 265, and actuates valve 225 such that no hydraulic fluid is allowed to enter or leave subchamber 210. As the volume of hydraulic fluid in subchamber 220 increases, the pressure of hydraulic fluid in subchamber 220 acts against piston assembly 145, causing piston assembly 145 to stroke back. As piston assembly 145 strokes back, hydraulic fluid is forced from subchamber 215 through valve 230 into return piping network 265. Also, drilling mud is drawn from suction manifold 120 through suction valve 150 into compression chamber 160.

Once piston assembly 145 returns to its fully stroked back position, illustrated by FIG. 10, the above-described process repeats. Thus, piston assembly 145 is driven to reciprocate within piston-cylinder assembly 105 under fluid pressure provided by hydraulic system 115 in a manner governed by control system 345.

As piston assembly 145 reciprocates, control system 345 actuates valve 225 (FIG. 2) to enable adjustment of the volume of hydraulic fluid within subchamber 210 so as to maintain the discharge pressure of drilling mud exhausted from piston-cylinder assembly 105 substantially at a pre-selected pressure setting, or within a pre-selected pressure range. If the pressure sensed by sensor 240 (FIG. 2) and communicated to control system 345 is lower than the pre-selected pressure, or pressure range, control system 345 actuates valve 225 to enable the addition hydraulic fluid from supply network 260 to subchamber 210. This causes piston cover 370/stepped piston 365 and, in turn, piston assembly 145 to stroke out, thereby increasing the pressure of drilling mud within compression cha