PISTONS FOR USE IN FLUID EXCHANGE DEVICES AND RELATED DEVICES, SYSTEMS AND METHODS.

Abstract

Pistons and related methods can be configured to separate fluids and to at least partially prevent a fluid from moving to one side of the piston from the other. Pressure exchange devices and systems may include such pistons.

Description

PISTONS FOR USE IN FLUID EXCHANGE DEVICES AND RELATED DEVICES, SYSTEMS AND METHODS PRIORITY CLAIM This application claims the benefit of the filing date of the United States of America Provisional Patent Application, Serial Number 62 / 758,373, filed on November 9, 2018, for Fluid Exchange Devices and Related Controls, Systems and Methods, the description of which is incorporated herein in its entirety by reference. TECHNICAL FIELD This description refers generally to pistons for exchange devices. More specifically, the embodiments of this description refer to pistons for use in fluid exchange devices for one or more of the exchange properties (e.g., pressure) between fluids and systems and methods. BACKGROUND OF THE INVENTION Industrial processes often involve hydraulic systems that include pumps, valves, impellers, and other components. Pumps, valves, and impellers are used to control the flow of fluids used in hydraulic processes. For example, some pumps can be used to increase (e.g., boost) the pressure in the hydraulic system, while others can be used to move fluids from one place to another. Some hydraulic systems include valves to control the flow path of a fluid. Valves can include control valves, ball valves, gate valves, globe valves, check valves, isolation valves, combinations thereof, and so on. Some industrial processes involve the use of caustic, abrasive, and / or acidic fluids. These types of fluids can increase the amount of wear on the components of a hydraulic system. Increased wear can result in higher maintenance and repair costs or require early equipment replacement. For example, abrasive, caustic, or acidic fluid can increase wear on the internal components of a pump, such as an impeller, shaft, vanes, nozzles, etc. Some pumps are rebuildable, and an operation may choose to rebuild a worn pump by replacing the worn parts. This can result in extended periods of downtime for the worn pump, leading to the need for redundant pumps or a drop in productivity. Other operations may replace worn pumps at a higher cost but with a reduced amount of downtime. nnzcnn / Lznz / Bm Well completion operations in the oil and gas industry often involve hydraulic fracturing (often called hydraulic fracturing or hydraulic fracking) to increase the release of oil and gas from rock formations. Hydraulic fracturing involves pumping a fluid (e.g., fracturing fluid, hydraulic fracturing fluid, etc.) containing a mixture of water, chemicals, and proppant (e.g., sand, ceramic) into a well at high pressure. The high fluid pressure increases the size and propagation of the fracture through the rock formation, releasing more oil and gas, while the proppant prevents the fractures from closing once the fluid is depressurized. Fracturing operations utilize high-pressure pumps to increase the pressure of the fracturing fluid.However, the proppant in hydraulic fracturing fluid increases wear and maintenance and substantially reduces the operating life of high-pressure pumps due to its abrasive nature. BRIEF DESCRIPTION OF THE INVENTION Several configurations may include a device or system for exchanging pressure between fluids. The device may include at least a tank, at least one piston in the tank, and a valve device. The tank may include a clean side to receive a clean fluid at a higher pressure and a dirty side to receive a downhole fluid (e.g., hydraulic fracturing fluid, drilling fluid) at a lower pressure. The piston may be configured to separate the clean fluid from the downhole fluid, at least partially preventing the downhole fluid from traveling from the dirty side to the clean side. The valve device may be configured to selectively place the clean fluid at the higher pressure into communication with the downhole fluid at the lower pressure via the piston, thereby pressurizing the downhole fluid to a second, higher pressure. Another embodiment may include a device or system for exchanging at least one property between fluids. The device may include at least a tank, at least one piston in the tank, and a valve device. The tank may include a first end for receiving a first fluid (e.g., a clean fluid) with a first property and a second end for receiving a second fluid (e.g., a dirty fluid) with a second property. The piston may be configured to separate the clean fluid from the dirty fluid and to substantially prevent the dirty fluid from moving from the second end to the first end. Another embodiment may include a piston for at least partially separating at least two fluid streams. The piston may be implemented in the devices or systems discussed above. The piston includes a body having an opening extending along an axis of the body, where the opening defines a fluid path through the piston, and at least one valve obstructing the opening. The at least one valve is configured to permit fluid flow in one direction along the fluid path through the opening and to at least partially inhibit fluid flow in the opposite direction along the fluid path through the opening. Another embodiment may include a method of operating a pressure exchange device comprising supplying a high-pressure fluid to a high-pressure inlet of a valve configured to direct the flow of the high-pressure fluid into a chamber; transferring a pressure from the high-pressure fluid to a dirty fluid through a piston in the chamber; allowing some of the high-pressure fluid to pass through the piston; and substantially preventing the dirty fluid from passing through the piston to the high-pressure fluid. BRIEF DESCRIPTION OF THE DRAWINGS Although the specification concludes with claims that clearly identify and assert what are considered to be embodiments of the present description, several features and advantages of the embodiments of this description can be more easily determined from the following description of example embodiments of the description when read in conjunction with the accompanying drawings, in which: Figure 1 is a schematic view of a hydraulic fracturing system, according to one modality of the present description; Figure 2 is a cross-sectional view of a fluid exchanger device, according to one embodiment of the present description; Figure 3A is a cross-sectional view of a control valve in a first position, according to one embodiment of the present description; Figure 3B is a cross-sectional view of a control valve in a second position, according to one embodiment of the present description; Figure 4 is a symmetrical view of a piston according to one embodiment of the present description; and Figure 5 is a cross-sectional view of a piston according to one embodiment of the present description. MODE IF TO CARRY OUT THE INVENTION The illustrations presented in this document are not intended to be actual views of any particular fluid exchanger or component thereof, but are simply idealized representations used to describe illustrative models. The drawings are not necessarily to scale. Common elements between figures may retain the same numerical designation. As used herein, relational terms such as first, second, above, below, etc., are generally used for clarity and convenience in understanding the description and accompanying drawings and do not connote or depend on any specific preference, orientation, or order, except where the context clearly indicates otherwise. As used in this document, the term and / or means and includes each and every combination of one or more of the associated listed elements. As used in this document, the terms vertical and lateral refer to the orientations shown in the figures. As used in this document, the term "substantially" or "approximately" in reference to a given parameter means and includes to a degree that a person skilled in the art would understand that the given parameter, property, or condition is met with a small degree of variation, such as within acceptable manufacturing tolerances. For example, a parameter that is "substantially" may be met at least 90%, at least 95%, at least 99%, or even 100%. As used in this document, the term fluid can mean and include fluids of any type and composition. Fluids may be in a liquid form, a gaseous form, or combinations thereof, and in some cases may include some solid material. In some embodiments, fluids can be converted between a liquid and a gaseous form during a cooling or heating process as described in this document. In some embodiments, the term fluid includes gases, liquids, and / or pumpable mixtures of liquids and solids. The modalities described herein may refer to exchange devices that can be used to exchange one or more properties between fluids (e.g., a pressure exchanger). Such exchangers (e.g., pressure exchangers) are sometimes called flow work exchangers or isobaric devices and are machines for exchanging pressure energy from a fluid system flowing at a relatively high pressure to a fluid system flowing at a relatively low pressure. In some industrial processes, high pressures are required in certain parts of the operation to achieve the desired results, after which the pressurized fluid is depressurized. In other processes, some fluids used are available at high pressures and others at low pressures, and it is desirable to exchange pressure energy between these two fluids. As a result, in some applications, a significant improvement in efficiency can be achieved if pressure can be transferred efficiently between two fluids. nnzcnn / ίζηζ / Β / γι In some embodiments, the exchangers as described herein may be similar to and include the various components and configurations of the pressure exchangers described in U.S. Patent No. 5,797,429 to Shumway, issued August 25, 1998, the description of which is incorporated herein in its entirety by this reference. Although some embodiments of the present description are described as being used and employed as a pressure exchanger between two or more fluids, those skilled in the art will understand that the embodiments of the present description can be employed in other implementations such as, for example, the exchange of other properties (e.g., temperature, density, etc.) and / or composition between one or more fluids and / or mixture of two or more fluids. In some configurations, a pressure exchanger can be used to protect moving components (e.g., pumps, valves, impellers, etc.) in processes where high pressures are needed in a fluid that has the potential to damage the moving components (e.g., abrasive fluid, caustic fluid, acidic fluid, etc.). For example, pressure exchange devices, according to the modalities of this description, can be implemented in hydrocarbon-related processes, such as hydraulic fracturing or other drilling operations (e.g., underground bottom-hole drilling operations). As discussed earlier, well completion operations in the oil and gas industry often involve hydraulic fracturing, drilling, or other downhole operations that use high-pressure pumps to increase the pressure of the downhole fluid (e.g., a fluid intended to be driven into an underground formation or borehole, such as hydraulic fracturing fluid, drilling fluid, or drilling mud). Proppants, chemicals, mud-producing additives, etc., in these fluids often increase wear and maintenance on the high-pressure pumps. In some embodiments, a hydraulic fracturing system may include a hydraulic power transfer system that transfers pressure between a first fluid (e.g., a clean fluid, such as a partially (e.g., mostly) or substantially proppant-free fluid or a pressure exchange fluid) and a second fluid (e.g., fracturing fluid, such as a proppant-laden fluid, an abrasive fluid, or a dirty fluid). Such systems may at least partially (e.g., substantially, mainly, completely) isolate the first high-pressure fluid from the second dirty fluid while still allowing the pressurization of the second dirty fluid with the first high-pressure fluid and without having to pass the second dirty fluid directly through a pump or other pressurization device. While some of the configurations discussed herein may be geared toward hydraulic fracturing operations, in other configurations, the exchanger systems and devices described herein may be used in other operations. For example, the devices, systems, and / or methods described herein may be used in other downhole operations, such as downhole drilling. Furthermore, the piston configurations described herein may be implemented in any other suitable fluid handling application. Figure 1 illustrates a system diagram of one modality of hydraulic fracturing system 100 that uses a pressure exchanger between a first fluid stream (e.g., a clean fluid stream) and a second fluid stream (e.g., a fracturing fluid stream). Although not explicitly described, it should be understood that each component of system 100 can be directly connected or coupled via a fluid conduit (e.g., a pipe) to an adjacent component (e.g., upstream or downstream). Hydraulic fracturing system 100 may include one or more devices for pressurizing the first fluid stream, such as, for example, frack pumps 102 (e.g., reciprocating pumps, centrifugal pumps, spiral pumps, etc.).System 100 may include multiple fracturing pumps 102, such as at least two fracturing pumps 102, at least four fracturing pumps 102, at least ten fracturing pumps 102, at least sixteen fracturing pumps, or at least twenty fracturing pumps 102. In some embodiments, the fracturing pumps 102 may supply relatively and substantially clean, high-pressure fluid to a pressure exchanger 104 from a fluid source 101. In some embodiments, the fluid may be supplied separately to each pump 102 (e.g., in a parallel configuration). After pressurization in the pumps 102, the clean, high-pressure fluid 110 may be combined and conveyed to the pressure exchanger 104 (e.g., in a series configuration). As used in this document, clean fluid may describe fluid that is at least partially or substantially free (e.g., substantially free or totally free) of chemicals and / or proppants typically found in a downhole fluid, and dirty fluid may describe fluid that contains at least partially chemicals and / or proppants typically found in a downhole fluid. The pressure exchanger 104 can transmit the pressure from the high-pressure clean fluid 110 to a low-pressure fracturing fluid (e.g., fracturing fluid 112) in order to provide a high-pressure fracturing fluid 116. The clean fluid can be expelled from the pressure exchanger 104 as a low-pressure fluid 114 after the pressure is transmitted to the low-pressure fracturing fluid 112. In some embodiments, the low-pressure fluid 114 can be a fluid that is at least partially or substantially clean and substantially free of chemicals and / or proppants, apart from a small amount that may pass into the low-pressure fluid 114 from the hydraulic fracturing fluid 112 in the pressure exchanger 104. In some configurations, the pressure exchanger 104 may include one or more pressure exchange devices (e.g., operating in parallel). In such configurations, the high-pressure inlets can be separated and supplied to the inlets of each of the pressure exchange devices. The outlets of each of the pressure exchange devices can be combined when the high-pressure hydraulic fracturing fluid exits the pressure exchanger 104. For example, and as described below with reference to Figure 4, the pressure exchanger 104 may include two or more (e.g., three) pressure exchange devices operating in parallel. As shown, the pressure exchanger 104 can be provided on a mobile platform (e.g., a truck trailer) that can be installed and removed relatively easily from a hydraulic fracturing well. After being expelled from the pressure exchanger 104, the clean, low-pressure fluid 114 can travel to and be collected in a mixing chamber 106 (e.g., mixing unit, mixer unit, etc.). In some embodiments, the low-pressure fluid 114 can be converted (e.g., modified, transformed, etc.) into the low-pressure fracturing fluid 112 in the mixing chamber 106. For example, a proppant can be added to the clean, low-pressure fluid 114 in the mixing chamber 106, creating a low-pressure fracturing fluid 112. In some embodiments, the clean, low-pressure fluid 114 can be discharged as waste. In many hydraulic fracturing operations, a separate process can be used to heat the hydraulic fracturing fluid 112 before it is discharged downhole (for example, to ensure proper mixing of the proppants in the hydraulic fracturing fluid). In some embodiments, using low-pressure clean fluid 114 to produce the fracturing fluid 112 can eliminate the step of heating the fracturing fluid. For example, the low-pressure clean fluid 114 may already be at an elevated temperature as a result of the hydraulic fracturing pumps 102 pressurizing the high-pressure clean fluid 110.After transferring pressure to the high-pressure clean fluid 112, which has been heated by pumps 102, the now low-pressure clean fluid 114 retains at least some of that thermal energy as it exits the pressure exchanger 104 into the mixing chamber 106. In some embodiments, using the already elevated low-pressure clean fluid 114 to produce the fracturing fluid can eliminate the heating stage of the fracturing fluid. In other embodiments, the elevated temperature of the low-pressure clean fluid 114 can reduce the amount of heating required for the hydraulic fracturing fluid. After adding the proppant to the fluid, now low-pressure fracturing fluid 114, the low-pressure fracturing fluid 112 can be expelled from the mixing chamber 106. The low-pressure fracturing fluid 112 can then enter the pressure exchanger 104 at the fracturing fluid end through a fluid conduit 108 connected (e.g., coupled) between the mixing chamber 106 and the pressure exchanger 104. Once in the pressure exchanger 104, the low-pressure fracturing fluid 112 can be pressurized by pressure transmission from the clean, high-pressure fluid 110 through the pressure exchanger 104. The high-pressure fracturing fluid 116 can then exit the pressure exchanger 104 and be delivered to the bottom of the well. Hydraulic fracturing systems generally require high operating pressures for the high-pressure fracturing fluid 116. In some modalities, the desired pressure for the high-pressure fracturing fluid 116 may be between approximately 8,000 PSI (55.158 kPa) and approximately 12,000 PSI (82.737 kPa), such as between approximately 9,000 PSI (62,052 kPa) and approximately 11,000 PSI (75,842 kPa), or approximately 10,000 PSI (68,947 kPa). In some embodiments, the high-pressure clean fluid 110 may be pressurized to a pressure at least substantially equal to or slightly greater than the desired pressure for the high-pressure fracturing fluid 116. For example, the high-pressure clean fluid 110 may be pressurized between approximately 0 PSI (0 kPa) and approximately 1000 PSI (6,894 kPa) greater than the desired pressure for the high-pressure fracturing fluid 116, such as between approximately 200 PSI (1,379 kPa) and approximately 700 PSI (4,826 kPa) greater than the desired pressure, or between approximately 400 PSI (2,758 kPa) and approximately 600 PSI (4,137 kPa) greater than the desired pressure, to account for any pressure loss during the pressurization and exchange process. Figure 2 illustrates one embodiment of a pressure exchanger 200. The pressure exchanger 200 can be a linear pressure exchanger in the sense that it is operated by moving or translating an actuating assembly substantially along a linear path. For example, the actuating assembly can be moved linearly to selectively place the low- and high-pressure fluids in at least partial communication (e.g., indirect communication where pressure from the high-pressure fluid can be transferred to the low-pressure fluid), as described in further detail below. nnzcnn / ίζηζ / Β / γι The linear pressure exchanger 200 may include one or more (e.g., two) chambers 202a, 202b (e.g., tanks, manifolds, cylinders, tubes, pipes, etc.). The chambers 202a, 202b (e.g., parallel chambers 202a, 202b) may include pistons 204a, 204b configured to substantially keep the high-pressure clean fluid 210 and the low-pressure clean fluid 214 (e.g., the clean side) separate from the high-pressure dirty fluid 216 and the low-pressure dirty fluid 212 (e.g., the dirty side) while permitting pressure transfer between the respective fluids 210, 212, 214, and 216. The pistons 204a, 204b may be sized (e.g., the outside diameter of the pistons 204a, 204b relative to the inside diameter of the chambers 202a, 204b) to permit the pistons 204a, 204b to travel through the chamber 202a, 202b while minimizing flow of fluid around pistons 204a, 204b. The linear pressure exchanger 200 may include a clean control valve 206 configured to control the flow of high-pressure clean fluid 210 and low-pressure clean fluid 214. Each of the chambers 202a, 202b may include one or more dirty control valves 207a, 207b, 208a and 208b configured to control the flow of low-pressure dirty fluid 212 and high-pressure dirty fluid 216. Although the embodiment in Figure 2 contemplates a linear pressure exchanger 200, other embodiments may include other types of pressure exchangers that involve other mechanisms for selectively placing low and high pressure fluids in at least partial communication (e.g., a rotary actuator such as those described in United States Patent No. 9,435,354, issued on September 6, 2016, the description of which is incorporated herein in full by reference, etc.). In some embodiments, the clean control valve 206, which includes an actuating stem 203 that moves one or more plugs 308 along (e.g., linearly along) a valve body 205 206, can selectively permit (e.g., inlet, placement, etc.) high-pressure clean fluid 210 supplied from a high-pressure inlet port 302 to enter a first chamber 202a on a clean side 220a of the piston 204a. The high-pressure clean fluid 210 can act on the piston 204a, moving the piston 204a in a direction towards the dirty side 221a of the piston 204a and compressing the dirty fluid in the first chamber 202a to produce the high-pressure dirty fluid 216. The high-pressure dirty fluid 216 can exit the first chamber 202a through the dirty discharge control valve 208a (e.g., outlet valve, high-pressure outlet).At substantially the same time, the low-pressure dirty fluid 212 may be entering the second chamber 202b through the dirty fill control valve 207b (e.g., inlet valve, low-pressure inlet). The low-pressure dirty fluid 212 may act on the dirty side 221b of piston 204b, moving piston 204b in a direction toward the clean side 220b of piston 204b in the second chamber 202b. The low-pressure clean fluid 214 may be discharged (e.g., emptied, expelled, etc.) through the clean control valve 206 as piston 204b moves in a direction toward the clean side 220b of piston 204b, reducing the space on the clean side 220b of piston 204b within the second chamber 202b.A cycle of the pressure exchanger is completed once each piston 204a, 204b moves a substantial length (e.g., most of the length) of its respective chamber 202a, 202b (a cycle of which may be a half cycle, with the piston 204a, 204b moving in one direction along the length of chamber 202a, 202b, and a full cycle, which includes the piston 204a, 204b moving in one direction along the length of chamber 202a, 202b and then moving in the other direction to return substantially to its original position). In some embodiments, only a portion of the length may be used (e.g., in reduced capacity situations). After the completion of a cycle, the actuating stem 203 of the clean control valve 206 can change position, allowing the high-pressure clean fluid 210 to enter the second chamber 202b, thereby changing the second chamber 202b to a high-pressure chamber and changing the first chamber.202a to a low-pressure chamber and repeating the process. In some embodiments, each chamber 202a, 202b may have a higher pressure on one side of the pistons 204a, 204b to move the piston in a direction away from the higher pressure. For example, the high-pressure chamber may experience pressures between approximately 8,000 PSI (55,158 kPa) and approximately 13,000 PSI (89,632 kPa), with the higher pressures in the high-pressure clean fluid 210 moving the piston 204a, 204b away from the high-pressure clean fluid 210, compressing and discharging the dirty fluid to produce the high-pressure dirty fluid 216. The low-pressure chamber 202a, 202b may experience much lower pressures, relatively, with the relatively higher pressures in the actual low-pressure chamber 202a, 202b still being adequate enough in the low-pressure dirty fluid 212 to move the piston 204a, 204b in a direction away from the low-pressure dirty fluid 212, discharging the low-pressure clean fluid 214.In some configurations, the low-pressure dirty fluid pressure 212 may be between approximately 100 PSI (689 kPa) and approximately 700 PSI (4,826 kPa), such as between approximately 200 PSI (1,379 kPa) and approximately 500 PSI (3,447 kPa), or between approximately 300 PSI (2,068 kPa) and approximately 400 PSI (2,758 kPa). Returning to Figure 1, in some embodiments, the system 100 may include an optional device (e.g., a pump) to pressurize the low-pressure dirty fluid 212 (e.g., to a pressure level suitable for moving the piston 204a, 204b towards side cleaning) as it is provided in chambers 202a, 202b. Referring again to Figure 2, if any fluid pushes past piston 204a, 204b (e.g., leak, blow-off, etc.), it will generally tend to flow from the higher-pressure fluid to the lower-pressure fluid. The high-pressure clean fluid 210 can be maintained at the highest pressure in the system so that it generally cannot become substantially contaminated. The low-pressure clean fluid 214 can be maintained at the lowest pressure in the system. Therefore, it is possible for the low-pressure clean fluid 214 to become contaminated by the low-pressure dirty fluid 212. In some embodiments, the low-pressure clean fluid 214 can be used to produce the low-pressure dirty fluid 212, substantially negating any detriment resulting from contamination.Likewise, any contamination of the dirty high-pressure fluid 216 by the clean high-pressure fluid 210 would have a minimal effect on the dirty high-pressure fluid 216. In some configurations, dirty control valves 207a, 207b, 208a, and 208b may be check valves (e.g., click valves, check valves, reflux valves, or one-way valves). For example, one or more of the dirty control valves 207a, 207b, 208a, and 208b may be a ball check valve, a diaphragm check valve, a swing check valve, a rocker disc check valve, a flapper valve, a lift check valve, an in-line check valve, a duckbill valve, etc. In additional modes, one or more of the dirty control valves 207a, 207b, 208a and 208b can be actuated valves (e.g., solenoid valves, pneumatic valves, hydraulic valves, electronic valves, etc.) configured to receive a signal from a controller and open or close in response to the signal. The dirt control valves 207a, 207b, 208a, 208b can be arranged in opposing configurations such that when chamber 202a, 202b is in the high-pressure configuration, the high-pressure dirty fluid opens the dirty discharge control valve 208a, 208b while the pressure in chamber 202a, 202b keeps the dirt fill control valve 207a, 207b closed. For example, the dirty discharge control valve 208a, 208b comprises a check valve that opens in a first direction away from chamber 202a, 202b, while the dirt fill control valve 207a, 207b comprises a check valve that opens in a second, opposite direction into chamber 202a, 202b. The dirty discharge control valves 208a, 208b can be connected to a downstream element (e.g., a fluid line, a common or separate manifold) such that the high pressure in the downstream element keeps the dirty discharge valve 208a, 208b closed in the chamber 202a, 202b, which is in the low-pressure setting. This setting allows the low-pressure dirty fluid to open the dirty fill control valve 207a, 207b and enter the chamber 202a, 202b. Figures 3A and 3B illustrate a cross-sectional view of one embodiment of a clean control valve 300 in two different positions. In some embodiments, the clean control valve 300 may be similar to the control valve 206 described above. The clean control valve 300 may be a multiport valve (e.g., 4-way valve, 5-way valve, LinX® valve, etc.). The clean control valve 300 may have one or more high-pressure inlet ports (e.g., one port 302), one or more low-pressure outlet ports (e.g., two ports 304a, 304b), and one or more chamber connection ports (e.g., two ports 306a, 306b). The clean control valve 300 may include at least two plugs 308 (e.g., plugs, pistons, discs, valve members, etc.). In some embodiments, the clean control valve 300 may be a linearly actuated valve.For example, the 308 plugs can be linearly actuated so that the 308 plugs move along a substantially straight line (e.g., along a longitudinal axis Loo of the clean control valve 300). The clean control valve 300 may include an actuator 303 configured to actuate the clean control valve 300 (e.g., an actuator coupled to a valve stem 301 of the clean control valve 300). In some embodiments, the actuator 303 may be electronic (e.g., solenoid, rack and pinion, ball screw, segmented screw, moving coil, etc.), pneumatic (e.g., tie rod cylinders, diaphragm actuators, etc.), or hydraulic. In some embodiments, the actuator 303 may allow the clean control valve 300 to move the valve stem 301 and plugs 308 at variable speeds (e.g., changing speeds, adjustable speeds, etc.). Figure 3A illustrates the clean control valve 300 in a first position. In the first position, the plugs 308 can be positioned so that high-pressure clean fluid can enter the clean control valve 300 through the high-pressure inlet port 302 and exit to a first chamber through the chamber connection port 306a. In the first position, low-pressure clean fluid can travel through the clean control valve 300 between the chamber connection port 306b and the low-pressure outlet port 304b (for example, it can exit through the low-pressure outlet port 304b). Figure 3B illustrates the clean control valve 300 in a second position. In the second position, the plugs 308 can be positioned so that high-pressure clean fluid can enter the clean control valve 300 through the high-pressure inlet port 302 and exit to a second chamber through the chamber connection port 306b. Low-pressure clean fluid can travel through the clean control valve 300 between the chamber connection port 306a and the low-pressure outlet port 304a (for example, it can exit through the low-pressure outlet port 304a). Referring now to Figures 2, 3A, and 3B, the clean control valve 206 is in the first position with the high-pressure inlet port 302 connected to the chamber connection port 306a, providing high-pressure clean fluid to the first chamber 202a. Once the cycle is complete, the clean control valve 206 can move the plugs 308 to the second position, thereby connecting the high-pressure inlet port 302 to the second chamber 202b through the chamber connection port 306b. In some embodiments, the 206 cleanout control valve may pass through a substantially fully closed position midway through its stroke between the first and second positions. For example, in the first position, the 308 plugs may maintain a fluid path between the high-pressure inlet port 302 and the chamber connection port 306a, and a fluid path between the chamber connection port 306b and the low-pressure outlet port 304b. In the second position, the 308 plugs may maintain a fluid path between the high-pressure inlet port 302 and the chamber connection port 306b, and a fluid path between the chamber connection port 306a and the low-pressure outlet port 304a. The transition between the first and second positions may involve at least substantially closing both fluid paths to change the connection of chamber port 306a from high-pressure inlet port 302 to low-pressure outlet port 304a and to change the connection of chamber port 306b from low-pressure outlet port 306b to high-pressure inlet port 302. The fluid paths may be closed at least substantially during a mid-stroke to allow the connection change. Opening and closing valves where fluids operate at high pressures can result in pressure pulsations (e.g., water hammer) that can damage system components when high pressure is suddenly introduced or withdrawn. As a result, pressure pulsations may occur during the mid-stroke when the fluid paths close and open, respectively.In some embodiments, the actuator 303 can be configured to move the plugs 308 at variable speeds throughout the stroke of the clean control valve 206. As the plugs 308 move from the first position to the second position, they can move at a high speed during the initial portion of the stroke, which does not involve the introduction of new flow from the high-pressure inlet port 302 into the chamber connection ports 306a and 306b. The plugs 308 can then decelerate to a low speed as they approach a closed position (for example, when the plugs 308 block the chamber connection ports 306a and 306b during the transition between the high-pressure inlet port 302 and the low-pressure outlet port 304a and connection 304b) in the middle portion of the stroke.The 308 plugs can continue at a lower speed, as the 302 high-pressure inlet port is placed in communication with one of the 306a, 306b chamber connection ports. After passing through the nnzcnn / Lznz / Em chamber connection ports. 306a, 306b, and 308 plugs can accelerate to another high speed as they approach the second position. The low speed in the middle of the stroke can reduce the rate at which the 206 cleaning control valve opens and closes, allowing the control valve to gradually clear, introduce, and / or remove high pressure from chambers 202a and 202b. In some embodiments, the movement of pistons 204a, 204b can be controlled by regulating the fluid flow rate (e.g., of the incoming fluid) and / or a pressure differential between the clean side 220a, 220b of pistons 204a, 204b and the dirty side 221a, 221b of pistons 204a, 204b, at least partially by moving the clean control valve 206. In some embodiments, it may be desirable for the piston 204a, 204b in the low-pressure chamber 202a, 202b to move at substantially the same speed as the piston 204a, 204b in the high-pressure chamber 202a, 202b by manipulating their pressure differentials in each chamber and / or controlling the fluid flow rates into and out of chambers 202a, 202b. However, piston 204a, 204b in the low-pressure chamber 202a, 202b may tend to move at a higher speed than piston 204a, 204b in the high-pressure chamber 202a, 202b. In some embodiments, the fluid flow rate and / or pressure differential can be varied to control the acceleration and deceleration of pistons 204a, 204b (for example, by manipulating and / or varying the stroke of the clean control valve 206 and / or by manipulating the pressure in the fluid streams with one or more pumps). For example, increasing the flow rate and / or pressure of the high-pressure clean fluid 210 when piston 204a, 204b is near a clean end 224 of chamber 202a, 202b at the beginning of the high-pressure stroke can increase the fluid flow rate and / or pressure differential in chamber 202a, 202b. The increased fluid flow rate and / or pressure differential can cause piston 204a, 204b to accelerate or move at a faster speed.In another example, the flow rate and / or pressure of the clean, high-pressure fluid 210 may decrease as the piston 204a, 204b approaches a dirty end 226 of the chamber 202a, 202b at the end of the high-pressure stroke. Decreasing the fluid flow rate and / or pressure differential may cause the piston 204a, 204b to decelerate and / or stop before reaching the dirty end of the respective chamber 202a, 202b. A similar control can be used with the stroke of the clean control valve 206 to prevent the piston 204a, 204b from traveling to the farthest extension of the clean end of the chambers 202a, 202b. For example, the clean control valve 206 can close one of the connection ports of chamber 306a, 306b before the piston 204a, 204b comes into contact with the farthest extension of the clean end of the chambers 202a, 202b, preventing any additional fluid flow and slowing and / or stopping the piston 204a, 204b. In some embodiments, the clean control valve 206 can open one of the connection ports of chamber 306a, 306b in communication with the high pressure inlet port 302 before the piston 204a, 204b nnzcnn / Lznz / Em contacts the furthest extension of the clean end of chambers 202a, 202b in order to slow, stop and / or reverse the movement of the piston 204a, 204b. If pistons 204a, 204b reach the clean end 224 or the dirty end 226 of their respective chambers 202a, 202b, the higher-pressure fluid can bypass piston 204a, 204b and mix with the lower-pressure fluid. In some embodiments, mixing the fluids may be desirable. For example, if pistons 204a, 204b reach the dirty end 226 of their respective chambers 202a, 202b during the high-pressure stroke, the high-pressure clean fluid 210 can bypass piston 204a, 204b (e.g., by traveling around piston 204a, 204b or through a valve in piston 204a, 204b), cleaning any residual contaminants from the surfaces of piston 204a, 204b. In some modalities, mixing the fluids may be undesirable.For example, if pistons 204a, 204b reach the clean end 224 of the respective chambers 202a, 202b during the low-pressure stroke, the dirty low-pressure fluid 212 can bypass piston 204a, 204b and mix with the clean low-pressure fluid, contaminating the clean area in the clean control valve 206 with the dirty fluid. In some embodiments, system 100 can prevent pistons 204a, 204b from reaching the clean end 224 of the respective chambers 202a, 202b. For example, the clean control valve 206 can include a control device 209 (e.g., sensor, safety, switch, etc.) to trigger a change in the position of the clean control valve 206 upon detecting the approach of piston 204a, 204b to the clean end 224 of the respective chamber 202a, 202b, so that system 100 can use the clean control valve 206 to change the flow path positions before piston 204a, 204b reaches the clean end 224 of chamber 202a, 202b. In some embodiments, system 100 can be configured to allow pistons 204a, 204b to reach the dirty end 226 of the respective chambers 202a, 202b during the high-pressure stroke. In some embodiments, the clean control valve 206 can include a control device 209 to activate the change of position of the clean control valve 206 upon detecting the approach of piston 204a, 204b to the dirty end 226 of the respective chamber 202a, 202b. In some embodiments, the control device can be configured so that the control valve 206 does not complete the change of direction of piston 204a, 204b until piston 204a, 204b has reached the maximum extension of the dirty end 226 of the respective chamber 202a, 202b.In some embodiments, the control device may include a time delay through programming or mechanical delay that allows the piston 204a, 204b to reach the maximum extension of the dirty end 226 of the chamber 202a, 202b. In some embodiments, system 100 can be configured to allow pistons 204a, 204b to reach the dirty end 226 of the respective chambers 202a, 202b during the high-pressure stroke nnzcnn / Lznz / Bm and prevent pistons 204a, 204b from reaching the clean end 224 of the respective chambers 202a, 202b during the low-pressure stroke. For example, system 100 can drive both pistons 204a, 204b a selected distance through the respective chambers 202a, 202b, where pistons 204a, 204b are kept a selected distance from the clean end 224 while allowing pistons 204a, 204b to travel relatively closer to, or come into contact with, the dirty end 226.In some embodiments, the 100 system can be configured so that the pressure differential across piston 204a, 204b in the low pressure chamber 202a, 202b can be less than the pressure differential across piston 204a, 204b in the high pressure chamber 202a, 202b so that piston 204a, 204b moves more slowly during the low pressure cycle than the high pressure cycle. In some embodiments, the control device 209 can be configured to activate the change of position of the clean control valve 206 upon detecting the approach of the piston 204a, 204b to the clean end 224 of the respective chamber 202a, 202b, so that the clean control valve 206 can change position before the piston 204a, 204b reaches the clean end 224 of the chamber 202a, 202b. In some embodiments, the control device 209 can be configured to activate the change of position of the clean control valve 206 upon detecting the approach of the piston 204a, 204b to the dirty end 226 of the respective chamber 202a, 202b. In some embodiments, the control device can be configured to activate the change of position of the clean control valve 206 by evaluating both pistons 204a, 204b when they approach respectively the clean end 224 and the dirty end 226 of the chambers 202a, 202b.For example, control device 209 can detect the approach of piston 204a, 204b to the dirty end 226 of chamber 202a, 202b and start a timer (e.g., mechanical timer, electronic timer, programmed time delay, etc.). If control device 209 detects the approach of piston 204a, 204b to the clean end 224 of chamber 202a, 202b before the time triggers the change of position of the clean control valve 206, control device 209 can override the timer and change the position of the clean control valve 206 to prevent piston 204a, 204b from reaching the clean end 224 of chamber 202a, 202b. In some embodiments, an automated controller can produce signals that can be transmitted to the clean control valve 206 directing the clean control valve 206 to move from the first position to the second position or from the second position to the first position (e.g., at a constant and / or variable rate). Referring back to Figure 2, the pressure exchanger 200 may include one or more bypass features 310 (for example, in one or more of the chambers 202a, 202b and / or in one or more of the pistons 204a, 204b) to bypass fluid around and / or through the pistons 204a, 204b. For example, the pistons 204a, 204b may include a bypass feature 310 to allow fluid to pass through the pistons 204a, 204b. In some embodiments, the bypass feature 310 may be associated with each of the pistons 204a, 204b (e.g., positioned on pistons 204a, 204b) where the bypass feature 310 comprises a valve, such as a one-way check valve, or other suitable valve type, as listed above, which may limit flow in one or more directions while permitting flow in one or more different directions. In additional modes, chambers 202a, 202b can define all or part of the bypass feature 310. For example, the entire bypass feature 310 can be in chambers 202a, 202b or it can be partially defined by chambers 202a, 202b and partially by pistons 204a, 204b. As discussed previously, system 100 can allow pistons 204a and 204b to reach one end (e.g., the dirty end 226) of their respective chambers 202a and 202b during a stroke. In such a case, bypass feature 310 can allow fluid to pass through it to reach one or more of the control valves 207a, 207b, 208a, and 208b (e.g., in a bottom discharge by supplying a high-pressure fluid overflow into chambers 202a and 202b). For example, system 100 can drive both pistons 204a and 204b a selected distance through their respective chambers 202a and 202b, allowing them to approach or contact end 226.As pistons 204a, 204b approach and / or come into contact with end 226, bypass feature 310 may be activated (e.g., by overcoming a bypass feature) and begin to allow fluid to pass around and / or through bypass feature 310. For example, obstruction of end 226 of chambers 202a, 202b and / or increased fluid pressure as pistons 204a, 204b approach end 226 may resist further movement of pistons 204a, 204b by applying an opposing force to pistons 204a, 204b. Since the force of the fluid flow is no longer substantially used to move the pistons 204a, 204, the fluid can overcome the bypass feature 310 (e.g., when a selected differential pressure is exceeded) to allow fluid flow through the pistons 204a, 204b. In this configuration, bypass feature 310 can be used to over-supply fluid (e.g., clean fluid) on one side of pistons 204a, 204b to chambers 202a, 202b. The fluid can pass through bypass feature 310 from pistons 204a, 204b to the other side of pistons 204a, 204b. As also discussed earlier, system 100 can prevent pistons 204a, 204b from reaching one end (e.g., the clean end 224) of the respective chambers 202a, 202b during a stroke. However, even if pistons 204a, 204b approach or reach the end 224, the bypass feature 310 can prevent fluid from passing through the bypass feature 310 to, for example, reach one or more of the clean control valves 206 (e.g., in the event of an excess supply of dirty fluid at low pressure in chambers 202a, 202b). The pistons 204a, 204b (e.g., an outside diameter of the pistons 204a, 204b) may be sized relative to an inside dimension of the chambers 202a, 202b to allow the pistons 204a, 204b to pass through the chambers 202a, 202b without binding, while minimizing leakage around the pistons 204a, 204b (e.g., minimizing contamination of the clean fluid). The geometry of the pistons 204a, 204b with respect to an inside dimension of the chambers 202a, 202b may minimize the displacement of proppants (e.g., sand) in the dirty fluid and their entrapment between the pistons 204a, 204b as they pass through the chambers 202a, 202b. In some embodiments, the pistons 204a, 204b may include abrasion-resistant materials or an abrasion-resistant coating (e.g., ceramics, carbides, metals, polymers, etc.). Furthermore, the material of the pistons 204a, 204b may be selected to have a medium density. This embodiment can provide at least some buoyancy of the pistons 204a, 204b in the fluid, thereby reducing wear at the bottom of the chambers 202a, 202b that can occur due to the weight of the pistons 204a, 204b. Figure 4 is an isometric view of a piston 400 with a portion of a bypass feature 401 shown in a transparent view for clarity. In some embodiments, the piston 400 and the bypass feature 401 may be similar and include one or more components of the pistons 204a, 204b, and bypass features 310 discussed earlier in relation to Figure 2. As shown in Figure 4, the piston 400 includes an outer sidewall 402 (e.g., a radial sidewall) that defines a further outer extension (e.g., an outside diameter) of the piston 400. The outer side wall 402 may surround (e.g., enclose) an inner portion of the piston 400 that includes the bypass feature 401. As shown, the piston 400 may include a first recess 404 defined in the piston 400 such that the bypass feature 401 is positioned in a central portion 406 of the piston 400 at the base of the recess 404. The central portion 406 of the piston 400 may be defined as a network with openings 408 (e.g., one, two, three, four, or more openings or channels through the central portion 406 of the piston 400) that allow fluid to pass through the piston 400 when the bypass feature 401 is in an open position that permits fluid flow through the piston 400. nnzcnn / Lznz / Bm Figure 5 is a cross-sectional view of a piston (e.g., piston 400 shown in Figure 4). As shown in Figure 5, piston 400 includes a first axial end 410 and an opposing second axial end 412. The first recess 404 (e.g., having a cylindrical, conical, or truncated conical shape) may extend from the first axial end 410 on piston 400 to the central portion 406. A second recess 414 (e.g., having a cylindrical, conical, or truncated conical shape) may extend from the second axial end 412 on piston 400 to the central portion 406. The openings 408 in the central part 406 of the piston 400 can extend between and connect (e.g., place in fluid communication) the first and second recesses 404, 414. The bypass feature 401 can be positioned in the center portion 406 of the piston 400 between the first and second recesses 404, 414. As shown, the bypass feature 401 can include a valve member 416 that contacts and defines a seal between a portion of the piston 400 (for example, a seat portion 418 of the center portion 406) and the first recess 404. As shown, the bypass feature 401 can comprise a one-way check valve. As noted above, in additional embodiments, the bypass feature 401 can comprise another fluid flow restriction feature, such as a multi-way check valve or another type of valve. In a closed position (for example, as shown in Figure 5), the valve member 416 can come into contact with the seat portion 418 and at least partially prevent (for example, substantially prevent completely) the fluid from passing through the openings 408 to the second recess 414. For example, in the closed position, the valve element 416 can prevent fluid flow from the first axial end 410 to the second axial end 412. In some embodiments, the valve element 416 can be pushed into the closed position. For example, the valve member 416 can be coupled to a deflection feature (e.g., a spring 420, such as a compression spring, torsion spring, Belleville spring, constant force spring, extension spring, etc.) in a mounting structure 422 (e.g., a rod coupled to the valve element 416 and the spring 420). The mounting structure 422 can allow the valve element 416 to move (e.g., along a piston axis 400) to an open position while the spring 420 is compressed by the force of fluid flow from the second axial end 412 to the first axial end 410. When the force of spring 420 exceeds the force of the fluid flow, spring 420 can force valve member 416 back to the closed position. In the open position, the valve member 416 can move (e.g., be displaced axially) from the seat portion 418 and allow fluid to pass through the openings 408 from the second bore 414 to the first bore 404. For example, clean fluid can pass from the second axial end 412 to the first axial end 410, the first axial end 410 of which may be positioned on a dirty side of the piston 400 in communication with dirty fluid. In embodiments with a deflection feature, the movement of the valve member 416 from the seat portion 418 can compress the spring 420. In some embodiments, the dimension and / or geometry of the piston 400 (e.g., near the outermost diameter of the piston 400) may be selected to minimize abrasion of the piston 400 and the chamber 202a, 202b (Figure 2). For example, the piston 400 may include a chamfered edge or surface 424 (e.g., a chamfered cylindrical wall) on one or both of the first axial end 410 and the second axial end 412. The chamfered surface 424 may extend from a respective axial end 410, 412 to the outer side wall 402. As shown, the entire outermost surface of the piston 400 at both axial ends 410, 412 may comprise a continuous arcuate surface leading from the axial ends 410, 412 to the outer side wall 402.In some embodiments, the piston 400 including the beveled surfaces 424 can act to create fluid vortices on the beveled surfaces 424 (e.g., an interface between the piston 400 and an inner wall of chamber 202a, 202b) that can suspend particles in the fluid through which the piston 400 moves in order to prevent, at least partially, the particles from becoming stuck between the piston 400 and chamber 202a, 202b (Figure 2). As discussed previously, piston 400 can be used in a system (e.g., system 100) that can detect or monitor the position of piston 400. In some embodiments, piston 400 may include one or more position-sensing features that allow the detection of the presence of piston 400 through, for example, a sensor (e.g., a contact or non-contact sensor, such as a magnetic sensor, an optical sensor, an inductive proximity sensor, a Hall effect sensor, an ultrasonic sensor, a capacitive proximity sensor, a contact, a button, a switch, etc.). For example, piston 400 may include one or more position-sensing features comprising one or more magnets 426 (e.g., relatively strong permanent magnets) positioned around piston 400 (e.g., spaced at intervals around the circumference of piston 400).The magnetic field produced by the magnets 426 can be detected by a complementary sensor (e.g., part of the control system of the linear pressure exchanger 200 (Figure 2)) to determine a position of the piston 400 (e.g., detecting the passage of the piston 400 by the sensor). Pressure exchangers can reduce the amount of wear experienced by high-pressure pumps, turbines, and valves in systems using abrasive, caustic, or acidic fluids. Reduced wear can allow systems to operate for longer periods with less downtime, increasing system revenue or productivity. Furthermore, repair costs can be reduced because fewer parts are subject to wear. In operations such as hydraulic fracturing, where abrasive fluids are used at high temperatures, repairs and downtime can result in losses of millions of dollars in a single operation. The modalities described herein can result in a reduction of the wear experienced by components in systems using abrasive, caustic, or acidic fluids at high temperatures.Reducing wear and tear will result in lower costs and increased revenue. Pistons, according to some embodiments of the present description, can act to minimize the flow of fluid on one side of the piston (e.g., hydraulic fracturing fluid) from the contaminant fluid (e.g., clean fluid) on the other side. Additionally, the piston can allow fluid to flow through a valve, permitting flow in one direction (e.g., allowing clean fluid to flow to a contaminated side of the piston) while preventing low fluid flow in another direction (e.g., preventing contaminated fluid from traveling to a clean side of the piston). The piston's geometry and / or material can further reduce abrasion as it moves through a chamber, while minimizing unwanted fluid flow around the piston and preventing particles from becoming lodged around its outer circumference.Furthermore, the geometry can create fluid vortices that can suspend particles in the fluid through which the piston moves, at least partially preventing particles from becoming trapped between the piston and the chamber. Finally, the piston may include one or more features to allow for the detection of its position. Although the description presented herein relates to certain illustrated embodiments, those skilled in the art will recognize and appreciate that it is not limited to them. Rather, many additions, deletions, and modifications may be made to the illustrated embodiments without departing from the scope of the description as claimed below, including its legal equivalents. Furthermore, features of one embodiment may be combined with features of another embodiment while still remaining within the scope of the description contemplated by the inventors.

Claims

1. A device for exchanging at least one property between fluids, the device comprising: at least one tank comprising: a first side for receiving a first fluid with a first property; and a second side for receiving a second fluid with a second property; and at least one piston in the at least one tank, the at least one piston being configured to separate the first fluid from the second fluid, the at least one piston being further configured to substantially prevent the second fluid from traveling from the second side to the first side. 2 - The device according to claim 1, wherein the at least one piston comprises a valve, the valve being configured to allow the first fluid to travel from the first side to the second side and to substantially prevent the second fluid from traveling through the valve from the second side to the first side.

3. - The device according to claim 1, wherein at least one end of the at least one piston comprises: a beveled edge portion, configured to create fluid vortices at an interface between the at least one piston and an inner wall of the at least one tank to minimize particles entering the interface between the at least one piston and the inner wall of the at least one tank. 4 - The device according to any of claims 1 to 3, further comprising at least one sensor configured to detect the presence of at least one piston. 5 - The device according to any of claims 1 to 3, further comprising at least one magnet positioned around a circumference of at least one piston, the at least one magnet being configured to produce a magnetic field for detection by an associated sensor. 6 - The device according to any of claims 1 to 3, wherein at least one piston is configured to substantially prevent the second fluid from traveling through the at least one piston from the second side to the first side. 7 - The device according to any of claims 1 to 3, wherein at least one piston is configured to allow the first fluid to move from the first side to the second side. 8 - The device according to any of claims 1 to 3, further comprising a valve device configured to selectively place the first fluid at a first pressure into communication with the second fluid at a second pressure via at least one piston to pressurize the second fluid to a higher pressure. nnzcnn / ίζηζ / Β / γι 9. A fluid pressure exchange system, the system comprising: at least one tank comprising: a clean side for receiving a clean fluid at a higher pressure; and a dirty side for receiving a downhole fluid at a lower pressure; at least one piston in the at least one tank, the at least one piston being configured to separate the clean fluid from the downhole fluid, the at least one piston being further configured to at least partially prevent the downhole fluid from traveling from the dirty side to the clean side; and a linearly actuated valve device configured to selectively place the clean fluid at the higher pressure into communication with the downhole fluid at the lower pressure through the at least one piston to pressurize the downhole fluid to a second, higher pressure.

10. The system according to claim 9, wherein at least one piston is configured to substantially prevent the downhole fluid from moving through the at least one piston from the dirty side to the clean side.

11. The system according to claim 9, wherein at least one piston is configured to allow the clean fluid to move from the clean side to the dirty side.

12. The system according to claim 9, wherein at least one piston comprises a valve, the valve being configured to allow clean fluid to travel from the clean side to the dirty side and to substantially prevent downhole fluid from traveling through the valve from the dirty side to the clean side.

13. The system according to any of claims 9 to 12, wherein an outer circumference of the at least one piston comprises a chamfer extending between a first axial end of the at least one piston and a radial side surface of the at least one piston and another chamfer extending between a second axial end of the at least one piston and the radial side surface of the at least one piston.

14. The system according to any of claims 9 to 12, wherein an outer circumference of the at least one piston is dimensioned and configured to allow the at least one piston to move through the at least one tank, while at least partially preventing the downhole fluid proppants from moving between the outer circumference of the at least one piston and an inner surface of the at least one tank.

15. A piston for at least partially separating at least two fluid streams, the piston comprising: a body having an opening extending along an axis of the body, the opening defining a fluid path through the piston; and at least one valve obstructing the opening, the at least one valve being configured to permit fluid flow in one direction along the fluid path through the opening and to at least partially inhibit fluid flow in an opposite direction along the fluid path through the opening.

16. The piston according to claim 15, wherein the opening defines a first recess at a first end of the body and a second recess at a second end of the body, the first recess and the second recess being separated by at least one valve.

17. The piston according to claim 15 or claim 16, wherein at least one valve comprises a check valve pushed into a closed position in one direction.

18. The piston according to claim 17, wherein the check valve is configured to move to an open position when a fluid traveling in one direction overcomes a check valve thrust force.

19. The piston according to claim 15 or claim 16, wherein the piston comprises an abrasion-resistant material configured to float at least partially in a fluid.

20. A method for operating a pressure exchange device comprising: supplying a high-pressure fluid to a high-pressure inlet of a valve configured to direct the flow of the high-pressure fluid to a chamber; transferring a pressure from the high-pressure fluid to a dirty fluid through a piston in the chamber; allowing some of the high-pressure fluid to pass through the piston; and substantially preventing the dirty fluid from passing through the piston to the high-pressure fluid.

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