Patent Publication Number: US-2022213763-A1

Title: Pressure adjuster for a downhole tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Non-Provisional application No. 62/842,836 entitled “Pressure Adjuster for a Downhole Tool,” filed May 3, 2019, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Wellbores may be drilled into a surface location or seabed for a variety of exploratory or extraction purposes. For example, a wellbore may be drilled to access fluids, such as liquid and gaseous hydrocarbons, stored in subterranean formations and to extract the fluids from the formations. Wellbores used to produce or extract fluids may be lined with casing around the walls of the wellbore. A variety of drilling methods may be utilized depending partly on the characteristics of the formation through which the wellbore is drilled. 
     The wellbores may be drilled by a drilling system that drills through earthen material downward from the surface. Some wellbores are drilled vertically downward, and some wellbores have one or more curves in the wellbore to follow desirable geological formations, avoid problematic geological formations, or a combination of the two. 
     SUMMARY 
     In some embodiments, a downhole tool includes a housing with a housing chamber inside the housing. A fluid chamber is located outside the housing. A seal separates the housing chamber from the fluid chamber, the seal at least partially maintaining a pressure differential between the housing chamber and the fluid chamber. A pressure adjuster between the housing chamber and the fluid chamber maintains the pressure differential below a maximum pressure differential. 
     In other embodiments, a downhole tool includes a housing with a housing chamber inside the housing. A partition connected to the housing separates a fluid chamber outside the housing from the housing chamber. The partition prevents the passage of particulates between the housing chamber and a fluid chamber. A pressure adjuster between the housing chamber and the fluid chamber maintains the pressure differential below a maximum pressure differential. 
     In yet other embodiments, a downhole tool includes a housing with a first end and a second end. A movable member is connected to the housing at the housing first end with a bearing. The bearing has a gap of less than 500 μm between the bearing and the movable member. The movable member is rotatable relative to the housing. The movable member includes a central support. A bearing surface inside the housing at the second end supports the central support. 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     Additional features and advantages of embodiments of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of such embodiments. The features and advantages of such embodiments may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more fully apparent from the following description and appended claims, or may be learned by the practice of such embodiments as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a representation of a drilling system, according to at least one embodiment of the present disclosure; 
         FIG. 2-1  is a cross-sectional view of a pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 2-2  is cross-sectional view of another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 3-1  is a cross-sectional view of yet another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 3-2  is a cross-sectional view of still another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 4  is a cross-sectional view of a further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 5  is a cross-sectional view of a still further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 6  is a cross-sectional view of a yet further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 7  is a cross-sectional view of another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 8-1  is a cross-sectional view of still another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 8-2  is a cross-sectional view of yet another pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 9  is a cross-sectional view of a further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 10  is a cross-sectional view of a still further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; 
         FIG. 11  is a cross-sectional view of a yet further pressure adjuster on a downhole tool, according to at least one embodiment of the present disclosure; and 
         FIG. 12  is a method chart of a method for operating a downhole tool, according to at least one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure generally relates to devices, systems, and methods for pressure adjustment between a movable member and a fluid chamber.  FIG. 1  shows one example of a drilling system  100  for drilling an earth formation  101  to form a wellbore  102 . The drilling system  100  includes a drill rig  103  used to turn a drilling tool assembly  104  which extends downward into the wellbore  102 . The drilling tool assembly  104  may include a drill string  105 , a bottomhole assembly (“BHA”)  106 , and a bit  110 , attached to the downhole end of drill string  105 . 
     The drill string  105  may include several joints of drill pipe  108  connected end-to-end through tool joints  109 . The drill string  105  transmits drilling fluid through a central bore and transmits rotational power from the drill rig  103  to the BHA  106 . In some embodiments, the drill string  105  may further include additional components such as subs, pup joints, etc. The drill pipe  108  provides a hydraulic passage through which drilling fluid is pumped from the surface. The drilling fluid discharges through selected-size nozzles, jets, or other orifices in the bit  110  for the purposes of cooling the bit  110  and cutting structures thereon, and for lifting cuttings out of the wellbore  102  as it is being drilled. 
     The BHA  106  may include the bit  110  or other components. An example BHA  106  may include additional or other components (e.g., coupled between to the drill string  105  and the bit  110 ). Examples of additional BHA components include drill collars, stabilizers, measurement-while-drilling (“MWD”) tools, logging-while-drilling (“LWD”) tools, downhole motors, underreamers, section mills, hydraulic disconnects, jars, vibration or dampening tools, other components, or combinations of the foregoing. 
     In general, the drilling system  100  may include other drilling components and accessories, such as special valves (e.g., kelly cocks, blowout preventers, and safety valves). Additional components included in the drilling system  100  may be considered a part of the drilling tool assembly  104 , the drill string  105 , or a part of the BHA  106  depending on their locations in the drilling system  100 . 
     The bit  110  in the BHA  106  may be any type of bit suitable for degrading downhole materials. For instance, the bit  110  may be a drill bit suitable for drilling the earth formation  101 . Example types of drill bits used for drilling earth formations are fixed-cutter or drag bits. In other embodiments, the bit  110  may be a mill used for removing metal, composite, elastomer, other materials downhole, or combinations thereof. For instance, the bit  110  may be used with a whipstock to mill into casing  107  lining the wellbore  102 . The bit  110  may also be a junk mill used to mill away tools, plugs, cement, other materials within the wellbore  102 , or combinations thereof. Swarf or other cuttings formed by use of a mill may be lifted to surface, or may be allowed to fall downhole. 
       FIG. 2-1  is a representation of an embodiment of a downhole tool  212 , according to at least one embodiment of the present disclosure. The downhole tool  212  may include a housing  214 . In at least one embodiment, the housing  214  may be a single, unitary structure that encloses other features/components of the present disclosure. In other embodiments, the housing  214  may include two or more structures, connected with mechanical connections, seals, welds, brazes, and other connections, to enclose other features/components of the present disclosure. The housing  214  may include a housing chamber  216  located inside the housing  214 . A partition  218  may be located in the housing  214  between the housing chamber  216  and a fluid chamber  220 . The partition  218  may be sealed against the housing using one or more rows of sealing members  221 , such as an O-ring. 
     In at least one embodiment, fluid may enter the downhole tool  212  through one or more housing ports  213  located in a sidewall of the housing  214 . Fluid entering through the housing ports  213  may engage a movable member  222 . For example, the movable member  222  may be a turbine for a power generator, and fluid entering through the housing ports  213  may cause the turbine to rotate. In other examples, the movable member  222  may be a valve, and the valve may block the housing ports  213  in a first valve configuration and open the housing ports  213  in a second valve configuration. The fluid may then be directed to a housing pathway  215  at a housing first end  217 . The fluid may exhaust to the fluid chamber  220  from the housing pathway  215 . In other embodiments, fluid may enter the housing path and the housing pathway  215  from the fluid chamber  220  and exhaust out the housing ports  213 . In at least one embodiment, the housing  214  may be permanently or selectively closed at a housing second end  219 . 
     In the embodiment shown in  FIG. 2-1 , the movable member  222  may be a rotary valve. The movable member  222  may include one or more flow restrictors  223  at an upper end of the movable member  222 . The flow restrictors  223  may extend past a top surface of the movable member  222  along an outer periphery of the movable member  222 . In the view shown in  FIG. 2-1 , the flow restrictors  223  are rotated out of alignment of the housing ports  213 . In this manner, the movable member  222  may be in an open configuration, and fluid may flow from the housing ports  213  and into the housing pathway  215 , where the fluid may be further directed to other parts of the downhole tool  212  or another location in the BHA. 
     When the movable member  222  is rotated, the flow restrictors  223  may block or occlude the housing ports  213 , thereby cutting off the flow of fluid from the housing pathway  215 . For example, the movable member  222  may include two flow restrictors  223  and the downhole tool  212  may include two housing ports  213 . As the movable member is rotated 90°, the flow restrictors  223  may block or unblock the housing ports  213 . In other examples, the movable member  222  may include a single flow restrictor  223 , or more than two flow restrictors  223 , including three, four, five, six, seven, or eight flow restrictors. The housing  214  may include the same number of housing ports  213 . 
     The fluid chamber  220  may include any fluid source. For example, the fluid chamber  220  may be located inside of a drill pipe and include drilling fluid located inside of the drill pipe. In other examples, the fluid chamber  220  may be located outside of the drill pipe and include drilling fluid located in an annulus of a wellbore between a drill pipe and the wellbore wall. In still other examples, the fluid chamber  220  may include a hydraulic reservoir pressurized by a hydraulic pump. In some embodiments, the fluid from the fluid chamber  220  may be a water based drilling fluid, an oil based drilling fluid, water, hydraulic oil, or any other fluid. 
     In at least one embodiment, the partition  218  may prevent the passage of a fluid between the housing chamber  216  and the fluid chamber  220 . In other embodiments, the partition  218  may allow the passage of the fluid between the housing chamber  216  and the fluid chamber  220  while preventing the passage of solids or particulates suspended in the fluid. For example, the partition  218  may be a seal between the housing chamber  216  and the partition  218 . In some embodiments, the partition  218  may be a seal that maintains a pressure differential between the fluid chamber  220  and the housing chamber  216 . 
     A movable member  222  may be located in the housing  214 . The movable member  222  may be translatable or movable relative to the housing  214  through the partition  218 . For example, the movable member  222  may be rotatable relative to the housing  214 . In other examples, the movable member  222  may be translatable relative to the housing  214 . In still other examples, the movable member  222  may be both rotatable and translatable relative to the housing  214 . 
     The movable member  222  may be any component of a downhole tool. For example, the movable member  222  may be a turbine from a power generator. In other examples, the movable member  222  may be a rotor in a rotary valve. In yet other examples, the movable member  222  may be a shuttle in a linear valve. In still other examples, the movable member  222  may be any movable component of a downhole tool. 
     In at least one embodiment, the partition  218  may be or include a bearing between the movable member  222  and the housing  214 . For example, one or both of the partition  218  and the movable member  222  may be manufactured from an ultrahard material. As used herein, the term “ultrahard” is understood to refer to those materials known in the art to have a grain hardness of about 1,500 HV (Vickers hardness in kg/mm2) or greater. Such ultrahard materials can include but are not limited to diamond, sapphire, moissantite, hexagonal diamond (Lonsdaleite), cubic boron nitride (cBN), polycrystalline cBN (PcBN), Q-carbon, binderless PcBN, diamond-like carbon, boron suboxide, aluminum manganese boride, metal borides, boron carbon nitride, PCD (including, e.g., leached metal catalyst PCD, non-metal catalyst PCD, and binderless PCD or nanopolycrystalline diamond (NPD)) and other materials in the boron-nitrogen-carbon-oxygen system which have shown hardness values above 1,500 HV, ultrahard ceramics, as well as combinations of the above materials and/or coatings of any of the above materials on a substrate. In some embodiments, the ultrahard material may have a hardness values above 3,000 HV. In other embodiments, the ultrahard material may have a hardness value above 4,000 HV. In yet other embodiments, the ultrahard material may have a hardness value greater than 80 HRa (Rockwell hardness A). For example, both the partition  218  and the movable member  222  may be made from PCD, and the interface of PCD on PCD has a low coefficient of friction. Thus, the movable member  222  may rotate easily against the partition  218 , and may have a long life due to the durability of the movable member  222  and the partition  218 . This allows for a tight gap between the movable member  222  and the partition  218 . In at least one embodiment, the partition  218  may include an ultrahard bearing surface against which the movable member  222  may move. 
     The housing  214  may include a passageway  224  through the partition  218  that hydraulically connects the fluid chamber  220  to the housing chamber  216 . The partition  218  has a partition dimension. The movable member  222  has movable member dimension. The movable member  222  may be inserted into the partition  218 . A gap may exist between the movable member  222  and the partition  218 , which may be the difference between the partition dimension and the movable member dimension. For example, in at least one implementation, a cylindrical movable member  222  may be inserted into a cylindrical bore of the partition  218 . The partition dimension may be a diameter of the cylindrical bore, and the movable member dimension may be a diameter of the movable member  222 . The gap may be the difference between the diameter of the cylindrical bore and the diameter of the movable member  222 . In at least one implementation, the gap may be considered a tolerance between the partition  218  and the movable member  222 . 
     A tight gap between the movable member  222  and the partition  218  may form a seal between the fluid chamber  220  and the housing chamber  216 . The movable member  222  may be inserted into the passageway  224 . In at least one embodiment, the movable member  222  and the partition  218  may form a seal between the fluid chamber  220  and housing chamber  216 . This seal may partially or completely reduce the flow of fluid between the fluid chamber  220  and the housing chamber  216 . The seal may be formed by a tight gap between the movable member  222  and the partition  218 . In some embodiments, the gap between the movable member  222  and the partition  218  may be in a range having an upper value, a lower value, or upper and lower values including any of 0 micrometers (μm), 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, or any value therebetween. For example, the gap may be 0 μm, or fully sealed. In another example, the gap may be less than 500 μm. In yet other examples, the gap may be any value in a range between fully sealed and 500 μm. In at least one embodiment, a gap of 20 μm or less may be critical to prevent particulates from migrating between the fluid chamber  220  and the housing chamber  216 . 
     The partition  218  may include seal that maintains a pressure differential between the fluid chamber  220  and the housing chamber  216 . Thus, a pressure differential may exist across the movable member  222 . In at least one embodiment, the tight gap between the movable member  222  and the partition  218  may contribute to maintaining the pressure differential due to the restricted fluid flow between the fluid chamber  220  and the housing chamber  216 . A greater gap may result in a lower pressure differential, and a lower gap may result in a higher pressure differential. 
     In at least one embodiment, as the movable member  222  is rotated or translated with respect to the partition  218 , at least some fluid may transfer between the fluid chamber  220  and the housing chamber  216 . Fluid transfer between the fluid chamber  220  and the housing chamber  216  may adjust the pressure differential. In this manner, as the movable member  222  moves relative to the partition  218 , a steady-state pressure differential may be achieved, despite changing drilling conditions, such as an increase in hydrostatic pressure. Furthermore, the movement of the movable member  222  relative to the partition  218  may prevent a build-up of particulates or solids suspended in the fluid at the interface between the movable member and the partition  218 . In other words, moving the movable member  222  may flush out the gap between the movable member  222  and the partition  218 . 
     When the movable member  222  is not moving relative to the partition  218 , as the pressure differential increases, fluid may be forced through the gap between the movable member  222  and the partition  218 . In some embodiments, as the fluid is being forced through the gap, the particulates or solids suspended in the fluid may not be flushed from the gap. These particulates or solids may build up at the gap. As the particulate or solid build-up increases, less fluid may transfer through the gap. This may cause the pressure differential to increase. In at least one embodiment, sufficient particulates or solids may build up until the gap is clogged, or effectively sealed off. Thus, as the pressure differential across the movable member  222  increases, fluid may not be able to transfer between the fluid chamber  220  and the housing chamber to adjust the pressure differential. 
     The movable member  222  may not move relative to the partition  218  in a variety of situations. For example, while tripping the downhole tool  212  into a wellbore, the movable member  222  may not move relative to the partition  218 . At the surface, both the housing chamber  216  and the fluid chamber  220  may be at or near the same pressure (e.g., surface pressure). In other words, at the surface the pressure differential may be zero or approximately zero. As the downhole tool  212  is tripped into the hole, the hydrostatic pressure increases. When particulates in the drilling fluid clog the gap, the pressure differential may increase at or near the same rate as the hydrostatic pressure. Furthermore, geologic pressure of the surrounding formation may begin to add to the hydrostatic pressure creating a combined pressure. In some embodiments, the combined pressure, and therefore the pressure differential, may be equal to or greater than 5,000 PSI (34.5 MPa), 10,000 PSI (68.9 MPa), 15,000 PSI (103 MPa), 20,000 PSI (138 MPa), 25,000 PSI (172 MPa), 30,000 PSI (207 MPa), or greater. 
     The pressure differential may place a load on the movable member  222  against the housing  214  and/or the partition  218 . This load may increase the initial force required to move the movable member  222 . In some embodiments, the initial force may be greater than an actuation force. For example, if the movable member  222  is a turbine on a power generator, the movable member  222  may be rotatable by the drilling fluid. The drilling fluid may exert a torque on the movable member  222 . If the initial force required to move the movable member  222  is greater than the torque exerted by the drilling fluid, then the movable member  222  may be stuck. In other words, a large pressure differential may pressure lock the movable member  222 . This may cause the downhole tool  212  to malfunction. The pressure differential below which the downhole tool  212  may reliably function may be a maximum pressure differential. 
     In some embodiments, the maximum pressure differential may be in a range having an upper value, a lower value, or upper and lower values including any of 50 PSI (345 KPa), 100 PSI (689 KPa), 250 PSI (1.72 MPa), 500 PSI (3.44 MPa), 750 PSI (5.17 MPa), 1,000 PSI (6.89 MPa), 1,250 PSI (8.62 MPa), 1,500 PSI (10.3 MPa), 1,750 PSI (12.1 MPa), 2,000 PSI (13.8 MPa), 2,250 PSI (15.5 MPa), 2,500 PSI (17.2 MPa), 3,000 PSI (20.7 MPa), 4,000 PSI (27.6 MPa), 5,000 PSI (34.5 MPa), 10,000 PSI (68.9 MPa), 15,000 PSI (103 MPa), 20,000 PSI (138 MPa), or any value therebetween. For example, the maximum pressure differential may be greater than 50 PSI (345 KPa). In another example, the maximum pressure differential may be less than 20,000 PSI (138 MPa). In yet other examples, the maximum pressure differential may be any value in a range between 50 PSI (345 KPa) and 20,000 PSI (138 MPa). In some embodiments, the maximum pressure differential may be greater than 20,000 PSI (138 MPa) or less than 50 PSI (345 KPa). In some embodiments, a maximum pressure differential below 5,000 PSI may be critical for the movable member  222  to reliably move upon actuation. In some embodiments, the maximum pressure differential may be the same or approximately the same as an operating pressure of the downhole tool  212 . In other embodiments, the maximum pressure differential may be greater than the operating pressure of the downhole tool  212 . 
     A pressure adjuster  226  may be connected to the partition  218  and/or the housing  214 . The pressure adjuster  226  may maintain the pressure differential below the maximum pressure differential. In other words, the pressure adjuster  226  may automatically adjust the pressure differential to below the maximum pressure differential. In some embodiments, the pressure adjuster  226  may include an adjuster housing  228  including a flow path  230 . The adjuster housing  228  may extend from and be connected to the partition  218 , or be integrally formed with the partition  218 . An adjuster housing cap  229  may be placed over the adjuster housing  228 . The adjuster housing  228  may be sealed to the adjuster housing cap  229  with one or more adjuster sealing members  225 , such as an O-ring. The adjuster sealing members  225  may seal the interior of the adjuster housing  228 , such as the flow path  230 , from the fluid chamber  220 . The flow path  230  may travel through the adjuster housing  228 , into the partition  218  and open into the housing chamber  216 . The flow path  230  may include an adjuster chamber  244  in the adjuster housing  228 . The adjuster chamber  244  may be in fluid communication with the housing chamber  216  and the fluid chamber  220 . In other words, the adjuster chamber  244  may be located in the flow path  230  between the housing chamber and the fluid chamber  220 . 
     A flow restrictor  232  may be located in the adjuster chamber  244 . In some embodiments, the flow restrictor  232  may be cylindrical, such as a piston. In other embodiments, the flow restrictor  232  may be spherical. In still other embodiments, the flow restrictor  232  may be conical or pyramidal. In yet other embodiments, the flow restrictor  232  may be any three-dimensional shape. 
     A resilient member  234  may exert a force on the flow restrictor  232  to urge or push the flow restrictor  232  against a seat  236 . The seat  236  may be located at a high pressure side of the adjuster chamber  244 , and may be a part of or integral to the adjuster housing  228 . The resilient member  234  may be any type of resilient member. For example, the resilient member  234  may be one or more coil springs, one or more wave springs, one or more Belleville washers, one or more pneumatic or hydraulic pistons, a bellows, a flexible material such as an elastomer, any other resilient member  234 , or combinations of the foregoing. 
     The resilient member  234  may urge or push the flow restrictor  232  against the seat  236  with a force sufficient to seal the flow path  230  from fluid passing between the fluid chamber  220  and the housing chamber  216 . For example, an opening  238  of the flow path  230  at the seat  236  may have an opening cross-sectional area. The portion of the flow restrictor  232  that contacts the seat  236  may have a restrictor cross-sectional area that is larger than the opening cross-sectional area. Therefore, as the resilient member  234  pushes the flow restrictor  232  against the seat  236 , the flow restrictor  232  may partially or fully block the transfer of fluid between the fluid chamber  220  and the housing chamber  216 . 
     The resilient member force with which the resilient member  234  pushes the flow restrictor  232  against the seat  236  may be sufficient to overcome the pressure differential between the fluid chamber  220  and the housing chamber  216 . In at least one embodiment, the force of the resilient member  234  may at least partially depend on the opening cross-sectional area. For example, a larger opening  238  cross-sectional area may require a lower force to seal the opening  238  than a smaller opening cross-sectional area. The resilient member  234  may be specifically selected or sized to apply a resilient member force that may seal the opening  238 . 
     As the pressure differential increases, the hydraulic force on the flow restrictor  232  due to the pressure differential may overcome the resilient member force, thereby pushing the flow restrictor  232  into the adjuster chamber  244 . This may allow fluid to enter the flow path  230 . In at least one embodiment, one or more flow restrictor fluid paths  240  may be located internal to the flow restrictor  232 . The one or more flow restrictor fluid paths  240  may pass all the way through the flow restrictor, from a first side of the flow restrictor  232  near the seat  236  to the opposite side, or a second side of the flow restrictor  232  near the housing chamber  216 . Thus, the flow restrictor  232  may have a pass-through fluid conduit, which may hydraulically connect the fluid chamber  220  to the housing chamber  216 . In other embodiments, fluid may pass around an outside of the flow restrictor  232 , or in an annulus in the flow path  230  between the flow restrictor and the adjuster housing  228 . In some embodiments, fluid may pass through both the flow restrictor fluid paths  240  in the flow restrictor  232  and around the outside of the flow restrictor  232 . 
     When the flow restrictor  232  is pushed against the seat  236 , flow to the flow restrictor fluid paths  240  may be blocked. As the pressure differential increases, the flow restrictor  232  may move into the adjuster chamber  244  in response to the pressure differential. As the flow restrictor  232  is pushed into the flow path  230 , fluid may enter one or more of the flow restrictor fluid paths  240 . This may cause the pressure differential to decrease. As the pressure differential decreases, the resilient member  234  may overcome the force applied by the lowered pressure differential, and seal the flow path  230  again. Thus, the resilient member  234  may be selected to maintain a relief pressure differential, or a pressure differential above which the pressure differential force is sufficient to overcome the resilient member force. Above the relief pressure differential, the pressure adjuster may relieve the pressure differential between the fluid chamber  220  and the housing chamber  216 . Therefore, in some embodiments, the pressure adjuster  226  may be a pressure-relief valve. 
     In some embodiments, the relief pressure differential may be in a range having an upper value, a lower value, or upper and lower values including any of 50 PSI (345 KPa), 100 PSI (689 KPa), 250 PSI (1.72 MPa), 500 PSI (3.44 MPa), 750 PSI (5.17 MPa), 1,000 PSI (6.89 MPa), 1,250 PSI (8.62 MPa), 1,500 PSI (10.3 MPa), 1,750 PSI (12.1 MPa), 2,000 PSI (13.8 MPa), 2,250 PSI (15.5 MPa), 2,500 PSI (17.2 MPa), 3,000 PSI (20.7 MPa), 4,000 PSI (27.6 MPa), 5,000 PSI (34.5 MPa), 10,000 PSI (68.9 MPa), 15,000 PSI (103 MPa), 20,000 PSI (138 MPa), or any value therebetween. For example, the relief pressure differential may be greater than 50 PSI (345 KPa). In another example, the relief pressure differential may be less than 20,000 PSI (138 MPa). In yet other examples, the relief pressure differential may be any value in a range between 50 PSI (345 KPa) and 20,000 PSI (138 MPa). In some embodiments, maximum pressure differential values below 5,000 PSI may be critical to allow the movable member  222  to move upon actuation of the downhole tool  212 . In some embodiments, the relief pressure differential may be the same or approximately the same as the maximum pressure differential. In some embodiments, the relief pressure differential may be less than the maximum pressure differential and greater than the operating pressure differential of the downhole tool  212 . In this manner, as the downhole tool  212  is tripped into a wellbore, the pressure differential may remain low enough that the downhole tool  212  may be actuated despite a large hydrostatic pressure, or a large difference in pressure between a starting location (e.g., the surface) and an operating location (e.g., downhole). 
     In at least one embodiment, the adjuster housing  228  may be located outside of the partition  218 . For example, the adjuster housing  228  may be attached to the end of the partition  218  away from the housing  214 . In other words, the pressure adjuster  226  may be independent of the housing  214  and/or the partition  218 . This means that the pressure adjuster  226  may be located in its own structure, the adjuster housing  228 . To allow fluid to travel between the housing ports  213  and the fluid chamber  220 , one or more branching conduits  242  may be placed in the adjuster housing  228  to direct fluid between the housing ports  213  and the fluid chamber  220 . 
     In the embodiment shown in  FIG. 2-1 , the pressure adjuster  226  is uni-directional, or operates to relieve pressure from a fluid chamber  220  that has a higher pressure than the housing chamber  216 . This pressure differential may occur, for example, when tripping the downhole tool  212  deeper into a wellbore. 
       FIG. 2-2  shows an embodiment of a downhole tool  212  where the pressure adjuster  226  operates to relieve pressure from a housing chamber that has a higher pressure than the fluid chamber. In this embodiment, the flow restrictor  232  may be flipped around with respect to the flow restrictor  232  shown in  FIG. 2-1  so that it seals against a seat  236  located near the housing  214 . A resilient member  234  may push the flow restrictor  232  against the seat  236  to seal the flow path  230  with a relief pressure differential. As the pressure in the housing chamber  216  increases, the pressure may push the flow restrictor away from the seat  236 , thereby allowing some fluid to escape into the fluid chamber  220 . In this manner, the housing chamber  216  may be the high pressure side and the fluid chamber  220  may be the low pressure side. This pressure differential may occur, for example, when tripping the downhole tool up toward the surface. 
     In some embodiments, the downhole tool  212  may include two pressure adjusters  226 , including one each of the pressure adjusters shown in  FIG. 2-1  and  FIG. 2-2 . In this manner, the downhole tool  212  may maintain a relief pressure differential while tripping both uphole and downhole. In some embodiments, a single pressure adjuster may be a two way valve that maintains a relief pressure differential while tripping both uphole and downhole. 
       FIG. 3-1  is a representation of a downhole tool  312 , according to at least one embodiment of the present disclosure. The downhole tool  312  may include a housing  314  and a housing chamber  316  inside the housing  314 . A partition  318  in the housing  314  may seal the housing chamber  316  from a fluid chamber  320 . In at least one embodiment, the partition  318  may include a bearing surface  319 . The bearing surface  319  may be fabricated from PCD. The movable member  322  may be fabricated from PCD. The bearing surface  319  may directly abut against the movable member  322  such that as the movable member moves relative to the housing  314 , the movable member  322  slides against the bearing surface  319 . Because the bearing surface  319  and the movable member  322  are fabricated from PCD, the movable member  322  may be inserted into the housing  314  against the bearing surface  319  with a tight gap. The tight gap between the bearing surface  319  and the movable member  322  may form a full or a partial seal between the fluid chamber  320  and the housing chamber  316 . 
     A flow path  330  may be located in the partition  318  providing hydraulic communication between the housing chamber  316  and the fluid chamber  320 . A pressure adjuster  326  may be located in the flow path  330 . The pressure adjuster may include a flow restrictor  332  located in an adjuster chamber  344  located in the flow path  330 . A resilient member  334  may push the flow restrictor  332  against a seat  336  in the adjuster chamber  344  with sufficient force to seal the flow path  330  with a relief pressure differential. In the embodiment shown, the resilient member  334  is a spherical ball that may sit against a circular seat  336 . In other embodiments, the resilient member  334  may be a cylindrical piston (as shown in  FIGS. 2-1 and 2-2 ), or any other shape that may form a seal with the seat  336 . 
     When the pressure differential between the fluid chamber  320  and the housing chamber  316  is greater than the relief pressure differential, the flow restrictor  332  may be pushed away from the seat  336 . Fluid may then pass through or around the flow restrictor  332  and into the housing chamber  316 . This may reduce the pressure differential to below the relief pressure differential such that the resilient member  334  pushes the flow restrictor  332  back against the seat. In the embodiment shown in  FIG. 3-1 , the pressure adjuster  326  is configured to adjust the pressure from a high-pressure fluid chamber  320  to a low-pressure housing chamber  316 . In at least one embodiment, including the pressure adjuster  326  in the partition  318  may reduce the length of the downhole tool  312  and/or reduce the complexity of manufacturing the downhole tool  312 . 
     In some embodiments, the downhole tool  312  may include a plurality of pressure adjusters  326 . For example, two or more pressure adjusters  326  may be installed in series in the flow path  330 . In other words, the same flow path  330  may include two or more pressure adjusters  326  installed one after the other. Several pressure adjusters  326  in series may provide for a more precise adjustment of the relief pressure differential and/or the maximum pressure differential. Further, pressure adjusters  326  in series may dampen the pressure increases experienced by the housing chamber  316  if the fluid chamber  320  experiences a rapid increase in hydrostatic or other pressure. 
     In other examples, two or more pressure adjusters  326  may be installed in parallel. In other words, the partition  318  may include two or more flow paths  330 , with each flow path  330  including a pressure adjuster  326 . This may allow for a larger volume of fluid to pass between the fluid chamber  320  and the housing chamber  316 . This may allow the pressure differential to reach the maximum pressure differential rapidly if the fluid chamber  320  experiences a rapid increase in hydrostatic or hydraulic pressure. 
     In at least one example, the downhole tool may include pressure adjusters  326  in both series and parallel. In some examples, at least one of the pressure adjusters  326  may be the pressure adjuster shown in  FIG. 2-1  and/or  FIG. 2-2 , in series or in parallel with another pressure adjuster  326 . 
       FIG. 3-2  is a representation of a downhole tool  312 , according to at least one embodiment of the present disclosure. In the embodiment shown, a pressure adjuster  326  may include a resilient member  334  that pushes a flow restrictor  332  toward a seat  336  near the housing chamber  316 . In this manner, the pressure adjuster may relieve a pressure from the housing chamber  316  to the fluid chamber  320 . 
     In some embodiments, the downhole tool  312  may include a plurality of pressure adjusters  326 . For example, two or more pressure adjusters  326  may be installed in series in the flow path  330 . In other words, the same flow path  330  may include two or more pressure adjusters  326  installed one after the other. Several pressure adjusters  326  in series may provide for a more precise adjustment of the relief pressure differential and/or the maximum pressure differential. Further, pressure adjusters  326  in series may dampen the pressure decrease in the housing chamber  316  if the fluid chamber  320  experiences a rapid decrease in hydrostatic or hydraulic pressure. 
     In other examples, two or more pressure adjusters  326  may be installed in parallel. In other words, the partition  318  may include two or more flow paths  330 , with each flow path  330  including a pressure adjuster  326 . This may allow for a larger volume of fluid to pass between the fluid chamber  320  and the housing chamber  316 . This may allow the pressure differential to reach the maximum pressure differential rapidly if the fluid chamber  320  experiences a rapid decrease in hydrostatic or hydraulic pressure. 
       FIG. 4  is a representation of a downhole tool  412 , according to at least one embodiment of the present disclosure. The downhole tool  412  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 3-2 . The downhole tool  412  may include two pressure adjusters  426 - 1 ,  426 - 2 . A first pressure adjuster  426 - 1  may be configured to adjust the pressure differential from a high pressure fluid chamber  420  to a low pressure housing chamber  416  (similar to the pressure adjuster  226  of  FIGS. 2-1 and 326  of  FIG. 3-1 ). A second pressure adjuster  426 - 2  may be configured to adjust the pressure differential from a high pressure housing chamber  416  to a low pressure fluid chamber  420 . Thus, the downhole tool  412  may maintain the maximum pressure differential regardless of whether the housing chamber  416  or the fluid chamber  420  has a higher pressure. In some embodiments, either the first pressure adjuster  426 - 1  or the second pressure adjuster  426 - 2 , or both, may have multiple pressure adjusters in series or in parallel. 
       FIG. 5  is a representation of an embodiment of a downhole tool  512 , according to at least one embodiment of the present disclosure. The downhole tool  512  may include a flow path  530  through a partition  518  in a housing  514 . The flow path  530  may place a housing chamber  516  and a fluid chamber  520  in fluid communication. The flow path  530  may include a pressure adjuster  526 . The pressure adjuster  526  may include an adjuster chamber  544 . The adjuster chamber may include a diaphragm  546 . The diaphragm  546  may be made from any resilient material, such as elastomer, rubber, spring steel, plastic, or any other resilient material. The diaphragm  546  may have a modulus of elasticity such that it flexes in the presence of a differential pressure. The diaphragm  546  may include an aperture  548 . As the diaphragm  546  flexes in response to the pressure differential, the diaphragm  546  may open an aperture  548 . When the aperture  548  is opened, fluid may travel between the fluid chamber  520  and the housing chamber  516 . The modulus of elasticity of the diaphragm  546  may therefore be selected to open the aperture at a relief pressure differential. Thus, the diaphragm  546  may be a pressure relief valve. 
     Because the diaphragm  546  is flexible both from the fluid chamber  520  to the housing chamber  516  and from the housing chamber  516  to the fluid chamber  520 , the diaphragm  546  may allow bi-directional communication of fluid between the fluid chamber  520  and the housing chamber  516 . In this manner, the pressure adjuster  526  may be bi-directional. 
       FIG. 6  is a representation of an embodiment of a downhole tool  612 , according to at least one embodiment of the present disclosure. The downhole tool  612  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 5 . In some embodiments, the downhole tool  612  may include a pressure adjuster  626  in any location that allows a flow path  630  to communicate fluid between a fluid chamber  620  and a housing chamber  616 . For example, in the embodiment shown, the pressure adjuster  626  may be located in a housing  614 . In this embodiment, the pressure adjuster  626  and the flow path  630  may be transverse to the movable member  622  and/or the housing pathway  615 . In other embodiments, the pressure adjuster  626  may be located at any other location that a flow path  630  may be created between the fluid chamber  620  and the housing chamber  616 . 
       FIG. 7  is an embodiment of a downhole tool  712 , according to at least one embodiment of the present disclosure. The downhole tool  712  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 6 . The downhole tool  712  may include a pressure adjuster  726 . A piston  750  may be connected to the pressure adjuster  726 . The piston may include an inner bore  752 . A sealing member  754  may be located in the inner bore  752 . The sealing member  754  may divide the inner bore  752  into two sections, a fluid reservoir  756  on a first side of the inner bore  752  near the pressure adjuster  726  and a pressurized fluid  758  on a second side of the inner bore  752  near a fluid chamber (not shown) of the downhole tool  712 . The sealing member  754  may seal the fluid reservoir  756  from the pressurized fluid  758 . 
     As the pressure of the pressurized fluid  758  increases, pressurized fluid  758  may push the sealing member  754  towards the pressure adjuster  726 . This may increase the pressure of the fluid in the fluid reservoir  756 . When the pressure in the fluid reservoir  756  exceeds the relief pressure differential of the pressure adjuster  726 , fluid from the fluid reservoir  756  may enter the housing chamber  716 , thereby decreasing the pressure differential. 
     The fluid reservoir  756  may include any fluid. In some embodiments, the fluid in the fluid reservoir  756  may be an oil based fluid, such as hydraulic oil or oil-based drilling fluid. In other embodiments the fluid in the fluid reservoir  756  may be a water based fluid, such as a water-based drilling fluid. In still other embodiments, the fluid reservoir  756  may include a lubricant, such as grease. Because fluid from the fluid reservoir  756  is the only fluid that is inserted into the housing chamber  716  during pressure adjustment, including a piston  750  with the pressure adjuster  726  may allow control over the fluid that enters the housing chamber  716  while the pressure adjuster  726  adjusts the pressure. This may help to keep the downhole tool  712  clean and ensure that it operates properly. 
     In some embodiments, the piston  750  may be a single-stroke piston. In other words, when the sealing member  754  reaches the pressure adjuster  726 , then no more of the fluid from the fluid reservoir  756  may enter the housing chamber  716 . In some embodiments, the piston  750  may expand in cross-sectional area near the pressure adjuster  726 . In this manner, when the sealing member  754  reaches the pressure adjuster  726 , fluid from the pressurized fluid  758  may travel around the sealing member  754  to reach the pressure adjuster. In other embodiments, the sealing member  754  may include a pressure relief valve, a burst disc, or other mechanism to allow fluid to flow through the sealing member  754 . 
       FIG. 8-1  is a representation of a downhole tool  812 , according to at least one embodiment of the present disclosure. The downhole tool  812  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 7 . The downhole tool  812  may include a flow path  830  connecting a housing chamber  816  to a fluid chamber  820 . A pressure adjuster  826  may be located in an adjuster chamber  844  in the flow path  830 . The pressure adjuster  826  may include a sealing member  854 . The sealing member  854  may seal the flow path  830  from fluid flow between the fluid chamber  820  and the housing chamber  816 . 
     As a pressure differential between the fluid chamber  820  and the housing chamber  816  increases, the pressure differential may act on the sealing member  854 . The pressure differential may cause the sealing member  854  to move in the adjuster chamber  844 . This may force fluid into or out of the housing chamber  816 , which may adjust the pressure differential. The flow path  830  may be open to both the housing chamber  816  and the fluid chamber  820 . Therefore, when the fluid chamber  820  has a higher pressure than the housing chamber  816 , then the sealing member  854  may move toward the housing chamber  816 , thereby increasing the pressure in the housing chamber  816 . When the housing chamber  816  has a higher pressure than the fluid chamber  820 , then the sealing member  854  may move toward the fluid chamber  820 , thereby reducing the pressure in the housing chamber  816 . In this manner, the pressure adjuster  826  may be a piston, or a compensation piston. Because the sealing member  854  may move toward both the housing chamber  816  and the fluid chamber  820 , the pressure adjuster  826  may be bi-directional. 
     In some embodiments, the sealing member  854  may be a spherical ball. In other embodiments, the sealing member  854  may be cylindrical. In still other embodiments, the sealing member  854  may be any shape that may move in and seal the adjuster chamber  844 . In some embodiments, the sealing member  854  may be a flexible diaphragm that stretches toward both the housing chamber  816  and the fluid chamber  820 . In other embodiments, the sealing member  854  may be a bellows or other expandable and retractable member to seal the flow path  830 . 
       FIG. 8-2  is a representation of a downhole tool  812 , according to at least one embodiment of the present disclosure. The downhole tool  812  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 8-1 . In at least one embodiment, the sealing member  854  of the pressure adjuster  826  may migrate toward either the housing chamber  816  or the fluid chamber  820 . In other words, the sealing member  854  may move toward the housing chamber  816  or the fluid chamber  820  more than an increasing pressure differential may account for. This may happen due to vibration of the downhole tool  812 , imperfections in the adjuster chamber  844 , pulses in the pressure differential, or any other reason. 
     To maintain the sealing member  854  in a neutral position, opposing positioning springs  860  may push the sealing member  854  back to a neutral position. The opposing positioning springs  860  may push on the sealing member  854  with a force up to a relief pressure differential force. In some embodiments, the opposing positioning springs  860  may move the sealing member  854  into the neutral position using the same or other mechanisms that cause the sealing member to migrate in the first place, such as vibration, imperfections, pressure pulses, and so forth. Maintaining the sealing member  854  in a neutral position may extend the useful life of the pressure adjuster  826  past a single stroke of the sealing member  854  in either direction. 
       FIG. 9  is a representation of a downhole tool  912 , according to at least one embodiment of the present disclosure. The downhole tool  912  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 8-2 . The downhole tool  912  may include a flow path  930  connecting a housing chamber  916  to a fluid chamber  920 . A pressure adjuster  926  may be located in the flow path  930 . The pressure adjuster  926  may include one or more flow restrictors  932  in an adjuster chamber  944 . 
     The flow restrictor  932  may have a flow restrictor cross-sectional area that is less than an adjuster chamber cross-sectional area. In this manner, fluid may flow through the flow path  930  while there is a pressure differential between the housing chamber  916  and the fluid chamber  920 . At high pressure differentials, the fluid flow through the flow path  930  may be sufficient that sediment and other suspended particles do not settle in the adjuster chamber  944  and clog the flow path. Therefore, the flow restrictor  932  may help to equalize the pressure differential between the housing chamber  916  and the fluid chamber  920 . At lower pressure differentials, sediment and other suspended particles may collect in the adjuster chamber  944 , and may clog the flow path. Thus, when the downhole tool  912  reaches the operating depth, a lower pressure differential may be experienced, and the flow path  930  may clog. This may allow an operating pressure differential to be maintained without a fluid leak through the flow path  930  during operation. 
     The flow restrictor  932  may have a radial clearance  945  between the flow restrictor  932  and the adjuster chamber  944 . In some embodiments, the radial clearance  945  may be in a range having an upper value, a lower value, or upper and lower values including any of 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, or any value therebetween. For example, the radial clearance  945  may be greater than 5 μm. In another example, the radial clearance  945  may be less than 500 μm. In yet other examples, the radial clearance  945  may be any value in a range between 5 μm and 500 μm. In some embodiments, a radial clearance of 50 μm or less may be critical for the movable member  922  to reliably move upon actuation. 
     The flow restrictor  932  may have an area percentage that is a percentage of a flow restrictor cross-sectional area relative to the adjuster chamber cross-sectional area. In some embodiments, the area percentage may be in a range having an upper value, a lower value, or upper and lower values including any of 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value therebetween. For example, the area percentage may be greater than 85%. In another example, the area percentage may be less than 99%. In yet other examples, the area percentage may be any value in a range between 85% and 99%. In some embodiments, area percentages greater than 85% may be critical for the movable member  922  to reliably move upon actuation. 
       FIG. 10  is a representation of an embodiment of a downhole tool  1012 , according to at least one embodiment of the present disclosure. The downhole tool  1012  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 9 . The downhole tool  1012  may include a flow path  1030  connecting a fluid chamber  1020  to a housing chamber  1016 . A pressure adjuster  1026  may be located in the flow path  1030 . The pressure adjuster  1026  may include a sealing member  1054  in an adjuster chamber  1044 . The pressure adjuster  1026  may include a first alternate path  1062 - 1  and a second alternate path  1062 - 2 . The sealing member  1054  may seal the adjuster chamber  1044  from fluid passing between the fluid chamber  1020  and the housing chamber  1016 . 
     Opposing positioning springs  1060  may act on the sealing member  1054  to maintain the sealing member  1054  in a neutral position. In the neutral position, the sealing member  1054  may block the opening into the adjuster chamber of both the first alternate path  1062 - 1  and the second alternate path  1062 - 2 . As the pressure differential between the fluid chamber  1020  and the housing chamber  1016  increases, the pressure differential may push against the sealing member  1054 . At a relief pressure differential, the sealing member  1054  may expose one of the first alternate path  1062 - 1  or the second alternate path  1062 - 2  in the adjuster chamber  1044 . 
     For example, when the pressure of the fluid chamber  1020  is greater than the pressure of the housing chamber  1016 , then the sealing member  1054  may move toward the housing chamber  1016 . When the pressure differential becomes greater than the relief pressure differential, then the first alternate path  1062 - 1  may be exposed. This may cause fluid to travel through the first alternate path  1062 - 1  and into the housing chamber  1016 . When the pressure differential is reduced to below the relief pressure differential, the sealing member  1054  may be returned by the opposing position springs  1060  to the neutral position. 
     Similarly, when pressure of the housing chamber  1016  is greater than the pressure of the fluid chamber  1020 , then the sealing member  1054  may move toward the fluid chamber  1020 . When the pressure differential exceeds the relief pressure differential, then the second alternate path  1062 - 2  may be exposed. This may cause fluid to travel through the second alternate path  1062 - 2  to the fluid chamber. When the pressure differential is reduced below the relief pressure, the sealing member  1054  may be returned to the neutral position by the opposing positioning springs  1060 . In this manner, the pressure adjuster  1026  may be bi-directional. 
       FIG. 11  is a representation of a downhole tool  1112 , according to at least one embodiment of the present disclosure. The downhole tool  1112  may include at least some of the features and characteristics of the downhole tools described with respect to  FIG. 2-1  through  FIG. 10 . The downhole tool  1112  may include a movable member  1122 . A housing  1114  may include a bearing  1165  at a housing first end  1117 . The movable member  1122  may rotate within the bearing with a close gap. In some embodiments, the gap may be between 10 and 100 μm, as described above with respect to  FIG. 2-1 . When a pressure differential is increased between a housing chamber  1116  in the housing  1114  and a fluid chamber (not shown), solids may collect at the bearing, and the torque required to rotate the movable member may be increased. 
     The housing chamber  1116  may include a bearing surface  1168  at a housing second end  1166 . The movable member  1122  may include a central support  1170 . The movable member  1122  may be supported by the central support  1170  at the bearing surface  1168 . Because the movable member  1122  is supported by the central support  1170 , the only friction to be overcome by a torque during operation is the friction of the central support  1170  against the bearing surface  1168 . By reducing the bearing area of the central support  1170 , the torque required to rotate the movable member  1122  may be reduced. 
     The central support  1170  engages the bearing surface  1168  with a bearing radius. In some embodiments, the central support  1170  may have a sharp point that engages the bearing surface  1168 . Thus, the bearing radius may be small, which may reduce the torque required to rotate the movable member  1122 . In some embodiments, the bearing radius may be in a range having an upper value, a lower value, or upper and lower values including any of 1 μm, 10 μm, 25 μm, 50 μm, 75 μm 100 μm, 250 μm, 500 μm, 750 μm, 1.0 millimeter (mm), 2.5 mm, 5.0 mm, 7.5 mm, 10 mm, 25 mm, 50 mm, or any value therebetween. For example, the bearing radius may be greater than 1 μm. In another example, the bearing radius may be less than 50 mm. In yet other examples, the bearing radius may be any value in a range between 1 μm and 50 mm. In some embodiments, a radial clearance of 1 mm or less may be critical for the movable member  1122  to reliably move upon actuation. In another embodiment, a radial clearance of 5 mm or less may be critical for the movable member  1122  to reliably move upon actuation. In yet other embodiments, a radial clearance of between 1 and 5 mm may permit the movable member  1122  to reliably move upon actuation. 
     The bearing area of the central support  1170  may be a support percentage, or the percentage of the bearing area with respect to a movable member cross-sectional area. In some embodiments, the support percentage may be in a range having an upper value, a lower value, or upper and lower values including any of 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any value therebetween. For example, the support percentage may be greater than 1%. In another example, the support percentage may be less than 25%. In yet other examples, the support percentage may be any value in a range between 1% and 25%. In some embodiments, support percentages below 10% may be critical for the movable member  1122  to be rotated at high differential pressures. 
     Due to the high rotational rates to which the movable member  1122  may be subjected, both the central support  1170  and the bearing surface  1168  may be made from an ultrahard material. For example, one or both of the central support  1170  and the bearing surface  1168  may be made from PCD, tungsten carbide (WC), cubic boron nitride, or any other ultrahard material. In other embodiments, general to hard materials such as ceramics or metals may be used. In some embodiments, the downhole tool  1112  may include a combination of a central support  1170  rotating on a bearing surface  1168  and one or more of the pressure adjusters discussed with respect to  FIG. 2-1  through  FIG. 10 . In some embodiments, the central support  1170  and the bearing surface  1168  may rotate on a bearing, such as a ball bearing. For example, the central support  1170  may include a ball at the contact point between the central support  1170  and the bearing surface  1168 . The ball may contact the bearing surface  1168  and rotate with respect to both the bearing surface  1168  and the central support  1170 . A ball bearing may rotate in response to a lower torque on the movable member  1122 . 
       FIG. 12  is a method chart of a method  1272  for operating a downhole tool, according to at least one embodiment of the present disclosure. The method  1272  may include sealing a housing chamber in a housing at  1274 . A movable member may be inserted in and rotatable relative to the housing chamber. The movable member may rotate against a bearing with a tight gap, the gap creating the seal. The method  1272  may further include generating a pressure differential across the seal between a fluid chamber and the housing chamber at  1276 . The pressure differential may be generated as a result of an increasing hydrostatic pressure in the fluid chamber or an increased pressure in the housing chamber. Generating the pressure differential may include clogging the seal with particles suspended in the fluid. 
     The method  1272  may further include reducing the pressure differential with a pressure adjuster at  1278 . Reducing the pressure differential may include overcoming a relief pressure differential in the pressure adjuster. Reducing the pressure differential may further include moving a sealing member or a flow restrictor along an adjuster chamber in response to the pressure differential. 
     The embodiments of the pressure adjuster have been primarily described with reference to wellbore drilling operations; the pressure adjusters described herein may be used in applications other than the drilling of a wellbore. In other embodiments, pressure adjusters according to the present disclosure may be used outside a wellbore or other downhole environment used for the exploration or production of natural resources. For instance, pressure adjusters of the present disclosure may be used in a borehole used for placement of utility lines. Accordingly, the terms “wellbore,” “borehole” and the like should not be interpreted to limit tools, systems, assemblies, or methods of the present disclosure to any particular industry, field, or environment. 
     One or more specific embodiments of the present disclosure are described herein. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     The articles “a,” “an,” and “the” are intended to mean that there are one or more of the features in the preceding descriptions. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value. 
     A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims. 
     The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements. 
     The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.