Patent Publication Number: US-2023138582-A1

Title: Cover, fluid end and plunger pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to the Chinese patent applications No. 202111282713.8 filed on Nov. 1, 2021, No. 202111283476.7 filed on Nov. 1, 2021, and No. 202111283958.2 filed on Nov. 1, 2021. The disclosures of all of these applications are hereby incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The embodiments of the present disclosure relate to a cover, a fluid end and a plunger pump. 
     BACKGROUND 
     At present, fracturing operation is the main stimulation method in the process of oil and gas field exploitation, and a plunger pump is the main equipment for pumping fracturing medium in the stimulation operation. In other words, in the whole process of oil and gas exploitation, any process that needs to deliver medium into the well under a predetermined pressure needs to be realized by the plunger pump. 
     SUMMARY 
     The embodiments of the present disclosure provide a cover, a fluid end and a plunger pump. 
     In one aspect, the embodiments of the present disclosure provide a cover, a fluid end, and a plunger pump, so as to simplify the structure of the fluid end and provide a large displacement output. 
     The embodiment of the present disclosure provides a cover, which includes: a body, the body being cylindrical, and the body including a first end, a second end, and a side surface connecting the first end and the second end; a main flow channel extending along an axis of the body; a plurality of subsidiary flow channels, each of the plurality of subsidiary flow channels being communicated with the main flow channel; a first opening located at the  first end and communicated with the main flow channel; and a plurality of second openings, located at the side surface of the body, each of the plurality of subsidiary flow channels being communicated with at least one of the plurality of second openings. 
     According to the cover provided by the embodiment of the present disclosure, the main flow channel is located on the axis of the body, and the main flow channel does not penetrate the body on the axis of the body. 
     According to the cover provided by the embodiment of the present disclosure, an aperture of the main flow channel is greater than an aperture of the subsidiary flow channel, 
     According to the cover provided by the embodiment of the present disclosure, the plurality of second openings are evenly distributed in a circumferential direction of the body. 
     According to the cover provided by the embodiment of the present disclosure, each of the plurality of subsidiary flow channels are obliquely arranged with respect to the main flow channel. 
     According to the cover provided by the embodiment of the present disclosure, an acute angle between a center line of the subsidiary flow channel and a center line of the main flow channel is in a range from 20 to 80 degrees. 
     According to the cover provided by the embodiment of the present disclosure, a distance between the subsidiary flow channel and the axis of the body gradually increases in a direction from the first end to the second end. 
     According to the cover provided by the embodiment of the present disclosure, the cover farther includes a drain channel, and a first drain outlet and a second drain outlet located at both ends of the drain channel the first drain outlet is located at the side surface of the body, and the second drain outlet is located at an end surface of the second end of the body. 
     According to the cover provided by the embodiment of the present disclosure, the drain channel is not communicated with the main flow channel, and is not communicated with the plurality of subsidiary flow channels. 
     According to the cover provided by the embodiment of the present disclosure,  the first drain outlet is located at a side of the side face close to an end surface of the first end. 
     According to the cover provided by the embodiment of the present disclosure, the cover further includes a valve-seat groove, the valve-seat groove is located at the first end and is communicated with the main flow channel, and the valve-seat groove has a relief groove at a side of the valve-seat groove away from the first end. 
     According to the cover provided by the embodiment of the present disclosure, the cover further includes a first sealing position and a second sealing position, the first sealing position is configured to arrange a first sealing ring, the second sealing position is configured to arrange a second sealing ring, the first sealing position and the second sealing position are both located at the side surface, and the first drain outlet is located between the first sealing position and the second sealing position. 
     According to the cover provided by the embodiment of the present disclosure, the cover further includes a first sealing groove and a second sealing groove, the first sealing groove is configured to receive a first sealing ring, the second sealing groove is configured to receive a second sealing ring, the first sealing groove and the second sealing groove are both located at the side surface, and the first drain outlet is located between the first sealing groove and the second sealing groove. 
     According to the cover provided by the embodiment of the present disclosure, the cover further includes a pulling hole, the pulling hole is located at the second end of the body, and the pulling hole is not communicated with the second drain outlet. 
     According to the cover provided by the embodiment of the present disclosure, the pulling hole is located on the axis of the body. 
     The embodiment of the present disclosure further provides a fluid enol, which includes any one of the covers described above. 
     According to the fluid end provided by the embodiment of the present disclosure, the fluid end further includes: a valve casing including an inner chamber, the inner chamber including a low pressure chamber, a pressure-alternating chamber, and a high pressure chamber; the cover is located in the low pressure chamber, the inner chamber of the valve casing has art inverted T-shaped structure, the pressure-alternating chamber and the low pressure chamber are arranged along an extending direction of a first axis of the inner  chamber, the pressure-alternating chamber and the high pressure chamber are arranged along an extending direction of a second axis of the inner chamber, and the first axis intersects with the second axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the valve casing has an inlet hole, and the inlet hole and the high pressure chamber are staggered in the extending direction of the first axis. 
     According to the fluid end provided by file embodiment of the present disclosure, the fluid end further includes a first valve assembly, the first valve assembly is configured to be opened to communicate the low pressure chamber with the pressure-alternating chamber or configured to be closed to separate the low pressure chamber from the pressure-alternating chamber, the first valve assembly includes a spring bracket, and the spring bracket has a hollowed-out structure and is limited with the valve casing by an inclined surface. 
     According to the fluid end provided by the embodiment of the present disclosure, a first sub-chamber and a second sub-chamber are provided at an intersection position of the inner chamber, the first sub-chamber and the second sub-chamber are arranged along an extending direction of the second axis, and the second sub-chamber is closer to a portion of the inner chamber extending along the first axis than the first sub-chamber is, a maximum size of the second sub chamber in the extending direction of the second axis is greater than a maximum size of the first sub-chamber in the extending direction of the second axis, and a size of the second sub-chamber in the extending direction of the first axis gradually increases in a direction from a position away from the first axis to a position close to the first axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the valve casing is provided with a protective sleeve at a position corresponding to both the first sub-chamber and the second sub-chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, the fluid end further includes a second valve assembly, the second valve assembly is configured to be opened to communicate the pressure-alternating chamber with the high pressure chamber or configured to be closed to separate the pressure-alternating chamber  from the high pressure chamber, and the second valve assembly and the second sub-chamber are located at opposite sides of the first sub-chamber. 
     The embodiment of the present disclosure further provides a plunger pump, which includes any one of the fluid ends described above. 
     In another aspect, the embodiments of the present disclosure provide a fluid end and a plunger pump, which is beneficial to maintaining and prolonging the service life of the valve casing. 
     The embodiment of the present disclosure provides a fluid end, which includes: a valve casing, including an inner chamber, the inner chamber including pressure-alternating chamber and a low pressure chamber; a first valve assembly configured to be opened to communicate the low pressure chamber with the pressure-alternating chamber or configured to be closed to separate the low pressure chamber from the pressure-alternating chamber; a first pressure bearing assembly located in the inner chamber; and a second pressure bearing assembly located in the inner chamber; the first valve assembly, the first pressure bearing assembly, and the second pressure bearing assembly are sequentially arranged along an extending direction of a first axis of the inner chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, the first pressure bearing assembly is detachably connected with the valve casing, and the second pressure bearing assembly is detachably connected with the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the first pressure bearing assembly includes a pressure-alternating cover and a pressure-alternating nut, the pressure-alternating cover is closer to the first valve assembly than the pressure-alternating Ina is, and the pressure-alternating nut is in a threaded connection with the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, a maximum length of the pressure-alternating cover on the first axis is less than a maximum length of the pressure-alternating nut on the first axis. 
     According to the fluid end provided by the embodiment of the present disclosure, a first sealing structure is arranged between the pressure-alternating cover and the valve casing, the valve casing has a drain channel, and the drain channel is configured to flow  fluid therethrough in the case of failure of at least a pan of the first sealing structure. 
     According to the fluid end provided by the embodiment of the present disclosure, the drain channel penetrates a body of the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the drain channel is obliquely arranged with respect to the first axis of the inner chamber, and an acute angle formed by the drain channel and the first axis of the inner chamber is greater than or equal to 30 degrees and less than or equal to 60 degrees. 
     According to the fluid end provided by the embodiment of the present disclosure, the first sealing structure includes a first seal and a second seal, and one end of the drain channel close to the pressure-alternating cover is located between the first seal and the second seal. 
     According to the fluid end provided by the embodiment of the present disclosure, the first valve assembly includes a first valve body, a first sealing element, and a first valve seat, and the pressure-alternating cover serves as a base seat of the first valve seat. 
     According to the fluid end provided by the embodiment of the present disclosure, the pressure-alternating cover has a low pressure fluid channel, and the low pressure fluid channel is communicated with an inlet hole of the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the second pressure bearing assembly includes a suction cover and a suction nut, the suction cover is closer to the first pressure bearing assembly than the suction nut is, and the suction nut is in a threaded connection with the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the pressure-alternating cover and the suction cover are respectively arranged at opposite sides of the pressure-alternating nut. 
     According to the fluid end provided by the embodiment of the present disclosure, the fluid end further includes a second valve assembly and a third pressure bearing assembly, the inner chamber further includes a high pressure chamber, the second valve assembly is configured to be opened to communicate the pressure-alternating chamber with the high pressure chamber or configured to be closed to separate the pressure-alternating chamber from the high pressure chamber, the third pressure bearing assembly is located in the  inner chamber and is arranged in sequence with the second valve assembly in an extending direction of a second axis of the inner chamber, a region of the inner chamber between the second valve assembly and the third pressure bearing assembly is the high pressure chamber, and the first axis intersects with the second axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the inner chamber has an inverted T-shaped structure, and the pressure-alternating chamber and the high pressure chamber are arranged along the extending direction of the second axis of the inner chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, the valve casing has an inlet hole, and the inlet hole and the high pressure chamber are staggered in the extending direction of the first axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the first pressure bearing assembly and the second pressure bearing assembly are respectively arranged on both sides of the inlet hole in the extending direction of the first axis. 
     According to the fluid end provided by the embodiment of the present disclosure, a first sub-chamber and a second sub-chamber are provided at an intersection position of the inner chamber, the first sub-chamber and the second sub-chamber are arranged along the extending direction of the second axis, and the second sub-chamber is closer to a portion of the inner chamber extending along the first axis than the first sub-chamber is, a maximum size of the second sub-chamber in the extending direction of the second axis is greater than a maximum size of the first sub-chamber in the extending direction of the second axis, and a size of the second sub-chamber in the extending direction of the first axis gradually increases in a direction from a position away from the first axis to a position close to the first axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the valve casing is provided with a protective sleeve at a position corresponding to both the first sub-chamber and the second sub-chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, the first valve assembly includes a spring bracket, and the spring bracket has a  hollowed-out structure and is limited with the valve casing by an inclined surface. 
     The embodiment of the present disclosure further provides a plunger pump, which includes any one of the fluid ends described above. 
     In another aspect, the embodiments of the present disclosure provide a fluid end, and the fluid end has a drain channel, which artificially creates a leakage point. Once the seal fails, it will be quickly and directly found, which is convenient for timely replacement of assembly parts, avoids the occurrence of large puncture leakage in the inner chamber and avoids safety accidents. 
     The embodiments of the present disclosure provide a fluid end, which includes a valve casing, including au inner chamber, the inner chamber including a pressure-alternating chamber and a low pressure chamber; a first valve assembly, located in the inner chamber, and configured to be opened to communicate the low pressure chamber with the pressure-alternating chamber or configured to be closed to separate the low pressure chamber from the pressure-alternating chamber; a pressure bearing, structure, at least a portion of the pressure hearing structure being located in the low pressure chamber; and a first sealing structure, located between the pressure bearing structure and the valve casing; at least one of the valve casing and the pressure bearing structure has a drain channel, and the drain channel is configured to flow fluid therethrougb in a case of failure of a part of the first sealing structure. 
     According to the fluid end provided by the embodiment of the present disclosure, the first sealing structure includes a first seal and a second seal, the drain channel includes a first drain outlet and a second drain outlet, the first drain outlet is closer to the first sealing structure than the second drain outlet is, and the first drain outlet is located between the first seal and the second seal. 
     According to the fluid end provided by the embodiment of the present disclosure, the drain channel is arranged in the valve casing, and the drain channel is obliquely arranged with respect to a first axis of the inner chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, an acute angle formed by the drain channel and the first axis of the inner chamber is greater than or equal to 30 degrees and less than or equal to 60 degrees.  
     According to the fluid end provided by the embodiment of the present disclosure, the pressure bearing structure includes a first pressure bearing assembly and a second pressure bearing assembly, and the first valve assembly, the first pressure bearing assembly, and the second pressure bearing assembly are sequentially arranged along an extending direction of the first axis of the inner chamber. 
     According to the fluid end provided by the embodiment of the present disclosure, the first pressure bearing assembly includes a pressure-alternating cover and a pressure-alternating nut, the pressure-alternating cover is closer to the first valve assembly than the pressure-alternating nut is, and the pressure-alternating nut is in a threaded connection with the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the pressure bearing structure includes a cover and a nut, the nut is in a threaded connection with the valve casing, and the drain channel is located in the cover. 
     According to the fluid end provided by the embodiment of the present disclosure, the cover includes: a body, the body being cylindrical, and the body including a first end., a second end, and a side surface connecting the first end and the second end; a main flow channel, extending along an axis of the body; a plurality of subsidiary flow channels, each of the plurality of subsidiary flow channels being communicated with the main flow channel; a first opening, located at the first end and communicated with the main flow channel; and a plurality of second openings, located at the side surface of the body, each of the plurality of subsidiary flow channels being, communicated with at least one of the plurality of second openings. 
     According to the fluid end provided by the embodiment of the present disclosure, the cover has a low pressure fluid channel, and the low pressure fluid channel is communicated with an inlet hole of the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the inner chamber of the valve casing has an inverted T-shaped structure, and the pressure-alternating chamber and the low pressure chamber are arranged along an extending direction of a first axis of the inner chamber. 
     According to the fluid end provided by the embodiment of the present  disclosure, the valve casing further includes a high pressure chamber the pressure-alternating chamber and the high pressure chamber are arranged along an extending direction of a second axis of the inner chamber, and the first axis intersects with the second axis. 
     According to the fluid end provided by the embodiment of the present disclosure, the valve casing has an inlet hole, and the inlet hole and the high pressure chamber are staggered in the extending direction of the first axis. 
     According to the fluid end provided by file embodiment of the present disclosure, the fluid end further includes a plunger, a packing assembly, a packing nut, a packing sleeve and a packing-sleeve nut, the inner chamber further including a plunger chamber, the plunger chamber is configured to place the plunger, the packing sleeve is located between the packing assembly and the valve casing, the packing-sleeve nut is configured to press the packing sleeve, and the packing nut is configured to press the packing assembly. 
     According to the fluid end provided by the embodiment of the present disclosure, a hardness of the packing sleeve is greater than a hardness of the valve casing, and the packing-sleeve nut is in a welded connection with the valve casing. 
     According to the fluid end provided by the embodiment of the present disclosure, the packing-sleeve nut is in a welded connection with the valve casing. 
     The embodiments of the present disclosure farther provide plunger pump, including any one of the fluid ends as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       in order to clearly illustrate the technical solution of the embodiments of the present disclosure, the drawings of the embodiments will be briefly described. It is obvious that the described drawings in the following are only related to some embodiments of the present disclosure and thus are not construed as any limitation to the present disclosure. 
         FIG.  1 A  is a cross-sectional view of a plunger pump; 
         FIG.  1 B  is a schematic diagram of at fluid end in the plunger pump illustrated in  FIG.  1 A ; 
         FIG.  1 C  is a schematic diagram of a valve casing in the fluid end illustrated in   FIG.  1 B ; 
         FIG.  2    is a cross-sectional view of a cover provided by an embodiment of the present disclosure; 
         FIG.  3    is a perspective view of a cover provided by an embodiment of the present disclosure, 
         FIG.  4    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  5    is a front view and a side view of a spring bracket in a fluid end provided by an embodiment of the present disclosure; 
         FIG.  6    is a perspective view of another cover provided by an embodiment of the present disclosure; 
         FIG.  7    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  8    is a cross-sectional view of a valve casing in a fluid end provided by an embodiment of the present disclosure; 
         FIG.  9    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  10    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  11    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  12 A  is a partial view of a drain channel in a valve casing of  FIG.  11   ; 
         FIG.  12 B  is a partial view of a packing sleeve and a packing-sleeve nut in the valve casing of  FIG.  10    or  FIG.  11   ; 
         FIG.  13    is a schematic diagram of respective regions of an inner chamber in a valve casing of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  14    is a schematic diagram of a valve casing in a fluid end provided by an embodiment of the present disclosure; 
         FIG.  15    is a perspective view of a fluid end provided by an embodiment of the present disclosure;  
         FIG.  16    is a schematic diagram of a valve casing in another fluid end provided by an embodiment of the present disclosure; 
         FIG.  17    is a schematic diagram of an intersection position of an inner chamber of a valve casing in a fluid end provided by an embodiment of the present disclosure; 
         FIG.  18    is a schematic diagram of an intersection position of an inner chamber of a valve casing in another fluid end provided by an embodiment of the present disclosure; 
         FIG.  19    is a schematic diagram of a second valve assembly in a fluid end provided by an embodiment of the present disclosure; 
         FIG.  20    is a schematic diagram of a valve casing on a discharge side of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  21    is a schematic diagram of a sealing structure on a discharge side of a fluid end provided by an embodiment of the present disclosure; 
         FIG.  22    is a schematic diagram of a valve casing on a suction side of a fluid end provided by an embodiment of the present disclosure; and 
         FIG.  23    is a schematic diagram of a sealing structure on a suction side of a fluid end provided by an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In order to make objectives, technical details, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments will be described in a clearly and fully understandable way in connection with the drawings related to the embodiments of the present disclosure. Apparently, the described embodiments are just a part but not all of the embodiments of the present disclosure. Based on the described embodiments herein, those skilled in the art can obtain other embodiment(s), without any inventive work, which should be within the scope of the present disclosure. 
     Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. The terms “first”, “second”, etc., which are used in the present disclosure, are not intended to indicate any sequence, amount or importance, but distinguish various components. The terms “comprise,” “comprising,” “include,”“including,” etc., are.  intended to specify that the elements or the objects stated before these terms encompass the elements or the objects and equivalents thereof listed after these terms, but do not preclude the other elements or objects. The phrases “connect”, “connected”, etc., are not intended to define a physical connection or mechanical connection, but may include an electrical connection, directly or indirectly. “On,” “under,” “right,” “left” and the like are only used to indicate relative position relationship, and when the position of the described object is changed, the relative position relationship may be changed accordingly. 
     As one of the key equipment for fracturing, the plunger pump is mainly used to transform the fracturing fluid with certain viscosity under normal pressure into a fracturing fluid with high pressure and large flow, so as to be injected into the ground formation, and the performance of the plunger pump directly affects the technical level of fracturing operation M oil and gas fields. At present, the structure of a fracturing pump at home and abroad generally adopts a reciprocating horizontal multi-cylinder plunger pump, such as three-cylinder plunger pump and five-cylinder plunger pump, which usually consists of a fluid end and a power end. The function of the fluid end is to convert mechanical energy into pressure energy of working fluid. The function of the power end is to transfer the kinetic energy of a prime mover to the fluid end through a deceleration transmission system and a crank-connecting rod mechanism. 
       FIG.  1 A  is a cross-sectional view of a plunger pump.  FIG.  1 B  is a schematic diagram of a fluid end in the plunger pump illustrated in  FIG.  1 A .  FIG.  1 C  is a schematic diagram of a valve casing in the fluid end illustrated in  FIG.  1 B . As illustrated in  FIG.  1 A , the plunger pump  003  includes a power end  002  and a fluid end  001 . As illustrated in  FIG.  1 A  and  FIG.  1 B , the fluid end  001  mainly includes a valve casing  01 , a plunder  02 , a valve assembly  03 , a valve assembly  04 , a sealing element, a cover  05 , and a nut  06 .  FIG.  1 A  further illustrates a clamp  07 , a pull rod  08 , a crosshead  09 , a connecting rod  010 , a housing,  011 , and a crankshaft  012 . As illustrated in  FIG.  1 B , the fluid end  001  further includes a valve seat  021 , a spring  022 , a suction cover  023 , a suction nut  024 , a spring  025 , a fluid discharge hole  026 , a packing assembly  027  for-sealing, and a packing nut  028 .  FIG.  1 C  illustrates a cross intersection structure of the valve casing  01 . 
     As illustrated in  FIG.  1 A  and  FIG.  1 B , the working principle of the plunger pump is as follows: under the drive of the prime mover, the crankshaft  012  of the power end   002  rotates to drive the connecting rod  010  and the crosshead  09  to reciprocate horizontally, and the crosshead  09  drives the plunger  02  to reciprocate horizontally in the valve casing  01  through the pull rod  08 . When the plunger  02  moves back, the interior volume of the valve casing  01  gradually increases, thus forming a local vacuum. At this time, the valve assembly  03  is opened, the valve assembly  04  is closed, and the medium enters the inner chamber of the valve casing  01 . When the plunger  02  moves back to a limit position, the inner chamber of the valve casing  01  is fully filled with the medium, and a sucking action is completed. When the plunger  02  moves forward, the interior volume of the valve casing  01  gradually decreases, the medium is squeezed, and the pressure increases. At this time, the valve assembly  04  is opened, and the valve, assembly  03  is closed. Under the pressure, the medium enters the fluid discharge hole  026 . When the plunger  02  moves forward to an extreme position, the medium receiving space within the valve casing  01  is minimum, and the liquid discharge is completed. Due to the continuous reciprocating motion of the plunger  02 , the processes of fluid suction and fluid discharge are alternately carried out, and the high pressure medium is continuously output. 
     Referring to  FIG.  1 A - FIG.  1 C , the valve casing of the fluid end usually has a cross intersection structure As illustrated in  FIG.  1 C , the inner chamber of the valve casing  01  is divided into a low pressure chamber  01   a , a pressure-alternating chamber  01   b , and a high pressure chamber  01   c  according to the pressure. However, the intersection line is just in the pressure-alternating chamber  01   b , and mechanical analysis illustrates that the stress concentration at the intersection line is obvious. Coupled with the effect of alternating load, fatigue cracks are easy to occur at the intersection line, which results in cracking and leakage of the valve casing  01  and frequent replacement of the valve casing on site. And the replacement is costly, time-consuming and laborious. 
     With the increasing difficulty of fracturing operation (indicated by the increase of working pressure), single pump with large displacement has become an urgent demand of the market If the stress concentration effect at the intersection has not been effectively alleviated, it will be difficult to prolong the service life of the valve casing. 
     The embodiments of the present disclosure provide a valve casing with a T-shaped inner chamber to prolong the service life of the valve casing, and provide a cover to  simplify the structure of the fluid end and improve the performance of the fluid end. The embodiments of the present disclosure further provide a fluid end and a plunger pump which include the cover and the valve casing with the T-shaped inner chamber. 
     The cover, the fluid end, and the plunger pump provided by the embodiments of the present disclosure are introduced below. 
       FIG.  2    is a cross-sectional view of a cover provided by an embodiment of the present disclosure,  FIG.  3    is a perspective view of a cover provided by an embodiment of the present disclosure.  FIG.  4    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure.  FIG.  5    is a front view and a side view of a spring bracket in a fluid end provided by an embodiment of the present disclosure.  FIG.  5 ( a )  is the front view of the spring bracket. FIG.  5 ( b ) is the side view of the spring bracket.  FIG.  6    is a perspective view of another cover provided by an embodiment of the present disclosure.  FIG.  7    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure.  FIG.  8    is a cross-sectional view of a valve casing in a fluid end provided by an embodiment of the present disclosure.  FIG.  9    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure. 
     As illustrated in  FIG.  2   ,  FIG.  3     FIG.  6    and  FIG.  7   , the embodiment of the present disclosure provides a cover  10 , and the cover  10  includes a body  100 , a main flow channel  1021 , a plurality of subsidiary flow channels  1022 , a first opening P 1 , and a plurality of second openings P 2 . As illustrated in  FIG.  2   ,  FIG.  3   ,  FIG.  6    and  FIG.  7   , the body  100  is cylindrical, and the body  100  includes a first end E 1 , a second end E 2 , and a side surface S 0  connecting the first end E 1  and the second end E 2 . The main flow channel  1021  extends along the axis of the body  100 ; each subsidiary flow channel  1022  is communicated with the main flow channel  1021 : the first opening P 1  is located at the first end E 1  and is communicated with the main flow channel  1021 ; the plurality of second openings P 2  are located at the side surface S 0  of the body  100 , and the subsidiary flow channel  1022  is communicated with at least one of the plurality of second openings P 2 . 
     The cover  10  provided by the embodiment of the present disclosure is beneficial to fluid passage and simplifying the structure of the fluid end, and the plunger pump including the cover can realize large displacement output.  
       FIG.  2   - FIG.  4   ,  FIG.  7    and  FIG.  9    illustrate a cover  10   a , and  FIG.  6    illustrates a cover  10   b.    
     For example, as illustrated in  FIG.  2    and  FIG.  7   , the main flow channel  1021  is located on the axis AO of the body  100 , and the main flow channel  1021  does not penetrate the body  100  on the axis of the body  100 . As illustrated in  FIG.  2    and  FIG.  7   , the left end of the main flow channel  1021  is communicated with the first opening P 1 , and the right end of the main flow channel  1021  is communicated with the subsidiary flow channel  1022 . For example, the main flow channel  1021  extends along the extending direction of the axis AO of the body  100 . 
     For example, as illustrated in  FIG.  2    and  FIG.  7   , in order to facilitate fluid passage, the aperture of the main flow channel  1021  is greater than the aperture of the subsidiary flow channel  1022 . 
     For example, as illustrated in  FIG.  3    and  FIG.  6   , in order to realize stable output with large displacement, the plurality of second openings P 2  are evenly distributed in the circumferential direction of the body  100 . Because the second openings P 2  are located at the side surface S 0 , the aperture of the subsidiary flow channel  1022  and the size of the second opening P 2  can be set larger to facilitate the fluid to pass through the cover. The embodiment of the present disclosure is illustrated by taking that the cover  19  includes four second openings P 2  evenly distributed in the circumferential direction of the body  100  as an example. 
     For example, as illustrated in  FIG.  2    and  FIG.  6   , in order to improve the performance of the cover and prolong the service life of the cover, the subsidiary flow channels  1022  are obliquely arranged with respect to the main flow channel  1021 . 
     In some embodiments, the plurality of subsidiary flow channels  1022  have the same inclination direction and the same inclination degree with respect to the main flow channel  1021 . As illustrated in  FIG.  2    and  FIG.  7   , the plurality of subsidiary flow channels  1022  are inclined to the right and have the same included angle with the main flow channel  1021 , 
     For example, as illustrated in  FIG.  2    and  FIG.  7   , the acute angle θ 1  between the center line L 2  of the subsidiary flow channel  1022  and the center line L 1  of the main flow  channel  1021  is in a range from 20 to 80 degrees. The cover illustrated in  FIG.  2    and  FIG.  7    is illustrated by taking that the center line L 1  of the main flow channel  1021  coincides with the axis A 0  of the main body  100  as an example. 
     For example, as illustrated in  FIG.  2    and  FIG.  7   , the distance between the subsidiary flow channel  1022  and the axis A 0  of the body  100  gradually increases in a direction from the first end E 1  to the second end E 2 . That is, as illustrated in  FIG.  2   , the subsidiary flow channel  1022  is inclined to the right. Of course, in some other embodiments, the subsidiary flow channel  1022  can also be inclined to the left, and in this case, the distance between the subsidiary flow channel  1022  and the axis A 0  of the body  100  gradually decreases in a direction from the first end E 1  to the second end E 2 . 
     For example, as illustrated in  FIG.  3   ,  FIG.  6    and  FIG.  7   , the cover  10  further includes a drain channel  1000 , and a first drain outlet  1001  and a second drain outlet  1002  at both ends of the drain channel  1000 . The first drain outlet  1001  is located at the side surface S 0  of the body  100 , and the second drain outlet  1002  is located at the end surface S 2  of the second end E 2  of the body  100 . 
     For example, as illustrated in  FIG.  2   - FIG.  4   , the cover  10   a  further includes a first sealing position PS 1  and a second sealing, position PS 2 , the first sealing position PS 1  is configured to be provided with a first sealing ring  1011   s  therein, the second sealing position PS 2  is configured to be provided with a second sealing ring  1012   s  therein, and the first sealing position PS 1  and the second sealing position PS 2  are located on the side surface S 0 . 
     For example, as illustrated in  FIG.  2   - FIG.  4   , the first drain outlet  1001  is located between the first sealing position PS 1  and the second sealing position PS 2 , 
     For example, as illustrated in  FIG.  6   , the cover  10   b  further includes a first sealing groove  1011  and a second sealing groove  1012 , the first sealing groove  1011  is configured to receive a first sealing ring  1011   s , the second sealing groove  1012  is configured to receive a second sealing ring  1012   s , the first sealing groove  1011  and the second sealing groove  1012  are both located at the side surface S 0 . The first sealing groove  1011  and the first sealing ring  1011   s  form a first seal SL 1 , and the second sealing groove  1012  and the second sealing ring  1012   s  form a second seal SL 2 . 
     For example, as illustrated in  FIG.  6   , the first drain outlet  1001  is located  between the first sealing groove  1011  and the second sealing groove  1012 , 
     For example, the first sealing groove  1011  and the second sealing groove  1012  form a sealing groove  101 . The first sealing ring  1011   s  and the second sealing ring  1012   s  forms the first sealing structure  101   s.    
     For example, the drain channel  1000  is configured to flow fluid there(trough in the case of failure of a part of the first sealing structure  101 . 
     For example, as illustrated in  FIG.  3   ,  FIG.  6    and  FIG.  7   , the drain channel  1000  is not in communication with the main flow channel  1021  and is not in communication with the subsidiary flow channel  1022 . 
     For example, as illustrated in  FIG.  3   ,  FIG.  6    and  FIG.  7   , the first drain outlet  1001  is located at a side of the side surface S 0  close to the end surface S 1  of the first end E 1   
     For example, as illustrated in  FIG.  4    and  FIG.  7   .  FIG.  9   , the fluid end further includes a valve casing  70 . The valve casing  70  includes an inner chamber  07 . For example, as illustrated in  FIG.  8    and  FIG.  9   , the inner chamber  07  of the valve casing  70  includes a low pressure chamber  07   a , a pressure-alternating chamber  07   b  and a high pressure chamber  07   c.    
     For example, in the embodiment of the present disclosure, the pressure of the thud in the high pressure chamber  07   c  is greater than the pressure of the fluid in the low pressure chamber  07   a , and the pressure of the fluid in the pressure-alternating chamber  07   b  can change alternately. 
     As illustrated in  FIG.  7    and  FIG.  9   , the fluid end includes a nut  20 , and the nut  20  is in a threaded connection with the valve casing  70 . 
     As illustrated in  FIG.  6   , one end (second drain outlet  1002 ) of the drain channel  1000  is formed by perforating the end surface  52  of the cover, and the other end (first drain outlet  1001 ) of the drain channel  1000  formed by perforating a circumference of the cover. The first drain outlet  1001  is located between the two seals (the first seal SL 1  and the second seal SL 2 ). When the first seal SL 1  fails, fluid leakage occurs, and the annular chamber between the valve casing  70  and the cover  10  will be filled with fluid, and then the fluid will flow to the gap between the cover  10  and the nut  20  along the drain channel  1000 . When a certain amount of fluid is accumulated, it will flow out along the outer circumference (at screw thread) or inner hole of the nut  20 . At this time, it is observed that there is fluid  leakage, indicating, that the first seal SL 1  has failed. Thus, the operator will judge the use condition of the first seal SL 1  according to whether there is fluid leakage herein, so as to react in time when the first seal SL 1  fails, while failure to react in time may cause the high pressure fluid to plunge into the low pressure fluid after the second seal SL 2  fails, resulting in crosstalk in pressure and equipment damage. 
     For example, as illustrated in  FIG.  2    and.  FIG.  7   , the cover  10  further includes a valve-seat groove  1013  the valve-seat groove  1013  is located at the first end E 1  and is communicated with the main flow channel  1021 , and the valve-seat groove  1013  has a relief groove  1013   a  at a side of the valve-seat groove  1013  away from the first end E 1  for reducing stress concentration. 
     For example, in order to facilitate disassembly and assembly of the cover during maintenance, the cover  10  further includes a pulling hole  1003 , the pulling hole  1003  is located at the second end E 2  of the body  100 . The pulling hole  1003  is not communicated with the second drain outlet  1002  and is not communicated with the drain channel  1000 . For example, the pulling hole  1003  is located on the axis of the body  100 . 
     For example, as illustrated in  FIG.  2   - FIG.  4   ,  FIG.  6   - FIG.  7    and  FIG.  9   , flow channels (main flow channel  1021 , subsidiary flow channels  1022 ) and the drain channel  1000  are provided at the inner side of than cover  10 , the pulling hole  1003  and the valve-seat groove  1013  are provided at the end surface of the covet  10 , and a sealing groove can be provided at the circumference of the cover  10 . Low pressure fluid flows in the flow channels, and the main flow channel  1021  and the subsidiary flow channels  1022  are intersected. The axis of the main flow channel  1021  (the center line L 1  of the main flow channel  1021 ) coincides with the axis of the cover  10 , and the subsidiary flow channels  1022  are evenly distributed in the circumferential direction of the cover. The bottom of the valve-seat groove  1013  is flat, the side surface of the valve-seat groove  1013  is conical, the root of the valve-seat groove  1013  is provided with a relief groove  1013   a  to reduce stress concentration, and the corresponding valve seat is also provided with a conical surface to match and fix with the valve-seat groove  1013 . 
     For example, in some embodiments, as illustrated in  FIG.  2    and  FIG.  3   , the sealing groove is not provided on the left side of the cover of the fluid end, the sealing groove  is provided on the valve casing, and the circumference of the cover  10  is in interference fit with the sealing element to avoid crosstalk in pressure of the high and low pressure fluids. As illustrated in  FIG.  8    and  FIG.  9   , after the cover  10  is worn by the sealing element (the first sealing ring  1011   s  and the second sealing ring  1012   s ), the cover can be replaced to reduce the cost of maintenance. It should be noted that, as illustrated in  FIG.  6   , a sealing groove  101  can also be provided on the left side of the cover, which is not limited to the case that the sealing groove is provided on the valve casing  70 .  FIG.  8    illustrates the sealing groove  1018  and the sealing groove  1019  in the valve casing  70 . As illustrated in  FIG.  7    and  FIG.  8   , the first sealing ring  1011   s  is arranged in the sealing groove  1018 , and the second sealing ring  1012   s  is arranged in the sealing groove  1019 . 
     The cover  10  provided by the embodiment of the present disclosure includes at least one of the following beneficial effects, 
     (1) The cover integrates functions of the end plug, the flow channel, and the base seat, and integrates multiple functions in itself, so that the entire structure of the fluid end is more compact and simple, and it can be fixed and limited by using the nut in the traditional fluid end. 
     (2) The cover is used as the base seat of the valve seat. When the valve seat is worn and needs to be replaced, it can be replaced with the cover as a whole, and other tools are not needed to pull it out again, so as to avoid lowering, the maintenance efficiency. After all, the maintenance time during fracturing operation is very short, and the maintenance efficiency on site can be greatly improved by using the whole replacement. 
     (3) The built-in drain channel of cover can be used to quickly and directly determine whether the seal is invalid, and prevent the equipment from being: damaged and prevent fracturing operation from being affected due to the crosstalk in pressure caused by untimely discovery of the invalid seal. 
     (4) The hollowed-out structure (flow channels) of the cover makes the low pressure fluid flow smoothly, and the fracturing fluid is generally sand-mixed fracturing and the risk of sand plugging can be reduced by the combined use of the plurality of subsidiary flow channels and the large-aperture main flow channel. 
     The embodiment of the present disclosure further provides a fluid end, which  includes any one of the covers  10  mentioned above. 
     The inner chamber of the valve casing of the fluid end provided by the embodiment of the present disclosure has a T-shaped structure, and the intersection position is designed in a “bell mouth” form, so that the problem of stress concentration at the intersection line of the inner chamber is alleviated. The valve casing  70  can be referred to as a T-shaped valve casing. 
     For example, as illustrated in  FIG.  8    and  FIG.  9   , the cover  10  is located in the low pressure chamber  07   a , the inner chamber  07  of the valve casing  70  has an inverted T-shaped structure, the pressure-alternating chamber  07   h  and the low pressure chamber  07   a  are arranged along the extending direction of the first axis A 1  of the inner chamber  07 , the pressure-alternating chamber  07   b  and the high pressure chamber  07   c  are arranged along the extending direction of the second axis A 2  of the inner chamber  07 , and the first axis A 1  intersects with the second axis A 2 . The embodiment of the present disclosure is illustrated by taking that the first axis A 1  is perpendicular to the second axis A 2  as an example. 
       FIG.  8    illustrates the first axis A 1  and the second axis A 2  of the inner chamber  07 . As illustrated In  FIG.  8   , the inner chamber  07  includes a horizontal chamber  0701  and a vertical chamber  0702 . 
     For example, as illustrated in  FIG.  8    and  FIG.  9   , the inner chamber of the valve casing  70  has a T-shaped structure. According to the installation positions of the first valve assembly and the second valve assembly, the inner chamber  07  is divided into a low pressure chamber  07   a , a pressure-alternating chamber  07   b , and a high pressure chamber  070 . The intersection position of the inner chamber  07  is designed a in a “bell mouth” form with smooth transition, which can effectively alleviate the stress concentration effect. 
     Compared with the valve casing of a traditional fluid end, the structure of the valve casing of the fluid end provided by the embodiment of the present disclosure has the following characteristics. 
     1) The stress concentration effect in the inner chamber is obviously alleviated. 
     The inner chamber with the cross intersection structure is illustrated in  FIG.  1 C , and the intersection position includes position Pa, position Pb, position Pc, and position Pd. The stress concentration points are at position Pc and position Pd, the stress concentration  is very obvious from the mechanical analysis, and fatigue cracks are easy to occur, leading to cracking of the valve casing. 
     There is no right angle at the intersection position of the inner chamber of the valve casing of the fluid end provided by the embodiment of the present disclosure, the transition of the intersection position of the inner chamber is smooth, the optimized design is carried out at the position where stress concentration is most likely to occur, the intersection position is in the shape of a bell mouth, there is no stress concentration point, and the stress concentration effect is obviously alleviated from the mechanical analysis. 
     2) The structure is simple and the sealing performance is strong. 
     The valve casing in a traditional fluid end has a separated structure, and the packing chamber, the suction chamber (low pressure chamber), and the discharge chamber (high pressure chamber) need to be fastened to the body of the valve casing with bolts. This structure is rather complicated and needs a variety of seals for sealing, which virtually increases many leakages. The higher the machining accuracy of sealing surfaces and the more the sealing surfaces, the more the working hours being needed, and the lower the machining efficiency, and finally the sealing cannot be fully guaranteed. 
     The valve casing of the fluid end provided by the embodiment of the present disclosure has an integral structure, which is tightly sealed and has high pressure resistant, uses fewer seals and does not need bolts, has a simple and compact structure, and has low risk of puncture leakage of the valve casing. 
     3) Maintenance is convenient. 
     In a traditional fluid end, the axis of the plunger is not collinear with the axis of the valve casing, and the plunger cannot lie pulled out from the suction side. When the plunger is damaged or the packing assembly needs to be replaced, the whole fluid end needs to be disassembled. Because the fluid end is heavy, the crane will be used to assist in this process, which greatly reduces the maintenance efficiency. During the actual fracturing operation, the employer will not leave a long time to replace the assembly parts. In some traditional fluid ends, although the axis of the plunger is collinear with the axis of the horizontal chamber of the valve casing, there are many inconveniences in maintenance. For example, when maintaining the plunger or packing assembly, the plunger has a large diameter  and cannot be pulled out from the inner chamber of the valve casing. The whole fluid end needs to be disassembled for maintenance. Even if the plunger has a small diameter and can be pulled out from the inner chamber of the valve casing, the suction side also needs to be disassembled before maintenance can be carried out. 
     The fluid end provided by the embodiment of the present disclosure does not have the above-mentioned problem of inconvenient maintenance, the axis of the plunger coincides with the first axis (horizontal axis) of the valve casing, the suction side is provided with a nut, and the axis of the nut coincides with the axis of the plunger, so the maintenance can be carried out according to the routine operation of the well site. 
     For example, the most efficient routine operation of maintaining the plunger or packing assembly on the well site is: disassembling the nut on the suction side, opening the horizontal chamber of the valve casing, disassembling the clamp, “disconnecting” the fluid end from the power end, pulling the plunger out from the suction side along the axis of the horizontal chamber of the valve casing by using a pulling tool, and carrying out normal maintenance; and after maintenance, reversing the operations according to the above actions to restore the assembly parts. The fluid end does not need to be disassembled from the plunger pump in the whole maintenance process. 
     For example, as illustrated in  FIG.  4    and  FIG.  7   - FIG.  9   , the valve casing  70  has an inlet hole  700 , and the inlet hole  700  and the high pressure chamber  07   c  are staggered in-the extending direction of the first axis A 1 . 
     For example, as illustrated in  FIG.  4    and  FIG.  9   , the fluid end further includes a first valve assembly V 1 , and the first valve assembly V 1  is configured to be opened to communicate the low pressure chamber  07   a  with the pressure-alternating chamber  07   b  or configured to be closed to separate the low pressure chamber  07   a  from the pressure-alternating chamber  07   b.    
     For example, as illustrated in  FIG.  4    and  FIG.  9   , the first valve assembly V 1  includes a valve body  1   a,  a sealing element  1   b  (playing a role of sealing), a valve seat  1   c , a spring  1   d,  and a spring bracket le. 
     For example, as illustrated in  FIG.  4    and  FIG.  9   , the sealing element  1   b  is embedded in the valve body in when the first valve assembly V 1  is opened, the valve body   1   a  embedded with the sealing element  1   b  moves to the left, and the low pressure chamber  07   a  and the pressure-alternating chamber  07   b  are communicated with each other. 
     As illustrated in  FIG.  5   , the spring bracket  1   e  has a hollowed-out structure, includes a main body e 1  and a hollowed-out structure e 0 , and is limited with the valve casing  70  by an inclined surface S 01 . The spring bracket le having the hollowed-out structure e 0  is beneficial to smoothing fluid passage, and is limited by the inclined surface S 01 , so as to prevent the spring, bracket  1   e  from shaking in the horizontal chamber of the valve casing  70 . Correspondingly, the horizontal chamber of the valve casing is also provided with an inclined surface to match with the inclined surface of the spring bracket  1   e , and the spring bracket  1   e  is in contact with the valve casing  70  through the inclined surface. 
     For example, as illustrated in  FIG.  9   , the fluid end further includes a second valve assembly V 2 , and the second valve assembly V 2  is configured to be opened to communicate the pressure-alternating chamber  07   b  with the high pressure chamber  07   c  or configured to be closed to separate the pressure-alternating chamber  07   b  from the high pressure chamber  07   c.    
     For example, as illustrated in  − PIG.  9 , the second valve assembly V 2  includes a valve body  2   a , a sealing element  2   b  (playing a role of sealing), a valve seat  2   c , a spring  2   d , and a base seat  2   f.    
     For example, as illustrated in  FIG.  9   , the sealing element  2   b  is embedded in the valve body  2   a . When the second valve assembly V 2  is opened, the valve body  2   a  embedded with the sealing element  2   b  moves upward, and the high pressure chamber  07   c  and the pressure-alternating chamber  07   b  are communicated with each other. 
     As illustrated in  FIG.  9   , the second valve assembly V 2  is close to a discharge hole  7005 , and is opened when the plunger moves forward, so as to flow high pressure fluid; the first valve assembly V 1  is close to the inlet hole  700 , and is opened when the plunger moves back, so as to flow low pressure fluid; the base seat  2   f  of the second valve assembly V 2  is directly embedded in the valve casing  70 , and the hardness of the base seat  2   f  is higher than the hardness of the valve casing  70 , which can prevent the valve casing  70  from being damaged during opening and closing (lapping) of the second valve assembly V 2  and prolong the service life of the valve casing  70 .  
     For example, as illustrated in  FIG.  8   , the intersection position  7006  of the inner chamber  07  of the valve casing  70  is formed into a bell mouth shape by machining. For example, the bell mouth shape can be machined by means of boring, but it is not limited to this case. 
     For example, as illustrated in  FIG.  8    and  FIG.  9   , the intersection position of the inner chamber  07  includes a first sub-chamber  071  and a second sub-chamber  072 , the first sub-chamber  071  and the second sub-chamber  072  are arranged along the extending direction of the second axis A 2 . The second sub-chamber  072  is closer to the portion (horizontal chamber) of the inner chamber  07  extending along the first axis A 1  than the first sub-chamber  071  is. In order to alleviate stress concentration, the maximum size h 2  of the second sub-chamber  072  in the extending direction of the second axis A 2  is greater than the maximum size h 1  of the first sub-chamber  071  in the extending direction of the second axis A 2 . The second valve assembly V 2  is not placed in the first sub-chamber  071  or the second sub-chamber  072 . The second valve assembly V 2  is located at the outer side of the first sub-chamber  071  and the second sub-chamber  072 . The first sub-chamber  071  and the second sub-chamber  072  can be empty cavities only for flowing fluid. For example, as illustrated in  FIG.  8    and  FIG.  9   , the second valve assembly V 2  and the second sub-chamber  072  are located on opposite sides of the first sub-chamber  071 . 
     For example, as illustrated in  FIG.  8    and  FIG.  9   , in order to alleviate stress concentration, the size D 1  of the second sub-chamber  072  in the extending direction of the first axis A 1  gradually increases in a direction from a position away from the first axis A 1  to a position close to the first axis A 1 . 
     For example, the portion of the valve casing  70  for forming the second sub-chamber  072  has an included angle of 0-80 degrees with the first axis A 1 . Further, for example, the portion of the valve casing  70  for forming the second sub-chamber  072  has an included angle of 30-60 degrees with the first axis A 1 . 
     For example, as illustrated in  FIG.  9   , the first sub-chamber  071  is a cylindrical chamber, but it is not limited to this case. For example, as illustrated in  FIG.  9   , the second sub-chamber  072  is a truncated cone chamber, but it is not limited to this case. 
     For example, as illustrated in  FIG.  9   , the valve casing  70  is provided with a  protective sleeve  73  at the positions corresponding to the first sub-chamber  071  and the second sub-chamber  072 . There is a protective sleeve  73  at the “bell mouth” position of the inner chamber  07  of the valve casing  70  to protect the inner chamber  07  and prolong the service life of the valve casing  70 . 
     For example, as illustrated in  FIG.  9   , the cover  10  has a revolving structure, which is horizontally placed inside the valve casing  70 , with the left side in contact with the first valve assembly V 1  and the right side in contact with the nut  20 . The nut is screwed with the valve casing  70 . 
     For example, as illustrated in  FIG.  9   , the fluid end includes a plunger  81 . The plunger  81  is a revolving body, one end of the plunger  81  is in contact with the fluid in the valve casing  70  and reciprocates, and the other end of the plunger  81  is connected to the power end of the plunger pump through a clamp  86 . For example, as illustrated in  FIG.  9   , the fluid end further includes a plunger side  70   c.    
     For example, as illustrated in  FIG.  8   , the inner chamber  09  further includes a plunger chamber  07   d , and the plunger chamber is configured to place the plunger  81 . The plunger chamber  07   d , the pressure-alternating chamber  07   b , and the low pressure chamber  07   d  are arranged in sequence along the extending direction of the first axis A 1  of the inner chamber  07 . 
     For example, in the embodiment of the present disclosure, the extending direction of the first axis A 1  can be the arrangement direction of the pressure-alternating chamber  07   b  and the low pressure chamber  07   a , or the extending direction of the first axis A 1  can be the arrangement direction of the plunger chamber  07   d , the pressure-alternating chamber  07   b , and the low pressure chamber  07   a . For example, in the embodiment of the present disclosure, the extending direction of the second axis A 2  can be the arrangement direction of the high pressure chamber  07   c  and the pressure-alternating chamber  07   b.    
     For example, as illustrated in  FIG.  9   , the fluid end further includes a packing assembly  82 , and the packing assembly  82  includes a package  821 , a spacer ring  822 , and a press ring  823 . 
     For example, as illustrated in  FIG.  9   , the package  821  includes three packing rings. Of course, the number of packing rings is not limited to that illustrated in the figure,  but can be determined as needed. For example, the material of the packing ring includes rubber, but is not limited to this case. 
     For example, as illustrated in  FIG.  9   , the plunger side of the valve casing, is provided with a lubricating oil passage  7007  for lubricating the package  821  (rubber element), so as to make the reciprocating motion of the plunger  81  smoother; the circumference of the plunger  81  is wrapped by the package  821 , the package  821  plays a role of sealing to prevent fluid leakage when the plunger  81  reciprocates. 
     For example, as illustrated in  FIG.  9   , the inner wall of the package  821  is in interference fit with the plunger  81 , which plays a role of sealing; when the plunger  81  reciprocates, it rubs against the inner wall of the package  821 , and the forced lubrication here can reduce the friction. 
     For example, the front end of the plunger  81  is provided with a pulling hole (bolt hole), which is matched with a pulling tool. During, maintenance, the clamp  86  is firstly disassembled and the plunger  81  is disconnected from the power end, and the plunger  81  is pulled out from the suction side  70   a  along the first axis A 1  of the valve casing  70  by the pulling tool. 
     For example, as illustrated in  FIG.  9   , the fluid end further includes a packing nut  83 , and the packing nut  83  is configured to press the packing assembly  82 . 
     For example, as illustrated in  FIG.  9   , the fixing of the package  821  is reinforced by the packing nut  83 , and the packing nut:  83  is in a threaded connection with the valve casing  70 . The functions of the packing, nut  83  include: preventing the package  821  from moving axially when the plunger  81  reciprocates, and expanding the package  821  by screwing and squeezing, which is beneficial to sealing. The spacer ring  822  and the press ring  823  are provided at both ends of the package  821 , respectively. The spacer ring  822  isolates the package  821  from the valve casing  70 , and the press ring  823  isolates the package  821  from the packing nut  83 , thus protecting the package  821  and prolonging the service life of the package  821 . For example, the spacer ring  822  and the press ring  823  can be metal pieces. 
     For example, as illustrated in  FIG.  9   , the fluid end further includes a packing sleeve  84  and a packing-sleeve nut  85 , the plunger chamber  07   d  is configured to place the plunger  81 , the packing sleeve  84  is located between the packing assembly  82  and the valve  casing  70 , and the packing-sleeve nut  85  is configured to press the packing sleeve  84 , 
     For example, as illustrated in  FIG.  9   , the packing sleeve  84  is axially limited by a shoulder and the packing-sleeve nut  85 . 
     For example, as illustrated in  FIG.  9   , at least one of the packing sleeve  84  and the packing-sleeve nut  85  is in a welded connection with the valve casing  70 . 
     For example, as illustrated in  FIG.  9   , the hardness of the packing sleeve  84  is greater than the hardness of the valve casing  70 . Because the hardness of the packing sleeve  84  is greater than the hardness of the valve casing  70 , when the valve casing  70  is damaged, the packing; sleeve  84  will not be damaged, so the packing sleeve  84  and the valve casing  85  can be fixed by welding. 
     For example, as illustrated in  FIG.  9   , the outer circumference of the package  621  is in contact with the packing sleeve  84 , and the inner circumference of the package  821  is in contact with the plunger  81 . The front end of the packing sleeve  64  is provided with a sealing element  7008  to avoid fluid leakage and damage to the valve casing caused by high pressure fluid entering the gap. The packing sleeve  84  is a wear-resistant element, which is in interference fit with the valve casing  70 . The hardness of the packing sleeve  84  is greater than the hardness of the valve casing. The packing sleeve  84  is provided to prevent the valve casing  70  from being damaged due to the rubbing of the package  821 , thus prolonging the service life of the valve casing. 
     For example, as illustrated in  FIG.  9   , the inner and outer circumferences of the packing-sleeve nut  85  are provided with threads, the outer threads of the packing-sleeve nut  85  are matched with the valve casing  70 , and the inner threads of the packing-sleeve nut  85  are matched with the packing nut  83 . To prevent the packing-sleeve nut  85  from loosening, when the plunger  81  reciprocates, the packing-sleeve nut  85  can be fixed with the valve casing  70  by welding. 
       FIG.  9    further illustrates a discharge side  70   b  of the fluid end. The suction side  70   a  of the valve casing  70  is provided with an inlet hole  700 , and the discharge side  70   b  is provided with a discharge hole  7005 . For example, the inlet hole  700  is connected with the inlet manifold, and low pressure fluid flows inside; the discharge hole  7005  is connected with the discharge flange, and high pressure fluid flows inside.  
       FIG.  9    further illustrates the body  77  of the valve casing  70  The valve casing  70  includes a body  77  and an inner chamber  07 . 
     For example, as illustrated in  FIG.  8    and  FIG.  9   , the valve casing  70  is provided with suction side threads  7001 , discharge side threads  7002 , and plunger side threads  7003 . The nut  20  is connected with the valve casing  70  through the suction side threads  7001 . The nut  50  is connected with the valve casing  70  through the discharge side threads  7002 . The packing-sleeve nut  85  is connected with the valve casing  70  through the plunger side threads  7003 . 
     For example, as illustrated in  FIG.  9   , the first valve assembly V 1  and the second valve assembly V 2  are both unidirectional valves. For example, as illustrated in  FIG.  9   , the first valve assembly V 1  and the second valve assembly V 2  can be interchanged. For example, the second valve assembly V 2  is placed vertically, the first valve assembly V 1  is placed horizontally, and the axial directions of the first valve assembly V 1  and the second valve assembly V 2  are perpendicular to each other. 
     As illustrated in  FIG.  4    and  FIG.  9   , for the first valve assembly V 1 , the valve seat  1   c  is arranged in the valve-seat groove  1013  of the cover  10 , and the left side of the cover  10  serves as the base seat of the valve seat  1   c  and is configured to fix the valve seat  1   c . For example, the cover  10  cooperates with the valve body  1   a , the sealing element  1   b , the spring  1   d,  and the spring bracket le to form a unidirectional valve. For example, the axis of the first valve assembly V 1  coincides with the axis of the cover W. When the plunger moves back, the valve body  1   a  is opened, and the low pressure fluid enters the valve casing  70 ; when the plunger moves forward, the valve body  1   a  is closed, preventing the low pressure fluid from entering the valve casing  70 . 
     For example, referring to  FIG.  9   , taking the fluid entering the fluid end as fracturing fluid as an example, the working principle of the fluid end is as follows. 
     During fluid suction, the plunger  81  moves back (moves to the left in a translation way), the first valve assembly V 1  is opened, the second valve assembly V 2  is closed, and the fracturing fluid flows into the pressure-alternating chamber  07   b  from the suction manifold through the inlet hole  700 , the subsidiary flow channel  1022 , and the main flow channel  1021  until the pressure-alternating chamber  07   b  is full of fracturing fluid; at this  time, the fluid in the inner chamber  07  is low pressure fluid. 
     During fluid discharge, the plunger S 1  moves forward (moves to the right in a translation way), the first valve assembly V 1  is closed, the second valve assembly V 2  is opened, and the fracturing fluid flows into the high pressure chamber  07   c  from the pressure-alternating chamber  07   b  and is discharged through the discharge hole  7005 ; at this time, the fluid in the inner chamber  07  is high pressure fluid. 
     The fluid end provided by the embodiment of the present disclosure has at least one of the following effects. 
     1) The stress concentration effect in the inner chamber is obviously alleviated. 
     There is no right angle at the intersection position of the inner chamber of the valve casing in the fluid end provided by the embodiment of the present disclosure, the transition of the intersection position of the inner chamber is smooth, the design in shape is carried out at the position where stress concentration is most likely to occur, the intersection position is in the shape of a bell mouth, there is no stress concentration point, and the stress concentration effect is obviously alleviated from the mechanical analysis. 
     2) The structure is simple and the sealing performance is strong. 
     The valve casing in the fluid end provided by the embodiment of the present disclosure has an integral structure, which is tightly sealed, and has high pressure resistant, uses fewer seals and does not need bolts, has a simple and compact structure, and has low risk of puncture leakage of the valve casing. 
     3) Maintenance is convenient. 
     According to the fluid end provided by the embodiment of the present disclosure, the axis of the plunger coincides with the first axis (horizontal axis) of the valve casing, the suction side is provided with a nut (the axis of the nut coincides with the axis of the plunger, and the nut is detachable), and the maintenance can be carried out according to the routine operation of the well site. 
     The embodiment of the present disclosure further provides a plunger pump, which includes any one of the fluid ends described above. Because the cover  10  is located at the suction side  70   a  of the fluid end, the cover  10  can also be referred to as a suction cover. 
     For example, the cover  10 , and the fluid end and the plunger pump which  include the cover  10 , can be applied to fracturing/cementing equipment in oil and gas fields. 
     The embodiment t of the present disclosure provides a fluid end with two sets of pressure bearing assemblies at the suction side and a plunger pump including the fluid end, thus being beneficial to maintaining and prolonging the service life of the valve casing. 
     The fluid end and the plunger pump provided by the embodiment of the present disclosure are introduced below. 
       FIG.  10    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure.  FIG.  11    is a cross-sectional view of a fluid end provided by an embodiment of the present disclosure.  FIG.  12 A  is a partial view of a drain channel in a valve casing of  FIG.  11   .  FIG.  12 B  is a partial view of a packing sleeve and a packing-sleeve nut in the valve casing of  FIG.  11   .  FIG.  13    is a schematic diagram of respective regions of an inner chamber in a valve casing of a fluid end provided by an embodiment of the present disclosure.  FIG.  14    is a schematic diagram of a valve casing in a fluid end provided by an embodiment of the present disclosure.  FIG.  15    is a perspective view of a fluid end provided by an embodiment of the present disclosure.  FIG.  16    is a schematic diagram of a valve casing in another fluid end provided by an embodiment of the present disclosure.  FIG.  17    is a schematic diagram of an intersection position of an inner chamber of a valve casing in a fluid end provided by an embodiment of the present disclosure.  FIG.  17 ( a )  is a cross-sectional view of the XV plane of the inner chamber of the valve casing.  FIG.  17  ( b )  is a schematic diagram of the YZ plane of the inner chamber of the valve casing.  FIG.  18    is a schematic diagram of an intersection position of an inner chamber of a valve casing in another fluid end provided by an embodiment of the present disclosure.  FIG.  18 ( a )  is a cross-sectional view of the XV plane of the inner chamber of the valve casing.  FIG.  18 ( b )  is a schematic diagram of the YZ plane of the inner chamber of the valve casing.  FIG.  15    illustrates the X direction, the V direction and the Z direction. For example, the X direction is the extending direction of the first axis A 1  mentioned later, and the direction is the extending direction of the second axis A 2  mentioned later. 
     For example, the valve casing illustrated in  FIG.  8    is the valve casing in the fluid end illustrated in  FIG.  9   . For example, the valve casing illustrated in  FIG.  13    is the valve casing in the fluid end illustrated in  FIG.  10   . For example, the valve casing illustrated  in.  FIG.  14    is the valve casing in the fluid end illustrated in  FIG.  11   . 
     The fluid ends illustrated in  FIG.  10    and  FIG.  11    both include T-shaped valve casings. The inner chamber of the T-shaped valve casing is T-shaped. The fluid end illustrated in  FIG.  10    includes one set of pressure bearing assembly, while the fluid end illustrated in  FIG.  11    includes two sets of pressure bearing assemblies. 
     As illustrated in  FIG.  11   , the embodiment of the present disclosure provides a fluid end, which includes: a valve casing  70 , a first valve assembly V 1 , a first pressure bearing assembly M 1 , and a second pressure bearing assembly M 2 . 
     As illustrated in  FIG.  10   ,  FIG.  11   ,  FIG.  13    and  FIG.  14   , the valve casing  70  includes an inner chamber  07 , and the inner chamber  07  includes a pressure-alternating chamber  07   b  and a low pressure chamber  07   a.    
     As illustrated in  FIG.  10   ,  FIG.  11    and  FIG.  13   , the first valve assembly V 1  is configured to be opened to communicate the low pressure chamber  07   a  with the pressure-alternating chamber  07   b  or configured to be closed to separate the low pressure chamber  07   a  from the pressure-alternating chamber  07   b.    
     As illustrated in  FIG.  11   , the first pressure bearing assembly M 1  is in contact with the first valve assembly V 1 . 
     As illustrated in  FIG.  1   , the second pressure bearing assembly M 2  and the first: pressure bearing assembly M 1  are arranged in sequence along the extending direction of the first axis A f of the inner chamber  07 . 
     As illustrated in  FIG.  11   , the first valve assembly V 1 , the first pressure bearing assembly M 1  and the second pressure bearing assembly M 2  are sequentially arranged along the extending direction of the first axis A 1  of the inner chamber  07 . 
       FIG.  11    and  FIG.  15    illustrate the suction side  70   a , the discharge side  70   b , and the plunger side  70   c  of the fluid end. 
     In the fluid end provided by the embodiment of the present disclosure, two sets of pressure bearing assemblies are arranged at the suction side  70   a , that is, the first pressure bearing assembly M 1  and the second pressure bearing assembly M 2  are arranged. The first valve assembly V 1  is connected with the valve casing  70  through the first pressure bearing assembly M 1 , instead of directly sitting on the valve casing  70 . The first valve  assembly V 1  is not in direct contact with the valve casing, which is convenient for maintenance and beneficial to prolonging the service life of the valve casing. 
     For example, as illustrated in  FIG.  11   , the first pressure bearing assembly M 1  is detachably connected with the valve casing  70 , and the second pressure bearing assembly M 2  is detachably connected with the valve casing  70 , so as to facilitate disassembling the plunger  81  from the suction side  70   a.    
     For example, as illustrated in  FIG.  11   , the first pressure bearing assembly M 1  includes a pressure-alternating cover  13  and a pressure-alternating: nut  23 , the pressure-alternating cover  13  is closer to the first valve assembly V 1  than the pressure-alternating nut  23  is, and the pressure-alternating nut  23  is in a threaded connection with the valve casing  70 . 
     For example, the pressure-alternating cover  13  bears an alternating load, and the pressure-alternating nut  23  bears an alternating load. The pressure-alternating cover  13  can also be referred to as an intermediate cover or directly referred to as a cover, and the pressure-alternating nut  23  can also be referred to as an intermediate nut or directly referred to as a nut. 
     For example, as illustrated in  FIG.  11   , the maximum length of the pressure-alternating cover  13  on the first axis A 1  is less than the maximum length of the pressure-alternating nut:  23  on the first axis A 1 . 
     In the fluid end provided by the embodiment of the present disclosure, the first valve assembly V 1  is not directly seated on the valve casing  70 , but indirectly connected with the valve casing  70  through the pressure-alternating cover  13 . The pressure-alternating cover  13  will move under force, so it is necessary to use the pressure-alternating nut  23  for fixing and limiting. For example, the pressure-alternating nut  23  is in contact with the pressure-alternating cover  13 , and the pressure-alternating nut  23  and the valve casing  70  are fastened by threads, which is not limited to this case. When the pressure-alternating cover  13  is subjected to an alternating load, the load will be transferred to the threads of the pressure-alternating nut  23 . Because the contact area between the pressure-alternating cover  13  and the pressure-alternating nut  23  is small and the threads of the pressure-alternating nut  23  is long, the stress at the threads of the pressure-alternating nut  23  is less than the stress at  the threads of the nut of the traditional fluid end through finite element analysis. The fluid end provided by the embodiment of the present disclosure can prolong the service life of the valve casing  70 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 A , a first sealing structure SE is provided between the pressure-alternating cover  13  and the valve casing  70 , the valve casing  70  has a drain channel  7000 , and the drain channel is configured to flow fluid therethrough in the case of failure of a part of the first sealing structure SE. 
     For example, as illustrated in  FIG.  11    and  FIG.  12 A , the drain channel  7000  penetrates the body  100  of the valve casing  70 . The drain channel  7000  penetrates into the inner chanter  07  from the outer side of the body  77  of the valve casing. 
     For example, as illustrated in  FIG.  11    and  FIG.  12 A , in order to facilitate manufacturing and make the valve casino, have high strength, the drain channel  7000  is obliquely arranged with respect to the first axis A 1  of the inner chamber  07 , and the acute angle θa formed by the drain channel  7000  and the first axis A 1  of the inner chamber  07  is greater than or equal to 30 degrees and less than or equal to 60 degrees. 
     For example, as illustrated in  FIG.  11   , the end of the drain channel  7000  that is away from the inner chamber  07  is closer to the suction side  70   a  than the end of the drain channel  7000  that is close to the inner chamber  07 . That is, as illustrated in  FIG.  11   , the end of the drain channel  7000  that is away from the inner chamber  07  is further to the right than the end of the drain channel  7000  that is close to the inner chamber  07 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 A , the first sealing structure SE includes a first seal SE 1  and a second seal SE 2 , and one, end of the drain channel  7000  close to the pressure-alternating cover  13  is located between the first seal SE 1  and the second seal SE 2  For example, the first seal SE 1  includes a sealing ring, and the second seal SE 2  includes a sealing ring. 
     As illustrated in  FIG.  10    and  FIG.  11   , the sealing groove of the first sealing structure SE is provided in the pressure-alternating cover  13 . In some other embodiments, the sealing groove of the first sealing structure SE can also be provided in the valve casing  70 . 
     For example, as illustrated in  FIG.  10    and  FIG.  11   , the first valve assembly V 1  includes a valve body  1   a,  a sealing element  1   b , and a valve seat  1   c,  and the  pressure-alternating cover  13  serves as the base seat of the valve seat  1   c.    
     For example, as illustrated in  FIG.  10    and  FIG.  11   , the first valve assembly V 1  further includes a spring  1  and a spring bracket  1   e.    
     For example, as illustrated in  FIG.  11   , the spring bracket  1   e  includes a hollowed-out structure e 0 , and is limited with the valve casing  70  by an inclined surface S 01 . The spring bracket  1   e  with the hollowed-out structure e 0  is beneficial to smoothing fluid passage, and is limited by the inclined surface  501 , so as to prevent the spring bracket  1   e  from shaking in the horizontal chamber of the valve casing  70 . Correspondingly, the horizontal chamber of the valve casing is also provided with an inclined surface to match with the inclined surface of the spring bracket  1   e , and the spring bracket  1   e  is in contact with the valve casing  70  through the inclined surface. 
     For example, as illustrated in  FIG.  11   , the sealing element  1   b  is embedded in the valve body  1   a.  When the first valve assembly V 1  is opened, the valve body  1   a  embedded with the sealing element  1   h  moves to the left, and the low pressure chamber  07   a  and the pressure-alternating chamber  07   b  are communicated with each other. 
     The first valve assembly V 1  of the fluid end illustrated in  FIG.  10    includes a base seat  1   f.  The pressure-alternating cover  13  in the fluid end illustrated in  FIG.  11    serves as the base seat of the first valve assembly V 1 . Moreover, the valve casing of the fluid end illustrated in  FIG.  11    is provided with a drain channel  7000 , while the valve casing of the fluid end illustrated in  FIG.  10    is not provided with a drain channel. 
     For example, as illustrated in  FIG.  10   ,  FIG.  11   ,  FIG.  13   ,  FIG.  14   , and  FIG.  16   , the valve casing  70  has an inlet hole  700 .  FIG.  10   ,  FIG.  11   ,  FIG.  13   , and  FIG.  14    illustrate a single-side inlet hole.  FIG.  16    illustrates dual-side inlet holes  700 : the inlet hole  700   a  and the inlet hole  700   b . The fluid feeding method of the valve casing  70  can be single-side fluid feeding or dual-side fluid feeding. For example, the single-side fluid feeding can meet the needs of the operation with small displacement and low sand ratio, and will not cause sand plugging; the dual-side fluid feeding can meet the needs of the operation with large displacement and high sand ratio, and dual-side inlet holes can ensure the stability of fluid feeding and reduce the risk of sand plugging. 
     For example, as illustrated in  FIG.  11   , the pressure-alternating cover  13  has a  low pressure fluid channel  130 , and the low pressure fluid channel  130  is communicated with the inlet hole  700  of the valve casing  70 . The low pressure fluid channel  130  can also be referred to as a first channel  130 . 
     For example, as illustrated in  FIG.  11   , the pressure-alternating nut  23  has a low pressure fluid channel  230 , and the low pressure fluid channel  130  is communicated with the inlet hole  700  of the valve casing  70 . The low pressure fluid channel  230  can also be referred to as a second channel  230 . 
     For example, as illustrated in  FIG.  11   , the second pressure bearing assembly M 2  includes a suction cover  33  and a suction nut  43 . The suction cover  33  is closer to the first pressure bearing assembly M 1  than the suction nut  43  is, and the suction nut  43  is in a threaded connection with the valve casing  70 . 
     For example, as illustrated in  FIG.  11   , the first pressure bearing, assembly M 1  and the second pressure bearing assembly M 2  are arranged on opposite sides of the inlet hole  700 , respectively. For example, as illustrated in  FIG.  11   , the first pressure bearing assembly MI and the second pressure bearing assembly M 2  are respectively arranged on both sides of the inlet hole  700  along the extending direction of the first axis A 1 . As illustrated in  FIG.  11    the first pressure bearing assembly M 1  is on the left side of the inlet hole  700 , and the second pressure bearing assembly M 2  is on the right side of the inlet hole  700 . 
     For example, as illustrated in  FIG.  11   , the pressure-alternating cover  13  and the suction cover  33  are arranged on opposite sides of the pressure-alternating nut  23 , respectively. For example, as illustrated in  FIG.  11   , the pressure-alternating nut  23  and the suction cover  33  are arranged on opposite sides of the inlet hole  700 , respectively. As illustrated in  FIG.  11   , the pressure-alternating nut  23  is arranged on the left side of the inlet hole  700 , and the suction cover  33  is arranged on the right side of the inlet hole  700 . 
     The first valve assembly V 1  of the fluid end illustrated in  FIG.  4    includes a base seat  1   f.  The pressure-alternating cover  13  in the fluid end illustrated in  FIG.  11    serves as the base seat of the first valve assembly V 1 , which makes the structure of the fluid end more compact. The base seat If illustrated in  FIG.  4    has a low pressure fluid channel  330 , and the low pressure fluid channel  330  is communicated with the inlet bole  700  of the valve casing  70 .  
     For example, as illustrated in  FIG.  10   ,  FIG.  1   ,  FIG.  13    and  FIG.  14   , the inner chamber  07  has an inverted T-shaped structure, the pressure-alternating chamber  07   b  and the high pressure chamber  07   c  are arranged along the extending direction of the second axis A 2  of the inner chamber  07 , and the first axis A 1  intersects with the second axis A 2 . Therefore, the fluid end includes an inner chamber  07  with an inverted T-shaped structure, and the valve casing  70  can be referred to as a T-shaped valve casing. The embodiment of the present disclosure is illustrated by taking that the first axis A 1  is perpendicular to the second axis A 2  as an example. 
     For example, as illustrated in  FIG.  11   , the fluid end further includes a second valve assembly V 2 , and the inner chamber  07  further includes a high pressure chamber  07   c . The second valve assembly V 2  is configured to be opened to communicate the pressure-alternating chamber  07   b  with the high pressure chamber  07   c  or configured to be closed to separate the pressure-alternating chamber  07   b  form the high pressure chamber  07   c.    
     For example, as illustrated in  FIG.  11   , the second valve assembly V 2  includes a valve body  2   a , a sealing element  2   b  (for sealing), a valve seat  2   c , a spring  2   d  and a base seat  2   f.    
     For example, as illustrated in  FIG.  1 . 1   , the sealing element  2   b  is embedded in the valve body  2   a . When the second valve assembly V 2  is opened, the valve body  2   a  embedded with the sealing element  2   b  moves upward, and the high pressure chamber  07   c  and the pressure-alternating chamber  07   b  are communicated with each other. 
     As illustrated in  FIG.  11   , the second valve assembly V 2  is close to a discharge hole  7005 , and is opened when the plunger moves forward, so as to flow high pressure fluid; the first valve assembly V 1  is close to the inlet hole  700 , and is opened when the plunger moves back, so as to flow low pressure fluid, the base seat  2   f  of the second valve assembly V 2  is directly embedded in the valve casing  70 , and the hardness of the base seat  2   f  is higher than the hardness of the valve casing  70 , which can prevent the valve casing  70  from being damaged during opening and closing (slapping) of the second valve assembly V 2  and prolong the service life of the valve casing  70 . 
     For example, as illustrated in  FIG.  11   , the fluid end further includes a third pressure bearing assembly M 3 , the third pressure bearing assembly M 3  is located in the inner  chamber, and the third pressure bearing assembly M 3  and the second valve assembly V 2  are sequentially arranged in the extending direction of the second axis A 2 . A region of the inner chamber  07  between the second valve assembly V 2  and the third pressure bearing assembly M 3  is the high pressure chamber  07   c.    
     As illustrated in  FIG.  11   , the third pressure bearing assembly M 3  includes a cover  40  and a nut  50 . The cover  40  can be referred to as a discharge cover  40 , and the nut  50  can be referred to as a discharge nut  50 . 
     For example, as illustrated in  FIG.  11   , the inlet hole  700  and the high pressure chamber  07   c  are staggered in the extending direction of the first axis A 1 . 
     For example, as illustrated in  FIG.  11    and  FIG.  14   , the intersection position of the inner chamber  07  includes a first sub-chanter  071  and a second sub-chamber  072 , the first sub-chamber  071  and the second sub-chamber  072  are arranged along the extending direction of the second axis A 2 . The second sub-chamber  072  is closer to the portion (horizontal chamber) of the inner chamber  07  extending along the first axis A 1  than the first sub-chamber  071  is. In order to reduce stress concentration, the maximum size h 2  of the second sub-chamber  072  in the extending direction of the second axis A 2  is greater than the maximum size h 1  of the first sub-chamber  071  in the extending direction of the second axis A 2 . The second valve assembly V 2  is not placed in the first sub-chamber  071  and the second sub-chamber  072 . The second valve assembly V 2  is located at the outer side of the first sub-chamber  071  and the second sub-chamber  072 . The first sub-chamber  071  and the second sub-chamber  072  can be empty cavities only for flowing fluid. 
     For example, as illustrated in  FIG.  11    and  FIG.  14   , in order to reduce stress concentration, the site D 1  of the second sub-chamber  072  in the extending direction of the first axis A 1  gradually increases in a direction from a position away from the first axis A to a position close to the first axis A 1  That is, the size D 1  of the second sub-chamber  072  in the extending direction of the first axis A 1  gradually increases from top to bottom. 
     For example, as illustrated in  FIG.  11    and  FIG.  14   , the portion of the valve casing  70  for forming the second sub-chamber  072  has an included angle of 30-80 degrees with the first axis A 1 . Further, for example, the portion of the valve casing  70  for forming the second sub-chamber  072  has an included angle of 30-60 degrees with the first axis A 1 .  
     For example, as illustrated in  FIG.  11   , the first sub-chamber  071  is a cylindrical chamber, but it is not limited to this case. For example, as illustrated in  FIG.  11   , the second sub-chamber  072  is a truncated cone chamber, but it is not limited to this case. 
     For example, as illustrated in  FIG.  11   , the valve casing  70  is provided with a protective sleeve  73  at the position corresponding to both the first sub-chamber  071  and the second sub-chamber  072 . There is a protective sleeve  73  at the “bell mouth” position of the inner chamber  07  of the valve casing  70  to protect the inner chamber  07  and prolong the service life of the valve casing  70 . 
     For example, as illustrated in  FIG.  11   , the intersection position  7006  of the inner chamber  07  of the valve casing  70  forms a bell mouth shape by machining. For example, the bell mouth shape can be machined by means of boring, but it is not limited to this case. 
     For example, as illustrated in  FIG.  4    and  FIG.  11   , a protective sleeve  73  is provided at the “bell mouth” position of the inner chamber of the valve casing  70  to prevent the inner chamber from being worn. After the inner chamber is worn, the roughness of the surface thereof will become larger, and coupled with high-pressure operation, the surface is prone to fatigue cracks. Therefore, the joint protection of “bell mouth” and protective sleeve  73  at the intersection position can reduce the risk of cracking and prolong the service life of valve casing. For example, the protective sleeve  73  can be installed at the inner side of the valve casing by means of cold installation, but it is not limited to cold installation, and the protective sleeve  73  can also be installed by means of machining or thermal processing. 
       FIG.  17    and  FIG.  18    illustrate the bell mouth  76 , the horizontal chamber  0701  and the body  77  of the valve casing  70 . 
     The inner chamber of the valve casing of the fluid end provided by the embodiment of the present disclosure has a T-shaped structure, and the intersection position is designed in a “bell mouth” form, so that the problem of stress concentration at the intersection line of the inner chamber is alleviated. 
     For example, as illustrated in  FIG.  11    and  FIG.  14   , the pressure-alternating cover  13  is located in the low pressure chamber  07   a , the pressure-alternating nut  23  is located in the low pressure chamber  07   a , the inner chamber  07  of the valve casing  70  has an inverted  T-shaped structure, the pressure-altercating chamber  07   b  and the low pressure chamber  07   a  are arranged along the extending direction of the first axis A 1  of the inner chamber  07 , the pressure-alternating chamber  07   b  and the high pressure chamber  07   c  are arranged along the extending direction of the second axis A 2  of the inner chamber  07 , and the first axis A 1  intersects with the second axis A 2 .  FIG.  14    illustrates the first axis A 1  and the second axis A 2  of the inner chamber  07 . As illustrated in  FIG.  14   , the inner chamber  07  includes a horizontal chamber  0701  and a vertical chamber  0702 . 
     For example, as illustrated in.  FIG.  11    and  FIG.  14   , the inner chamber of the valve casing  70  has a T-shaped structure. According to the installation positions of the first valve assembly and the second valve assembly, the inner chamber  07  is divided into a low pressure chamber  07   a , a pressure-alternating chamber  07   b , and a high pressure chamber  07   c . The intersection position of the inner chamber  07  is designed in a “bell mouth” form with smooth transition, which can effectively alleviate the stress concentration effect. 
     Compared with the valve casing in a traditional fluid end, the structural features of the valve casing in the fluid end provided by the embodiment of the present disclosure are as described above, and will not be repeated here. 
     The fluid end provided by the embodiment of the present disclosure does not have the above-mentioned problem of inconvenient maintenance, the axis of the plunger coincides with the first axis (horizontal axis) of the valve casing, the suction side is provided with a first pressure bearing assembly M 1  and a second pressure bearing assembly M 2 , and the axis of the first pressure bearing assembly M 1  and the axis of the second pressure bearing assembly M 2  both coincide with the axis of the plunger, so the maintenance can be carried out according to the routine operation of the well site. 
     For example, as illustrated in  FIG.  11   , the pressure-alternating cover  13  has a revolving structure, which is horizontally placed inside the valve casing  70 , with the left side in contact with the first valve assembly V 1  and the right side in contact with the pressure-alternating nut  23 . The pressure-alternating nut  23  is screwed with the valve casing  70 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the fluid end includes a plunger  81 . The plunger  81  is a revolving body, one end of the plunger  81  is in contact with  the fluid in the valve casing  70  and reciprocates, and the other end of the plunger  81  is connected to the power end of the plunger pump through a clamp  86 . 
     For example, as illustrated in  FIG.  11    and.  FIG.  12 B , the fluid end further includes a packing assembly  82 , and the packing assembly  82  includes a package  821 , a spacer ring  822 , and a press ring  823 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the package  821  includes three packing rings. Of course, the number of packing rings is not limited to that illustrated in the figure, but can be determined as needed. For example, the material of the packing ring includes rubber, but is not limited to this case, 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the plunger side  70   c  of the valve casing  70  is provided with a lubricating oil passage  7007  for lubricating the package  821  (rubber element), so as to make the reciprocating motion of the plunger  81  smoother the circumference of the plunger  81  is wrapped by the package  821 , the package  821  plays a role of sealing to prevent fluid leakage when the plunger  81  reciprocates. 
     For example, as illustrated in  FIG.  11    and  FIG.  1213   , the inner wall of the package  821  is in interference fit with the plunger  81 , which plays a role of sealing; when the plunger  81  reciprocates, it rubs against the inner wall of the package  821 , and the forced lubrication can reduce the friction. 
     For example, the front end of the plunger  81  is provided with a pulling hole (bolt hole), which is matched with a pulling tool. During maintenance, the clamp  86  is firstly disassembled and the plunger  81  is disconnected from the power end, and the plunger  81  is pulled out from the suction side  70   a  along the first axis A 1  of the valve casing  71 ) by the pulling tool. 
     For example, as illustrated in  FIG.  11    and  FIG.  128   , the fluid end further includes a packing nut  83 , and the packing nut  83  is configured to press the packing assembly  82 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the fixing of the package  821  is reinforced by the packing nut  83 , and the packing nut  83  is in a threaded connection with the valve casing  70 . The functions of the packing nut  83  include: preventing the package  821  from moving axially when the plunger  81  reciprocates, and expanding the package  821   by screwing and squeezing, which is beneficial to sealing. The spacer ring  822  and the press ring  823  are provided at both ends of the package  821 , respectively. The spacer ring  822  isolates the package  821  from the valve casing  70 , and the press ring  823  isolates the package  821  from the packing nut  83 , thus protecting the package  821  and prolonging the service life of the package  821 . For example, the spacer ring  822  and the press ring.  823  can be metal pieces. 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the fluid end further includes a packing sleeve  84  and a packing-sleeve nut  85 , the plunger chamber  07   d  is configured to place the plunger  81 , the packing sleeve  84  is located between the packing assembly  82  and the valve casing  70 , and the packing-sleeve nut  85  is configured to press the packing sleeve  84 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the packing sleeve  84  is axially limited by a shoulder and the packing-sleeve nut  85 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , at least one of the packing sleeve  84  and the packing-sleeve nut  85  is in a welded connection with the valve casing  70 . 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the hardness of the packing sleeve  84  is greater than the hardness of the valve casing  70 . Because the hardness of the packing sleeve  84  is greater than the hardness of the valve casing  70 , when the valve casing  70  is damaged, the packing sleeve  84  will not be damaged, so the packing sleeve  84  and the valve casing  85  can be fixed by welding. 
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the outer circumference of the package  821  is in contact with the packing sleeve  84 , and the inner circumference of the package  821  is in contact with the plunger  81  The front end of the packing sleeve  84  is provided with a sealing element  7008  to avoid fluid leakage and damage to the valve casing caused by high pressure fluid entering the gap. The packing sleeve  84  is a wear-resistant element, which is in interference fit with the valve casing  70 . The hardness of the packing sleeve  84  is greater than the hardness of the valve casing. The packing sleeve  84  is provided to prevent the valve casing  70  from being damaged due to the rubbing of the packing sleeve  821 , thus prolonging the service life of the valve casing.  
     For example, as illustrated in  FIG.  11    and  FIG.  12 B , the inner and outer circumferences of the packing-sleeve nut  85  are provided with threads, the outer threads of the packing-sleeve nut  85  are matched with the valve casing  70 , and the inner threads of the packing-sleeve nut  85  are matched with the packing nut  83 . To prevent the packing-sleeve nut  85  from loosening when the plunger  81  reciprocates, the packing-sleeve nut  85  can be fixed with the valve casing  70  by welding. 
       FIG.  11   ,  FIG.  14    and  FIG.  15    further illustrates a discharge side  70   b  of the fluid end. As illustrated in  FIG.  11    and  FIG.  15   , the suction side  70   a  of the valve casing  70  is provided with an inlet hole  700 , and the discharge side  70   b  is provided with a discharge hole  7005 . For example, the inlet hole  700  is connected with the inlet manifold, and low pressure fluid flows inside, the discharge hole  7005  can be connected with the discharge flange, and high pressure fluid flows inside. 
     For example, as illustrated in  FIG.  10   ,  FIG.  11    and  FIG.  14   , the valve casing  70  is provided with suction side threads  7001 , discharge side threads  7002  and plunger side threads  7003 . The suction nut  43  is connected with the valve casing  70  through the suction side threads  7001 . The nut  50  is connected with the valve casing  70  through the discharge side threads  7002 . The packing-sleeve nut  85  is connected with the valve casing  70  through the plunger side threads  7003 . 
     For example, as illustrated in  FIG.  10    and  FIG.  11   , the first valve assembly V 1  and the second valve assembly V 2  are both unidirectional valves. For example, as illustrated in  FIG.  10    and  FIG.  11   , the first valve assembly V 1  and the second valve assembly V 2  can be interchanged. For example, the second valve assembly V 2  is placed vertically, the first valve assembly V 1  is placed horizontally, and the axial directions of the first valve assembly V 1  and the second valve assembly V 2  are perpendicular to each other. 
     For example, as illustrated in  FIG.  10    and  FIG.  11   , the second valve assembly V 2  is placed vertically, the first valve assembly V 1  is placed horizontally and the valve seats of the first valve assembly V 1  and the second valve assembly V 2  are fixed with the valve casing through conical surfaces. Due to the limitation of the aperture of the first valve assembly V 1  illustrated in  FIG.  10   , the plunger cannot be pulled out from the suction side during maintenance and needs to be pulled out from the opposite side, which makes  maintenance more complicated, but the scheme is simple and compact in structure and strong in interchangeability Moreover, the valve seat and the base seat directly “sit” in the valve casing to bear alternating, load, the bearing surfaces are the conical surface and the inclined surface of the valve casing, the load will not be transferred to the threads on the suction side, so the valve casing has a long service life and strong stability. The valve body embedded with the sealing element forms a valve-body assembly, and the valve seat and the base seat form a valve-seat assembly. The valve-body assembly and the valve-seat assembly are matched by an inclined surface, the valve body is in rigid contact with the valve seat, the sealing element in the valve assembly is in non-rigid contact with the base seat, and the sealing element in the valve assembly plays a sealing role. 
     As illustrated in  FIG.  11   , for the first valve assembly V 1 , the valve seat  1   c  is arranged in the valve-seat groove of the pressure-alternating cover  13 , and the left side of the pressure-alternating cover  13  serves as the base seat of the valve seat  1   c  and is configured to fix the valve seat  1   c.  For example, the pressure-alternating cover  13  cooperates with the valve body  1   a,  the sealing element  1   b.  the spring  1   d,  and the spring bracket  1   e  to form a. unidirectional valve. For example, the axis of the first valve assembly V 1  coincides with the axis of the pressure-alternating cover  13 . When the plunger moves back, the valve body  1   a  is opened, and the low pressure fluid enters the valve casing  70 ; when the plunger moves forward, the valve body  1   a  is closed, preventing the low pressure fluid from entering the valve casing  70 . 
     For example, referring to  FIG.  11   , taking the fluid entering the fluid end as fracturing fluid as an example, the working principle of the fluid end is as follows. 
     During liquid suction, the plunger  81  moves back (translates to the left), the first valve assembly V 1  is opened, the second valve assembly V 2  is closed, and the fracturing fluid flows into the pressure-alternating chamber  07   b  from the suction manifold through the inlet hole  700 , the low pressure fluid channel  230 , arid the low pressure fluid channel  130  until the pressure-alternating chamber  07   h  is full of fracturing fluid; at this time, the fluid in the inner chamber  07  is low pressure fluid. 
     During fluid discharge, the plunger  81  moves forward (translates to the right), the first valve assembly V 1  is closed, the second valve assembly V 2  is opened, and the  fracturing fluid flows into the high pressure chamber  07   c  from the pressure-alternating chamber  07   b  and is discharged through the discharge hole  7005 ; at this time, the fluid in the inner chamber  07  is high pressure fluid. 
       FIG.  19    is a schematic diagram of a second valve assembly in a fluid end provided by an embodiment of the present disclosure. As illustrated in.  FIG.  19   , the valve body  2   a  includes a lug boss a 1  and a clamping jaw a 2 . The function of the lug boss a 1  includes limiting the spring  2   d  to prevent the spring  2   d  from moving radially. The function of the lug boss a 1  also includes limiting the opening height of the valve body  2   a . When the second valve assembly V 2  is opened, the lug boss a 1  of the valve body  2   a  is in rigid contact with the lug boss of the discharge cover  40 , so that the opening height of each time is uniform. 
     As illustrated in  FIG.  19   , the inner hole of the base seat  2   f  is in clearance fit with the clamping jaw a 2 , so as to guide the clamping jaw a 2  and prevent the valve body  2   a  from deflecting under the impact of high pressure fluid. The valve seat  2   c  and the base seat  21  have a separated structure, and the hardness of the valve seat  2   c  is greater than the hardness of the base seat  2   f  The purpose is to prevent the inclined surface of the valve seat  2   c  from being worn when the valve body  2   a  slaps the valve seat  2   c , to avoid poor sealing caused by wearing the valve seat  2   c , and to avoid reducing the service life of the valve seat and the valve body. 
     The structure and function of the first valve assembly can be referred to the above description. The difference is that the lug boss of the valve body  1   a  is in rigid contact with the lug boss of the spring bracket. 
       FIG.  20    is a schematic diagram of a valve casing on a discharge side of a fluid end provided by an embodiment of the present disclosure.  FIG.  21    is a schematic diagram of a sealing structure on a discharge side of a fluid end provided by an embodiment of the present disclosure.  FIG.  22    is a schematic diagram of a valve casing on a suction side of a fluid end provided by an embodiment of the present disclosure.  FIG.  23    is a schematic diagram of a sealing structure on a suction side of a fluid end provided by an embodiment of the present disclosure. 
       FIG.  19    illustrates a sealing element  1021 , the sealing element  1021  includes a  sealing ring, and a sealing groove is provided at the corresponding position of the base seat  2   f . As illustrated in  FIG.  10    and  FIG.  11   , the sealing element  102 . 1  is provided to realize the sealing between the second valve assembly V 2  and the valve casing  70 . 
       FIG.  20    illustrates a sealing, groove  901 , and  FIG.  21    illustrates a sealing element  902 . The sealing element.  902  is provided to seal the high pressure chamber of the inner chamber. 
       FIG.  22    illustrates a sealing groove  903 , and  FIG.  23    illustrates a sealing element  904 . The sealing element  904  is provided to seal the low pressure chamber of the inner chamber. 
     For example, the sealing element and the groove for receiving the sealing, element can be referred to as a sealing structure. For example, the sealing element  904  and the groove for receiving the sealing element  904  can be referred to as a second sealing structure, and the sealing element  902  and the groove for receiving the sealing element  902  can be referred to as a third sealing structure. The sealing element includes a sealing ring. 
     For example, in the embodiment of the present disclosure, the fluid end includes: a valve casing, including an inner chamber, the inner chamber including a pressure-alternating chamber and a low pressure chamber; a first valve assembly, located in the inner chamber, and configured to be opened to communicate the low pressure chamber with the pressure-alternating chamber or configured to be closed to separate the low pressure chamber from the pressure-alternating chamber; a pressure bearing structure  99 , at least a part of the pressure bearing structure  99  being located in the low pressure chamber, and a first sealing structure, located between the pressure bearing structure  99  and the valve casing. At least one of the valve casing and the pressure bearing structure  99  has a drain channel, and the drain channel is configured to flow fluid therethrough in the case of failure of a part of the first sealing structure. For example, the pressure bearing structure  99  is located in the inner chamber. 
     For example, the drain channel can be the drain channel  1000  or the drain channel  7000  as described above. 
     For example, in some embodiments, as illustrated in  FIG.  7    and  FIG.  9   , the pressure bearing structure  99  can include the cover  10  described above. In this case, the drain  channel  1000  is provided in the cover  10 . 
     For example, as illustrated in  FIG.  7    and.  FIG.  9   , the pressure bearing structure  99  includes a cover  10  and a nut  20 , the nut  20  is screwed with the valve casing  70 , and the drain channel  100  is located in the cover  10 . 
     For example, in some other embodiments, as illustrated in  FIG.  11   , the pressure bearing structure  99  can include the first pressure bearing assembly M 1  described above. In this case, the drain channel  7000  is provided in the valve casing  70 . 
     For example, the first sealing structure can be the first sealing structure  101   s  or the first sealing structure SE as described above. 
     For example, as illustrated in  FIG.  9   , the first sealing structure  101   s  includes a first seal SL 1  and a second seal SL 2 , the drain channel  1000  includes a first drain outlet  1001  and a second drain outlet  1002 , the first drain outlet  1001  is closer to the first sealing structure  101   s  than the second drain outlet  1002  is, and the first drain outlet  1001  is located between the first seal SL 1  and the second seal SL 2 . 
     For example, as illustrated in  FIG.  12 A ., the first sealing structure SE includes a first seal SE 1  and a second seal SE 2 , the drain channel  1000  includes a first drain outlet  1001  and a second drain outlet  1002 , the first drain outlet  1001  is closer to the first sealing structure  101   s  than the second drain outlet  1002  is, and the first drain outlet  1001  is located between the first seal SE 1  and the second seal SE 2 . 
     For example, as illustrated in  FIG.  11   , the pressure bearing structure  99  includes a first pressure bearing assembly M 1  and a second pressure bearing assembly M 2 , and the first valve assembly V 1 , the first pressure bearing assembly M 1  and the second pressure bearing assembly M 2  are arranged in sequence along the extending direction of the first axis A 1  of the inner chamber. 
     For example, as illustrated in  FIG.  11   , the first pressure bearing assembly M 1  includes a pressure-alternating cover  13  and a pressure-alternating nut  23 . The pressure-alternating cover  13  is closer to the first valve assembly V 1  than the pressure-alternating nut  23  is, and the pressure-alternating nut  23  is screwed with the valve casing  70 . 
     The arrangement of the components on the left side of the fluid end illustrated  in  FIG.  10    and  FIG.  11   , such as the packing assembly  82 , the packing nut  83 , the packing sleeve  84  and the packing sleeve nut  85 , etc., can be referred to the above description, and will not be repeated here. 
     The embodiment of the present disclosure further provides a plunger pump, which includes any one of the fluid ends described above. 
     For example, the fluid end and the plunger pump described above can be applied to fracturing/cementing equipment in oil and gas fields. 
     What have been described above are only specific implementations of the present disclosure, the protection scope of the present disclosure is not limited thereto. Any modifications or substitutions easily occur to those skilled in the art within the technical scope of the present disclosure should be within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.