Abstract:
A seal assembly for providing a seal around a non-stationary rod includes a seal housing with a hollow body with first and second ends. The first end has a first opening to allow the non-stationary rod to pass therethrough and the second end has a second opening to allow the non-stationary rod to pass therethrough. A seal cartridge is disposed within the seal housing and radially moveable within the seal housing. A rod seal is disposed in an internal diameter of the seal cartridge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    Reciprocating pumps are used in a wide number of applications to pump fluid, and are particularly adapted to pumping large volumes of fluid at pressure.  FIG. 1A  shows cross-section of a power end  101  of a prior art reciprocating pump. This design of pump is known as a triplex reciprocating pump because there are three sections like what is shown in  FIG. 1A . 
         [0004]    The power end  101  provides the reciprocating axial motion for a piston to pump fluid in the section of the reciprocating pump known as the fluid end (not shown). In the modular design typical of reciprocating pumps, the fluid end is fastened to plate  120  on the power end. Rotating shaft  104  is rotated by an electric motor powered by a separate power source or may be directly powered by combustion. Rotating shaft  104  drives each section in the triplex reciprocating pump. A crosshead  102  converts the rotational motion of the rotating shaft  104  into axial reciprocation within cylinder  107 . A rod  110 , commonly referred to as a pony rod, connects the crosshead  102  to a piston (not shown) in the fluid end to provide the pumping force. The piston may be, for example, a piston rod or plunger. The pony rod and piston rod or plunger could be the same rod, but are usually separate components for the large reciprocating pumps typical for pumping fluid because the resulting unitary rod would be difficult for personnel to install and replace. Within this disclosure, “piston” will be used as the generic term to refer to any configuration of pistons, rods, or plungers that pumps the fluid. 
         [0005]    The rod  110  passes through an opening in partition  106  in which a seal assembly  1 B is installed, which is shown in greater detail in  FIG. 1B . The movement of the rotating shaft  104  and crosshead  102  is lubricated by fluid, such as oil, that is pooled in lower section  103  in the power end  101 . Seal assembly  1 B acts as a bearing for the pony rod  110  while also trying to prevent the fluid from flowing out of the power end  101  as the pony rod  110  reciprocates. The seal assembly  1 B and the pony rod  110  are accessible by removing cover  111 . This prior art seal assembly  1 B includes a seal body  155  with a seal  156  to seal the outer diameter of the seal body  155  with the inside of the opening in partition  106 . The seal body  155  holds a seal arrangement that includes multiple chevron seals  160 , in this case four, to seal around the pony rod  110 . A back-up ring  161  traps the chevron seals  160  on the seal body  155 . A gland  150  holds the seal assembly together and is attached to the partition  106  by multiple threaded fasteners  151  and  152 . The back-up ring  161  and the chevron seals  160  are retained on the seal body  155  by the gland  150 . 
         [0006]    Though this sealing arrangement has been in use for many years, fluid often leaks past the rod seals as the pony rod  110  reciprocates, with more leaking as the pony rod  110  reciprocates at higher speeds. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0007]    In one aspect, the disclosure relates to a seal assembly for providing a seal around a non-stationary rod. The seal assembly includes a seal housing with a hollow body with first and second ends. The first end has a first opening to allow the non-stationary rod to pass therethrough, and the second end has a second opening to allow the non-stationary rod to pass therethrough. A seal cartridge is disposed within the seal housing and radially moveable within the seal housing. A rod seal is disposed in an internal diameter of the seal cartridge. 
         [0008]    In another aspect, the disclosure relates to a reciprocating pump with a power end and a fluid end. The power end includes a reciprocating crosshead converting rotational motion from a rotating shaft to a reciprocal motion. The fluid end includes a fluid inlet, a fluid outlet, and a piston. A pony rod extends from the reciprocating crosshead to the piston. The reciprocating pump further includes a partition between the reciprocating crosshead and the fluid end. The partition includes an opening through which the pony rod extends. A seal assembly is disposed at the opening in the partition to provide a seal between the seal housing and the opening in the partition through which the pony rod extends. The seal assembly includes a seal housing with a hollow body with first and second ends. The first end has a first opening to allow the non-stationary rod to pass therethrough and the second end has a second opening to allow the non-stationary rod to pass therethrough. A seal cartridge is disposed within the seal housing and radially moveable within the seal housing. A rod seal is disposed in an internal diameter of the seal cartridge. 
         [0009]    Other exemplary embodiments and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  is a partial cross-section of a power end of a reciprocating pump with a prior art rod seal; 
           [0011]      FIG. 1B  is a detailed cross-section of the prior art rod seal shown in  FIG. 1A ; 
           [0012]      FIG. 2A  is a partial cross-section of a reciprocating pump with a self-aligning rod seal in accordance with one embodiment; and 
           [0013]      FIG. 2B  is a detailed cross-section of the self-aligning rod seal shown in  FIG. 2A . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Embodiments of the disclosure relate generally to a sealing assembly for sealing around a non-stationary rod. Non-stationary rods that may be sealed around using embodiments of the disclosure include but are not limited to reciprocating rods, oscillating rods and rotating rods. In the description that follows, like parts are generally marked throughout the specification and drawings with the same reference numerals, respectively. 
         [0015]    With reference against to  FIG. 1A , one contributing factor to the leaking of fluid past the seal assembly  1 B is the irregular motion of the pony rod  110 . The crosshead  102  oscillates up and down within cylinder  107  due to the rotating shaft  104 . The result is that the connected pony rod  110  moves up and down in a sinusoidal manner as it reciprocates back and forth through seal assembly  1 B. To accommodate the sinusoidal movement, the lips of the chevron seals  160  flex with the pony rod  110 , but the flexing is asymmetric and at the limit for providing a complete seal around the pony rod  110 . The sinusoidal movement also can act like a pump to force fluid past the series of seals  160 . 
         [0016]    In  FIG. 2A , a partial cross-section of a reciprocating pump in accordance with one embodiment is shown.  FIG. 2A  shows a portion of the fluid end  201 , which is fastened to plate  120  on the power end  101 . Pony rod  110  is connected to piston  202 , which extends into the fluid end  201  to provide the pumping action for the reciprocating pump. Seal assembly  2 B seals between the pony rod  110  and the opening in partition  106 . Fluid leaks due to oscillation of the pony rod  110  are reduced or eliminated by allowing portions of the seal assembly to float in the radial direction with the pony rod  110  as it reciprocates. 
         [0017]      FIG. 2B  shows seal assembly  2 B in greater detail. Seal assembly  2 B includes a seal cartridge  215  contained within a seal housing  210 . The seal housing  210  includes a seal  213  on its outer diameter to seal with the inside of the opening in partition  106 . The seal cartridge  215  contains sealing elements on its inner diameter to seal around the pony rod  110 . In this embodiment, the sealing elements are wiper seals  225   a  and  225   b  on opposite sides of a rod seal  226 . The wiper seals  225   a  and  225   b  clean the outer diameter of the pony rod  110  to provide a cleaner surface for the rod seal  226  to seal around. Each of the sealing elements is disposed in a respective groove in the inner diameter of the seal cartridge  215 . Those having ordinary skill in the art will appreciate that many combinations of rod seals, with or without wiper seals, may be used to provide the seal around the pony rod  110  without departing from the scope of the disclosure. 
         [0018]    Seal assembly  2 B is held in place by gland  150 , which is secured to partition  106  by threaded fasteners  151  and  152 . In other embodiments, the gland  150  may be threaded and secured directly to the partition  106  without separate threaded fasteners. By using a common method of securing seal assemblies to partition  106 , seal assembly  2 B may be designed to be retrofit with reciprocating pumps already in service. Those having ordinary skill in the art will appreciate that other mechanisms for securing the seal assembly  2 B may be employed without departing from the scope of the disclosure. The seal housing  210  has an open end to receive the seal cartridge  215  and allow the fastening of gland  150  to provide compression of the seal cartridge  215  and its internal sealing elements, described further below. A gasket or O-ring  212  may be provided between the end of the seal housing  210  and gland  150  to provide a seal. 
         [0019]    Continuing with  FIG. 2B , the seal cartridge  215  is axially restrained between gland  150  and the inside surface of the seal housing  210 . The seal cartridge  215  includes a seal  216  between its end and the gland  150 . On the opposite end, the seal cartridge  215  includes a biasing element  220  between the seal cartridge  215  and the inside surface of the seal housing  210 . The biasing element  220  provides a force between the opposite end of the seal cartridge  215  and the gland  150  to aid the effectiveness of seal  216 . Suitable biasing elements include various springs, such as spring washers, helical springs, and wave springs. In another embodiment, the biasing element  220  may be an elastomeric element, such as but not limited to an elastomeric O-ring. In yet another embodiment, the biasing element  220  may be the same as seal  216  in order to avoid improper assembly of seal assembly  2 B. 
         [0020]    During operation of the reciprocating pump, seal cartridge  215  is able to move radially within the seal housing  210 . As a result, the wiper seals  225   a  and  225   b  and rod seal  226  are able to be substantially centered about the pony rod  110  as it oscillates up and down with the crosshead  102 . Biasing element  220  keeps the seal  216  between the seal cartridge  215  and the gland  150  to block that potential leak path as the seal cartridge  215  floats radially. Gasket  212  between the seal housing  210  and the gland  150  blocks that potential leak path. Any fluid that leaks behind the seal cartridge  215  may be drained back into the power end  101  through one or more drain holes  211  formed in the seal housing  210 . 
         [0021]    Embodiments of the disclosure may provide one or more of the following advantages. By allowing the seal cartridge  215  to float radially with the pony rod  110 , the sealing elements within the seal cartridge  215  are substantially centered about the pony rod  110 . Preventing misalignment of the sealing elements relative to the pony rod  110  reduces or eliminates fluid leakage that could otherwise occur with the up and down oscillation of the pony rod  110 . With alignment maintained, the seal cartridge  215  and the sealing elements may also be selected to have closer tolerances around the pony rod  110  without concern for interference that could occur with prior art seal assemblies. The closer tolerances further reduce potential fluid leakage around the pony rod  110 . 
         [0022]    The modular design of the embodiments disclosed herein may also be easier to assemble in the field than conventional seal assemblies. Most of the components may be assembled together before placing them around the pony rod  110  inside the reciprocating pump. For example, seal  213  can be placed in the outside groove on the seal housing  210 . Biasing element  220 , seal  216 , wiper seals  225   a  and  225   b , and rod seal  226  can each be placed in their respective grooves in and on the seal cartridge  215 . The seal cartridge  215  can then be placed into the seal housing  210 . The only steps to be carried out inside the reciprocating pump would be to insert the pony rod  110  through opening in the seal housing  210  and place the seal housing  210  inside the opening in partition  106 . The seal assembly  2 B is then completed by securing the gland  150  to partition  106 . 
         [0023]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.