Abstract:
A piston rod assembly for coupling between a power end and a fluid end of a high pressure reciprocating pump. Part cylindrical members are clamped together via pistons arranged orthogonally to the rod axis. The members grip the power and fluid end components in a knuckle joint or ball and socket. By providing orthogonal loading, a large contact area is obtained between the members and the components, which gives a mechanical advantage in keeping the parts together even when a maximum reciprocating force is applied by the pump.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to high pressure reciprocating pumps such as those used to pump drilling mud in the oil production industry, including those pumps commonly referred to in the industry as mud and slush pumps. In particular, the invention relates to a piston rod assembly, suitable for rapid replacement between a power end and a fluid end of a reciprocating pump. 
     It is necessary with high pressure reciprocating pumps to replace the piston or other dynamic component with relative regularity and it is therefore advantageous if this task can be performed quickly and easily. Typical quick release piston rod assemblies, such as those disclosed in GB 2,190,170 and U.S. Pat. No. 5,904,701, have axially arranged links to the power and fluid ends, held in place by radial pins. Tension is then applied to the pins via axial pistons to couple the fluid and power ends together. 
     A disadvantage of these assemblies is that connectors with suitably sized apertures must be arranged at each of the power and fluid ends. The use of radial pins, to which longitudinal tension is applied, provides weak points on the assembly which can be prone to fracture during high reciprocation. A further disadvantage of these assemblies is that the relative angle between the power end and fluid end must be taken into account when positioning the assembly. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a piston rod assembly which obviates at least some of the disadvantages of the prior art. 
     According to the present invention there is provided a piston rod assembly, for coupling between a power end and a fluid end of a high pressure reciprocating pump, the assembly comprising one or more clamping members arranged relative a rod axis between the power end and the fluid end, each member having a first end adapted to grip a power end component and a second end adapted to grip a fluid end component, at least one member including one or more tensioning means, wherein said tensioning means comprise a piston to provide a load in said tensioning means orthogonal to said first rod axis and thereby secure said components against release. 
     Preferably the clamping members are part cylindrical bodies which when arranged on the rod axis provide a substantially cylindrical body. Preferably there are two clamping members, an upper clamping member and a lower clamping member. 
     Preferably the first and second ends include a contact face parallel to the rod axis on an inner surface. 
     Preferably the face provides a recess on the inner surface in which a portion of the power end component or fluid end component may be located such that the component is gripped and held when the clamping members are brought together by the tensioning means. Advantageously each component end and the first/second end provide a knuckle joint. Alternatively, they may provide a ball and socket. 
     This clamping is obtained without any need of relative angle position between the power end component and the fluid end component. Further when the load is applied on the rod axis, the large contact area between the faces and the components provides a large mechanical advantage thus facilitating a large force to solidly assemble the parts together even when a maximum reciprocating force is provided by the pump. 
     Preferably each piston is slideable within an hydraulic cylinder. More preferably each piston includes a stem adapted to receive a nut or a lock. Preferably said stems extend from one clamping member through an aperture in an adjacent clamping member. The nut may then engage the stem to couple the clamping members. Preferably also a spring is arranged within the hydraulic cylinder to tension the said stem. Advantageously, the assembly includes non-rotational means for preventing rotation of said stem. The non-rotational means may be a pin locating in a matching recess arranged parallel to the stem. 
     Preferably a space is defined between a base of the cylinder and a base of the piston for accommodating hydraulic fluid. Preferably the assembly includes a fluid inlet port to permit the input of hydraulic fluid to the cylinder. Advantageously a chamber may be included in each member to provide a common feed for hydraulic fluid to all cylinders within the member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will be described by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional side elevation of a piston rod assembly, according to an embodiment of the present invention; 
         FIG. 2  is a sectional schematic view of a fluid inlet port of a piston rod assembly according to an embodiment of the present invention; and 
         FIGS. 3   a  &amp;  3   b  are sectional views of tensioning means in first ( 3   a ) and second ( 3   b ) operating positions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is initially made to  FIG. 1  of the drawings which illustrates a piston rod assembly, generally indicated by reference numeral  10 , according to an embodiment of the present invention. Piston rod assembly  10 , is located between a power end component  12  and a fluid end component  14 . The components  12 , 14  form parts of a high pressure reciprocating pump as will be recognised by those skilled in the art. In particular the piston rod assembly  10  can be used in a high pressure reciprocating oilfield mud pump. 
     The piston rod assembly  10  may be considered as a clamping link by virtue of its purpose i.e. to provide a releasable coupling between the power end component  12  and the fluid end component  14  which is secure during the high reciprocating force applied by the pump. Assembly  10  comprises two half-cylindrical clamps  16 , 18 . Each clamp  16 , 18  has an inner planar surface  20 , 22  respectively. The surfaces  20 , 22  are arranged on and lie parallel to the rod axis. The rod axis is a central line located between the end components  12 , 14 . 
     The piston rod assembly  10  includes two tensioning modules  24   a,b  to connect the clamps  16 , 18 . Each tensioning module includes a piston  26   a,b , a piston stem  28   a,b , and a disc spring stack  30   a,b  arranged within a cylindrical housing  32   a,b  with the lower clamp  18 . These elements  28 , 30 , 32  are all disposed orthogonally to the rod axis of the assembly  10 . Covers  34   a,b , held in place by screws  36   a - d , close the housings  32   a,b  retaining the spring force. The upper clamp  16  includes apertures  38   a,b  through which extend the stems  28   a,b  from the lower clamp  18 . Each aperture  38  widens to provide a lip  40   a,b  parallel to the rod axis. A nut  42   a,b  is screwed to the stem  28   a,b  and may be tightened against the lip  40   a,b.    
     Below each piston  26   a,b  in a space defined by the base of the piston  26   a,b  and the base of the housing  32   a,b  is a fluid chamber  44   a,b . Hydraulic fluid  46  may enter this chamber  44  and exert a force upon the piston  26   a,b . The chambers are connected to a fluid line  48  located along the length of the assembly  10 . The fluid line  48  is sealed, but includes an inlet port  50  illustrated in  FIG. 2 . 
     Referring to  FIG. 2 , the inlet port  50  is now seen in a perpendicular aspect. Like parts to those of  FIG. 1  have been given the same reference numeral to aid clarity. A female connector  52  is located with the port  50 . By inserting a male connector  54  into the female connector  52  pressurising hydraulic fluid  46  can be inserted into the fluid line  48 . It will be recognised by those skilled in the art that the fluid  48  may be supplied from a reservoir  56 , utilising a pump  58 , through a check valve  60 . The connectors  52 , 54  are preferably quick release connectors and the male connector  54  is a differential pressure fastening, which avoids the need to screw in any device, thus making the task of pressurising and releasing very fast. 
     Returning to  FIG. 1 , on the inner surface  20 ,  22  are arranged recesses  62   a,b . When the clamps  16 ,  18  meet the recesses  62   a, b  form circumferential grooves around the inner surface  20 ,  22  equidistantly from the rod axis. Each component end  12 ,  14  includes a protrusion  66 ,  68  which may be likened to a door knob or knuckle in profile. Each protrusion  66 , 68 , lies within a recess  62   a,b  and a large contact surface area  64   a, b  is provided between the protrusion  66 , 68  and the inner surface  20 , 22 . Additionally as each recess  62   a, b  has an angled surface facing toward the ends  12 ,  14  respectively; the protrusions  66 ,  68  are effectively gripped by the clamps  16 ,  18 . To aid the fitting of each protrusion  66 ,  68  into each recess  62   a, b , bearing pads  70 ,  72  are located at the distal ends of the protrusions  66 ,  68 . The bearing pads  70 ,  72  may be formed of a material which provides some give and has a relatively high elastic modulus. 
     Reference is now made to  FIGS. 3   a  and  3   b . Like parts to those of  FIGS. 1 and 2  have been given identical reference numerals to aid clarity. These Figures show operating positions of the assembly and will be described fully hereinafter. Additionally these figures illustrate further features of the assembly  10 . An anti-rotation pin  74  is located within the base of the piston  26  and extends into the base of the housing  32 . The anti-rotation pin  74  prevents the piston  26  rotating during movement of the nut  42 . Also included in the assembly  10  is a grease nipple  76  as is known in the art. The grease nipple  76  fills grease into the disc spring stack  30  to protect the stack  30  from rust. 
     In use, the lower clamp  18  including the tensioning modules  24  are located against protrusions  66 , 68  of a power end component  12  and a fluid line component  14  of a pump. The protrusions  66 , 68  rest in the recesses  62   a,b . the upper clap  16  is then placed over the lower clamp  18  such that the stems  28   a,b  locate through the apertures  38   a,b  respectively. Nuts  42   a,b  are located on the stems  28   a,b  and hand tightened to align the protrusions  66 , 68  against the surface  64   a,b . This process can be done without the need to ensure that the end components  12 , 14  are perfectly aligned as tightening the nuts  42  will bring the ends  12 , 14  into alignment. Fluid  48  is then introduced to the line  46 . Pressure will consequently build up in the chambers  44   a,b  and the pistons  26   a,b  will be forced upwards by a short distance, orthogonal to the rod axis. This is illustrated in  FIG. 3   a . The nuts  42   a,b  are given freedom to be tightened by further rotation along the stems  28   a,b  towards the lips  40   a,b . It should be noted that the apparatus and method described herein allows the nuts  40   a,b  to be tightened by hand by means of a socket wrench. It will be appreciated that this is a considerable advantage over the requirement of using heavy tools. 
     When fluid pressure in the chambers  44   a,b  is released by removal of the fluid  46 , the pistons  26   a,b  are pushed outwards towards the base of the housing  30   a,b  by the spring stacks  30   a,b . This places in shear (locking arrangement) the clamps  16 , 18  and the bearing pads  70 , 72 . The end components  12 , 14  are now securely attached to the clamping link or assembly  10 . This is illustrated in  FIG. 3   b . Further with the load applied on the rod axis, the large contact area  64   a,b  between the surfaces  20 , 22  and the components  66 , 68  provides a large mechanical advantage thus facilitating a large force to solidly assemble the parts together even when a maximum reciprocating force is provided by the pump. 
     These steps may be repeated any number of times to release or couple the assembly  10  between the ends  12 , 14 . 
     The principal advantage of the present invention is that by applying a force orthogonally to the rod axis a greater securing force is provided to clamp the assembly to the component ends. This also dispenses with the need to provide apertures through the end components for locking pins. 
     A further advantage of the present invention is that in bringing the clamps together to grip the ends, the ends need not be in perfect alignment initially. Additionally any dirt which becomes trapped between the clamps, will merely provide a spacing which can be made up be the stacking springs. In this way the dirt will not cause loosening of the clamps during reciprocation of the pump in use. 
     A yet further advantage of the present invention is that the assembly can be quickly made up without the need for heavy tool to tighten the nuts. 
     It will be appreciated by those skilled in the art that various modifications may be made to the invention herein described without departing from the scope thereof. For example, any number of tensioning modules may be incorporated, as could numbers of clamps depending on the shape of the protrusions at each of the ends. Additionally, though spring stacks have been used to provide tension in the piston housings, other elastic members could be substituted. Further, a water flushing pipe as is known in the art may be incorporated to remove dirt and provide lubrication and cooling to the system.