This invention relates in general to connecting rods used in reciprocating pump crankshafts, and, in particular, to a multi-piece connecting rod fabricated out of steel and a lighter weight material to lighten its weight.
Connecting rods are used in various kinds of pumps used in oilfield operations. A connecting rod can be used, for example, in a reciprocating pump. The reciprocating pump can be used to pump fluid such as chemicals, cement, or other media into a well. Reciprocating pumps typically increase the pressure within a cylinder by reciprocating a plunger longitudinally within the cylinder. The connecting rod typically has a body and two ends. One end bolts to the crank shaft and the other end pivotally secures to a crosshead. The crosshead strokes longitudinally within a crosshead housing and is connected to a pony rod, which in turn in connected to the plunger.
In a one prior example, one end of a connecting rod is connected to the plunger via a crosshead and the other end is connected to a crankshaft. The crosshead has a semi-cylindrical cavity that receives one end of the connecting rod. To secure the end of the connecting rod to the crosshead, a wrist pin is inserted through a hole formed in the crosshead end of the connecting rod. The wrist pin thus secures the end of the connecting rod to the crosshead and allows for the translation of the crankshaft's rotational movement into linear movement of the crosshead and thereby the plunger. Connecting rods are typically fabricated out of a single piece of steel. The steel construction provides the connecting rod with the strength to bear the forces experienced during operation, especially at the crosshead. As such, the connecting rod is heavy and adds to the overall pump weight, which can make the transportation of reciprocating pumps more difficult. For example, these pumps are often mounted on trailers that are brought to the wellsite. The trailers cannot exceed the weight capacity of any bridges that it must cross or weight limits on highways.
Thus, it would be desirable to provide a connecting rod for use in reciprocating pumps that is lighter and yet maintains the ability to bear the forces experienced during pump operation.
In an embodiment of the present invention, a reciprocating pump assembly has a pump located inside a housing. The pump has a crankshaft that rotates and a crosshead that is connected to a plunger via a pony rod. The plunger pumps fluid through cylinders in the pump when it is moved longitudinally within the cylinders. A connecting rod has a body and connects at one endpiece to the crankshaft and at another endpiece to the crosshead to thereby translate the crankshaft's rotational movement into linear movement of the crosshead and thereby energize the plunger.
In this embodiment, the endpiece that is connected to the crosshead is made of steel has an interference fit with the body of the connecting rod, which is made of a lighter material, preferably aluminum. In addition, fasteners may be used for added security. Alternatively, the fasteners may be omitted. This endpiece can be secured to the crosshead by a wrist pin that traverses a hole formed in the endpiece. The wrist pin allows the connecting rod's endpiece to pivot during pump operation. The crankshaft end piece may be of aluminum and integral with the body. This multi-piece design using a lighter aluminum metal results in a lighter connecting rod and thus reduces the weight of the pump. This can result in making transportation of the pump easier and less costly.
Referring to
Referring to
In one embodiment, a gear 24 is mechanically connected to crankshaft 25 and is rotated by the motor through gears 26 and 24. A multi-piece connecting rod 27 is connected to the crankshaft 25 at one end. The connecting rod 27 connects to a crosshead 29 through a crosshead wrist pin 31, which holds connecting rod 27 longitudinally relative to crosshead 29. The crosshead 29 has a concave semi-cylindrical portion to receive the end of the connecting rod. Crosshead 20 reciprocates within a stationary crosshead housing. The multi-piece connecting rod 27 pivots about wrist pin 31 as crankshaft 25 rotates with the other end of connecting rod 27. A pony rod 33 extends from crosshead 29 in a longitudinally opposite direction from crankshaft 25. Connecting rod 27 and crosshead 29 convert rotational movement of crankshaft 25 into longitudinal movement of pony rod 33.
A plunger 35 is connected to pony rod 33 for pumping the fluid passing through cylinder 17. Cylinder 17 includes an interior or cylinder chamber 39, which is where plunger 35 pressurizes the fluid being pumped by reciprocating pump 12 (
Plunger 35 reciprocates and moves longitudinally within cylinder 17, as crankshaft 25 rotates. As plunger 35 moves longitudinally away from cylinder chamber 39, the pressure of the fluid inside chamber 39 decreases, creating a differential pressure across inlet valve 41, which actuates valve 41 and allows the fluid to enter cylinder chamber 39 from fluid inlet 19. The fluid being pumped enters cylinder chamber 39 as plunger 35 continues to move longitudinally away from cylinder 17 until the pressure difference between the fluid inside chamber 39 and the fluid in fluid inlet 19 is small enough for inlet valve 41 to actuate to its closed position. As plunger 35 begins to move longitudinally towards cylinder 17, the pressure on the fluid inside of cylinder chamber 39 begins to increase. Fluid pressure inside cylinder chamber 39 continues to increase as plunger 35 approaches cylinder 17 until the differential pressure across outlet valve 43 is large enough to actuate valve 43 and allow the fluid to exit cylinder 17 through fluid outlet 21. In one embodiment, fluid is only pumped across one side of plunger 35, therefore reciprocating pump 12 is a single-acting reciprocating pump.
Referring to
The crosshead end of the multi-piece connecting rod 27 comprises a steel endpiece 59 that is attached to the aluminum body 57 preferably via an interference fit. For added security, in this embodiment two fasteners 61 may also be used to connect endpiece 59 to body 57, as shown in
In this embodiment, a cylindrical wrist pin hole 65 extends through crosshead end 59 perpendicular to an axis of connecting rod body 57. Wrist pin hole 65 connects the endpiece 57 of the connecting rod 27 to the crosshead 29 via the crosshead wrist pin 31. The forward end 68 of crosshead endpiece 59 is convex and partially cylindrical. The crosshead 29 (
In an additional embodiment illustrated in
In an additional embodiment the aluminum body 80 of the multi-piece connecting rod 82 has a hollow interior 84 that extends approximately the length of the body 80, resulting in a cross-section such as that shown in
Reciprocating pumps 12 are large, and heavy pieces of equipment because the pressures required can be high, up to 20,000 psi. The fluid volumes pumped are also high. Often, pumps of this type are transported to various sites on trailers. Road and bridge weight limits must be met by the trailer. Lightening the weight of the pump by using lighter weight materials for the connecting rod 27 is thus desirable because it makes pump 12 transportation easier and less costly. However, a lighter weight material such as aluminum may not have the ability to withstand the wear and forces at the connection to the crosshead 29. By using a multi-piece connecting rod 27, the pump's weight is lightened because the body 57 of the connecting rod 27 is fabricated out of a light weight material such as aluminum. The lightweight body 57 can then be fastened to the endpiece 59, which is fabricated out of steel and has the strength required to withstand the stress and wear at the crosshead 29.
This written description uses examples to disclose the invention, including the best mode, and also enable a person of ordinary skill in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
This application claims priority to provisional application 61/143,289 filed Jan. 8, 2009.
Number | Date | Country | |
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61143289 | Jan 2009 | US |