This invention relates in general to oilfield reciprocating pumps, and in particular to a crosshead between a connecting rod and pony rod that is readily removable.
One type of reciprocating pump is employed for fracturing oil and gas wells. During a fracturing operation, a series of frac pumps convey large volumes of fluid into the well. The fluid typically comprises water containing proppants, such as sand. The frac pumps are capable of high pressures, such as 15,000 psi, for causing the earth formation to crack or fracture. The proppants flow into the cracks to prop them open when the pressure is removed.
A typical frac pump has a crankshaft rotated by a power source, such as an engine. Several connecting rods have ends rotatably mounted to the crankshaft. The opposite end of each connecting rod is pivotally connected to a crosshead assembly to convert rotary motion of the crankshaft into linear motion. Each crosshead assembly comprises a crosshead member reciprocally carried within a stationary crosshead case. The crosshead member has an end that contains a partially cylindrical recess that is lined with a bushing. Each connecting rod pivotally mounts to one of the crosshead members in sliding engagement with the bushing. A pony rod secures to an opposite end of each crosshead member. Each pony rod connects to a plunger that is stroked by the pony rod within a cylinder of a fluid end of the pump.
Because of the high pressures and high stroke rate, operators must change the bushings frequently. Normally, the replacement of the bushing requires the operator to disconnect the connecting rod from the crankshaft. This procedure is time consuming.
In this invention, the crosshead assembly includes a first crosshead member that reciprocates linearly within a stationarily mounted crosshead case. A retainer pivotally joins the forward end of the connecting rod to the first crosshead member. A second crosshead member has a partially cylindrical recess facing in an aft direction with a bushing located within the recess. The forward end of the connecting rod is in pivotal engagement with the bushing. The second crosshead member is releasably secured to the first crosshead member to allow removal of the second crosshead member and the bushing from the crosshead case without detaching the forward end of the connecting rod from the first crosshead member.
Preferably, a plurality of threaded crosshead member fasteners are employed to secure the second crosshead member to the first crosshead member. The crosshead member fasteners having heads located on a forward end of the second crosshead member so as to be accessible from the forward end. In the preferred embodiment, the first crosshead member comprises a crosshead housing having a cavity, and the second crosshead member comprises an insert mounted in the cavity of the crosshead housing. Preferably, the first crosshead member has an aft end with a window into which the forward end of the connecting rod is inserted.
A pony rod having an aft end is mounted to a forward end of the second crosshead member. A plunger is mounted to a forward end of the pony rod. The pony rod strokes the plunger within a cylinder of a fluid end unit. In the preferred embodiment, the pony rod has an external flange that overlies the heads of the crosshead member fasteners. A plurality of threaded pony rod fasteners extend through the external flange into the second crosshead member.
The second crosshead member may have a neck protruding from the forward end of the second crosshead member. If so, the pony rod has a cavity that slides over the neck. Preferably, the retainer for joining the connecting rod to the first crosshead member comprises a wrist pin that inserts through a hole in the forward end of the connecting rod. The wrist pin is secured to the first crosshead member, such as by threaded fasteners. In the preferred embodiment, he first crosshead member has an enclosure wall surrounding the second crosshead member and a transverse wall extending transversely across the enclosure wall. The wrist pin fasteners extend through the transverse wall into the wrist pin. The enclosure wall of the first crosshead member may have holes adjacent opposite ends of the wrist pin for removing the wrist pin from the forward end of the connecting rod.
Referring to
Each connecting rod 19 has a forward end that is connected to a crosshead 21. Each crosshead 21 strokes linearly within a stationary crosshead case 23, which is mounted to the pump frame. A pony rod 25 secures to the forward end of each crosshead 21, and a plunger 27 connects to the forward end of pony rod 25 by a clamp 26. The power end of pump 11 causes plunger 27 to stroke linearly within a cylinder in a fluid end block 29. Each cylinder has an access cover 30 secured to fluid end block 29 for inserting and withdrawing one of the plungers 27. Tie rods 31 connect fluid end block 29 to the aft end portion of pump 11. As plunger 27 strokes, fluid is brought into the chamber in forward end 29 from intake 32 and discharged at higher pressure out a discharge (not shown). Intake and discharge valves 33 open and close to draw fluid in and discharge fluid from the chamber.
Referring to
Connecting rod end 47 inserts into window 46 and recess 45. Connecting rod end 47 is generally cylindrical on its exterior and is separated from recess 45 by a bushing 49. Bushing 49 comprises one-half of a sleeve formed of a metal, such as bronze, for serving as a bearing for connecting rod end 47. In this embodiment, a cylindrical wrist pin 51 extends through a transverse bore formed in connecting rod end 47. Wrist pin 51 has an axis that is perpendicular to the longitudinal axis of crosshead 21. A sleeve bearing 53 locates between wrist pin 51 and the bore within connecting rod end 47. Wrist pin 51 has an aft side that is in contact with the forward side of transverse wall 41.
Fasteners such as bolts 55 are preferably employed to fasten insert 43 to the forward side of transverse wall 41. Bolts 55 extend through insert 43 and engage threaded holes formed within the forward side of transverse wall 41. Bolts 55 have heads on the forward end of insert 43. The heads may be fully recessed within counterbores 57 on the so as to provide a smooth or flush forward end for insert 43. Once secured, the forward end of insert 43 may be recessed a short distance from crosshead housing forward end 39.
Referring again to
Pony rod 25 attaches to the forward end of insert 43. Pony rod 25 has an external flange 61 with a bolt pattern. Pony rod bolts 63 extend from flange 61 into threaded holes in insert 43. In this embodiment, flange 61 covers the recessed heads of insert bolts 55, as shown also in
Referring to
Periodically, bushing 49 must be replaced for wear. This is handled by removing access cover 30 and disconnecting pony rod 25 from plunger 27 by releasing clamp 26. The operator removes plunger 27 from the fluid end block 29 or at least moves it sufficiently forward in fluid end block 29 so that pony rod 25 may be removed from the side. The operator removes pony rod 25 by unscrewing bolts 63. Once pony rod 25 is detached, the operator then unscrews bolts 55, releasing insert 43 from transverse wall 41. The operator pulls insert 43 and bushing 49 forward toward fluid end block 29. The operator may install a pulling tool in threaded hole 71 to assist in this pulling motion. Once insert 43 and bushing 49 have been removed, the remaining components will appear as in
While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the claims.
This application claims priority to provisional application Ser. No. 61/219,521, filed Jun. 23, 2009.
Number | Date | Country | |
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61219521 | Jun 2009 | US |