Plunger Pump, Plunger, and Method of Manufacturing Plunger Pump
A plunger pump includes a pump fluid end having a fluid chamber and a suction bore, discharge bore, and plunger bore in communication with the fluid chamber. A plunger is arranged to reciprocate into and out of the fluid chamber through the plunger bore. The plunger has a plunger body with an inner cavity and an insert disposed in the inner cavity such that the combined stiffness of the insert and plunger body is greater than the stiffness of the plunger body. A crank mechanism is coupled to the plunger and operable to reciprocate the plunger.
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FIELDThe field relates to construction of high pressure plunger pumps.
BACKGROUNDWell service pumps are used in the oil and gas industry to pump fluids down a well for various purposes. One common use of well service pumps is in hydraulic fracturing of formations. The pump can be used to pump a high pressure fluid containing solids into the well, where the high pressure fluid will expand fractures in the formation or fracture the formation, leaving larger fluid passages through which formation fluids can flow into the well. The solids in the fluid will remain in the larger fluid passages to prop the fluid passages open, thereby increasing well production.
Well service pumps are commonly plunger pumps, which are a type of reciprocating positive displacement pumps. In these pumps, a plunger reciprocates axially in a fluid end, with a packing retained between the fluid end and plunger preventing leakage during the reciprocating motion of the plunger. A small annular gap is typically provided between the outer diameter of the plunger and the inner diameter of the packing to prevent galling or surface damage to the plunger as the plunger reciprocates. However, slight increases in gap clearance may have a detrimental effect on the life of the packing due primarily to accelerated packing material extrusion.
High plunger compressive strength is typically needed to help maximize packing life and the operational efficiencies of the pump. Many conventional high pressure well service plunger pumps use plungers of solid construction to achieve high plunger compressive strength. However, larger diameter and/or longer stroke plungers with solid construction are often unwieldy to handle during routine maintenance operations. Hollow plungers have been proposed, but these hollow plungers tend to deflect diametrically under loads.
Plunger pumps use a crank mechanism to provide the reciprocating motion of the plunger. The crank mechanism typically includes an extension rod that is rigidly attached to a crosshead that is constrained to move axially by the frame of the pump. The crosshead is coupled to an eccentric crankshaft via a wrist pin and connecting rod. As the crankshaft rotates, the connecting rod transfers this motion to the crosshead. Because the crosshead is constrained to move axially, the rotational motion will be converted into reciprocating motion, which is transferred to the plunger via the extension rod.
The wrist pin is retained to the crosshead and is supported using a bearing located internally within the connecting rod. An annular gap is typically provided between the outer diameter of the wrist pin and the inner diameter of the wrist pin bearing to allow distribution of a lubrication film and to prevent load transfer from the relatively large rod to the much smaller wrist pin. This annular gap allows deformation of the connecting rod bearing surface during high load conditions, which can create uneven loading and premature bearing failure, such as galling.
Many conventional fluid ends feature a valve over valve arrangement, where the suction and discharge valves are positioned vertically, one valve above the other, and perpendicular to the intersecting plunger bore. This provides a rather compact fluid end design, which is desirable for mobile applications. However, the intersection of these two bores creates a surface discontinuity, significantly increasing stresses within these highly localized areas. These surfaces normally fail due to fatigue as they are also exposed to cyclical loadings.
SUMMARY OF THE DISCLOSUREThe subject matter disclosed herein relates to improvements in a plunger pump. In one illustrative embodiment, a plunger pump comprises a pump fluid end having a fluid chamber and a suction bore, discharge bore, and plunger bore in communication with the fluid chamber. A plunger is arranged to reciprocate into and out of the fluid chamber through the plunger bore. The plunger has a plunger body with an inner cavity and an insert disposed in the inner cavity to increase the stiffness of the plunger. A crank mechanism is coupled to the plunger and operable to reciprocate the plunger.
It is to be understood that both the foregoing general description and the following detailed description are exemplary of certain embodiments of the invention and are intended to provide an overview or framework for understanding the disclosure. The accompanying drawings illustrate various exemplary embodiments of the invention and are included to provide a further understanding of the disclosure and the principles and operation of the disclosed embodiments.
The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
In the following detailed description, numerous specific details may be set forth in order to provide a thorough understanding of the disclosed embodiments. However, it is to be understood that other embodiments of the invention may be practiced without incorporating some or all of the specific details that are a part of these disclosed embodiments. In other instances, well-known features or processes may not be described in detail in the disclosed embodiments so as not to unnecessarily obscure the disclosure. In addition, like or identical reference numerals may be used to identify common or similar elements between the embodiments.
A plunger 28 is arranged in the plunger bore 20a and may reciprocate into and out of the fluid chamber 16. The reciprocating motion is provided by a crank mechanism 34 that is located in the pump power end 14. During the suction stroke of the plunger 28, the plunger 28 is withdrawn from the fluid chamber 16 into the plunger bore 20a, and fluid is drawn from the suction manifold 21, through the suction valve 23a, into the fluid chamber 16. During the discharge stroke of the plunger 28, the plunger 28 is extended from the plunger bore 20a into the fluid chamber 16, whereby the plunger 28 forces the fluid in the fluid chamber 16 through the discharge valve 23b and into the discharge port 25.
The plunger 28 slides through a packing arrangement 30 mounted at an end of the plunger bore 20a. In one illustrative embodiment, as shown in
In one illustrative embodiment, as shown in
The inner cavity 38 occupies a substantial volume of the plunger body 36. For example, the inner cavity 38 may occupy 30% to 60% of the volume of the plunger body 36. The plunger 28 with the inner cavity 38 will have a substantially reduced weight compared to a solid plunger made of the same material and size.
In one embodiment, an insert 44 is disposed inside the inner cavity 38 to increase the stiffness of the plunger 28 and prevent diametric deflection of the plunger 28 under load. That is, the combined stiffness of the insert 44 and plunger body 36 is greater than the stiffness of the plunger body 36 alone. In one embodiment, one of the properties of the insert 44 is that the shape and size of the insert 44 are such that there is an interference fit between the inner surface 46 of the plunger body 36 and the outer surface 48 of the insert 44. The interference fit between the surfaces 46, 48 will place the plunger body 36 in tension during the relaxed state of the plunger pump, such as during the suction stroke of the pump. This tension will act as a pre-tension that will help to partially counteract hydraulic forces encountered during the discharge stroke of the pump. Another property of the insert 44 may be that the stiffness of the insert 44 is comparable to, e.g., approximately equal to, or higher than the stiffness of the plunger body 36. Stiffness is a measure of rigidity of a body and is a function of material properties and geometry.
In one embodiment, the shape of the insert 44 is the same as the shape of the inner cavity 38. For example, both the insert 44 and inner cavity 38 could be cylindrical in shape. In one embodiment, the volume of the insert 44 is substantially less than the volume of the inner cavity 38. For example, the volume of the insert 44 may be 30% to 70% of the volume of the inner cavity 38. The length of the insert 44 may be the same as or may be shorter than the length of the inner cavity 38. The insert 44 may be hollow as shown or may be solid. In general, a hollow insert will add less weight to the plunger 28 compared to a solid insert of the same material and length. For overall weight management of the plunger 28, the insert 44 along with the plunger body 36 and end cap 42 may be made of lightweight material such as aluminum. However, it is possible to use alternate materials for construction of these parts, from low cost steel to extremely lightweight composites. Also, it is not necessary that the material of the insert 44 is the same as that of the plunger body 36 and end cap 42.
Returning to
The crosshead 54 is arranged inside a cylinder 26 supported inside the pump power end 14. The axial axis of the cylinder 26 is generally aligned with that of the plunger bore 20a. The connecting rod 56 is coupled at one end to the crosshead 54 and at the other end to the crankshaft 60. As the crankshaft 60 rotates, the connecting rod 56 will transfer this rotational motion to the crosshead 54. Because the crosshead 54 is constrained to move linearly by the cylinder 26, the rotational motion will be converted into reciprocating motion, which will be transferred to the plunger 28 via the adapter plate 50.
As mentioned earlier, an extension rod may be used in lieu of an adapter plate to couple the plunger to the crosshead.
In
Retaining the wrist pin 78 to the connecting rod 56 as described above eliminates the need to provide a wrist pin bearing internally within the connecting rod, i.e., within the hole 76, to support rotation of the wrist pin 78. If a wrist pin bearing had to be provided in the hole 76, it would be necessary to maintain an annular space between the wrist pin and the wrist pin bearing for lubrication film and to prevent load transfer from the relatively large connecting rod end to the much smaller wrist pin, especially during the pump's discharge stroke. However, the annular space will allow deformation of the connecting rod bearing surface during high load conditions, creating uneven loading and premature bearing failure, such as galling. The need for a wrist pin bearing, and annular space between the wrist pin and wrist pin bearing, is eliminated by retaining the wrist pin 78 to the connecting rod 56 such that the wrist pin 78 and connecting rod 56 essentially form a single body.
The wrist pin 78 may be retained to the connecting rod 56 by a suitable retainer fastener. In the embodiment of
In all the embodiments described above, lubrication ports may be provided as necessary to allow lubricant to be applied to the bearing and bushing surfaces.
Returning to
A valve cage retainer 110 is arranged in the fluid chamber 16 and attached to the pump fluid end 12. The suction valve 23a is mounted below the valve cage retainer 110 and is biased against a suction valve seat 104a by means of a spring 106a. The suction valve 23a is lifted off the suction valve seat 104a when the force of the fluid from the suction manifold 21 overcomes the force of the spring 106a. When the suction valve 23a is lifted off the suction valve seat 104a, fluid will flow into the fluid chamber 16. The arrangement of the valve cage retainer 110 is such that the valve cage retainer 110 does not prevent the plunger 28 from extending into the fluid chamber 16. A removable end cover 112 may be mounted in the access bore 20b opposite to the plunger 28.
In
The fillet surfaces 124, 126 remove the material that typically exhibits high stress levels in the pump fluid end, greatly improving the overall strength of the pump fluid end. The reduced diameter bore 128 also helps improve the structure integrity of the discharge bore 18b. In addition, the tapered discharge valve seat bore 120 is translated away from the plunger axis 134. This allows a smoother transition between the fluid chamber 16 and the discharge valve seat bore 120.
While exemplary embodiments of the invention have been described herein, 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 claimed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims
1. A plunger pump, comprising:
- a pump fluid end having a fluid chamber, a suction bore in communication with the fluid chamber, a discharge bore in communication with the fluid chamber, and a plunger bore in communication with the fluid chamber;
- a plunger arranged to reciprocate into and out of the fluid chamber through the plunger bore, the plunger having a plunger body with an inner cavity and an insert disposed in the inner cavity, wherein a combined stiffness of the plunger body and insert is greater than a stiffness of the plunger body; and
- a crank mechanism coupled to the plunger and operable to reciprocate the plunger.
2. The plunger pump of claim 1, wherein the inner cavity occupies 30% to 60% of the volume of the plunger body.
3. The plunger pump of claim 1, wherein the insert is configured such that there is an interference fit between an outer surface of the insert and an inner surface of the plunger body.
4. The plunger pump of claim 3, wherein the insert is a hollow insert.
5. The plunger pump of claim 3, wherein the insert is a solid insert.
6. The plunger pump of claim 3, wherein a volume of the insert is 30% to 70% of a volume of the inner cavity.
7. The plunger pump of claim 1, wherein the crank mechanism comprises a crosshead coupled to the plunger, a connecting rod coupled to the crosshead, and a crankshaft coupled to the connecting rod.
8. The plunger pump of claim 7, wherein a coupling between the crosshead and connecting rod comprises a wrist pin coupled to the crosshead and retained to the connecting rod such that there is no relative rotation between the wrist pin and the connecting rod.
9. The plunger pump of claim 8, wherein the wrist pin is retained to the connecting rod by inserting a retainer fastener through the connecting rod into a hole inside the wrist pin.
10. The plunger pump of claim 7, wherein a coupling between the crosshead and connecting rod comprises a pair of surface holes in the connecting rod and a pair of wrist pins engaging the surface holes and retained to the crosshead.
11. The plunger pump of claim 7, wherein the crank mechanism further comprises an extension rod coupling the plunger to the crosshead.
12. The plunger pump of claim 7, wherein the crank mechanism further comprises an adapter plate coupling the plunger to the crosshead.
13. The plunger pump of claim 7, wherein the wrist pin is received in a hole in the connecting rod, and wherein the hole and wrist pin are configured such that there is an interference fit between the wrist pin and the connecting rod.
14. The plunger pump of claim 1, wherein the suction bore intersects the plunger bore, and wherein a transition between the suction bore and plunger bore comprises a fillet surface.
15. The plunger pump of claim 14, wherein the discharge bore intersects the plunger bore, and wherein a transition between the discharge bore and plunger bore comprises a combination of a fillet surface, a reduced diameter bore, a tapered surface, and an enlarged diameter bore.
16. The plunger pump of claim 14, wherein a tapered valve seat is formed in each of the suction bore and discharge bore.
17. A plunger for a plunger pump, comprising:
- a plunger body having an inner cavity defined therein and an open end; and
- an insert disposed in the inner cavity, the insert being configured such that a combined stiffness of the insert and plunger body is greater than a stiffness of the plunger body; and
- an end cap mounted at the open end and adapted for coupling to an adapter plate or extension rod of a crank mechanism.
18. The plunger of claim 17, wherein the inner cavity occupies 30% to 60% of the volume of the plunger body.
19. The plunger of claim 17, wherein the insert is configured such that there is an interference fit between an outer surface of the insert and an inner surface of the plunger body.
20. The plunger of claim 17, wherein the insert is a hollow insert.
21. The plunger of claim 17, wherein the insert is a solid insert.
22. The plunger of claim 17, wherein a volume of the insert is 30% to 70% of a volume of the inner cavity.
23. A method of manufacturing a plunger pump, comprising:
- forming a pump fluid end having a fluid chamber, a suction bore and a discharge bore disposed along a first axis and intersecting with the fluid chamber, and a plunger bore disposed along a second axis that is perpendicular to the first axis and intersecting with the fluid chamber;
- forming a plunger having a plunger body with an inner cavity;
- disposing an insert in the inner cavity such that a combined stiffness of the plunger body and insert is greater than a stiffness of the plunger body;
- arranging the plunger in the plunger bore; and
- coupling a crank mechanism to the plunger to reciprocate the plunger into and out of the fluid chamber through the plunger bore.
24. The method of claim 23, wherein coupling the crank mechanism comprises coupling a crosshead of the crank mechanism to the plunger and coupling a connecting rod of the crank mechanism to the crosshead, wherein coupling the connecting rod comprises retaining a wrist pin coupled to the crosshead to the connecting rod such that there is no relative motion between the wrist pin and the connecting rod.
25. The method of claim 23, wherein forming the pump fluid end comprises forming a first transition between the suction bore and plunger bore comprising a first fillet surface and forming a second transition between the discharge bore and plunger bore comprising a second fillet surface.
Type: Application
Filed: Nov 11, 2013
Publication Date: May 14, 2015
Applicant: National Oilwell Varco, L.P. (Houston, TX)
Inventors: Jason Neal Whaley (Bells, TX), Manuel Moeller (Tulsa, OK), Heath Gregory Folk (Houston, TX)
Application Number: 14/076,437
International Classification: F04B 53/14 (20060101);