RECIPROCATING PUMP

Abstract

A reciprocating pump including a sleeve comprising a first flow path element and a plunger receivable in the sleeve is provided. The plunger includes a fluid contact face and second flow path element in fluid communication with the fluid contact face. The sleeve and the fluid contact face define a compression chamber comprising an inlet and an outlet. The sleeve and the plunger are moveable relative to one another for adjusting overlap between the first flow path element and the second flow path element for diverting flow of fluid from the compression chamber and out of the second flow path element during a discharge stroke to control flow of fluid pumped out of the outlet.

Description

TECHNICAL FIELD

This invention relates to reciprocating pumps, and more particularly reciprocating pumps having flow control for use for example in mud-pumping and frac-pumping applications in the oil-and-gas industry and in reciprocating gas compressors.

BACKGROUND

Reciprocating pumps are commonly used in applications where high volumes of fluid need to be pumped at high pressures. Highest efficiency reciprocating pumps are most commonly driven by a crank or cam mechanism. Since any given crank or cam mechanism provides for a constant stroke of the plunger, currently two methods are usually used for controlling volumetric flow of these pumps:

• • changing the liner/plunger size (liners and plungers of smaller diameter provide for less flow per stroke of the pump and vice versa),
  • changing the speed of the pump (slowing down the pump will result in less “strokes per minute” which will result in less flow of fluid and vice versa).

Both methods have serious limitations. Changing the liners and plungers is labour-intensive and requires skilled labour, and the pump must be taken out of service while the change is being done, resulting in “down time” of the pump. Controlling the speed may be practical within a limited range if a diesel or gas engine is being used as a prime mover. However, if an electric motor is used as a prime mover, very expensive and inefficient speed controls need to be used, such as VFD or DC controllers. In order to achieve an appropriate match between pumping requirements and capabilities of the engines used as prime movers, expensive, multispeed transmissions are often used, especially in frac-pumping applications where such transmissions are often 6, 7 or even 8-speed units. Mud-pumping applications often use 2-speed transmissions. In reciprocating gas compressor applications, various factors influence the discharged flow of gas, including temperature, humidity and the age of the engine.

Accordingly, there is a need for efficient and inexpensive apparatus and methods for controlling the volumetric flow of fluid discharged from reciprocating pumps.

SUMMARY

The present invention provides for “active” stroke control of reciprocating pumps. Some or all of a plunger stroke can be rendered ineffective by diverting fluid away from the compression chamber of a pump. Controlling the amount of this ineffective portion of the stroke is used to control the actual volume of fluid being pumped out of a pump and downstream of a discharge valve.

One aspect of the invention provides a reciprocating pump having a sleeve and a plunger receivable in the sleeve. The sleeve has a first flow path element. The plunger has a fluid contact face and a second flow path element in fluid communication with the fluid contact face. The sleeve and the fluid contact face define a compression chamber having an inlet and an outlet. The sleeve and the plunger are moveable relative to one another for adjusting overlap between the first flow path element and the second flow path element for diverting flow of fluid from the compression chamber and out of the second flow path element during a discharge stroke to control flow of fluid pumped out of the outlet.

Another aspect of the invention provides a reciprocating pump having a sleeve and a plunger receivable in the sleeve. The sleeve has a sidewall with a control hole. The plunger has a fluid contact face and a helical channel in fluid communication with the fluid contact face. The sleeve and the fluid contact face define a compression chamber with an inlet and an outlet. The sleeve and the plunger are rotatable relative to one another about a common longitudinal axis to adjust the overlap between the control hole and the helical channel for diverting flow of fluid from the compression chamber and out of the control hole during a discharge stroke to control flow of fluid pumped out of the outlet.

A further aspect of the invention provides a reciprocating pump having a sleeve and a plunger receivable in the sleeve. The sleeve has a sidewall with a helical channel. The plunger has a fluid contact face, a sidewall, and a bore in fluid communication with the fluid contact face. A first end of the bore defines a control hole formed in the sidewall. The sleeve and the fluid contact face define a compression chamber with an inlet and an outlet. The sleeve and the plunger are rotatable relative to one another about a common longitudinal axis to adjust the overlap between the control hole and the channel for diverting flow of fluid from the compression chamber and out of the control hole during a discharge stroke to control flow of fluid pumped out of the outlet.

Another aspect of the invention provides a reciprocating pump having a sleeve and a plunger receivable in the sleeve. The plunger has a fluid contact face, and the sleeve and the fluid contact face define a compression chamber with an inlet and an outlet. The pump also includes an accumulator in fluid communication with the compression chamber for diverting flow of fluid away from the compression chamber during a discharge stroke to control flow of fluid pumped out of the output. The accumulator has a housing, a control element slidingly receivable in the housing, a moveable stop, and a force means biasing the control element away from the moveable stop. The control element has a fluid contact face, and the fluid contact face and the housing defining an accumulation chamber. The moveable stop is configured to adjustably define a maximum volume of fluid diverted to the accumulation chamber by restricting movement of the control element.

A further aspect of the invention provides a method of controlling flow of fluid pumped by a reciprocating pump during a discharge stroke. The method includes the steps of:

(a) providing a reciprocating pump with a sleeve and a plunger receivable in the sleeve, the sleeve having a first flow path element, the plunger having a face and a second flow path element in fluid communication with the face, wherein the sleeve and the face define a compression chamber comprising an inlet and an outlet, and the sleeve and the plunger are rotatable along a common axis relative to one another; and
(b) rotatably adjusting overlap between the first flow path element and the second flow path element to divert flow of fluid from the compression chamber and out of the control hole.

Another aspect of the invention provides a method of controlling flow of fluid pumped by a reciprocating pump during a discharge stroke. The method includes the steps of:

(a) providing a reciprocating pump with a compression chamber and an accumulator in fluid communication with the compression chamber, the accumulator having a housing; a control element slidingly receivable in the housing, the control element having a fluid contact face, the fluid contact face and the housing defining an accumulation chamber; and a moveable stop configured to restrict movement of the control element to define a maximum volume of the accumulation chamber; and
(b) moving the moveable stop to adjust the maximum volume of the accumulation chamber to control a volume of fluid diverted from the compression chamber to the accumulation chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which show non-limiting embodiments of the invention:

FIG. 1 is a perspective see-through view of one embodiment according to the present invention;

FIGS. 2A to 2C are side see-through views of the embodiment shown in FIG. 1 at sequential stages of a discharge stroke from bottom dead centre to top dead centre;

FIGS. 3A to 3C are side see-through views of the embodiment shown in FIG. 1 at sequential stages of a discharge stroke from top dead centre to top dead centre;

FIGS. 4A to 4C are side see-through views of the embodiment shown in FIG. 1 at sequential stages of a discharge stroke from top dead centre to top dead centre; and

FIG. 5 is a schematic view of one embodiment according to the present invention.

LIST OF REFERENCE CHARACTERS

• 10 reciprocating pump
• 12 plunger
• 14 sleeve
• 16 overflow chamber
• 18 fluid contact face of plunger 12
• 20 compression chamber
• 22 axis
• 24 control hole
• 26 channel
• 100 reciprocating pump
• 112 plunger
• 114 sleeve
• 118 fluid contact face of plunger 112
• 120 compression chamber
• 128 discharge valve
• 130 discharge manifold
• 132 suction valve
• 134 suction manifold
• 136 hydraulic cylinder
• 138 fluid port
• 140 piston
• 141 fluid contact face of piston 140
• 142 stop
• 143 accumulation chamber
• 144 air pressure source

DETAILED DESCRIPTION

It will be appreciated that numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Furthermore, this description is not to be considered as limiting the scope of the embodiments described herein in any way, but rather as merely describing the implementation of the various embodiments described herein.

FIG. 1 shows a plunger 12, sleeve 14 and overflow chamber 16 of the “wet end” of a reciprocating pump 10 according to one embodiment of the present invention.

The “power end” of plunger 12, shown at the bottom right of FIG. 1, is connected to the cross-head of the pump (not shown) which is, in turn, connected to the crankshaft via a connecting rod (not shown). Rotary motion of the crankshaft is converted into a linearly oscillating motion of plunger 12. Plunger 12 can move between top dead centre (“TDC”, or the position furthest away from the crankshaft where the crank-throw and connecting rod are in line) and Bottom Dead Centre (“BDC”, or the position nearest to the crankshaft where the crank-throw and connecting rod are in line). Reciprocating pump 10 may also be a cam-driven pump. Movement from TDC to BDC is referred to as the suction stroke; movement from BDC to TDC is referred to as the discharge stroke. Reference herein to the term “stroke” of the plunger will be to the discharge stroke unless otherwise stated.

The “wet end” of plunger 12, shown at the upper left of FIG. 1, and in particular fluid contact face 18 is in contact with the fluid being pumped and, with the surrounding walls of sleeve 14, define compression chamber 20. Reference herein to the term “fluid” includes liquids, including suspensions such as drilling mud, and gases.

A typical reciprocating pump also comprises a pump-head assembly which incorporates inlets or suction valves and outlets or discharge valves (not shown), each allowing flow of fluid in one direction only (either into the sleeve or out of it).

Reference is now made to FIGS. 2A to 2C. Sleeve 14 is rotated about axis 22 such that a first flow path element, such as control hole 24 formed in a sidewall of sleeve 14, overlaps with a second flow path element, such as channel 26 formed in a sidewall of plunger 12, throughout the discharge stroke. Channel 26 may be helical. Reference herein to the term “channel” includes any formation on and/or in the plunger through which fluid can flow including cutouts, grooves, bores and the like. Fluid can thus be diverted from compression chamber 20 through helical channel 26, through control hole 24, into overflow chamber 16 and back to a fluid port (not shown) upstream of the suction valve of pump 10. As this diverted fluid flow is uninterrupted during the discharge stroke, pump 10 runs completely unloaded, that is, no fluid is actually pumped.

Reference is now made to FIGS. 3A to 3C. Sleeve 14 is rotated about axis 22 such that control hole 24 overlaps with helical channel 26 only at the beginning and the end of the discharge stroke, allowing the path of flow to be diverted only for these portions of the discharge stroke. Near the middle of the stroke, control hole 24 faces a solid wall of plunger 12 thus interrupting the diverted flow path and forcing the fluid to exit compression chamber 20 through the discharge valve. Pump 10 thus runs loaded only at the middle of the discharge stroke.

Reference is now made to FIGS. 4A to 4C. Sleeve 14 is rotated about axis 22 such that control hole 24 overlaps with helical channel 26 only near the middle of the stroke. Near the beginning and the end of the stroke, control hole 24 faces the solid wall of plunger 12 thus interrupting the diverted flow path and forcing the fluid to exit compression chamber 20 through the discharge valve. Pump 10 thus runs loaded only at the beginning and end of the discharge stroke.

Sleeve 14 can also be rotated about axis 22 such that control hole 24 never overlaps with helical channel 26. In this position (not shown), flow of fluid cannot be diverted through control hole 24, forcing all of the fluid to exit compression chamber 20 through the discharge valve. Pump 10 thus runs fully loaded throughout the discharge stroke.

Control of the diverted fluid flow can be achieved through a number of combinations of channels and control holes. In some embodiments a plurality of channels and/or control holes may be provided. In some embodiments, the channel may be provided on the sleeve and the control hole may be defined by a first end of a bore formed in the plunger (with another end of the bore formed at the fluid contact face of the plunger). In some embodiments, the plunger (instead of the sleeve) may be rotated to effect flow control. In some embodiments, both the plunger and the sleeve may be rotated to effect flow control. The channels and control holes may be any suitable size or shape that, in overlapping cooperation during a discharge stroke, permit incremental, graduated or step-wise control of fluid flow.

FIG. 5 shows a reciprocating pump 100 according to another embodiment of the invention. Many components shown, notably plunger 112, sleeve 114, fluid contact face 118, and compression chamber 120 are similar in all aspects to equivalents components of reciprocating pump 10. Outlet or discharge valve 128, discharge manifold 130, inlet or suction valve 132 and suction manifold 134 are also shown. An accumulator, in the form of a hydraulic cylinder 136 in this particular embodiment, is connected to compression chamber 120 by the means of a fluid port 138. A control element, in the form of a piston 140 in this particular embodiment, can slide dynamically inside hydraulic cylinder 136, and pushed back and forth by pressure from fluid from compression chamber 120, towards stop 142, and by pressure from a force means 144 biasing piston 140 away from stop 142. A fluid contact face 141 of piston 140 and hydraulic cylinder 136 define an accumulation chamber 143.

Force means 144 may be any suitable source of pressure for biasing piston 140 away from stop 142. In the illustrated embodiment, force means 144 is a source of air pressure. In other embodiments, force means 144 may, for example, be spring (e.g. a compression spring), a deformable resilient member, or the like.

Stop 142 is moveable and can be adjusted to restrict the travel of piston 140 during the pump operation, thereby defining a maximum volume of fluid that can be diverted to hydraulic cylinder 136 from compression chamber 120. Stop 142 may be any suitable mechanical, electrical, or magnetic means for restricting the travel of piston 140. In the illustrated embodiment, stop 142 is an annular ring disposed in the hydraulic cylinder 136, wherein the travel of piston 140 is restricted by abutment of a bearing surface 146 of piston 140 against the annular ring.

Before plunger 112 starts its discharge stroke, piston 140 will be moved away from stop 142 against the head of hydraulic cylinder 136, driven by air pressure from air pressure source 144. Suction pressure of the fluid is typically around 25 psi.

At start of discharge stroke of plunger 112, piston 140 will start moving towards stop 142 by the pressure of fluid from compression chamber 120. Since pressure in discharge valve 128 is considerably higher than the air pressure from air pressure source 144 behind piston 140, no fluid will pass through discharge valve 128 until piston 140 hits stop 142. Once piston 140 hits stop 142, pressure will start increasing in compression chamber 120 and usable flow of fluid will start and last until the end of the discharge stroke of plunger 112.

Once plunger 112 starts its suction stroke, piston 140 will start moving away from stop 142 driven by air pressure from air pressure source 144. Only once piston 140 hits the end of its stroke opposite stop 142, suction valve will open 132 and “new” fluid will enter compression chamber 120.

Flow control is thus effected by controlling the position of stop 142; moving it closer to fluid port 138 of hydraulic cylinder 136 will reduce the volume of accumulation chamber 143 and thus increase the effective pump flow; moving it away from fluid port 138 of hydraulic cylinder 136 will increase the volume of accumulation chamber 143 and thus reducing the effective pump flow.

The pumps described above are particularly suitable for use in high pressure and/or high volume applications such as mud-pumping and frac-pumping applications in the oil-and-gas industry, as well as in reciprocating gas compressor applications. Reciprocating pump 100 is particularly suitable for reciprocating gas compressor applications.

Claims

1. A reciprocating pump comprising:

(a) a sleeve comprising a first flow path element;

(b) a plunger receivable in the sleeve, the plunger comprising: i. a fluid contact face and ii. a second flow path element in fluid communication with the fluid contact face;

wherein the sleeve and the fluid contact face define a compression chamber comprising an inlet and an outlet;

and wherein the sleeve and the plunger are moveable relative to one another for adjusting overlap between the first flow path element and the second flow path element for diverting flow of fluid from the compression chamber and out of the second flow path element during a discharge stroke to control flow of fluid pumped out of the outlet.

2. A reciprocating pump according to claim 1, wherein the sleeve comprises a sidewall, and the first flow path element comprises a control hole formed in the sidewall of the sleeve.

3. A reciprocating pump according to claim 2, wherein the plunger comprises a sidewall, and the second flow path element comprises a channel formed in the sidewall of the plunger.

4. A reciprocating pump according to claim 1, wherein the sleeve comprises a sidewall, and the first flow path element comprises a channel formed in the sidewall of the sleeve.

5. A reciprocating pump according to claim 4, wherein the plunger comprises a sidewall, the second flow path element comprises a bore formed in the plunger, and a first end of the bore defines a control hole formed in the sidewall of the plunger.

6. A reciprocating pump according to claim 5, wherein the sleeve and the plunger are rotatable relative to one another about a common axis for adjusting the overlap between the control hole and the channel.

7. A reciprocating pump according to claim 6, wherein the overlap is adjustable between a range of no overlap, whereby no fluid is diverted away from the compression chamber, and complete overlap whereby fluid is completely diverted away from the compression chamber.

8. A reciprocating pump according to claim 7, wherein the sleeve is rotatable.

9. A reciprocating pump according to claim 7, wherein the plunger is rotatable.

10. A reciprocating pump according to claim 9, wherein the channel is helical.

11. A reciprocating pump according to claim 3, wherein the control hole is in fluid communication with an overflow chamber.

12. A reciprocating pump according to claim 6, wherein the channel is in fluid communication with an overflow chamber.

13. A reciprocating pump according to claim 12, wherein the overflow chamber is in fluid communication with a fluid port upstream of the inlet.

14. A reciprocating pump according to claim 13, wherein the sleeve comprises a hollow cylinder with an opening for receiving the plunger.

15. A reciprocating pump according to claim 14, wherein the plunger comprises a cylinder.

16. A reciprocating pump according to claim 15, wherein the control hole is round.

17. A reciprocating pump comprising:

(a) a sleeve comprising a sidewall, the sidewall comprising a control hole;

(b) a plunger receivable in the sleeve, the plunger comprising: i. a fluid contact face and ii. a helical channel in fluid communication with the fluid contact face;

wherein the sleeve and the fluid contact face define a compression chamber comprising an inlet and an outlet;

and wherein the sleeve and the plunger are rotatable relative to one another about a common longitudinal axis to adjust the overlap between the control hole and the helical channel for diverting flow of fluid from the compression chamber and out of the control hole during a discharge stroke to control flow of fluid pumped out of the outlet.

18. A reciprocating pump according to claim 17, wherein the sleeve is rotatable.

19. A reciprocating pump according to claim 18, wherein the control hole is in fluid communication with an overflow chamber.

20. A reciprocating pump according to claim 19, wherein the overflow chamber is in fluid communication with a fluid port upstream of the inlet.

21. A reciprocating pump according to claim 20, wherein the sleeve comprises a hollow cylinder with an opening for receiving the plunger.

22. A reciprocating pump according to claim 21, wherein the plunger comprises a cylinder.

23. A reciprocating pump comprising:

(a) a sleeve comprising a sidewall, the sidewall comprising a helical channel;

(b) a plunger receivable in the sleeve, the plunger comprising: i. a fluid contact face; ii. a sidewall; iii. a bore in fluid communication with the fluid contact face, a first end of the bore defining a control hole formed in the sidewall;

wherein the sleeve and the fluid contact face define a compression chamber comprising an inlet and an outlet;

and wherein the sleeve and the plunger are rotatable relative to one another about a common longitudinal axis to adjust the overlap between the control hole and the channel for diverting flow of fluid from the compression chamber and out of the control hole during a discharge stroke to control flow of fluid pumped out of the outlet.

24. A reciprocating pump according to claim 23, wherein the sleeve is rotatable.

25. A reciprocating pump according to claim 24, wherein the helical channel is in fluid communication with an overflow chamber.

26. A reciprocating pump according to claim 25, wherein the overflow chamber is in fluid communication with a fluid port upstream of the inlet.

27. A reciprocating pump according to claim 26, wherein the sleeve comprises a hollow cylinder with an opening for receiving the plunger.

28. A reciprocating pump according to claim 27, wherein the plunger comprises a cylinder.

29. A reciprocating pump comprising:

(a) a sleeve;

(b) a plunger receivable in the sleeve, the plunger comprising a fluid contact face, wherein the sleeve and the fluid contact face define a compression chamber comprising an inlet and an outlet;

(c) an accumulator in fluid communication with the compression chamber for diverting flow of fluid away from the compression chamber during a discharge stroke to control flow of fluid pumped out of the output, the accumulator comprising: i. a housing; ii. a control element slidingly receivable in the housing, the control element comprising a fluid contact face, the fluid contact face and the housing defining an accumulation chamber; iii. a moveable stop configured to adjustably define a maximum volume of fluid diverted to the accumulation chamber by restricting movement of the control element; and iv. a force means biasing the control element away from the moveable stop.

30. A reciprocating pump according to claim 29 wherein the housing comprises a hydraulic cylinder.

31. A reciprocating pump according to claim 30 wherein the control element comprises a piston, and a travel of the piston is adjustably restricted by the moveable stop.

32. A reciprocating pump according to claim 31 wherein a first pressure exerted by the force means is less than a second pressure sufficient to pump fluid out of the outlet.

33. A reciprocating pump according to claim 32 wherein the force means comprises a spring.

34. A reciprocating pump according to claim 33 wherein the spring comprises a compression spring.

35. A reciprocating pump according to claim 32 wherein the force means comprises a source of fluid pressure.

36. A reciprocating pump according to claim 35 wherein the fluid pressure is air pressure.

37. A reciprocating pump according to claim 31 wherein the moveable stop comprises an annular ring disposed in the housing, wherein the travel of the piston is restricted by abutment of a bearing surface of the piston against the annular ring.

38. A method of controlling flow of fluid pumped by a reciprocating pump during a discharge stroke, the method comprising:

(a) providing a reciprocating pump comprising a sleeve and a plunger receivable in the sleeve, the sleeve comprising a first flow path element, the plunger comprising a face and a second flow path element in fluid communication with the face, wherein the sleeve and the face define a compression chamber comprising an inlet and an outlet, and the sleeve and the plunger are rotatable along a common axis relative to one another; and

(b) rotatably adjusting overlap between the first flow path element and the second flow path element to divert flow of fluid from the compression chamber and out of the control hole.

39. A method according to claim 38 wherein step (b) comprises rotating the sleeve.

40. A method according to claim 38 wherein step (b) comprises rotating the plunger.

41. A method according to claim 40 further comprising:

(c) allowing fluid flowing out of the second flow path element to flow to an overflow chamber.

42. A method according to claim 41 further comprising:

(d) allowing fluid from the overflow chamber to flow to a fluid port upstream of the inlet.

43. A method of controlling flow of fluid pumped by a reciprocating pump during a discharge stroke, the method comprising:

(a) providing a reciprocating pump comprising a compression chamber and an accumulator in fluid communication with the compression chamber, the accumulator comprising: i. a housing; ii. a control element slidingly receivable in the housing, the control element comprising a fluid contact face, the fluid contact face and the housing defining an accumulation chamber; and iii. a moveable stop configured to restrict movement of the control element to define a maximum volume of the accumulation chamber;

(b) moving the moveable stop to adjust the maximum volume of the accumulation chamber to control a volume of fluid diverted from the compression chamber to the accumulation chamber.

44. A method according to claim 43 wherein step (a) comprises providing a force means to bias the control element away from the moveable stop.

45. A method according to claim 44 wherein step (a) comprises maintaining a first pressure exerted by the force means to be less than a second pressure sufficient to pump fluid out of an outlet of the reciprocating pump.

46. (canceled)

47. (canceled)