US20070009367A1

US20070009367A1 - Close fit cylinder and plunger

Info

Publication number: US20070009367A1
Application number: US11/111,116
Authority: US
Inventors: Dieter Tischler; Eric Roll; Jose Munoz; Christopher Tucker; Weishun Ni; Mitchell Reineck
Original assignee: KMT Waterjet Systems Inc
Current assignee: KMT Waterjet Systems Inc
Priority date: 2005-04-21
Filing date: 2005-04-21
Publication date: 2007-01-11
Also published as: WO2006116343A2; WO2006116343A3

Abstract

A pump that includes a cylinder housing having a through bore. A cylinder liner is disposed substantially within the through bore and includes a substantially uniform aperture having a first diameter. A plunger includes an engagement portion having a second diameter smaller than the first diameter. The first diameter and the second diameter are sized to define a first diametrical clearance that is less than about 0.1 percent of the second diameter.

Description

BACKGROUND

The present invention relates to a cylinder/plunger arrangement for a high-pressure pump. More particularly, the invention relates to a cylinder/plunger arrangement for a high-pressure pump that reduces leakage without the use of additional mechanical seals.
Pumps are commonly used to move fluids from one place to another and to pressurize fluids for storage or use. Many different types of pumps are suited to pumping fluids, including reciprocating plunger pumps that employ one or more plungers that reciprocate within a bore or cylinder to move or pressurize the working fluid.
In some applications, pumps capable of delivering high-pressure fluid are required. For example, water-jet cutting may require fluid that is pressurized to a working pressure in excess of 10,000 pounds per square inch. The high-pressure water flows through a nozzle to cut a workpiece, such as a sheet of steel. These pumps are susceptible to large internal leakage and inefficiency due to the high working pressure of the fluid. In addition, leakage of the working fluid can cause erosion of the pump components that further reduces the pump efficiency, and increases operational costs due to the additional maintenance and down time.

SUMMARY

The invention provides a pump including a cylinder housing having a through bore. A cylinder liner is disposed substantially within the through bore and includes a substantially uniform aperture having a first diameter. A plunger includes an engagement portion having a second diameter that is smaller than the first diameter. The first diameter and the second diameter are sized to define a first diametrical clearance that is less than about 0.1 percent of the second diameter.
The invention further provides a pump that includes a cylinder housing that has a through bore. A cylinder liner is disposed substantially within the through bore and includes a substantially uniform aperture that has a first diameter. A plunger includes an engagement portion that has a second diameter and a clearance portion that has a third diameter. The first diameter and the second diameter are sized to define a first diametrical clearance and the first diameter and the third diameter are sized to define a second diametrical clearance that is between about 5 and 20 times the first diametrical clearance.
The invention also provides a pump that includes a plurality of pumping elements. Each pumping element includes a cylinder housing that has a through bore. Each pumping element also includes a cylinder liner disposed substantially within the through bore and including a substantially uniform aperture having a first diameter. The pumping elements also include a plunger that has a drive end, an engagement portion opposite the drive end that has a second diameter, and a clearance portion between the drive end and the engagement portion that has a third diameter. The first diameter and the second diameter are sized to define a first diametrical clearance and the first diameter and the third diameter are sized to define a second diametrical clearance that is between about 5 and 20 times the first diametrical clearance. The pump also includes a drive member coupled to each drive end and operable to move each plunger in a reciprocating fashion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a pump including a drive end and a pressure end;
FIG. 2 is a section view of the pump of FIG. 1 taken along line 2-2 of FIG. 1;
FIG. 3 is a perspective view of a pressure end of the pump of FIG. 1;
FIG. 4 is a perspective view of another pressure end of a pump;
FIG. 5 is section view of the pressure end of FIG. 3 taken along line 5-5 of FIG. 3;
FIG. 6 is a perspective view of a pumping unit of the pressure end of FIG. 3;
FIG. 7 is a section view of the pumping unit of FIG. 6 taken along line 7-7 of FIG. 6; and
FIG. 8 is an exaggerated enlarged view of a portion of the pumping unit of FIG. 6 taken along line 8-8 of FIG. 7.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
FIG. 1 illustrates a pump 10 that is suited to delivering a high-pressure fluid (e.g., water, oil, etc.) for use in one or more applications. The particular pump 10 illustrated is capable of delivering fluid at a pressure of at least about 10,000 pounds per square inch (psi) (70 MPa) with pressures in excess of 50,000 psi (350 MPa) being common. Pumps 10 of this type are well suited to applications such as water jet cutters that require high-pressure water be delivered to a nozzle.
The pump 10 includes a drive portion 15 and a pressure portion 20 attached to the drive portion 15. The pressure portion 20 includes a pressure plate 25 and five pumping units 30 connected to the pressure plate 25 and extending above the pressure plate 25. Of course, other constructions may include more or fewer pumping units 30 as desired. For example, FIG. 4 illustrates a pressure portion 20 a that includes only three pumping units 30. The pressure portion 20 a of FIG. 4 is capable of reaching the same pressure levels as the pressure portion 20 of FIG. 1. However, the volumetric output of a pump 10 with only three pumping units 30 is generally lower than the volumetric output of the pump 10 with five pumping units 30. Thus, the number of pumping units 30 can be varied to achieve the desired flow rate of pressurized fluid for the particular application.
As shown in FIG. 2, the drive portion 15 includes a drive shaft 35 that extends from the lower end of the drive portion 15 to allow for its connection to a drive member, such as but not limited to an electric motor, a transmission, a sprocket, a pulley, a gear, or another drive mechanism. The drive shaft 35 is supported for rotation by two tapered roller bearings 40 that are positioned within a drive housing 45 and one bearing 50 positioned within the pressure plate 25. The bearings 40 positioned in the drive housing 45 are arranged to carry a thrust load in either direction, thus eliminating the need for a thrust bearing. Of course, other types of bearings and support arrangements can be employed if desired.
The drive shaft 35 supports a swash plate 55 (sometimes referred to as a wobble plate) near the end of the drive shaft 35 opposite the end extending from the pump 10. The swash plate 55 includes an engagement surface 60 that is skewed relative to a drive axis 65 of the drive shaft 35. Thus, as the drive shaft 35 rotates, a high point 70 and a low point 75 defined by the engagement surface 60 rotate about the drive axis 65.
Other constructions may employ other arrangements for the drive portion 15. For example, one construction employs a crankshaft rather than a swash plate 55. The crankshaft includes one or more throw portions that convert the rotation of the crankshaft into a reciprocating motion that is similar to that achieved using a swash plate 55. Thus, the invention should not be limited to the particular drive portion 15 illustrated herein.
With continued reference to FIG. 2, the pressure portion 20 attaches to a drive skirt 80 that, in turn attaches to the drive housing 45. As discussed, the pressure portion 20 includes one or more pumping units 30. As shown in FIG. 5, each pumping unit 30 is positioned over an aperture 85 that extends through the pressure plate 25. Each pumping unit 30 includes a plunger 90 that extends into the aperture 85 and supports a drive collar 95 near the lowermost end. A drive pin 100 (shown in FIG. 2) interconnects the drive collar 95 and the swash plate 55 such that rotation of the swash plate 55 produces a reciprocating motion of the drive pin 100 and the plunger 90. A bushing 105 (shown in FIG. 2) can be positioned to surround at least a portion of the drive pin 100 and to guide the pin 100 during pump operation. In most constructions, the plunger has a diameter that is less than about 1.5 inches (38.1 mm) with larger diameters being possible.
With continued reference to FIG. 5, each pumping unit 30 includes a pump cylinder 110 that cooperates with the plunger 90 to at least partially define a fluid space 115 for the fluid being pumped. A check valve 120 is disposed on top of the pump cylinder 110 to enclose the fluid space 115. The check valve 120 allows the pumped fluid to pass in only one direction, thus inhibiting unwanted reverse flow within the pump 10. As one of ordinary skill in the art will realize, many different check valves 120 will function with the invention. As such, the invention should not be limited to the check valve 120 illustrated herein.
Turning to FIGS. 6 and 7, the pump cylinder 110 and plunger 90 are shown in greater detail. The pump cylinder 110 includes a plurality of apertures 125 that provide a flow path for coolant into the pump cylinder 110 and/or allow for the removal of leakage, as will be described with regard to FIG. 7. In addition, the pump cylinder 110 includes a threaded portion 130 that receives the check valve 120. As shown in FIG. 7, the pump cylinder 110 includes a through bore 135 that has a bore diameter 140 (shown in FIG. 8). A cylinder liner 145 is positioned within the bore 135 and extends along at least a portion of the length of the through bore 135. In most constructions, the cylinder liner 145 is a circular tube that includes an outside diameter 150 (shown in FIG. 8) and an inside diameter 155 (shown in FIG. 8). The outside diameter 150 is larger than the bore diameter 140 of the cylinder 110 to establish an interference fit. The magnitude of the interference fit assures that, once installed, the cylinder liner 145 remains in compression. More specifically, the interference fit establishes a residual compressive stress in the cylinder liner 145 that is large enough to maintain the cylinder liner 145 in compression during normal pump operating conditions.
The plunger 90 includes an engagement portion 160 that extends from near the end opposite the drive collar 95. The engagement portion 160 defines a plunger diameter 165 (shown in FIG. 8) that is slightly smaller than the inside diameter 155 of the cylinder liner 145 such that the plunger 90 fits within the cylinder liner 145 with clearance between the plunger 90 and the cylinder liner 145. The plunger diameter 165 and the inside diameter 155 cooperate to define an engaged diametrical clearance 170 (shown in FIG. 8). In most constructions, the plunger diameter 165 and the inside diameter 155 are sized to produce a diametrical clearance 170 that is less than about 0.1 percent of the plunger diameter 165. In preferred constructions, the diametrical clearance 170 is about 0.062 percent of the plunger diameter 165. For example, in constructions that employ a plunger 90 having a plunger diameter 165 of 0.375 inches (9.5 mm), the diametrical clearance 170 would be less than about 0.0004 inches (0.01 mm), with a preferred diametrical clearance 170 of about 0.00023 inches (0.006 mm). Experimentation has shown that diametrical clearances 170 in this range reduce leakage between the plunger 90 and cylinder liner 145. However, the diametrical clearance 170 is still sufficient to allow some fluid to leak between the plunger 90 and the cylinder liner 145. This leakage provides a hydrodynamic layer between the plunger 90 and the cylinder liner 145 that cools the components, lubricates the plunger 90 and cylinder liner 145, and maintains the plunger 90 centered within the cylinder liner 145 such that the plunger 90 does not contact the cylinder liner 145 during pump operation. Once the leakage passes the plunger 90, it gathers in a leakage space 175 where it can be removed via the apertures 125 in the pump cylinder 110. Thus, the plunger 90 and the cylinder liner 145 cooperate to control leakage without the use of other mechanical sealing mechanisms.
In most constructions, the engagement portion 160 extends from near the end of the plunger opposite the drive collar 95 for a length of between about two and one half and eight times the plunger diameter 165 with preferred constructions having an engagement length that is about four times the plunger diameter 165. Thus, continuing the above example, the 0.375 inch (9.5 mm) diameter plunger would include an engagement length between about 0.94 inches (23.8 mm) and 2.25 inches (57.2 mm) with a preferred length of at least about 1.5 inches (38.1 mm). Experimentation has shown that the pressure of leaking fluid between the plunger 90 and the cylinder liner 145 drops significantly (e.g., more than about 75 percent) after traveling about 2 inches (51 mm) along the length of the plunger 90. After traveling about 2.5 inches (63.5 mm) the pressure drops to a level that can be easily managed and drained away from the pumping unit 30. Of course, the length of the engagement portion 160 may vary with the diametrical clearance 170 or other factors. For example, if a slightly larger diametrical clearance 170 is employed, the length of the engagement portion 160 may need to be greater than 2.5 inches (63.5 mm) to achieve the same drop in pressure. Thus, the invention should not be limited to engagement portions 160 of the length discussed herein.
As illustrated in FIG. 8, some constructions may provide a step 180 in the plunger 90. Specifically, the plunger 90 includes a tapered portion that extends from the engagement portion 160 to a clearance portion 185 (shown in FIG. 7) that has a clearance diameter 190. The clearance diameter 190 is sized to define a diametrical clearance 195 between the clearance portion 185 of the plunger 90 and the cylinder liner 145 that is between about 5 and 20 times the engaged diametrical clearance 170. In preferred constructions, the diametrical clearance 195 between the clearance portion 185 of the plunger 90 and the cylinder liner 145 is about 10 times the engaged diametrical clearance 170. Thus, continuing the example from above, the diametrical clearance 195 between the clearance portion 185 of the plunger 90 and the cylinder liner 145 would be between about 0.002 inches (0.05 mm) and 0.008 inches (0.20 mm), with a preferred diametrical clearance 195 of about 0.0023 inches (0.06 mm).
Working fluid (typically water) leaks between the plunger 90 and the cylinder liner 145 during pump operation. The reduced clearance of the clearance portion reduces the quantity of the leakage. However, the reduced flow area also produces an increase in flow velocity of the leaking fluid. As the clearance is reduced, the velocity increases, thus producing a high-velocity jet that is capable of eroding one or both of the plunger 90 and the liner 145. The increased diametrical clearance 195 adjacent the clearance portion 185 of the plunger 90 greatly increases the flow area available to the leakage flow. The increase in flow area produces a corresponding reduction in flow velocity. The reduced flow velocity reduces the likelihood of erosion of the cylinder liner 145 and/or plunger 90 due to the jet formed by the escaping fluid. It should be noted that FIG. 8 greatly exaggerates the various clearances 170, 195 between the components for illustrative purposes. It should also be noted that pumps of the type described herein are particularly suited for use in producing a high-pressure flow of water. Water exhibits unique properties, especially at high pressures, when compared to other fluids (e.g., oil fuel, diesel, and the like). These properties make it more difficult to produce high-pressure water using pumps with small clearances.
During pump operation, the plunger 90, and the cylinder liner 145 are subjected to large forces. In addition, pump operation can produce significant heating of the various components. The extreme operating environment of the high-pressure pump 10 makes material selection very important. With the small diametrical clearances 170, 195 employed, thermal expansion of the plunger 90 and the cylinder liner 145 should occur at similar rates. Additionally, the high-pressure within the cylinder liner 145 will cause expansion of the liner 145, thus requiring a material capable of expanding under the pressure without premature failure.
The heating that occurs within the pump 10 makes ceramic materials a particularly suitable choice, with other materials (e.g., metals, composites, and the like) also being possible. Plungers 90 and cylinder liners 145 manufactured from several different materials (e.g., alumina ceramic, zirconia ceramic, zirconia toughened alumina (ZTA) ceramic, tungsten carbide, and 440C stainless steel, and the like) were tested to determine if they would be suitable for use in the environment of the pump 10. While many of the materials tested were suitable for use, it was found that a cylinder liner 145 manufactured using an alumina ceramic and a plunger 90 manufactured using a ZTA ceramic provided good fatigue life, and therefore long operating life (generally in excess of 1000 hours), while being less susceptible to erosion during operation and failure during pump assembly. One alumina ceramic suitable for use as a liner 145 is AmAlOx 87 sold by Astro Met, Inc. located at 9974 Springfield Pike Road, Cincinnati, Ohio 45215. AmAlOx 87 alumina is a 99.95% alumina ceramic that provides high purity, high strength, high density, and small grain size. Typically, properties of AmAlOx 87 alumina include a bulk density of 3.97 g/cm3, flexural strength of 70 kpsi (482 MPa), Vickers Hardness of 2000 and a grain size of 2 microns. The small grain size allows for extremely tight tolerances and surface finishes of 2 microinches Ra to be achieved when proper finishing techniques are used. Of course, alumina ceramics with different material properties, other alumina ceramics, or other materials could be employed if desired.
Astro Met, Inc. also provides a material well suited for use in the manufacture of the plunger 90. The material is sold as ZTA-96 and is a zirconia toughened alumina ceramic that exhibits excellent wear and corrosion resistance along with high strength, high temperature stability, and good toughness. It was found that alumina ceramic also worked well as a plunger material, with ZTA exhibiting better toughness. Other materials, (e.g., ceramics with different material properties, other ceramics, metals, etc.) may also be suitable for use in the manufacture of the plunger 90.
During pump operation, the drive shaft 35, illustrated in FIG. 2, rotates about the drive axis 65. As the drive shaft 35 rotates, the swash plate 55 rotates such that the high point 70 and the low point 75 pass beneath each pumping unit 30 once per revolution. As the high point 70 passes a particular pumping unit 30, the drive pin 100 and the plunger 90 move downward. The downward motion reduces the pressure within the fluid space 115 which actuates the check valve 120 and allows fluid to be drawn into the fluid space 115. The downward motion of the drive pin 100 and the plunger 90 ceases as the low point 75 passes beneath the pumping unit 30. As the low point 75 passes, the drive pin 100 and the plunger 90 begin to move upward, thereby reducing the volume of the fluid space 115 and causing a pressure rise. Once the pressure within the fluid space 115 reaches a predetermined level, the high-pressure fluid passes through the check valve 120. During the upward movement of the plunger 90, some fluid leaks between the plunger 90 and the cylinder liner 145 as has been described. The leaking fluid is drained from the pumping unit 30 via the pump cylinder apertures 125. The high point 70 again returns to a point beneath the pumping unit 30 and the cycle repeats.
As one of ordinary skill in the art will realize, the pump 10 illustrated in FIG. 2 is a fixed displacement pump 10. During each revolution, a fixed volume of liquid will be pumped. The invention described herein will function equally well with variable displacement pumps (e.g., variable angle swash plate pumps). As such, the invention should not be limited to fixed displacement pumps 10 as illustrated herein.
Thus, the invention provides, among other things, a new and useful pumping unit 30 for a high-pressure pump 10. More particularly, the invention provides a new and useful pumping unit 30 that includes a plunger 90 and a cylinder liner 145 that cooperate to control leakage without the use of other mechanical sealing mechanisms. Various features and advantages of the invention are set forth in the following claims.

Claims

1. A pump comprising:

a cylinder housing including a through bore;

a cylinder liner disposed substantially within the through bore and including a substantially uniform aperture having a first diameter;

a plunger including an engagement portion having a second diameter smaller than the first diameter, the first diameter and the second diameter sized to define a first diametrical clearance that is less than about 0.1 percent of the second diameter.

2. The pump of claim 1, wherein the plunger includes a clearance portion having a third diameter.

3. The pump of claim 2, wherein the first diameter and the third diameter are sized to define a second diametrical clearance that is between about 5 and 20 times the first diametrical clearance.

4. The pump of claim 1, wherein the first diametrical clearance is about 0.06 percent of the second diameter.

5. The pump of claim 1, wherein the through bore defines a bore diameter and the cylinder liner defines an outside diameter that is larger than the bore diameter to define an interference fit between the cylinder housing and the cylinder liner.

6. The pump of claim 1, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about 2.5 times the second diameter.

7. The pump of claim 1, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about four times the second diameter.

8. The pump of claim 1, wherein at least one of the cylinder liner and the plunger are manufactured from a ceramic material.

9. The pump of claim 1, wherein the cylinder liner includes an alumina oxide ceramic.

10. The pump of claim 1, wherein the cylinder liner includes a zirconia toughened alumina ceramic material.

11. The pump of claim 1, wherein the plunger includes a zirconia toughened alumina ceramic material.

12. The pump of claim 1, wherein the plunger is adapted to reciprocate within the cylinder liner to raise the pressure of a fluid to a pressure greater than about 10,000 pounds per square inch.

13. The pump of claim 1, wherein the plunger cooperates with the cylinder liner to define the sole seal therebetween.

14. A pump comprising:

a cylinder housing including a through bore;

an elongated plunger including an engagement portion having a second diameter and a clearance portion having a third diameter, the first diameter and the second diameter sized to define a first diametrical clearance and the first diameter and the third diameter sized to define a second diametrical clearance that is between about 5 and 20 times the first diametrical clearance.

15. The pump of claim 14, wherein the second diameter is less than about 1.5 inches.

16. The pump if claim 14, wherein the first diametrical clearance is less than about 0.1 percent of the second diameter.

17. The pump of claim 14, wherein the first diametrical clearance is about 0.06 percent of the second diameter.

18. The pump of claim 14, wherein the through bore defines a bore diameter and the cylinder liner defines an outside diameter that is larger than the bore diameter to define an interference fit between the cylinder housing and the cylinder liner.

19. The pump of claim 14, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about 2.5 times the second diameter.

20. The pump of claim 14, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about four times the second diameter.

21. The pump of claim 14, wherein at least one of the cylinder liner and the plunger are manufactured from a ceramic material.

22. The pump of claim 14, wherein the cylinder liner includes an aluminum oxide ceramic.

23. The pump of claim 14, wherein the cylinder liner includes a zirconia toughened alumina ceramic material.

24. The pump of claim 14, wherein the plunger includes a zirconia toughened alumina ceramic material.

25. The pump of claim 14, wherein the plunger is adapted to reciprocate within the cylinder liner to raise the pressure of a fluid to a pressure greater than about 10,000 pounds per square inch.

26. A pump comprising:

a plurality of pumping elements, each pumping element including:

a cylinder housing including a through bore;

a cylinder liner disposed substantially within the through bore and including a substantially uniform aperture having a first diameter; and

an elongated plunger including a drive end, an engagement portion opposite the drive end and having a second diameter, and a clearance portion between the drive end and the engagement portion and having a third diameter, the first diameter and the second diameter sized to define a first diametrical clearance and the first diameter and the third diameter sized to define a second diametrical clearance that is between about 5 and 20 times the first diametrical clearance; and

a drive member coupled to each drive end and operable to move each elongated plunger in a reciprocating fashion.

27. The pump of claim 26, wherein the second diameter is less than about 1.5 inches.

28. The pump if claim 26, wherein the first diametrical clearance is less than about 0.1 percent of the second diameter.

29. The pump of claim 26, wherein the first diametrical clearance is about 0.06 percent of the second diameter.

30. The pump of claim 26, wherein the through bore defines a bore diameter and the cylinder liner defines an outside diameter that is larger than the bore diameter to define an interference fit between the cylinder housing and the cylinder liner.

31. The pump of claim 26, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about four times the second diameter.

32. The pump of claim 26, wherein the engagement portion extends along a long axis of the plunger for a length that is at least about 2.5 times the second diameter.

33. The pump of claim 26, wherein at least one of the cylinder liner and the plunger are manufactured from a ceramic material.

34. The pump of claim 26, wherein the cylinder liner includes an aluminum oxide ceramic.

35. The pump of claim 26, wherein the cylinder liner includes a zirconia toughened alumina ceramic material.

36. The pump of claim 26, wherein the plunger includes a zirconia toughened alumina ceramic material.

37. The pump of claim 26, wherein the plunger is adapted to reciprocate within the cylinder liner to raise the pressure of a fluid to a pressure greater than about 10,000 pounds per square inch.

38. The pump of claim 26, wherein the plurality of pumping units includes exactly one of three and five pumping units.

39. The pump of claim 26, wherein the drive member includes a swash plate that is rotatable about a drive axis to sequentially reciprocate each plunger of the plurality of pumping units.

40. The pump of claim 26, wherein the drive member includes a crankshaft that is rotatable about a drive axis to sequentially reciprocate each plunger of the plurality of pumping units.