US 3776558 A
A packing assembly for a pump includes a pair of packings arranged in tandem along the plunger of a reciprocating pump or along the shaft of a centrifugal pump to provide axially-spaced sealing intervals. The tandem packing arrangement permits the pump to be operated through two stages, with separate packings providing the seal in each stage.
Description (OCR text may contain errors)
United States Patent [1 1 Maurer et al.
TANDEM PACKING FOR A RECIPROCATING PUMP Inventors: William C. Maui-er, Houston; Joe K.
Heilhecker, Bellaire; Everett H. Lock, Houston, all of Tex.
Esso Production Research Company, Houston, Tex.
Filed: Mar. 17, 1972 Appl. No.: 235,514
U.S. Cl 277/9, 277/58, 277/71, 92/165 Int. Cl F16j 15/18 Field of Search 277/3, 9, 2, 16, 277/32, 58, 59, 70, 71, 72, 74; 92/165 References Cited UNITED STATES PATENTS 3/1954 Tremolada 277/32 Dec. 4, 1973 3,514,114 5/1970 Monahan 277/3 Primary ExaminerWilliam T. Dixson, Jr. Assistant Examiner-Robert L Smith Att0rneyJames A. Reilly et a1.
[5 7] ABSTRACT A packing assembly for a pump includes a pair of packings arranged in tandem along the plunger of a reciprocating pump or along the shaft of a centrifugal pump to provide axially-spaced sealing intervals. The tandem packing arrangement permits the pump to be operated through two stages, with separate packings providing the seal in each stage.
9 Claims, 1 Drawing Figure TANDEM PACKING FOR A RECIPROCATING PUMP BACKGROUND OF THE INVENTION 1. Field of the Invention:
This invention relates to packings for pumps.
2. Description of the Prior Art:
A major problem associated with high-pressure pumps is that of providing a satisfactory seal for the plunger of a reciprocating pump or the shaft of a centrifugal pump. The seal is normally in the form of soft, non-abrasive packing adapted to seal the radial space between the pump plunger (or shaft) and the fluid end housing. The failure of the packing is a particularly serious problem when the fluid being pumped contains suspended particles of silt, clay, sand or a similar abrasive material. The abrasive material tends to erode the packing, causing early and frequent failure.
Packing failure is normally evidenced by the leakage of fluid past the packing. A small amount of leakage can be tolerated but when this becomes excessive, the pumping operations must be temporarily discontinued to permit replacement of the packing. In certain processes, it may be inconvenient and sometimes may even jeopardize the success of the process to interrupt pumping operations immediately upon packing failure. Two examples of processes that cannot tolerate long shutdown periods are found in well drilling and well fracturing operations. In the drilling of wells by rotary drilling methods, a drilling fluid is continuously circulated through a tubular drill string and serves several essential functions in the drilling operation. It .is desirable to perform maintenance and repair work on the drilling pumps when the circulation of the drilling fluid in the well is not required. This work is normally done at the same time the drill bit is being replaced, which requires withdrawing the entire drill string from the bore-hole. This operation normally requires several hours and thus provides ample time for pump maintenance and repair. The pump packing frequently fails before the bit has become sufficiently worn to require replacement. In this event, it is desirable to delay repacking the pump until the bit must be withdrawn from the borehole. However, with most conventional pumps, the packing must be replaced immediately upon packing failure.
Well fracturing normally involves the injection of a fluid into a subterranean formation at a pressure sufficient to open a fracture therein and the placement of propping agent particles in the fracture. The propping agent particles suspended in the fracturing fluid are carried to and deposited in the fracture. The fracturing fluid must be pumped into a subterranean formation at a sufficiently high velocity to prevent the propping agent particles from settling. During this operation, if pumping is interrupted even for a short period of time, the particulate material tends to settle in the borehole and plug the formation. Here again, it is desirable to delay repacking the pump until the process has been completed.
SUMMARY OF THE INVENTION The present invention provides an improved packing assembly for pumps. It should be noted that the term pump refers to any mechanical device used to raise, transfer, or compress fluids and specifically includes reciprocating pumps, centrifugal pumps, compressors,
and hydraulic rams. Briefly, the improved packing assembly includes two sets of packings-an inner packing and an outer packing-designed to separately provide a seal for the pump plunger or shaft. The separate packings are arranged in tandem and provide a sea] at axially-spaced intervals. A novel feature of this design is that the separate packings can be used in sequence so that the operating life of the packing can be extended even after one of the packings has failed. A support member is provided between the packings and serves to bear the hydraulic loading imposed on the inner packing. A vent port communicates with the axial space separating the two packings so that fluid leaking past the inner packing is vented to the atmosphere. Thus, it is seen that the outer packing is not hydraulically loaded during the initial stage of operation. When leakage past the inner packing becomes excessive, the outer packing can be activated merely by closing the vent port. This causes the buildup of pressure in the axial space separting the two packings. The resultant hydraulic loading on the outer packing deforms the packing elements thereof into engagement with the surfaces being sealed.
The packing assembly preferably is in the form of an insert cartridge adapted to be connected to the fluid end housing. The cartridge includes a sleeve containing the two sets of packings. Formed in the sleeve is a vent port for relieving the pressure between the packings, and passages for delivering lubricant, coolant, or a wash fluid to the packings. The cartridge design permits rapid replacement of the packing since the sleeve and packings can be withdrawn from the fluid end housing as a unit and replaced with a new unit.
BRIEF DESCRIPTION OF THE DRAWING The drawing schematically illustrates, in longitudinal section, a portion of a pump containing a packing assembly constructed according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The prsent invention will be described with reference to a reciprocating pump. It should be realized, however, that the improved packing can also be used in centrifugal pumps, compressors, hydraulic rams and the like. In all of these devices, a member such as a plunger or shaft is movably mounted in a housing. The packing serves to seal the radial space between the housing and the movable member.
As shown in the drawing, the fluid end of a reciprocating pump comprises separate steel forgings which include a fluid end housing 10 mounted on pump frame 11 and a crossbore body, shown partially as 12, coupled to the housing 10. The crossbore body 12 can be similar in structure to that disclosed in assignees copending Application Ser. No. 179,705, filed September 13, 1971. Other structures my also be employed. The
ing action draws fluid into the pump fluid end and discharges it at high pressures. in order to seal the annular space between the plunger and housing 10, a packing is normally provided in an end section of the housing 10.
The plunger packing in accordance with the present invention is provided by two separate packings arranged in tandem along the pump plunger. This arrangement provides separate seals at axially-spaced intervals and permits the pump to be operated through two stages before the packing must be replaced. In the preferred embodiment, the plunger packing is in the form of a packing cartridge 17 adapted to be installed on the pump fluid end. However, it will be apparent from the following detailed description that the tandem packing arrangement is not restricted to the cartridge design.
At the rear extremity of the fluid end housing 10, the bore 14 is enlarged, as by a counterbore, to provide an annular recess in the housing 10. The recess is sized to receive the cartridge 17 and is defined by radial surface 18 and a cylindrical surface 19. An interally threaded section 20 is provided at the mouth of the recess. The inner extremity of the recess, defined by surface 18, is disposed sufficiently close to the front end of the plunger 15 in its fully retracted position to permit the plunger 15 to be tilted sufficiently to place its rear end radially clear of the front end of the drive rod 16. This distance normally will be less than about one inch. As described in more detail below, thisarrangement permits the packing to be replaced without removing a pony rod section from the drive rod 16.
The packing cartridge 17 includes a sleeve 21 and a pair of packings 22 and 23 mounted in the sleeve 21. The sleeve 21 may be constructed from standard steel bar stock. A bar of the proper length is bored to form an axial opening therethrougha portion of the opening is shown as 24and then counterbored to form enlarged sections 25 and 26. These sections extend from opposite ends inwardly into the bar and terminate a short axial distance apart leaving an annular shoulder 27 therebetween. The outer periphery of the bar is machined to provide the sleeve 21 with a threaded section 28 and a cylindrical section 29. The threads of section 28 mate with the housing threads 20, and the cylindrical section 29 fits in close conformity with the internal surface 19 of housing 10. A forward end of the sleeve 21 carries a face seal such as an elastomeric O-ring 30.
With the sleeve 21 mounted on the housing 10, its forward end containing the face seal 30 is disposed internally of the housing 10. The face seal 30 is compressed into sealing engagement with the radial surface -18 formed in the housing 10. The outer end 31 of the sleeve 21 is exposed and may be provided with a hex head or similar structure sized to fit a wrench.
The packings 22 and 23, respectively, fit in the enlarged sections 25 and 26 of the sleeve 21. The outer packing 22 may include a plurality of seal rings 32, an adaptor 33 and a lantern ring 34. It is preferred that the packing 22 also include a compression spring 35 for maintaining a minimum force on the ring assembly. One end of the spring 35 engages the annular shoulder 27 and the opposite end through a spring adaptor 36 applies a force on the stackup of rings. This entire assembly is maintained within the enlarged section 25 by a nut 37 threadedly connected to the outer end 31 of the sleeve 21.
The inner packing 23 may be similar in construction as assembly 22 comprising seal rings 38, adaptor 39, lantern ring 40, compression spring 41, and spring adaptors 42 and 43. The rings 38, 39, 40 and 42 arranged in stacked relation and preloaded by spring 41 are supported within the enlarged section 26 on an annular shoulder 27.
With the sleeve 21 attached to the fluid end housing 10 and in surrounding relation to the plunger 15, the enlarged sections 25 and 26 in combination with the outer periphery of the plunger 15 define annular spaces. The packings 22 and 23 mounted in the sleeve 21 provide seals for these spaces. The sealing intervals are separated by an axial space indicated at 44. A vent port 46 formed in the sleeve 21 communicates with the axial space 44. The vent port 46 extends from the sleeve outer end 31 axially through a portion thereof and into enlarged section 25. The compression spring 35 maintains the rings clear of the vent port 46. Means are provided for selectively closing the vent port. A plug 51 adapted to be screwed into a threaded outlet 45 of the vent port 46 may be used for this purpose. Alternatively, a valve connected in fluid communication with the vent port 46 may be used.
The lantern rings 34 and 40 of packings 22 and 23 are flanked on either side by a plurality of seal rings. Lubricating passages 47 and 48 formed in the sleeve 21 serve to deliver lubricant to the packings 22 and 23, respectively. Each of the lubricating passages 47 and 48 has an inlet at the outer end 31 of sleeve 21, and has an outlet in fluid communication with one of the lantern rings 34 and 40. A lubricating pump, not shown, is connected to each of the passages 47 and 48 and delivers a suitable lubricant such as oil to the packings 22 and 23.
When the fluid to be pumped is corrosive or contains abrasive material, the sleeve 21 can be provided with another passage 49 for delivering a wash fluid to the pressure side of the inner packing 23. Passage 49 has an inlet at the outer end 31 of the sleeve 21 and an outlet in fluid communication with the interior of the sleeve 21 at a point in advance of the packing rings of assembly 23. A pump (not shown) connected to passage 49 delivers a wash fluid such as water to flood the pressure side of the packing assembly 23. Passage 49 may also be used to deliver a coolant to the interior of sleeve 21 if desired.
The seal rings 32 and 38 are preferably of the selfenergizing type. They may be conventional V rings, U rings, W rings, and the like. These rings are normally molded rings of elastomeric material containing fibrous reinforcement. The self-energizing seal rings are provided with lips that deform under hydraulic loading into sealing engagement with the surfaces being sealed.
In assembling the cartridge 17, the outer packing 22 is inserted into the sleeve 21. The nut 37 is then screwed into the sleeve end 31 compressing the spring 35. The inner packing 23 is then placed in the enlarged section 26 of sleeve 21. The spring retainer 43 is placed in advance of the compression spring 35 and serves to maintain the compression spring in proper alignment. The cartridge 17 is then telescopically positioned about the plunger 15 and directed into the recess end of housing 10. The sleeve 21 is screwed into the housing 10 until the face seal 30 abuts the radial surface 18 formed in the housing 10. It should be noted that the face seal 30 is compressed sufficiently to provide a pressurized barrier at the joint of the members being assembled. Screwing the sleeve 21 into the housing also compresses the spring 41 to provide a preload force on the rings 38, 39, 40 and 42.
An alternate procedure for installing the cartridge 17 on the pump fluid end is to preassemble the cartridge 17 and a plunger 15. The worn plunger and packing are then withdrawn as a unit from the pump and replaced with a new assembly. It should be noted that the plunger or packing can be replaced without disconnecting a pony rod section from the drive rod 16. This is possible because the recessed end of the housing 10 permits the plunger to be tilted sufficiently such that its outer end radially clears the front end of the drive rod 16. The mouth of the bore 14 at 50 may be enlarged slightly to facilitate the tilting of the plunger 15.
With the cartridge 17 properly installed on the housing 10, the pump may be operated through two stages with the inner packing 23 providing the plunger seal during an initial stage and the outer packing 22 providing the plunger seal in a subsequent stage. In the initial stage, the vent port 46 is left open so that fluid leaking past the inner packing 23 is discharged to the atmosphere. This prevents the buildup of pressure in the space 44 separating the packings 22 and 23. In the absence of pressure in this space, the outer packing 22 will not be deformed and therefore will not be subjected to severe wear. It should be noted that the preloading afforded by the compression spring 35 is smallin the order of 190 poundsand merely serves to maintain the rings in a tightly packed condition. This preload force is negligible compared to the hydraulic loading of the pressurized fluid. For example, the hydraulic loading on 3% ID. X 4% OD. packing of a pump operating at 10,000 psi is 62,800 pounds.
Annular shoulder 27 bears the hydraulic load imposed on the inner packing 23 and prevents this load from being transmitted to packing 22. The pump may be operated through the initial stage until the seal rings of the inner packing 23 fail. This will be evidenced by the discharge of fluid from the vent port 46. The vent port 46 is then closed as by inserting a plug in end 45 permitting the pump to be operated through a second stage wherein the plunger seal is provided by the outer packing 22. Closing the vent port 46 causes the pressure to increase with space 44. The buildup of pressure in this space energizes the seal rings 32 of assembly 23. The pump then may be operated until the outer packing 23 fails.
Alternatively, the vent port can be connected to a pump which delivers a coolant or wash fluid to the pressure side of packing 22.
Although the tandem packing arrangement of the present invention is disclosed herein with reference to the cartridge 17, it should be noted that other designs are possible. For example, the inner packing 23 can be provided directly between a plunger and the housing 10. The outer packing 22 may be mounted in a sleeve which is adapted to be attached to the housing 10. This sleeve may be constructed to provide a support comparable to annular shoulder 27 described above for bearing the hydraulic loading imposed on the inner packing 23. Whether the design calls for a cartridge or not, the ultimate function of the packings is the same: to seal the enlarged annular space between the plunger 15 and housing 10. In this regard, it should be noted that the cartridge attached to the housing may be viewed as a part thereof.
The advantages of the tandem packing arrangement can be more fully appreciated when viewed with reference to well drilling or well fracturing operations discussed above. Assuming that drilling operations are in progress, it is essential that drilling fluid be circulated through the drill string. In the event that the inner packing 23 fails, the second packing 22 can be activated merely by closing the vent port 46. This can be accomplished without interrupting the drilling opera tions and permits continued drilling until the drill bit becomes sufiiciently worn to require replacement. The tandem packing arrangement not only improves the efficiency of the operation but under certain conditions avoids hazards resulting from interrupting pumping operations. For example, it is undesirable to interrupt pumping operations for long periods of time because of the danger of sticking the drill pipe.
In fracturing operations, the tandem packing ar' rangement of the present invention permits completion of pumping operations. For example, if the fluid laden with particulate material is being pumped and the inner packing 23 fails, the pumping operations may be continued merely by closing the vent port 46 which activates the outer packing 22. The life of the outer packing 22 which has not been subjected to as severe wear as the inner packing 23 is well within the time required to complete the pumping operations.
As mentioned previously, the improved packing of the present invention can be used on reciprocating pumps, centrifugal pumps, compressors, and similar devices. Its preferred application, however, is in reciprocating pumps because of the serious packing problems associated with this type of pump.
1. A replaceable packing cartridge for sealing the annular space between a pump housing and a moveable member which comprises: a sleeve adapted to be detachably mounted to said housing in surrounding relation to said member and having an outer exposed portion and an inner end disposed adjacent said housing, said sleeve containing inner and outer packing assemblies and means for separately supporting said packing assemblies, said sleeve having formed therein a vent passage which extends from said exposed portion to the interior of said sleeve at a point between said packing assemblies; and means for selectively closing said vent passage whereby said pump in which said packing cartridge is mounted may be operated through a first stage with the vent passage open wherein the inner packing assembly provides the seal for said annular space and a second stage with the vent passage closed wherein the outer packing assembly provides the seal for said annular space.
2. A packing cartridge as defined in claim 1 wherein said inner packing assembly includes a plurality of selfenergizing seal rings and a lantern ring interposed between two of said seal rings, and said sleeve has formed therein a lubricating passage which extends from said exposed portion to the interior of said sleeve and is in fluid communication with said lantern ring.
3. A packing cartridge as defined in claim 2 wherein said sleeve has formed therein a third passage for conducting a wash fluid which extends from said exposed portion to the interior of said sleeve at a point in advance of the seal rings of said inner packing.
4. A packing cartridge as defined in claim 3 wherein said sleeve includes a face seal between said inner end and the adjacent housing.
5. A replaceable packing cartridge for sealing the annular space between a pump housing and a pump plunger which comprises: a sleeve adapted to be detachably mounted on said housing in surrounding relation to said plunger and having an outer exposed portion and an inner end disposed adjacent said housing, said sleeve having formed therein an inner packing chamber and an outer packing chamber separated by a support shoulder; inner and outer packing assemblies mounted in said inner and outer packing chambers, respectively, each of said packing assemblies including a plurality of self-energizing seal rings, said inner packing assembly further including a lantern ring positioned between two of said seal rings thereof, said sleeve having formed therein a lubricating passage which extends from said exposed portion to said inner chamber and being in fluid communication with said lantern ring, and a vent passage which extends from said exposed portion and being in fluid communication with the interior of said sleeve at a point between the seal rings of said inner and outer packing assemblies; and means for selectively closing said vent passage whereby said pump containing said packing cartridge may be oper ated through a first stage with said vent passage open wherein said inner packing provides the plunger seal and through a second stage with said vent passage closed wherein said outer packing provides the plunger seal.
6. A packing cartridge as defined in claim 5 wherein said inner packing assembly further includes a spring for maintaining the rings of said inner packing in compression.
7. A packing cartridge as defined in claim 6 wherein said sleeve has formed therein a flow passage for conducting a wash fluid which extends from said exposed portion to said inner chamber at a point opposite said spring.
8. A packing cartridge as defined in claim 5 wherein said outer packing assembly further includes a lantern ring interposed between two of said seal rings thereof and said sleeve has formed therein a second lubricating passage which extends from said exposed portion to said outer chamber in fluid communication with said lantern ring of said outer packing.
9. A packing cartridge as defined in claim 5 wherein said inner and outer packing assemblies each include a spring for maintaining the rings thereof in compression. l=