Pumps – Expansible chamber type – Having pumping chamber pressure responsive distributor
Reexamination Certificate
2002-05-06
2003-04-08
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Having pumping chamber pressure responsive distributor
C417S454000, C417S568000, C277S370000, C277S437000
Reexamination Certificate
active
06544012
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to high-pressure plunger pumps used, for example, in oil field operations. More particularly, the invention relates to plunger packing and stress reduction in plunger pump housings.
BACKGROUND
Plunger Pump Stress Failure
Engineers typically design high-pressure oil field plunger pumps in two sections; the (proximal) power section and the (distal) fluid section. The power section usually comprises a crankshaft, reduction gears, bearings, connecting rods, crossheads, crosshead extension rods, etc. The fluid section usually comprises a housing which in turn comprises suction, discharge and cylinder bores, plus plungers, packing, valves, seats, high-pressure seals, etc.
FIG. 1
is a cross-sectional schematic view of a typical fluid section showing its connection to a power section by stay rods. A plurality of fluid sections similar to that illustrated in
FIG. 1
may be combined, as suggested in the Triplex fluid section design schematically illustrated in FIG.
2
.
Each individual bore in a fluid section housing is subject to fatigue due to alternating high and low pressures which occur with each stroke of the plunger cycle. Fluid section housings typically fail due to fatigue cracks in one of the four areas defined by the intersecting suction, plunger and discharge bores as schematically illustrated in FIG.
3
.
Among the designs proposed in the past for reducing pump housing fatigue failures in high-pressure fluid sections has been the Y-block housing design. The Y-block design, which is schematically illustrated in
FIG. 4
, reduces stress concentration in a fluid section housing by increasing the angles of bore intersections above 90°. In the illustrated example of
FIG. 4
, the bore intersection angles are approximately 120°. A more complete cross-sectional view of a Y-block plunger pump fluid section is schematically illustrated in FIG.
5
.
Although several variations of the Y-block design have been evaluated, none have become commercially successftul for several reasons. One such reason is that mechanics find field maintenance on Y-block fluid sections difficult. For example, replacement of plungers and/or plunger packing is significantly more complicated in Y-block designs than in the earlier designs represented in FIG.
1
. In the earlier designs, provision is made to push the plunger distally in the cylinder bore, continuing out through an access port labeled the suction valve/plunger cover in the illustration. This operation, which would leave the plunger packing easily accessible from the proximal end of the cylinder bore, is impossible in a Y-block design.
The Y-block configuration, while reducing stress in a fluid section housing, makes it necessary to remove the plunger from the proximal end of the cylinder bore. But because the proximal end of the cylinder bore is very close to the power section, plungers must be removed in two pieces. And even a two-piece plunger, schematically illustrated in
FIG. 5
, is itself a maintenance problem. The plunger pieces are often heavy and slippery, the connection between plunger pieces is subject to premature failures, and plunger pieces must be connected and disconnected in a confined space with limited visibility and accessibility. Nevertheless, the plunger pieces must be removed entirely from the cylinder bore in order to change conventional plunger packing.
Plunger Packing
A brief review of plunger packing design will illustrate some of the problems associated with packing and plunger maintenance in Y-block fluid sections.
FIG. 6
is an enlarged view of the packing in an earlier (but still currently used) fluid section such as that illustrated in FIG.
1
. In
FIG. 6
, the packing and packing brass are installed in the packing box of the fluid section. Note that packing brass is a term used by field mechanics to describe bearing bronze, where the bronze has the appearance of brass.
In the fluid section portion schematically illustrated in
FIG. 6
, the packing box is an integral part of the fluid section housing; it may also be a separate unit bolted to the fluid section housing. The packing is retained, tightened and adjusted by turning the gland nut. Removing the gland nut, however, does not allow one to remove the packing rings. Because packing rings must block high-pressure fluid leakage past the plunger, they are typically quite stiff, and they remain substantially inaccessible while the plunger (or any piece of it) remains in the cylinder bore.
FIG. 7
schematically illustrates portions of a plunger pump housing and components including a gland nut and plunger parts, with the plunger pressure end within the packing box. Note, however, that the plunger pressure end cannot be rotated for removal until it clears the packing brass. This illustrates the necessity for a two-piece plunger in which the two pieces must be separated as they are individually removed from the cylinder bore.
The necessity for a multi-piece plunger in Y-block fluid section housings has not been eliminated by the recent introduction of packing assemblies such as those called “cartridge packing” by UTEX Industries in Houston, Tex. An example of such cartridge packing is schematically illustrated in FIG.
8
. Note that removal of the gland nut exposes the packing cartridge housing, which in turn may be fitted with attachment means to allow extraction of the packing cartridge from the packing box (requiring proximal travel of the packing cartridge housing of approximately three to five inches).
This extraction, though, is not practical while a plunger piece lies within the packing box because of the excessive drag of the compressed packing rings on the plunger and packing box walls. Such compression can not be released unless all plunger pieces are removed from the packing box because the packing rings in the above cartridge packing assemblies are pre-compressed when the assemblies are manufactured. Further, any slight misalignment of apparatus used to extract such a cartridge packing assembly tends to cause binding of the (right cylindrical, i.e., not tapered) assembly within the (right cylindrical) bore. Analogous difficulties occur if an attempt is made to replace such a cartridge packing assembly while a plunger or part thereof lies in the packing box area. Hence, even if such cartridge packing assemblies were used in Y-block fluid section housings, multi-piece plungers would preferably be used and field maintenance would be significantly complicated and expensive.
SUMMARY
The invention comprises methods and apparatus to reduce or eliminate the above described problems of premature fluid section pump housing fatigue failure and difficult field maintenance related to plungers and/or plunger packing. In a preferred embodiment of the invention, a Y-block plunger pump housing comprises a suction valve bore having a substantially circular cross-section and a first centerline. Bore centerlines are used herein to assist the reader in understanding how each bore in the fluid section pump housing is spatially related to other bores in the pump housing and other fluid section components.
A discharge valve bore intersects said suction valve bore, said discharge valve bore having a substantially circular cross-section and a second centerline, said first centerline preferably being coplanar with and intersecting said second centerline at a reference point, and said first and second centerlines subtending a first obtuse angle.
A cylinder bore intersects said suction valve bore and said discharge valve bore, said cylinder bore having a proximal packing area (relatively nearer the power section) and a distal transition area (relatively more distant from the power section). The packing area has a substantially circular cross-section and a third centerline. The third centerline is coplanar with said first and second centerlines and intersects them at or near said reference point to allow substantially unimpeded fluid flow from said suction bore to said discharge bore under the influence of reciprocating plun
Gilstad Dennis W.
Liu Han L.
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