Note: Descriptions are shown in the official language in which they were submitted.
CA 02303103 2002-09-27
BIASED SEAL ASSEMBLY FUR HIGH PRESSURE FLUID PUMP
S TECHNICAL FIELD
This invention relates to seals for high pressure fluid pumps having
reciprocating plungers.
BACKGROUND OF THE INVENTION
In high pressure fluid pumps having reciprocating plungers, it is
necessary to provide a seal around the plunger to prevent the leakage of high
pressure fluid. In such pumps, the seal must be able to operate in a high
pressure
environment, withstanding pressures in excess of 10,000 psi, and even up to
and
beyond 50,000-70,000 psi.
Currently available seal designs for use in such an environment
include an extrusion resistant seal that seals against the plunger and is
supported
by a back-up ring. The back-up ring and seal may be supported by a seal
carrier
and may be biased toward the seal carrier with a coil spring that encircles
the
plunger. The spring may be held in place against the seal with a collar that
has a
bore through which the plunger passes and that has a flange encircling one end
of
the spring.
One problem with current seal designs is that the tolerances for
clearance between the plunger and the back-up ring may be very difficult to
achieve and maintain. Very typically, therefore, the plunger and the back-up
ring
come into contact, generating fiictional heating, which in turn may cause the
seal
to fail. Another problem with current seal designs is that components of the
seal
may wear over time, causing fluid to leak around the plunger.
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SUMMARY OF THE INVENTION
The present invention is directed toward methods and apparatuses
for sealing components of a high pressure pump having a reciprocating plunger.
The apparatus may include a cylinder having a cylinder wall with at least one
opening, an elongated plunger extending through the opening, and a spring
disposed about the plunger. The spring may have an inner surface facing toward
the plunger and an outer surface facing away from the plunger. The assembly
may further comprise a seal having a sealing surface that seals against the
plunger and an engaging surface that engages at least one of the inner and
outer
surfaces of the spring to restrict lateral motion of the spring relative to
the
plunger.
The seal may have several shapes. For example, the seal may
include a continuous flange that extends around to the circumference of the
spring. Alternatively, the seal may include a plurality of spaced-apart
projections
that engage the spring. In a further embodiment, the flange may have a first
engaging surface adjacent the inner surface of the spring and a second
engagement surface adjacent the outer surface of the spring.
The present invention is also directed toward a method for
restricting motion of a spring disposed about a plunger of a high pressure
pump.
The method may comprise sealably engaging a seal with the plunger, engaging
the seal with at least one of the inner surface and the outer surface of the
spring
toward one end of the spring, and restricting lateral motion of the spring
relative
to the plunger. Alternatively, the method may include engaging both the inner
and outer surfaces of the spring, and may further include engaging an opposite
end of the spring. Where the spring is a coil spring, the method may include
engaging a portion of one coil of the spring corresponding to half a diameter
of a
filament that comprises the spring, or may include engaging more than one coil
of the spring.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial cross-sectional plan view of a pump assembly
having a seal Garner and seal in accordance with an embodiment of the
invention.
Figure 2 is an enlarged partial cross-sectional plan view of the seal
and seal Garner illustrated in Figure 1.
Figure 3 is a detailed cross-sectional plan view of the seal carrier
illustrated in Figures 1 and 2.
Figure 4 is a partial cross-sectional plan view of a seal assembly
having a seal that engages an outer surface of a spring in accordance with
another
embodiment of the invention.
Figure 5 is a partial cross-sectional plan view of a seal assembly
having a seal that engages an inner surface of a spring in accordance with
still
another embodiment of the invention.
Figure 6 is a partial cross-sectional plan view of a seal assembly
having a seal that engages inner and outer surfaces of a spring in accordance
with
yet another embodiment of the invention.
Figure 7 is an isometric view of a seal having projections in
accordance with still another embodiment of the invention.
Figure 8 is a partial cross-sectional plan view of a seal assembly
having a back-up ring in accordance with yet another embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
A high pressure fluid seal assembly 10 is provided in accordance
with one embodiment of the present invention, as illustrated in Figure 1. The
seal assembly 10 is for use in a high pressure pump assembly 22 having a
reciprocating plunger 14 coupled to a drive mechanism 26. The plunger 14
reciprocates in a high pressure cylinder 24. The seal assembly 10 is
positioned
adjacent the plunger 14 at one end of the cylinder 24 to restrict and/or
prevent the
leakage of high pressure fluid from a high pressure region 23 within the high
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pressure cylinder 24. A check valve 30 at the opposite end of the cylinder 24
includes a plurality of inlet ports 31, an outlet port 32, and a poppet 33
that seals
the inlet ports. The check valve 30 directs fluid through the inlet ports 31
and
into the cylinder 24 when the plunger 14 partially withdraws from the cylinder
during an intake stroke. The check valve 30 directs pressurized fluid out of
the
cylinder 24 through the outlet port 32 when the plunger 14 moves into the
cylinder during a pressure stroke.
A collar or retainer 50 may be located within the cylinder 24
between the seal assembly 10 and the check valve 30 to reduce the volume
within
the cylinder and thereby increase the pressure generated with each pressure
stroke of the plunger 14. The collar 50 also applies a biasing force to the
poppets
33 via a poppet spring 34 and to the components of the seal assembly 10 via a
seal spring 60, as will be discussed in greater detail below.
As illustrated in Figure 2, the seal assembly 10 includes a seal
carrier 12 having a bore 13 through which the reciprocating plunger 14 passes.
The seal carrier 12 has a first annular groove 15 in which an annular seal 17
is
positioned. The annular seal 17 has a sealing surface 55 that seals against
the
plunger 14. An annular elastomeric seal 25 is provided around the outer
circumference of annular seal 17, to energize the annular seal 17 during the
start
of the pressure stroke. The seal spring 60 engages the annular seal 17 and
urges
it toward the first annular groove 15 to restrict motion of the annular seal
17
away from the seal carrier 12. The seal carrier 12 has an integral, annular
guidance bearing 19 that is positioned in a second annular groove 16 within
the
bore 13. The second annular groove 16 and the guidance bearing 19 positioned
therein are axially spaced apart from the first annular groove 15 and the
annular
seal 17 contained therein.
Figure 3 is a detailed cross-sectional view of the seal carrier 12 and
the guidance bearing 19 shown in Figure 2. As shown in Figure 3, an inner
diameter 20 of the guidance bearing 19 is smaller than an inner diameter 21 of
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the seal carrier bore 13 in a region 11 between the seal 17 (Figure 2) and the
guidance bearing 19. For example, in one embodiment, the inner diameter 20 is
.0005-.0015 inch smaller than the inner diameter 21. In this manner, an end
region 18 (Figure 2) of the annular seal 17 is supported by region 11 of the
seal
carrier 12; however, the region 11 of seal carrier 12 is not in contact with
the
plunger 14, because the diameter 21 of the bore 13 in region 11 is greater
than
the inner diameter 20 of the guidance bearing 19.
An embodiment of the seal assembly 10 shown in Figures 1-3
therefore supports the seal 17 directly with the seal carrier 12, eliminating
the
need for a back-up ring. The integral guidance bearing 19 prevents the plunger
14 from contacting the seal carrier 12, thereby reducing frictional heating in
the
vicinity of the seal 17, which in turn extends the life of the seal. To
further
increase the longevity of the assembly 10, the materials for the components
are
selected to minimize the friction between the plunger 14 and the guidance
bearing 19 and between the plunger 14 and the seal 17. In one embodiment, the
plunger 14 is made of partially stabilized zirconia ceramic, the guidance
bearing
19 is made of a resin impregnated graphite, and the seal 17 is made of an
ultra-high molecular weight polyethylene. However, it should be noted that a
variety of materials may be used, and the materials selected for one component
may depend on the materials selected for another component.
To further increase the reliability of the seal 17, the seal assembly
10 is preferably manufactured by pressing the guidance bearing 19 into the
seal
carrier 12, and machining the bore 13 through the guidance bearing and through
region 11 of the seal carrier in the same machining setup. As discussed above,
the inner diameter of the bore 13 in region 11 is machined slightly larger
than the
inner diameter 20 of the bore through the guidance bearing. However, by
machining both areas in the same setup, the concentricity of the elements is
improved, as compared to prior art systems wherein elements of a seal assembly
are machined independently and then assembled.
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Returning to Figure 2, the seal 17 may be biased toward the seal
carrier 12 by the seal spring 60, as discussed above. In one embodiment, the
seal
spring 60 may include a wire filament coiled about the plunger 14 to form a
plurality of coils 64 that encircle the plunger. Each coil 64 may have an
inner
surface 61 facing the plunger 14 and an outer surface 62 facing away from the
plunger. In other embodiments, the seal spring 60 may have other shapes that
also bias the annular seal 17 toward the seal carrier 12.
It has been found that the seal springs may flex transverse to the
axis of the plunger 14 and rub against either the plunger or the collar 50.
Accordingly, the seal springs may wear down and may place an uneven load on
the seals against which the seal springs bear, causing the seals to leak.
Alternatively, the seal springs may cause either the collar 50 or the plunger
14 to
wear, reducing the useful life of these components.
One approach to addressing the spring wear problem has been to
increase the size of the bore through the collar 50, reducing the likelihood
that
the outer surface of the seal springs will contact the inner surface of the
bore.
One problem with this approach is that the seal springs may flex transversely
by
a greater amount when positioned in the larger bore. Therefore, even if the
outer
surface of the seal spring does not contact the inner surface of the bore, the
inner
surface of the spring may be more likely to contact the plunger 14, causing
the
seal spring and the plunger to wear and placing an uneven load on the seal.
Accordingly, in one embodiment of the present invention, the
annular seal 17 may include a body 28 and an annular flange portion 54. The
flange portion 54 extends away from the body concentric with the seal spring
60,
the plunger 14 and the annular seal 17, and engages the outer surface 62 of
the
seal spring. For example, the flange portion 54 may have an engaging surface
56
that engages two of the coils 64 of the seal spring 60. Accordingly, the
engaging
surface 56 may be curved to correspond to the curved shape of the coils 64. In
other embodiments, the engaging surface 56 may engage more or fewer coils 64
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and/or other portions of the seal spring 60, as is discussed in greater detail
below
with reference to Figures 4-9. In further alternate embodiments, the engaging
surface 56 may engage seal springs 60 having shapes other than the
axisymmetric
coiled shape shown in Figure 2.
An advantage of the seal 17 and the flange portion 54 is that they
may engage the outer surface 62 of the seal spring 60 and restrict motion of
the
seal spring transverse to the axis of the plunger 14. Accordingly, the seal
spring
60 may be less likely to contact the plunger 14 and/or the collar 50,
potentially
increasing the life of the plunger, the collar, and the seal spring.
Furthermore, by
reducing friction between the seal spring 60, the plunger 14, and the collar
S0,
the heat generated in the cylinder 24 may be reduced, thereby increasing the
life
of the seal 17.
As shown in Figure 2, the collar 50 may include a flange portion
54a having an engaging surface 56a. The engaging surface 56a may be
positioned to engage the outer surface 62 of the seal spring 60, opposite the
portion of the seal spring engaged by the engaging surface 56 of the seal 17.
By
engaging the outer surface 62 of both ends of the seal spring 60, the collar
50 and
the seal 17 may together further reduce the likelihood that the seal spring 60
will
move transverse to the plunger 14, and may further increase the life of the
components of the seal assembly.
Figure 4 is a partial cross-sectional plan view of a seal assembly 10
having a seal 117 with a shortened annular flange 154 in accordance with
another
embodiment of the invention. The flange 154 has an engaging surface 156 that
engages a portion of the seal spring 60 approximately equal to half a diameter
D
of the filament comprising the seal spring. In other embodiments, the flange
154
may engage a greater or lesser portion of the seal spring 60, so long as it
engages
enough of the seal spring to restrict and/or prevent lateral motion of the
seal
spring relative to the plunger 14. An advantage of the seal 117 when compared
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to the seal 17 shown in Figure 2 is that it may require less material to
manufacture.
Figure 5 is a partial cross-sectional plan view of a seal assembly 10
having a seal 217 with an annular flange 254 adjacent the plunger 14. The seal
217 may therefore sealably engage a larger portion of the plunger 14, and may
accordingly provide a better seal with the plunger. The flange 254 has an
engaging surface 256 that engages the inner surface 261 of a seal spring 260
to
restrict and/or prevent lateral motion of the seal spring 260 relative to the
plunger
14 and the collar 50. The engaging surface 256 may engage a single coil 264 of
the seal spring 260, or may engage a greater or lesser portion of the spring,
as
discussed above with respect to Figures 2 and 4. The collar 50 may engage the
outer surface 262 of the seal spring 260, as shown in Figure 5, or
alternatively
may engage the inner surface 261 of the seal spring 260, so long as the collar
50
remains spaced apart from the plunger 14.
Figure 6 is a partial cross-sectional plan view of a seal assembly 10
having a seal 317 with an inner flange 354a spaced apart from an outer flange
354b. The inner flange 354a has an engaging surface 356a that engages the
inner
surface 61 of the seal spring 60, and the outer flange 354b has an engaging
surface 356b that engages the outer surface 62 of the spring. Accordingly, the
seal 317 may further prevent lateral motion of the spring 60 relative to the
plunger 14.
Figure 7 is an isometric view of a seal S 17 having a plurality of
engaging members 554 spaced around the circumference of a bore 557. The bore
557 may be sized to slidably engage the plunger 14 (Figure 2) and the engaging
members 554 may include engaging surfaces 556 positioned to engage the seal
spring 60 (Figure 2). In the embodiment shown in Figure 7, the engaging
surfaces 556 are configured to engage the outer surface 62 (Figure 2) of the
seal
spring 60, and in other embodiments, the engaging surfaces may be configured
to
engage the inner surface 61 (Figure 2) of the seal spring. In the embodiment
CA 02303103 2002-09-27
shown in Figure 7, the spring guide 517 may include six engaging members
554 and may include a greater or lesser number of engaging members in other
embodiments.
Figure 8 is a partial cross-sectional plan view of a seal assembly 10
that includes a seal carrier 6I2 retaining an annular seal 617 and a back-up
ring
634. The back-up ring 634 may support the annular seal 617 relative to the
plunger 14. The annular seal 617 may include a flange portion 654 that engages
the outer surface 62 of the seal spring 60. Alternatively, the flange portion
654
may be configured to engage the inner surface 61 of the seal spring 60 in a
manner similar to that shown in Figure 5, or both the inner and the outer
surfaces
61, 62 in a manner similar to that shown in Figure 6. In any case, the annular
seal 617 may engage enough of the seal spring 60 to restrict and/or prevent
contact between the seal spring 60 and one or both of the collar 50 and the
plunger 14.
An improved high pressure fluid seal assembly has been shown and
described. From the foregoing, it will be appreciated that, although specific
embodiments of the invention have been described herein for purposes of
illustration, various modifications may be made without deviating from the
spirit
of the invention. Thus, the present invention is not limited to the
embodiments
described herein, but rather as defined by the claims which follow.
