Note: Descriptions are shown in the official language in which they were submitted.
; ~ CA 0223499~ 1998-04-14
HIGH PRESSURE SEAL ASSEMBLY
BACKGROUND OF THE INVENTION
This invention relates to a high pressure seal assembly which enables
two or more individual seals to accommodate a pressure difference greater than that
which can be normally accommodated by the individual seals themselves.
In the field of high pressure fluids, it is often necessary to provide a
seal between two bodies in which a first area of the two bodies is in communication
with a fluid under high pressure and a second area is at a pressure different from
and significantly lower than the high pressure. It is generally necessary to prevent
the leakage of fluid between the two areas and this is normally accommodated by
the provision of a resilient seal or packing which is designed to prevent fluid
communication while resisting the difference in pressure between the two areas.
Normally seals can be designed to accommodate even relatively high
pressures. However when the pressures reach particularly high pressures of the
order of 4000 to 5000PSI, it is more difficult to prevent leakage. The present
invention is particularly but not exclusively concerned with the sealing of liquids such
as abrasive fluids which are generated in high pressure pumps, actuators or the like.
In some high pressure pumps, for hydraulic fluid, fluid is allowed to
bypass the seals and is then recirculated in the system.
In other fields, such as the oilfield where high pressure water is used
for cutting and where abrasive fluids are pumped such as cement slurries and sand
mixtures, it is not allowable for leakage through the seal (or packing) to occur and
intention of the seal is to fully prevent transfer of the liquid from the high pressure
zone to the low pressure zone beyond the sealing arrangement.
Limited leakage brush seals and labyrinth type seals are therefore
completely unsuitable for an arrangement of this type. Examples of such labyrinth
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and limited leakage brush seals are shown in U.S. Patents 2,018,37~ (Mason issued
October 22, 1935); 21946,609 (Comery issued July 26, 1960); 3,231,285 (Weltmer
issued January 25, 1966); 4,756,536 (Belcher issued July 12, 1988) and 5,106,104(Atkinson issued April 21, 1992).
5 SUMMARY OF THE INVENTION
It is one object of the present invention to provide an improved seal
which enables the seal to accommodate higher pressures than can be
accommodated with a single sealing member.
According to one aspect of the invention there is provided a seal
10 assembly comprising: a first body having a first surface; a second body having a
second surface; the bodies being mounted with the first surface closely adjacent to
and spaced from the second surface and such that relative movement occurs
between the first surface and the second surface; a first area of the first and second
surfaces being in communication with a fluid under pressure such that the first area
15 is at a first pressure and a second area of the first and second surfaces sp~cecl from
the first area being separated from the fluid under pressure such that the second
area is at a second pressure; a seal arrangement being located between the firstand second surfaces so as to divide the first area from the second area such that the
fluid pressure is applied across the seal arrangement and such that the seal
20 arrangement moves with one of the bodies relative to the other of the bodies; the
seal arrangement comprising: a first continuous seal member, a second continuousseal member spaced from the first and defining therebetween a chamber bounded
by the first and second surfaces and the first and second seal members; a fluid
communication duct communicating from a source of compensation fluid under
25 pressure; and fluid pressure control means arranged to supply the compensation
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fluid to the chamber through the duct at a compensation pressure intermediate the
first pressure and the second pressure.
Preferably the duct passes through one of the first and second
surfaces to the chamber.
Freferably the seal members are arranged to prevent the passage
thereby of the fluid.
Preferably the seal members are elastomeric O-ring seals each
mounted in an annular seat in one of the surfaces for engaging the other of the
surfaces.
Preferably there is provided a third continuous seal member spaced
from the second seal member and defining a second chamber between the second
seal member and the third seal member, and wherein there is provided a second
duct communicating to the second chamber from a source of compensation fluid
under pressure, the fluid pressure control means being arranged to supply the
15 compensation fluid to the second chamber through the duct at a pressure
intermediate the compensation pressure and the second pressure.
Preferably the first surface and second surfaces are cylindrical,
wherein the seal members are annular so as to surround the first surface and
wherein the chamber is annular surrounding the first surface.
Preferably there is a significant difference between the first pressure
and the compensation pressure and between the compensation pressure and the
second pressure so as to divide the pressure difference between the first and
second pressures into parts which can be accommodated by the seal members
without leaking.
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Preferably the pressure difference between the first pressure and the
second pressure is divided by the seal members and the compensation pressure
into a plurality of substantially equal pressure drops.
Preferably the source of compensation fluid is connected to the fluid
5 under pressure so as to receive pressure therefrom.
Preferably the pressure control means comprises a pressure relief
valve having a pressure relief setting less than the first pressure such that the
compensation pressure is equal to the difference between the first pressure and the
pressure relief setting.
Preferably there are at least three seal members, each divided from
the next by a respective one of a plurality of chambers, wherein the source of
compensation fluid for each of the plurality of chambers is connected to the fluid
under pressure so as to receive pressure therefrom and wherein the fluid pressure
control means is arranged to provide in the compensation fluid for each chamber a
15 different pressure to divide the difference in pressure from the first pressure to the
second pressure into a series of pressure drops across the chambers.
Preferably the source of compensation fluid for each of the chambers
is connected to the fluid under pressure so as to receive pressure therefrom andwherein the pressure control means comprises for each chamber a respective one
20 of a plurality of pressure relief valves, each having a pressure relief setting different
from that of the other valves and less than the first pressure such that the
compensation pressure of each is equal to the difference between the first pressure
and the pressure relief setting of each.
Preferably the fluid under pressure varies in pressure so as to
25 periodically fall below said first pressure and wherein there is provided a one-way
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check valve to allow fluid to flow from the chamber in response to a-drop in the first
pressure.
Preferably the compensation fluid in the chamber is separated from the
fluid under pressure by a separation member movable in response to changes in the
5 pressure of the fluid under pressure such that the pressure in the compensation fluid
is proportional to the pressure in the fluid under pressure.
P~eferably there is provided a spring biasing the movable member to
maintain a pressure in the compensation fluid when the pressure in the fluid under
pressure falls below a predetermined minimum.
Preferably the separation member comprises a piston in a cylinder
separate from the first and second bodies.
Freferably the first body comprises a cylinder and the second body
comprises a piston movable in the cylinder and wherein the fluid communication
duct and the pressure control means are located in the body of the piston.
Preferably the source of compensation fluid for each of the chambers
is connected to the fluid under pressure so as to receive pressure therefrom andwherein the pressure control means comprises for each chamber a respective one
of a plurality of separation members each movable in response to changes in the
pressure of the fluid under pressure such that the pressure in the compensation fluid
20 in each chamber is proportional to the pressure in the fluid under pressure, the
separation members being arranged such that each provides a different proportionof the first pressure to the respective chamber.
Preferably each of the plurality of the separation members comprises a
piston in a cylinder separa~e from the first and second bodies.
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Preferably the pressure in the source of compensation fluid under
pressure is separate from the fluid under pressure and is generated independently
therefrom and is controlled at a pressure dependent thereon.
One embodiment of the invention will now be described in conjunction
5 with the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic vertical cross sectional view through a
reciprocating piston pump having a sealing arrangement according to the present
invention.
Figure 2 is a similar vertical cross sectional view through a
reciprocating piston pump having a second embodiment of sealing arrangement
according to the present invention.
Figure 3 is a schematic vertical cross sectional view through a
reciprocating piston pump having a third e",bodiment of sealing arrangement
accordi, lg to the present invention.
Figure 4 is a schematic vertical cross sectional view through a
reciprocating piston pump having a fourth embodiment of sealing arrangement
according to the present invention.
Figure 5 is a schematic vertical cross sectional view through a
reciprocating piston pump having a fifth embodiment of sealing arrangement
according to the present invention.
Figure 6 is a schematic vertical cross sectional view through a rotary
union or coupling for connection of high pressure fluid to a rotating tube having a
sealing arrangement similar to that of Figure 3.
In the drawings like characters of reference indicate corresponding
parts in the different figures.
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DETAILED DESCRIPTION
In Figure 1 is shown schematically a reciprocating pump 10 having a
piston 11 and a cylinder 12 which thus generates suction at an input 13 and
pressure at an output 14 each connecting with a chamber 15 of the cylinder abovethe piston head.
While the embodiments illustrated relate to a reciprocating pump, the
present invention can also relate to rotary elements including rotary pumps. Yetfurther the present invention also relates to actuators which are responsive to high
pressure fluid to actuate rotation or linear movement of one element relative to1 0 another.
in general, therefore, the present invention relates to the provision of a
sealing arrangement between two relatively movable surfaces each related to a
respective one of two bodies.
In the embodiment shown in Figure 1, the piston forms a first body and
has a first outer cylindrical surface 16 while the cylinder forms a second body and
has an inner cylindrical surface 17. It is necess~ry therefore to provide a sealing
arrangement between the high pressure zone of the surfaces indicated at 18 whichis adjacent the chamber 15 and a lower pressure zone 19 which is adjacent the
open end of the cylinder and thus is at ambient pressure.
The sealing arrangement is defined by four individual seals 20, 21, 22
and 23. Each of these seals is a resilient sealing member which is received within
an annular chamber 24 in one of the surfaces so as to project from the chamber and
engage the other of the surfaces. In the embodiment shown the annular recess 24 is
provided in the surface 17 whereas of course the recess could be provided in thesurface 16. The resilient sealing members are formed of a solid elastomeric material
which is intended to prevent passage of any fluid from one side of the sealing to the
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other side of the sealing member. This is entirely different from th-e brush type of
seal which is intended to allow passage of a limited amount of fluid such as air. The
intention is that no fluid passes from the zone 18 to the zone 19.
Between the seal members 20 and 21 is provided an annular chamber
5 25 which is bounded by the seal 20 on one side, the seal 21 on the opposite side
and by the cylindrical surfaces 16 and 17. Similarly between the seals 21 and 22 is
provided a second chamber 26 and between the seal members 22 and 23 is
provided a third chamber 27. Each of these chambers connects with a respective
one of three supply ducts 28, 29 and 30, each of which passes through the wall of
10 the cylinder to communicate with a mouth in the surface 17.
A pressure control system generally indicated at 31 communicates
pressure from the chamber 15 to each of the chambers 25, 26 and 27. The
pressure control system 31 includes a supply duct 32 connected to an outlet in the
chamber 15. The supply duct 32 connects to an inlet 33 in a cylinder 34 within
15 which is mounted a sliding piston 35. Thus the fluid from the chamber 15 passes
through the duct 32 to the lefthand side of the piston within the cylinder 34. Aseparate fluid on the righthand side of the piston 35 within a chamber 36 of thecylinder 34 is communicated through a duct 37 to each of the chambers 25, 26 and27. A spring 38 provides a bias on the piston 35 pushing the piston to the right so as
20 to apply pressure to the fluids within the chamber 36 in the event that the pressure
drops within the chamber 15 on a suction stroke or otherwise. An indicator rod 39 is
connected to the piston and provides a flag 40 on the end of the cylinder 34 forindicating when the piston 35 has collapsed to the right hand end of the cylinder, for
example on leakage of fluid. The fluid in the chamber on the left hand side of the
25 piston 35 is the fluid from the chamber 15 whereas the fluid on the right hand side of
the piston 35 is a separate fluid maintained separate from the fluid in the chamber
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15 and can thererore be provided by clean oil to avoid communicatir~g contaminants
from the chamber 15 to the chambers 25, 26 and 27. The oil provides a lubricating
environment for the seals and, in the case of abrasive fluids, the chambers,
particularly 25, are maintained at a pressure which is near to, equal to or even more
5 than the pumping pressure to provide a better environment for longer seal life.
The duct 37 is connected to the chamber 25 through a valve assembly
41. Similarly the duct 37 is connected to the chamber 26 through a valve assembly
42 and the duct 37 is connected to the chamber 27 through a valve assembly 43.
Each of the valve assemblies 41, 42 and 43 is similar in that each includes a one-
way check valve 44 and a pressure relief valve 45. The one-way check valve 44
allows pressure to discharge from the respective chamber 25, 26 or 27 in the event
that the pressure within the chamber 36 falls below the pressure within the
respective chamber 25, 26 or 27.
The pressure relief valve 45 is of a known type available from many
15 manufacturers. The characteristics of the pressure relief valve are that the valve
prevents flow of fluid from the duct 37 to the respective chamber 25, 26 or 27 unless
the difference in pressure between the duct 37 and the respective chamber is
greater than the setting of the pressure relief valve.
The pressure relief valve 45 of the valve assembly 41 is set at a
20 different setting from the pressure relief valve of the valve assembly 42 and the
pressure relief of the valve assembly 43.
In one example, the pressure in the duct 37 is at 4000PSI. The setting
of the pressure relief valve of the valve assembly 41 is at 1000PSI. In this way the
pressure within the chamber 25 reaches a value of 3000PSI, that is the difference
25 between the pressure at the duct 37 and the setting of the valve.
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Similarly the pressure relief valve of the assembly 42 is~set at 2000PSI
so that the pressure within the chamber 26 reaches 2000PSI.
The setting of the valve of the assembly 43 is 3000PSI so that the
pressure within the chamber 27 reaches 1000PSI.
It will be appreciated that these pressures will vary as the pressure in
the chamber 15 varies from the maximum of 4000PSI to the suction stroke. During
the suction stroke, the fluid in the chambers 25, 26 and 27 drains to the chamber 36
down to a pressure within that chamber set by the spring 38. Thus the pressure
within the chambers 25, 26 and 27 is maintained at a relatively small positive
10 pressure to prevent generation of a suction in those chambers which could cause
fluid to be drawn into those chambers from the zones 18 and 19.
It will be appreciated therefore that in this example the pressure at the
zone 18 is 4000PSI, the pressure in the chamber 25 is 3000PSI, the pressure within
the chamber 26 is 2000PSI, the pressure within the chamber 27 is 1000PSI and the15 pressure in the zone 19 is 0 or atmospheric.
Thus each seal member has applied across that seal member a
pressure difference of only 1000PSI which can be readily accommodated by
conventional seals.
Pressure relief valves are generally of available in various different
20 types including direct acting and pilot operated. Pressure relief valves are generally
used to release an overpressure situation and the setting of the relief valve can
generally be adjusted for accommodating different required relief pressures. Therelief valve is therefore commercially available but is not generally intended for use
in the system of the present invention.
In Figure 2 is shown a similar arrangement including the cylinder 12,
the piston 11 and the chamber 15. Further, the seal arrangement includes seals 50,
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51, 52, 53 which are similar to the seals 20, 21, 22, and 23 except that the seals are
carried in recesses on the outside surface 16 of the piston for engagement with the
inside surface 17 of the cylinder.
The seals similarly define chambers 55, 56 and 57 similar to the
5 chambers 25, 26 and 27.
In this embodiment the communication from the chamber 15 to the
chambers 55, 56 and 57 occurs through the body of the piston. In this embodimentthe valve assemblies 61, 62 and 63, similarly to the valve assemblies 41, 42 and 43,
are miniaturized and located in the body of the piston. In this embodiment there is
no cylinder 31 and piston 35 separating the fluid in the chamber 15 from the
chambers 55, 56 and 57 but instead the fluid is directly communicated between
these chambers. This arrangement is therefore more suitable for location where
space is limited since the system is located within the piston and cylinder assembly
and is more suitable for a system in which the fluid in the chamber 15 is not of a
15 corrosive or abrasive nature.
Figure 3 shows a yet further embodiment similar to that of Figure 1
which includes the piston 11 and the cylinder 12 defining a chamber 15. The
arrangement of Figure 3 further includes a cylinder 64 similar to the cylinder 34
including a piston 65. In this embodiment there is no spring 38 nor an indicator flag
20 40 but these could be used.
This arrangement uses as a pressure control system 66 three cylinders
67, 68 and 69 each of which includes double piston assembly 71, 72, 73. The
double pistons are of differential sizes so that the pressure applied to one end of the
piston is decreased due to an increase in the area of the second part of the piston.
25 In between a double piston arrangement is a vented cylinder section 74. The output
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,
from the right hand side of each double piston is communicated through a respective
one of three ducts 75, 76 and 77 to the chambers 25, 26 and 27.
Each of the double pistons 71, 72 and 73 therefore communicates a
portion of the pressure from the chamber 15 to each of the chambers 25, 26 and 27.
This proportion varies in dependence upon the difference in area of the double
piston assemblies. Thus a higher pressure is communicated to the chamber 25, a
medium pressure is communicated to the chamber 26 and a lower pressure is
communicated to the chamber 27 in a similar manner to that described in regard to
Figure 1. Since each of these pressures is directly proportional to the pressure in
the chamber 15, the ratio of the pressures between the zone 18, each of the
chambers 25, 26 and 27 and the zone 19 is maintained constant.
Turning now to Figure 4, there is shown a similar arrangement
including a piston 11 and a cylinder 12. In this arrangement, a chamber 80 is
defined between two seal members 81 and 82. In this arrangement there is no
connection between the chamber 80 and the chamber 15 but instead pressure is
generated within the chamber 80 by a pump 83 actuated by a lever 84. In this
arrangement the pressure within the chamber is maintained constant at a pressureintermediate the maximum pressure in the chamber 15 and the suction pressure at
the chamber 15.
In Figure 5 is shown a yet further arrangement including the piston 11,
the cylinder 12 and the chamber 15. In this arrangement there are four seals 90, 91,
92 and 93 defining chambers 94, 95 and 96.
In this arrangement the pressure to the chambers 94, 95 and 96 is
controlled in dependence upon the pressure in the chamber 15 using a pressure
sensor 97 which supplies a sensor signal to a computer control module 98 which
controls injection pumps 99A, 99B and 99C all of which are actuated to supply fluid
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,,
under pressure to the chambers 94, 95 and 96 in proportion to the~pressure in the
chamber 15 and at selected ratios so as to provide the graduated pressure drops as
defined previously across the seal members 90, 91, 92 and 93.
Figure 6 is a schematic vertical cross sectional view through a rotary
5 union or coupling for connection of high pressure fluid to a rotating tube having a
sealing arrangement similar to that of Figure 3. The rotating shaft 101 is mounted in
a stationary support 102 with a supply 103 of high pressure fluid. The shaft is
sealed relative to the support by two sealing arrangements 104, 105 each of which is
of the construction generally shown in Figure 3. The sealing arrangements include
10 cylinders 67, 68 and 69 but does not include a cylinder corresponding to cylinder 64.
The cylinders in this embodiment supply the chambers of both of the two separatesealing arrangements 104,105.
Since various modifications can be made in my invention as herein
above described, and many apparently widely different embodiments of same made
15 within the spirit and scope of the claims without departing from such spirit and
scope, it is intended that all matter contained in the accompanying specification shall
be inle,~urete.l as illustrative only and not in a limiting sense.
