U.S. patent number 3,740,057 [Application Number 05/148,027] was granted by the patent office on 1973-06-19 for shaft seal.
This patent grant is currently assigned to Thermo Electron Corporation. Invention is credited to Edward F. Doyle, Thomas LeFeuvre.
United States Patent |
3,740,057 |
Doyle , et al. |
June 19, 1973 |
SHAFT SEAL
Abstract
A rotary shaft seal is characterized by a buffer compartment
filled with fluid maintained at a pressure which equals or exceeds
the pressures along the shaft with which the seal is associated.
The relatively high buffer pressure within the seal is effective to
prevent passage of material along the shaft from one side of the
seal to the other. In one preferred embodiment, the device for
applying pressure to the buffer fluid within the compartment is
responsive to the pressures along the shaft adjacent to opposite
sides of the seal. The intensity of pressure applied to fluid
within the buffer compartment is a function of the pressures along
the shaft. This preferred embodiment is an effective driveshaft
seal for the expander in a Rankine cycle engine, wherein the
pressure applying device responds to both the pressure within the
expander and the pressure outside the expander and applies to fluid
in the buffer compartment a pressure higher than either of
them.
Inventors: |
Doyle; Edward F. (Dedham,
MA), LeFeuvre; Thomas (Woburn, MA) |
Assignee: |
Thermo Electron Corporation
(Waltham, MA)
|
Family
ID: |
22523916 |
Appl.
No.: |
05/148,027 |
Filed: |
May 28, 1971 |
Current U.S.
Class: |
277/366; 417/901;
277/369; 60/682; 277/387; 277/929; 277/927; 277/408 |
Current CPC
Class: |
F16J
15/40 (20130101); Y10S 277/927 (20130101); Y10S
277/929 (20130101); Y10S 417/901 (20130101) |
Current International
Class: |
F16J
15/40 (20060101); F16j 015/00 () |
Field of
Search: |
;277/3,12,17,27,28,59,61,62,63,67,70,81,83,86 ;60/36 ;417/901 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rothberg; Samuel B.
Assistant Examiner: Smith; Robert I.
Claims
We claim:
1. A shaft seal interposed between relatively rotatable shaft means
and casing wall means through which said shaft means extends, said
casing wall means having a first pressure zone on one side thereof
and a second pressure zone on the other side thereof, said shaft
seal comprising:
a. first sealing means mounted in fixed relationship to said shaft
means and forming first and second sealing surface areas each
surrounding said shaft means;
b. second sealing means mounted in fixed relationship to said
casing wall means and forming first and second sealing surface
areas, said first and second surface areas formed by said second
sealing means mating in sealing engagement with said first and
second sealing surface areas of said first sealing means,
respectively;
c. means forming a buffer fluid compartment communicating with said
first and second sealing means at their points of sealing
engagement;
d. first means communicating with said first pressure zone;
e. second means communicating with said second pressure zone;
and
f. means responsive to said first and second communicating means
for applying to buffer fluid within said compartment a pressure
which at least substantially equals the greater of the pressures in
said first and second pressure zones, thereby to inhibit passage of
material along said shaft means from either of said pressure zones
to the other.
2. A shaft seal according to claim 1 wherein said pressure applying
means is responsive to the pressures in both said first and second
pressure zones.
3. A shaft seal according to claim 1 wherein said pressure applying
means comprises:
a. means forming a hermetically sealed expansible chamber
communicating with said buffer fluid compartment; and
b. means responsive to both the pressure in said first pressure
zone and the pressure in said second pressure zone for applying to
said expansible chamber and thereby to said compartment a pressure
at least substantially equaling the greater of either the pressure
in said first pressure zone or the pressure in said second pressure
zone.
4. A shaft seal according to claim 3 wherein said pressure applying
means further comprises means for constantly applying pressure to
said expansible chamber and thereby to said compartment in addition
to the pressure applied thereto by said means responsive to the
pressures in said first and second pressure zones, whereby the
pressure applied to said compartment exceeds the greater of either
the pressure in said first pressure zone or the pressure in said
second pressure zone.
5. A shaft seal according to claim 3 wherein said expansible
chamber comprises a buffer fluid reservoir.
6. A shaft seal according to claim 1 wherein said means responsive
to said first and second communicating means is in hermetically
sealed fluid connection with said buffer fluid compartment.
7. In a Rankine cycle system including
an expander having means forming a working fluid chamber and
a rotary shaft extending from said working fluid chamber into an
environmental zone, wherein the pressure in said working fluid
chamber rises above environmental zone pressure during certain
conditions and drops below environmental zone pressure during
certain other conditions, a shaft seal comprising:
a. a first sealing means on said shaft in fixed, fluid tight
relationship thereto and having first and second sealing surface
areas surrounding said shaft;
b. second sealing means in fixed, fluid tight relationship to said
means forming said working fluid chamber and having first and
second sealing surface areas in sealing engagement with said first
and second sealing surface areas, respectively, of said first
sealing means;
c. means forming a buffer fluid compartment in communication with
said first and second sealing means at their points of engagement
for maintaining a supply of buffer fluid at said points of
engagement; and
d. means in hermetically sealed fluid communication with said
compartment constantly applying pressure to buffer fluid therein
which at least equals the greater of either the pressure in said
working fluid chamber or the pressure in said environmental zone,
said pressure being applied during both operating and non-operating
conditions of the Rankine cycle system, thereby to eliminate the
tendency of material to pass along said shaft from said working
fluid chamber into said environmental zone when pressure in said
working fluid chamber is above environmental zone pressure and from
said environmental zone into said working fluid chamber when
pressure in said working fluid chamber is below environmental zone
pressure.
8. In a Rankine cycle system according to claim 7 a shaft seal
wherein said pressure applying means applies to buffer fluid within
said compartment a pressure greater than either the pressure of
said working fluid chamber or the pressure of said environmental
zone.
9. In a Rankine cycle system according to claim 7 a shaft seal
wherein:
a. said first sealing means comprises an annular flange surrounding
said rotary shaft;
b. said second sealing means comprises a pair of annular sealing
surfaces for sealing engagement with opposite sides of said annular
flange; and
c. said buffer fluid compartment surrounds said annular flange
along and between the points of engagement of said annular flange
with said pair of annular sealing surfaces.
10. In a Rankine cycle system according to claim 9 a shaft seal
further comprising means forming a fluid inlet and a fluid outlet
for said buffer fluid compartment wherein said buffer fluid
compartment surrounds said annular flange, eccentrically thereof,
whereby rotary movement of said annular flange within said buffer
fluid compartment during operation of the Rankine cycle system
produces a pumping action for drawing buffer fluid into said
compartment through said inlet and expelling buffer fluid from said
compartment and through said outlet.
11. In a Rankine cycle system according to claim 10 a shaft seal
further comprising:
a. means connecting said inlet and outlet means to form a closed
loop in which said buffer fluid travels; and
b. reservoir means communicating with said closed loop for
providing a continuing supply of buffer fluid to replenish any
buffer fluid which passes from said compartment into said working
fluid chamber or said environmental zone.
12. In a Rankine cycle system according to claim 11 a shaft seal
wherein:
a. said reservoir means comprises a flexible, hermetically sealed
buffer fluid confining means; and
b. said means constantly applying pressure applies pressure to said
flexible, hermetically sealed fluid confining means for exerting
pressure on buffer fluid in said compartment.
13. In a Rankine cycle system according to claim 10 a shaft seal
wherein said means constantly applying pressure is responsive to
the pressure in said environmental zone and the pressure in said
working fluid chamber.
14. In a Rankine cycle system according to claim 10 a shaft seal
wherein said means constantly applying pressure comprises:
a. spring means for continuously applying pressure to said buffer
fluid confining means; and
b. means responsive to the pressure in said working fluid chamber
and the pressure in said environmental zone for applying to said
buffer fluid confining means a pressure in addition to pressure
applied thereto by said spring means, which at least substantially
equals the higher of the pressures in the aforesaid zones,whereby
the buffer fluid pressure in said compartment always exceeds both
the pressure in said working fluid chamber and the pressure in said
zone of environmental pressure to prohibit passage of material
along said shaft from said zone into said working fluid chamber or
from said working fluid chamber into said zone.
15. In a Rankine cycle system according to claim 7 a shaft seal
further comprising:
a. fluid conduit means having both inlet and outlet means connected
to said buffer fluid compartment to form a closed loop; and
b. means forming a pump for causing fluid in said compartment to
travel through said closed loop during rotation of said shaft.
16. In a Rankine cycle system according to claim 7, a shaft seal
wherein said pressure applying means comprises:
a. first means communicating with pressure external of said
chamber;
b. second means communicating with pressure internal of said
chamber; and
c. means responsive to said first and second communicating means
for applying to buffer fluid within said compartment a pressure at
least substantially equal to the greater of either said first or
second pressure levels.
17. In a Rankine cycle system including an
expander casing means forming a chamber to contain fluid lubricant
and organic Rankine cycle working fluid, the interior and exterior
of said chamber being characterized by different pressure levels,
and
rotary drive shaft means extending through said casing, a shaft
seal comprising:
a. first sealing means in fixed, fluid tight relationship to said
shaft means and having a first surface portion and a second surface
portion;
b. second sealing means in fixed, fluid tight relationship to said
expander casing means and in sealing engagement with both said
first and second surface portions of said first sealing means;
c. means forming a buffer fluid compartment in communication with
said first and second sealing means at their points of sealing
engagement for maintaining a supply of buffer fluid at said points
of engagement;
d. hermetically sealed compressible reservoir means in fluid
communication with said compartment;
e. first means for continuously applying pressure to said reservoir
means and thereby to buffer fluid within said compartment; and
f. second means for continuously applying pressure to said
reservoir means to thereby continuously pressurize buffer fluid
within said compartment in addition to pressure applied thereto by
said first pressure applying means, the magnitude of which is
functionally related to the greater of either the pressure internal
of said chamber or the pressure external of said chamber.
18. In a Rankine cycle system according to claim 17 a shaft seal
wherein said second pressure applying means applies pressure to
said buffer fluid which is at least substantially as great as the
greater of either the pressure within said chamber or the pressure
without said chamber, whereby the pressure applied to said buffer
fluid within said compartment is always greater than either the
pressure within said chamber or the pressure without said
chamber.
19. In a Rankine cycle system according to claim 18, a shaft seal
wherein said compressible reservoir is for buffer fluid.
20. In a Rankine cycle system according to claim 19 a shaft seal
further comprising means for indicating the amount of buffer fluid
in said reservoir.
21. In a Rankine cycle system according to claim 17, a shaft seal
wherein said second pressure applying means comprises:
a. first means communicating with pressure external of said chamber
for applying to said reservoir means a first pressure level having
a magnitude substantially equal to said external pressure;
b. second means communicating with pressure internal of said
chamber for applying to said reservoir means a second pressure
level having a magnitude substantially equal to said internal
pressure; and
c. means associated with said reservoir means and responsive to
said first and second communicating means for applying to buffer
fluid within said compartment a pressure at least substantially
equal to the greater of either the pressure internal of said
chamber or the pressure external of said chamber.
22. A shaft seal interposed between relatively rotatable shaft
means and casing wall means through which said shaft means extends,
said casing wall means having a first pressure zone on one side
thereof and a second pressure zone on the other side thereof, the
pressure in said first pressure zone being greater than the
pressure in said second pressure zone under some conditions and
less than the pressure in said second zone under other conditions,
said shaft seal comprising:
a. first sealing means mounted in fixed relationship to said shaft
means and forming first and second sealing surface areas each
surrounding said shaft means;
b. second sealing means mounted in fixed relationship to said
casing wall means and forming first and second sealing surface
areas, said first and second surface areas formed by said second
sealing means mating in sealing engagement with said first and
second sealing surface areas of said first sealing means,
respectively;
c. means forming a buffer fluid compartment communicating with said
first and second sealing means at their points of sealing
engagement; and
d. means in hermetically sealed fluid communication with said
compartment for continuously applying to buffer fluid within said
compartment, under all conditions, a pressure which at least
substantially equals the greater of the pressures in said first and
second pressure zones, thereby to inhibit passage of material along
said shaft means from either of said pressure zones to the other
under all conditions.
Description
BACKGROUND OF THE INVENTION
The passage of a rotary shaft through the casing of a driving or
driven apparatus is attended by a sealing problem which is
particularly difficult when the pressures within or surrounding the
casing are subject to significant variation so that first one and
then the other of the pressures is higher. A highly effective seal
is required to prevent passage of the material from the
surroundings into the casing and to prevent passage of the material
from the casing into the surroundings.
One situation involving the problem outlined above is presented by
the driveshaft of an expander in a Rankine cycle engine. Typically,
a rotary driveshaft passes through the expander casing and engages
the device to be driven. During operation of the engine, pressure
within the expander casing fluctuates over a wide range extending
above and below the pressure surrounding the casing, which is
typically the ambient atmosphere. During extended periods of
non-operation, the pressure in the casing falls to a substantially
sub-atmospheric level due in part to the cooling attending
shut-down of the engine. It is essential to prevent passage of
fluid within the expander into the atmosphere and to prevent the
passage of air into the expander.
Fluids contained within the expander casing include a lubricant,or
lubricants, and the working fluid for the Rankine cycle engine.
Both fluids are present at the location where the shaft passes
through the expander casing. Typically, the working fluid is
sufficiently expensive that its conservation becomes an extremely
important matter in efficient operation of the Rankine cycle
engine. Further, a pre-determined optimum amount of working fluid
must be maintained within the system to enable it to operate at
peak efficiency. When the pressure in the casing is above
atmospheric pressure, fluids in the casing continually tend to be
forced out into the atmosphere along the driveshaft. Loss of these
fluids is accompanied by a substantial reduction in operating
efficiency and a substantial increase in operating expense.
It is also of primary importance in Rankine cycle systems that
material in the surrounding environment be kept out of the expander
casing. Foreign material entering the casing is distributed
throughout the system to the detriment of system performance. The
surrounding environment, as pointed out above, is typically the
ambient atmosphere. Entry of air into the engine is particularly
deleterious to system performance. This detriment apparently
results from nitrogen and oxygen, which constitute the major gases
in the atmosphere. Nitrogen collects in the condenser of the system
and substantially reduces the operating efficiency of the condenser
and thereby of the system. Oxygen, in the presence of the working
fluid and lubricant, accelerates their rates of thermal
decomposition and, accordingly, substantially increases the expense
required to operate the system.
SUMMARY OF THE INVENTION
The present invention relates to a seal for preventing movement of
material either into or out of a casing along a rotary shaft. The
sealing elements include a first means mounted on the shaft forming
a first pair of sealing surface areas and a second means mounted on
the casing forming a second pair of sealing surface areas in
sealing engagement with the first sealing surface areas. A buffer
fluid chamber containing pressurized buffer fluid surrounds the
sealing elements. Buffer fluid pressure is maintained sufficiently
high that the tendency of buffer fluid to pass between the sealing
surfaces at least equals the tendency of material to pass between
the sealing surfaces from either inside or outside of the casing.
Thereby, passage of material past the sealing surface areas either
into or out of the casing is effectively prevented.
Small amounts of the buffer fluid may pass the sealing surfaces and
enter the casing or the environment surrounding the casing.
Accordingly, the buffer fluid is selected so as not to be harmful
to material within the casing or harmful when present in the
environment. The buffer fluid may be a suitable lubricating
fluid.
The seal is particularly effective when used on the expander
driveshaft in a sealed Rankine cycle engine. To prevent passage of
the fluid from the expander casing along the driveshaft into the
atmosphere and to prevent passage of the atmosphere into the
expander casing, the buffer fluid pressure is constantly maintained
at a pressure level equaling or above both atmospheric pressure and
any anticipated crankcase pressure. In a preferred embodiment of
this invention, the buffer fluid pressure is maintained at the
desired level by apparatus responsive to both atmospheric pressure
and the pressure within the expander casing.
It is a primary object of this invention to provide a rotary shaft
seal which prevents passage of material in either direction along a
shaft past the seal.
It is a further object of this invention to provide a rotary shaft
seal which prevents passage of material in either direction along a
shaft past the seal wherein the seal is responsive to pressures
surrounding the shaft on opposite sides thereof for maintaining
within the seal a buffer pressure which equals or exceeds the
pressures surrounding the shaft.
It is also an object of this invention to provide a rotary shaft
seal for the expander of a Rankine cycle engine which prevents
passage of fluids from the expander to the atmosphere and from the
atmosphere into the expander.
A further object of this invention is to provide a rotary shaft
seal for the expander of a Rankine cycle engine which is responsive
to both the pressure within the expander and atmospheric pressure
for maintaining within the seal a buffer pressure which equals or
exceeds both the pressure within the expander and the atmospheric
pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a preferred embodiment of the rotary shaft seal
of this invention;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG.
1;
FIG. 3 illustrates an alternate embodiment of the apparatus shown
in FIG. 2;
FIG. 4 is a cross-sectional view taken along line 4--4 of FIG.
1;
FIG. 5 presents an alternate embodiment of the rotary shaft seal
shown in FIG. 1;
FIG. 6 illustrates an alternate embodiment of the apparatus shown
in FIG. 4;
FIG. 7 illustrates another alternate embodiment of the apparatus
shown in FIG. 4;
FIG. 8 is a schematic view of a Rankine cycle system according to
this invention;
FIG. 9 is a sectional view of a reciprocating piston expander
constructed according to this invention; and
FIG. 10 is a schematic view showing a turbine expander constructed
according to this invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1, a rotary shaft 10, to which a driven member 8
is attachable, extends through a casing 12, the casing being
comprised of parts 14 and 16. A structure 11 establishes a seal
between the shaft and the casing.
The sealing structure 11 includes a first sealing element in the
form of a ring 18 and a pair of sealing elements 26 and 26'. The
sealing ring 18 is affixed to shaft 10 near an outer portion of the
casing 12. The sealing ring 18 may be formed of any suitable
material such as hardened steel, cast iron or the like. Mounted on
the casing 12 are substantially identical sealing elements 26 and
26', each of which sealing engages a separate sealing area of the
sealing ring 18, as will be more fully described below. The
interface between the sealing ring 18 and the driveshaft 10 is
sealed hermetically by static O-ring seal 20. The interface between
the the casing 12 and the sealing elements 26 and 26' is provided
with hermetic O-ring seals 27 and 27'.
Since the sealing elements 26 and 26' are substantially identical,
only sealing element 26 will be described. In sealing element 26',
like primed numerals designate like parts.
The sealing element 26 comprises an outer enclosure 28 supporting a
sealing ring 30 of suitable material such as carbon, an O-ring 32,
spring means 34, means 36 for confining the O-ring 32, and means 38
for confining the carbon sealing ring 30. The carbon sealing ring
30 is positioned for direct engagement with the sealing ring 18 and
is pressed into continuous firm sealing engagement by the spring
means 34. The O-ring 32 establishes a static seal between the
carbon sealing ring 30 and the enclosure 28 to prevent passage of
material between the carbon sealing ring and the enclosure. The
means 36 maintains the O-ring in proper sealing engagement with the
carbon sealing ring and the enclosure 28. The means 38 confines the
carbon sealing ring 30 to maintain it in fixed position relative to
the enclosure 28, thereby avoiding movement of the carbon sealing
ring 30 relative to the shaft 10 when the shaft 10 and the mating
ring 18 rotate. The means 38 may engage the carbon sealing ring 30
in a detent, not shown, or in any other suitable manner.
The elements 18, 26 and 26' of the sealing structure 11 are mounted
adjacent the journal box where the driveshaft 10 passes through the
casing 12. The sealing ring 18 is firmly pressed against a shoulder
22 of the driveshaft by a threaded retaining member 24. The sealing
element 26 abuts a journal bearing 40. The bearing face 42 of the
carbon sealing ring 30 associated with the sealing element 26 is
positioned in sealing engagement with one surface area of the
sealing ring 18. The sealing element 26' is positioned so that its
bearing surface 42' sealingly engages an opposite surface area of
the sealing ring 18. The sealing element 26' is firmly secured in
position by a retaining ring 44.
Surrounding the points of sealing engagement between the sealing
elements 26, 26' and 18 is a compartment 48 for containing a buffer
fluid. The compartment is so formed that buffer fluid contained
therein will be continuously present at the interface between the
sealing ring 18 and the sealing rings 30 and 30'.
When the driveshaft 10 is rotated, heat is generated due to the
frictional engagement between the sealing ring 18 and the carbon
sealing rings 30 and 30'. This heat builds up in the buffer fluid
within the compartment 48. Accordingly, a method of circulating and
cooling the buffer fluid is required. The amount of heat generated
is such that the buffer fluid temperature may be maintained at the
proper level by circulation of the buffer fluid through a closed
cooling loop 55. The cooling loop is formed by lines 50 and 54
which lead from buffer fluid outlet 52 and buffer fluid inlet 56,
respectively, and are connected by coupling 58. Circulation of the
buffer fluid may be produced by any convenient means. For example,
a pumpingstructure may be included within the sealing structure 11
or a pump, not shown, may be installed along the closed loop
55.
In FIG. 1, pumping action is produced by cooperation between the
sealing element 18 and the buffer fluid compartment 48 in a manner
which is best described with reference to FIG. 2. The buffer fluid
compartment 48 is formed eccentrically within the casing 12 so that
the central axes of the sealing ring 18 and of the buffer fluid
compartment 48 do not coincide. When heat is generated by
frictional engagement between the sealing elements, the sealing
ring 18 acts as an impeller within the compartment 48 to build a
relatively high pressure adjacent the outlet 52 and a relatively
low pressure adjacent the inlet 56. The small pressure differential
created in this manner is enough to establish the required flow of
buffer fluid through the loop 55. The heat exchange which takes
place along the lines forming the loop is sufficient to maintain
the temperature of the buffer fluid at the appropriate level.
An alternate embodiment of buffer fluid pump is illustrated in FIG.
3. In this embodiment, the sealing ring 18 and the buffer fluid
compartment 48 are concentrically formed within the casing 10. The
sealing ring 18 has formed thereon a series of vanes 60 which serve
as impellers to build a pressure differential between the inlet 56
and the outlet 52.
For the sealing structure 11 to prevent passage of fluid or other
material in either direction along the driveshaft 10 under any and
all circumstances, the pressure of the buffer fluid must constantly
be maintained at a level equal to or higher than the pressure
surrounding the shaft at opposite sides of the sealing elements 26
and 26'.
To provide the required buffer fluid pressure, there is provided a
pressure source 62 joined by a connecting line 64 to the loop 55.
The pressure source 62 may operate in a number of ways to maintain
the required pressure level in the buffer fluid compartment 48. One
preferred embodiment is illustrated in FIGS. 1 and 4. A housing 65
comprises support means 66, a first end section 68 and a second end
section 70. Formed within the housing 65 is a hermetically sealed
buffer fluid reservoir 72. The reservoir 72 is defined by a first
flexible diaphragm means 74 and a second flexible diaphragm means
76. The flexible diaphragm means 74 and 76 include within their
central portion rigid plates 78 and 80, respectively. A buffer
fluid level indicator 108 bearing indicia 109 extends from plate 78
through chamber 84. Within the reservoir 72 is established a port
82 which communicates with the connecting line 64. Adjacent one
side of the reservoir is a first pressure chamber 84 formed by
first end section 68; adjacent the other side of the reservoir is a
second pressure chamber 86 formed by the second end section 70. A
compression spring 88 is interposed between plate 78 and surface 90
of the first end section 68. Interposed between the plate 80 and
surface 94 of the second end section 70 is a compression spring 92.
The springs constantly exert pressure on the plates and thus on the
buffer fluid within the reservoir 72. In addition, pressure is
applied to the buffer fluid within the reservoir 72 by pressure
within the pressure chambers 84 and 86. The additional pressure
applied to the buffer fluid is substantially equivalent to either
the pressure in the first pressure chamber 84 or the second
pressure chamber 86, as will be explained in more detail below.
Within the first pressure chamber 84 is a stop 96 for limiting
movement of the plate 78; within the second pressure chamber 86 is
a stop 98 for limiting movement of the plate 80.
The first and second pressure chambers are provided for applying
pressure to the buffer fluid in response to the pressure
surrounding the driveshaft on opposite sides of the sealing
elements 26 and 26'. In the embodiment of FIG. 1, for example, the
sealing element 26' is exposed to a zone of pressure outside the
casing 12 and the sealing element 26 is exposed to pressure inside
the casing 12. Accordingly, the first pressure chamber 84 is
constructed to respond to pressure outside the casing by direct
communication through ports 100 and 102. Also, a line 104 extends
from the second pressure chamber 86 to the interior of the casing
12 to enable the second pressure chamber to respond to pressure
within the casing 12.
Operation of the sealing structure 11 depicted in FIGS. 1, 2 and 4
will now be described. The sealing structure prohibits
communication between the first pressure zone on one side of the
sealing elements 26 and 26' and a second pressure zone on the
opposite side of these sealing elements, regardless of pressure
fluctuations or of which pressure is higher than the other. The
buffer fluid chamber 48, the loop 55, the line 64, and the
reservoir 72 are all filled with buffer fluid. The pressure applied
to the reservoir 72 by the springs 88 and 92 is transmitted to the
buffer fluid within the compartment 48 by means of the line 64 and
the loop 55. The springs thus constitute a pressure source
constantly acting on the buffer fluid.
The first pressure chamber 84 is at a first pressure level
corresponding to the pressure level outside the casing 12 and the
second pressure chamber 86 is at the pressure level of the interior
of the casing. A pressure equivalent to the higher pressure of the
pressures within the chambers 84 and 86 is applied to the reservoir
72, in addition to the pressure applied to the reservoir by opposed
springs 88 and 92. That is, when pressure in the second pressure
chamber 86 exceeds pressure in the first chamber 84, the first and
second flexible diaphragm means 74 and 76 flex so that the
reservoir 72 advances toward the stop 96 until the stop is abutted
by the plate 78. The springs continue to act upon the reservoir
while a force equivalent to the pressure in the second pressure
chamber 86 is applied thereto.Conversely, when pressure in the
first pressure chamber 84 exceeds the pressure in the second
pressure chamber 86, the first and second flexible diaphragm means
flex to permit the reservoir 72 to advance toward the stop 98 until
this stop is abutted by the plate 80. In this condition, pressure
substantially equivalent to the relatively high pressure in the
chamber 84 is applied to the buffer fluid in addition to the
pressure applied thereto by the springs.
The springs 88 and 92 are preferably calibrated so that pressure on
the buffer fluid within the compartment 48 always exceeds pressures
surrounding sealing elements 26 and 26'. However, the springs may
be calibrated to apply a minimum force effective only to overcome
any frictional resistance within the pressure source 62 or
eliminated entirely. In the latter event, the buffer fluid pressure
will substantially equal the highest of the pressures surrounding
the sealing elements 26 and 26'. Since the pressure across the
sealing faces of elements 18, 26 and 26' is always characterized by
either equilibrium or relatively high buffer fluid pressure, there
is never a tendency for material to pass along the shaft 10 from
one side of the sealing elements 26 and 26' to the other side of
these sealing elements.
There is a tendency for a small amount of buffer fluid to pass
between the sealing faces of the sealing ring 18 and the carbon
sealing rings 30 and 30'. In event of passage, a small portion of
the buffer fluid may be lost either to one side or the other of the
sealing elements 26 and 26'. Fluid which passes from the buffer
fluid compartment 48 is replenished from the reservoir 72. As the
fluid is exhausted from the reservoir, flexible diaphragm means 74
and 76 advance toward each other to reduce reservoir volume. The
reservoir may or may not need periodic recharging of buffer fluid
depending on the life of the system within which the sealing
structure 11 is used. Within the practical limits of reservoir
size, the supply of buffer fluid has been found sufficient for
extended periods.
The sealing structure 11 operates in the manner described, whether
or not the driveshaft 10 is rotating within the casing 12, and is
therefore equally effective when the system in which it is used is
operating and when the system is not operating.
The amount of buffer fluid in reservoir 72 at any given time is
measured by reading indicia 109 on the buffer fluid indicator means
108 with respect to a reference point, such as the surface of
housing 65. To obtain a reading, the indicator means 108 must be in
the fully advanced position so that the plate 80 abuts the stop 98.
In this position, the indicia 109 provides a reading of the
distance between the plates 78 and 80 and therefore of the volume
of fluid within the reservoir 72. When the pressure in the chamber
84 exceeds the pressure in the chamber 86, the plate 80 will be
caused to abut the stop 98 so that the position of the indicator
108 inherently provides a reading of the reservoir contents.
Further advancement of the indicator means 108 is prohibited by the
resistance of the stop 98 and the buffer fluid within the reservoir
72. When the pressure in the chamber 86 exceeds that in the chamber
84 (the condition shown in FIG. 4), the indicator means is advanced
against a resistance level which is a function of the pressure
differential between the two pressure chambers. When a second
resistance level resulting from engagement of the plate 80 with the
stop 98 is encountered, the indicator means 108 is fully advanced
and a reading may be taken.
Various alternate embodiments of the sealing structure 11 will now
be described. Like numerals will be used to designate like
parts.
FIG. 5 illustrates an alternate embodiment of the sealing structure
involving primarily the sealing elements interposed between the
driveshaft 10 and the casing 12. Mounted within the casing 12 are a
pair of opposed static sealing rings 110 between which is formed a
buffer fluid chamber 112 eccentric with respect to the longitudinal
axis of the driveshaft 10. Mounted on the driveshaft 10 are a pair
of assemblies 114 biased away from each other into engagement with
the sealing rings 110 by a compression spring 116. Each of the
assemblies 114 comprises a means 118 which provides a static seal
between the shaft 10 and the assemblies 114 and positions a rotary
carbon sealing ring 120 in sealing engagement with the static
sealing ring 110. O-rings 122, 124, 126 and 128 hermetically seal
the buffer fluid chamber 112 from the zones of pressure present
along the driveshaft 10. Inlet 56 and outlet 52 are provided to
connect the chamber 112 with the pressure source 62, in the manner
described above in connection with FIGS. 1, 2 and 4. It will be
appreciated that the embodiment of FIG. 5 operates substantially in
the same manner as the one described in connection with FIGS. 1, 2
and 4 except that the static sealing elements are mounted on the
casing 12 and rotary sealing elements are mounted on the driveshaft
10.
In connection with FIGS. 6 and 7, there will be described two other
embodiments of the sealing structure 11 primarily involving the
pressure source 62. FIG. 6 shows one embodiment of pressure source
62 for applying force to the buffer fluid independent of pressures
surrounding the driveshaft 10. A housing 65 is provided with a
flexible bellows diaphragm 140 which divides the interior of the
housing 65 into a buffer fluid reservoir 142 and a pressure chamber
144. The housing 65 is provided with a port 82 for connection to
the line 64 to establish communication with the loop 65. There is
further provided a port 146 for the admission of compressed gas
into the pressure chamber 144. Compressed gas admitted through port
146 fills the pressure chamber 144 to provide sufficient pressure
on buffer fluid within the buffer fluid reservoir 142 to maintain
the buffer fluid within the buffer fluid compartment 148, shown in
FIG. 1, at a level which equals or exceeds the pressures
surrounding the driveshaft 10 on opposite sides of the elements 26
and 26'. The pressure applied to the reservoir 142 by the source of
compressed gas is calibrated to always provide at least the minimum
pressure required for compartment 148.
The pressure source 62 shown in FIG. 7 includes a housing 65
divided into three sections by a first flexible diaphragm means 150
and a second flexible diaphragm 152. The flexible diaphragm means
150 and 152 provide hermetic sealing between the three sections of
the interior of the housing 65.
A chamber 154 is provided with ports 156 which establish
communication with one pressure zone. A chamber 158 communicates
through line 104 with another pressure zone. A buffer fluid
reservoir 160 communicates through a port 82 and the line 64 with
the loop 55 and thence with the compartment 48. The diaphragm means
150 includes a rigid plate-like structure 162. From structure 162,
a sleeve 164 projects into chamber 158 and a projection 164 extends
through the chamber 154. The projection 164 forms a fluid level
indicator. Indicia 166 thereon serves to indicate the amount of
fluid present within the buffer fluid reservoir 160. The diaphragm
means 152 includes a second plate-like structure 168 from which
projection 170 extends upward into the chamber 158 and telescopes
within the sleeve 164. A retaining means 172 is mounted within the
chamber 158. Opposed between the retaining means 172 and the
structure 168 is a compression spring 174.
The spring 174 continuously applies pressure to buffer fluid within
the reservoir 160 and thus to fluid within the compartment 48. When
the pressure in the chamber 158 is greater than the pressure in the
chamber 154, the diaphragms 150 and 152 are urged apart from each
other. (The diaphragm 150, as shown in FIG. 7, is in the transitory
state, moving away from the diaphragm 152.) The diaphragm 150
advances to the partition 176 and the diaphragm 152 is pressed
firmly against buffer fluid in the reservoir 160. Under this
condition, the pressure of the fluid within the chamber 158 is
imparted to buffer fluid within the reservoir 160 in addition to
the pressure applied thereto by the spring 174. When the pressure
within the chamber 154 exceeds that within the chamber 158, the
diaphragm 150 advances toward the diaphragm 152. This advancement
continues until the terminal portion 178 of the sleeve 164 engages
the terminal portion 180 of the projection 170. When this occurs,
the projection and the sleeve are effectively coupled together so
that pressure within the chamber 154 is applied to buffer fluid
within the reservoir 160 in addition to pressure applied thereto by
the spring 174.
The fluid level indicating means 164 provides for the determination
of the amount of buffer fluid within the reservoir 160. When the
pressure in chamber 154 exceeds that in chamber 158, the diaphragms
are effectively coupled as described above, and the indicia 166 on
the projection 164 will indicate the amount of fluid within the
reservoir 160. In this circumstance, the projection 154 will not be
susceptible of further downward movement into the housing 65. When
the pressure in chamber 168 exceeds that in chamber 154, the
diaphragm 150 will be pressed against the member 176 and the
indicia 166 on the projection 164 will indicate that the reservoir
is full. When the reservoir is indicated full, to determine that
this is actually a correct reading, the projection 164 must be
pressed inwardly of the housing 165, against the force applied
thereto by the pressure differential between the chambers 158 and
154, until a second level of resistance is encountered beyond which
the projection is no longer movable. The reading at the second
level of resistance is the correct indication of the amount of
fluid within the reservoir 160. If upon pressing the projection 164
inwardly on the housing 165, it is immediately immovable, the
reservoir 160 is full of buffer fluid.
Turning now to FIGS. 8 and 9, there will be described a Rankine
cycle system constructed according to this invention to prevent
passage of the fluid from the system into the atmosphere and
passage of material from the atmosphere into the system.
The Rankine cycle system is described briefly in connection with
FIG. 8. A vapor generator 182 heats organic working fluid fed
thereto by a pump 184. The vaporized working fluid is then directed
to an expander 186 which expands the vapor through a substantial
temperature and pressure drop to produce work and rotate the
driveshaft 10. The working fluid then passes from the expander 186
through a separator 188 which removes any lubricants from the
organic working fluid, which lubricants are returned to the
expander by a line 190. The working fluid then enters the vapor
side 192 of a regenerator 194 and gives up some of the heat energy
remaining therein to working fluid passing through the liquid side
196 of the regenerator. From the vapor side 192 of the regenerator,
the working fluid passes through the condenser 198 and is fully
condensed. The pump 184 then drives the condensed working fluid
through the liquid side 196 of the regenerator 194 and back to the
vapor generator 182. The working fluid is heated as it is driven
through the liquid side of the regenerator by exhaust vapor passing
through the vapor side of the regenerator. The vapor generator 182
vaporizes the working fluid and the cycle is repeated.
FIG. 9 illustrates a reciprocating expander for a Rankine cycle
system of the type shown in FIG. 8. The expander is provided with a
casing 200 comprising parts 202 and 204. Within the casing 200 is a
vapor inlet manifold 206 and valves 208 and 210 cooperatively
arranged with respect to reciprocating pistons 212 and 214. Each of
the pistons have associated therewith a piston rod 216 and 218. The
piston rods are connected to a crankshaft 220 which is supported
within the casing 200 at one end by a journal box 222. A driveshaft
10 extends from the opposite end of the crankshaft and is supported
in the casing 200 by a journal box 224. Adjacent the journal box
224 are sealing elements 18, 26 and 26' surrounded by a buffer
fluid compartment 48. The sealing elements, compartment and other
associated parts are constructed and mounted in substantially the
same fashion as described above in connection with FIG. 1. Lines 50
and 54 extend from the compartment 48 to form the loop 55 which is
connected by line 64 to the pressure source 62. Extending from the
pressure source 62 is a line 104 establishing communication between
pressure source and the interior of the casing 200. The line 104
should enter the casing 200 at a place relatively near the journal
224 so that it may enable the pressure source 62 to accurately
sense the pressure adjacent the sealing element 26.
The operation of the apparatus of FIG. 9 will now be described in
connection with the buffer fluid compartment as shown in FIG. 2 and
the pressure source as shown in FIG. 4.
The expander 186 is characterized by wide variations of internal
pressures. The pressure in the casing 200 may extend to levels well
above atmospheric pressure under certain conditions and, under
other conditions, drop substantially below atmospheric pressure.
Consequently, the shaft seal is required to prevent passage of
material from within the casing to the atmosphere when the casing
pressure is relatively high and to prevent passage of material from
the atmosphere into the casing when the casing pressure is
relatively low.
Vaporized working fluid admitted into the inlet manifold 206 from
the vapor generator 182 is alternately directed first into cylinder
211 and then into cylinder 213 by valves 208 and 210, respectively,
in a typical manner understood in the art. Working fluid is
exhausted from the cylinders through exhaust ports of the type
shown at 215 in the cylinder 211. Alternate reciprocation of the
pistons 212 and 214 results from the admission into the cylinders
211 and 213 and exhaust therefrom of vaporized working fluid.
Reciprocation of the pistons rotates the crankshaft 220 which in
turn causes the driveshaft 10 to rotate within the casing 200.
When the Rankine cycle expander is operating and the driveshaft 10
is rotating within the casing 200, the sealing ring 18 acts as an
impeller to circulate buffer fluid through the cooling loop 55. If
any buffer fluid passes between the sealing ring 18 and the sealing
elements 26 and 26', it is replenished from the reservoir 72.
During operation, when the pressure in the casing 200 exceeds
atmospheric pressure, the casing pressure is transmitted through
line 104 to the second pressure chamber 86 of the pressure source
62. This pressure is then applied by the pressure source 62 to the
buffer fluid system. There is also applied to the buffer fluid
system the pressure resulting from compression springs 88 and 92.
The result is that the pressure of the buffer fluid within the
buffer fluid compartment 48 is equal to the pressure in the casing
200 plus the pressure from the compression springs 88 and 92. On
the other hand, during long periods of shut-down of the Rankine
cycle system, the pressure within the casing 200 typically drops
below atmospheric pressure. Under this circumstance, the first
pressure chamber 84 which communicates with the atmosphere by means
of ports 100 and 102 is subjected to a relatively high pressure
which overcomes the influence of the pressure within the second
pressure chamber 86. The atmospheric pressure is then applied to
the buffer fluid system together with the pressure of compression
springs 88 and 92 so that buffer fluid within the buffer fluid
compartment 48 is subjected to a pressure equal to the atmospheric
pressure plus the pressure applied by the compression springs.
Expanders are characterized by sealing arrangements between the
pistons and cylinders which permit passage of working fluid past
the pistons and cylinders into the portion of the expander casing
which contains lubricant, with the result that working fluid
becomes intermixed with the lubricant. The tendency of material to
pass from the interior of the epxander to the exterior thereof
along the driveshaft establishes the potential loss of both working
fluid and lubricant. For example, in the expander 186 of FIG. 9,
working fluid tends to pass between the cooperating piston and
cylinder assemblies to the portion 201 of the casing 200 which
serves as a lubricant containing crankcase. The crankcase 201 thus
contains a mixture of lubricant and working fluid which passes
through the journal 224 and would tend to pass between the sealing
element 18 and sealing elements 26 and 26' except for the pressure
of buffer fluid within the compartment 48.
FIG. 10 is a schematic view showing a turbine 300 embodying this
invention. The sealing structure 11 is interposed between the
casing of the turbine 300 and its driveshaft 10 to prevent passage
of material from one side of the sealing structure to the other
along the driveshaft. It should be understood that this invention
is not limited to expanders but may be used on pumps and other
apparatus wherein an effective shaft seal is required.
This invention has been described by several preferred embodiments.
It will be apparent that modifications and changes may be made
without departing from the scope of the invention as set forth in
the following claims.
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