Thrust controlled rotary apparatus

The invention comprises an improved rotary apparatus comprising an outer body member having an internal generally axially directed first thrust area. An inner body member is mounted within the outer body member for relative rotation of the two body members. The inner body member has a second generally axially directed thrust area generally opposed to the first thrust area. The body members define fluid passageways and the thrust areas define a fluid-receiving space therebetween in communication with the passageways. First and second annular seals of differing diameters seal between the thrust areas, and a thrust control system is provided for selectively varying the fluid pressure in the annular portion of the fluid-receiving space bounded by the two seals by selectively providing pressure equalizing communication between that portion and a plurality of zones of differing pressures external to the annular portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to rotary machines and particularly to fluid 
handling apparatus such as, for example, tubo-expanders. Such a machine 
typically comprises a stationary housing or stator having a rotor mounted 
therein on a rotary shaft. The stator has an inlet into which a high 
pressure gas is introduced. This gas passes through the stator to a series 
of nozzles which direct the gas radially and tangentially toward the 
rotor, the latter having a series of radially outwardly opening inlets 
aligned with the stator nozzles. From the rotor inlets, the gas passes 
through one or more flowways in the rotor and exits through one or more 
axially opening rotor outlets located radially inwardly of the rotor 
inlets. The gas expands as it passes through the rotor and, due to the 
configuration of the stator nozzles and rotor flowways, causes the rotor 
to rotate in a manner well known in the art. 
Other types of fluid handling machines such as radial turbines, 
centrifigual pumps, centrifugal compressors, and the like have generally 
similar rotors although in some, e.g. the centrifugal pump, the operation 
is generally reversed, the axially opening ends of the rotor flowways 
serving as inlets and the radially opening ends as outlets. In any such 
device it is customary to employ a seal between the rotor and stator on 
one or both sides of the radially opening ends of the rotor flowways. 
Usually some fluid leaks past such seals and, in fact, some of the 
preferable seals for certain systems are designed to permit a limited 
amount of leakage. When such leakage is toward the axial openings in the 
rotor, the effect thereof is minimal since the gas may be entrained in the 
stream of like gas flowing through the apparatus. However, gas leaking 
toward the closed end of the rotor enters a space formed between that end 
and a generally opposed internal axially directed face of the stator. The 
gas may become trapped in this space thus imposing a thrust load on the 
rotor and its shaft. Vent means may be provided to alleviate this problem. 
2. Description of the Prior Art 
In my prior U.S. Pat. No. 3,895,689, issued July 22, 1975, there is 
disclosed a system for balancing the thrust in a rotary fluid handling 
apparatus of the type described above. In brief, means are associated with 
the thrust bearings associated with the rotary shaft to monitor the thrust 
load thereon. The monitoring system is operatively associated with a valve 
or the like in the vent line from the area adjacent the closed end of the 
rotor. Thus the valve may be operated in accord with the readings of the 
monitoring system to increase or decrease the fluid pressure behind the 
rotor and therefore balance the thrust thereon. However, the range of 
thrust loads which may be thus imposed on the back of the rotor is limited 
to a range bounded by the pressure which would naturally build up behind 
the rotor without venting and the pressure which exists at the zone of the 
apparatus to which the area is vented. 
SUMMARY OF THE INVENTION 
The present invention provides an improved system for thrust control of the 
aforementioned type of rotary apparatus which may include a more versatile 
range of applicable thrust values than in the system of U.S. Pat. No. 
3,895,689. 
In particular, the closed end of the rotor in the present invention and the 
opposed internal generally axially directed area of the stator form thrust 
areas between which a fluid-receiving space is defined. First and second 
annular seals of different diameters seal between the thrust areas and 
bound a first annular portion of the fluid-receiving space. Thrust control 
means are provided for selectively varying the fluid pressure in this 
first portion whereby the thrust on the rotor may be varied. 
Preferably, this thrust control means is operative to selectively provide 
pressure equalizing communication between the first portion of the 
fluid-receiving space and a plurality of zones of differing pressures 
external to said first portion. These zones may be various zones of the 
fluid passageways through the rotor and stator. Where one of these zones 
is of a pressure higher than the pressure prevailing on the other sides of 
the aforementioned seals from the first portion of the fluid-receiving 
space, the fluid introduced into the first portion serves the additional 
purpose of sweeping dust and other impurities away from the seals as it 
leaks therethrough. 
In a preferred form of the invention, the first seal means is spaced 
radially inwardly from the radially outer extremities of the 
aforementioned thrust areas whereby a second portion of the 
fluid-receiving space is defined radially outwardly of the first seal 
means. Similarly, the second seal means is spaced radially outwardly from 
the radially inner extremities of the thrust areas whereby a third portion 
of the fluid-receiving space is defined radially inwardly of the second 
seal means. Each of these latter portions may be in pressure equalizing 
communication with a respective zone of the fluid passageways through the 
rotor and stator. Due to the differing pressures prevailing at these zones 
and to the presence of the seals, the three portions of the 
fluid-receiving space will then ordinarily have different pressures, the 
pressure of the first portion being intermediate that of the other two 
portions. Then the thrust control means may comprise conduit means 
connecting the first portion with respective ones of the other portions 
and bypassing the respective seals and valve means in the conduit means 
whereby the first portion may be selectively placed in pressure equalizing 
communication with either of the other two portions. 
The thrust control means may further comprise means for selectively 
providing pressure equalizing communication between the first portion of 
the fluid-receiving space and a third zone of the fluid passageway means 
of even higher pressure than the first two zones. Similarly, means may be 
provided for allowing pressure equalizing communication between the first 
portion of the fluid-receiving space and a fourth zone of lower pressure 
than the other three zones. 
Accordingly, it is a principal object of the invention to provide an 
improved means for controlling the thrust on a rotary apparatus. 
Another object of the present invention is to provide a highly versatile 
and variable thrust control system for varying the fluid pressure behind 
the rotor of such an apparatus. 
Still another object of the present invention is to provide such a system 
which utilizes for thrust control, fluid from different pressure zones 
within a fluid handling apparatus. 
Yet a further object of the present invention is to provide such a system 
which may additionally be used to protect seals within the apparatus by 
sweeping dust and other impurities away from the seals. 
Still other objects, features and advantages of the present invention will 
be made apparent by the following description of the preferred 
embodiments, the drawings and the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a fluid handling device in the form of 
a turbo-expander having a stationary housing or stator 10 and a rotor 12 
disposed coaxially within the stator 10. Rotor 12 is secured to a shaft 14 
by a bolt 16 and washer 18 for rotation within the stator 10. The shaft 14 
extends past the rotor 12 to a bearing structure, including radial and 
thrust bearings, which may be of the type illustrated in my prior U.S. 
Pat. No. 3,895,689 or of any other type well known in the art. Likewise, 
the thrust control system to be described below may be operated either 
manually or automatically in accord with measurements of the thrust on the 
thrust bearings of such assembly in a manner disclosed in my 
aforementioned prior patent. 
The stator 10 and rotor 12 define a fluid passageway system through the 
apparatus. In particular, the stator 10 includes an inlet 20 through which 
high pressure gas is admitted into the apparatus from a conduit 22 leading 
to a suitable source of such gas. The inlet 20 leads into an annular 
stator chamber 24 generally surrounding the open central portion of the 
stator in which rotor 12 is mounted. The gas from chamber is injected into 
said central portion and thus into the rotor 12 through a plurality of 
nozzles 26 circumferentially spaced about the rotor 12. 
Rotor 12 has a plurality of flowways 28 therethrough. The flowways 28 have 
respective inlet ends 28a opening generally radially outwardly and 
disposed in register with the nozzles 26. From its respective inlet 28a, 
each flowway 28 curves radially inwardly and axially to the left, as 
viewed in FIG. 1, to terminate in a respective outlet end 28b located 
radially inwardly of the inlet ends 28a but opening axially into the open 
central portion of the stator 10. The gas then passes through this central 
open portion of the stator to one end 30 thereof which serves as an outlet 
to which a suitable removal conduit (not shown) may be connnected. 
The gas which passes through the turbo-expander is at its highest pressure 
at the inlet 20. As the gas passes through the nozzles 26 the pressure 
drops somewhat. Although the nozzles 26 open generally radially inwardly 
toward the registering inlets 28a of the rotor 12, they are also 
tangentially inclined with respect to the rotor. This inclination together 
with the configuration of flowways 28 and the expansion of the gas as it 
passes through the flowways 28 serves to impart rotary motion to the rotor 
12 and the attached shaft 14 in a manner well known in the art. 
Consequently, the pressure of the gas at the outlets 28b is substantially 
lower than that at the zone including the outlet ends of nozzles 26 and 
inlets 28a. As the gas passes to the outlet 30 there is a further pressure 
drop, so that the lowest gas pressure exits at the outlet 30. 
Since it is necessary to provide some clearance between the rotor and 
stator, some of the fluid exiting the nozzles 26 will pass into this 
clearance space (which may be considered a part of the passageways defined 
by the rotor and stator) rather than into the rotor flowways 28. To 
control the flow of this fluid, an annular rotary seal 32 is provided 
between the rotor and stator. The rotor 12 may be considered as having a 
front or open end, i.e. the end including the outlets 28b, the opposite 
end being considered the back or closed end of the rotor. Seal 32 is 
disposed on the side of inlets 28a toward the open end of the rotor. While 
the seal 32 as shown is of the labyrinth type, numerous other types of 
rotary seals may be employed. In any event, some leakage of fluid past 
seal 32 is probable and indeed sometimes desirable. Fluid so leaking will 
pass into the area adjacent the outlets 28b and will simply be entrained 
in the stream of fluid exiting the apparatus. 
A similar seal may be employed on the other side of inlets 28a, i.e on the 
side toward the closed end of the rotor 12. However, since this end of the 
rotor is essentially closed, and since the shaft 14 is sealed to the 
stator 10 at 36, fluid leaking past this latter seal may build up in the 
space 34 behind the rotor and impose an undesired thrust load thereon. To 
alleviate this fluid pressure build-up, one or more vent bores 38 are 
provided through the rotor 12. Each bore 38 extends from the space 34 
behind the rotor 12 to a zone of one of the flowways 28 which is adjacent 
the respective flowway outlet 28b. As mentioned above, the pressure 
prevailing near these outlets 28b is relatively low, so that high pressure 
fluid in space 34 will naturally be vented from this latter area by the 
bores 38. 
However, whereas in prior art devices, vent bores such as 38 merely served 
as passive means to reduce pressure build-up, the present invention 
actively utilizes fluid pressure within space 34 as well as pressures 
prevailing in various zones of the passageways through the rotor and 
stator to actively control the thrust load on the rotor 12 and its 
attached shaft 14. 
Referring now to FIG. 2 in conjunction with FIG. 1, the area surrounding 
the closed end of the rotor 12 is shown in greater detail. The area of the 
back or closed end of the rotor 12 extending from the outer diameter at 
40a adjacent the inlets 28a to the intersection 40b with shaft 14 forms a 
generally axially directed thrust area 40. By this is meant that over the 
annular area between 40a and 40b there are, with the exception of the 
relatively small openings of bores 38, surfaces which, while they may be 
curved or inclined, face at least partially in an axial direction so that 
they are capable of reacting against an axially directed force thereon. 
Similarly, stator 10 defines an opposing internal thrust area 42. The 
aforementioned fluid-receiving space 34 is defined between areas 40 and 
42. 
As shown, the outer part of thrust area 42 has two counterbores and thrust 
area 40 has a generally mating stepped configuration. At the first 
counterbore there is provided a first annular labyrinth seal 44 which 
seals between the rotor 12 and stator 10. A second annular labyrinth seal 
46 is formed at the second counterbore. The first seal 44 is spaced 
radially inwardly from the radially outer extremities of the thrust areas 
40 and 42, and the second seal 46 is spaced radially outwardly from the 
radially inner extremities of the thrust areas. Thus the seals 44 and 46 
divide the fluid-receiving space 34 into three coaxial annular portions: a 
first or middle portion 34a between the two seals, a second or outer 
portion 34b located radially outwardly of seal 44, and a third or inner 
portion 34c located radially radially inwardly of seal 46. 
It can be seen that portion 34b of the fluid-receiving space is in pressure 
equalizing communication, specifically open fluid communication, with the 
relatively high pressure zone of the turbo-expander passageways including 
the outlet ends of nozzles 26. Portion 34c of the fluid-receiving space is 
in pressure equalizing communication with a lower pressure zone of the 
turbo-expander passageways, namely the zone adjacent and including the 
rotor outlets 28b, via bore or bores 38. Since seals 44 and 46 are of a 
type which permit some leakage therepast, the pressure of fluid in portion 
34a of the fluid-receiving space will ordinarily be intermediate those of 
portions 34b and 34c. Furthermore, it can be seen that the thrust force 
imposed on the rotor 12 by the fluid in any one of the portions of the 
fluid-receiving space will be the product of the pressure within that 
portion and the annular area defined by the radially inner and outer 
extremities of that portion. For example, the force exerted by the fluid 
in portion 34a will be the pressure of the fluid in portion 34a times the 
annular area between seals 44 and 46. Thus the total force imposed on the 
rotor by the fluid in space 34 will be the sum of the forces exerted in 
the various portions of space 34. 
A bore 48 in stator 10 has its inner end in open fluid communication with 
portion 34a of space 34 and its outer end in communication with a line 50. 
Together, bore 48 and line 50 provide a conduit through which various 
pressure zones of the turbo-expander passageways may be placed in pressure 
equalizing communication with portion 34a to vary the thrust force imposed 
by the fluid in that portion of the fluid-receiving space 34. As mentioned 
above, two such zones are already in fluid communication with the other 
two portions, 34b and 34c respectively, of space 34. Thus it is 
particularly convenient to provide for communication between portion 34a 
and these two pressure zones via portions 34b and 34c. 
Accordingly, a bore 52 is provided in stator 10 with one end in open 
communication with portion 34b of space 34 and the other end in 
communication with a line 54. Lines 50 and 54 are interconnected by a line 
56. Thus bore 52, lines 54, 56 and 50, and bore 48 form a by-pass around 
seal 44. A valve 58 is disposed in line 54 so that this by-pass may be 
selectively opened and closed. When valve 58 is opened, portions 34a and 
34b of the space 34 are in pressure equalizing communication, specifically 
open fluid communication. As mentioned above, the pressure ordinarily 
prevailing in portion 34b is higher than that ordinarily prevailing in 
portion 34a, in particular being equal to that in the zone of the 
turbo-expander passageways including the outlet ends of nozzles 26. Thus 
opening the valve 58 has the effect of raising the pressure within portion 
34a to that prevailing at the outlet ends of nozzles 26 and thereby 
increasing the thrust load on the rotor 12 acting to urge it to the left 
as viewed in the drawings. 
A similar by-pass is provided around seal 46 by a bore 60 communicating 
with portion 34c of space 34 and with a line 62 which is in turn connected 
to line 56 and thence to line 50 and bore 48. A valve 64 is provided in 
line 62. As mentioned, the pressure ordinarily prevailing in portion 34c, 
i.e. with all valves closed, is less than that in portion 34a, and in 
particular is equal to that in a relatively low pressure zone of the 
turbo-expander passageways including rotor outlets 28b. By opening valve 
64, portions 34a and 34c of the fluid-receiving space are placed in 
pressure equalizing communication, the pressure of portion 34a being 
lowered to that of the rotor outlets 38b, and the thrust load is 
consequently reduced. 
If it is desired to increase the thrust on the rotor 12 even more than is 
possible by opening valve 58, this may be done by opening a valve 66 in a 
line 68 leading from the stator inlet 30 to the line 56 and thence to line 
50 and bore 48. As mentioned above, inlet 20 is the zone of highest 
pressure in the turbo-expander. Thus opening valve 66 provides for a very 
large increase in the pressure in portion 34a and a correspondingly large 
increase in the thrust on the rotor. 
Another salient effect of opening valve 66 is that, since the pressure in 
inlet 20 is higher than those prevailing in either of portions 34b or 34c, 
the fluid introduced into portion 34a by the opening of valve 66 will leak 
past both seals 44 and 46 tending to sweep dust and other impurities away 
from the seals and thereby reduce seal wear. Thus, over and above any need 
to increase the thrust load on the rotor 12, valve 66 may be periodically 
opened to clean the seals 44 and 46. In accord with this seal-cleaning 
function, it is desirable that the fluid entering portion 34a from line 68 
itself be as free from impurities as practical. Therefore a suitable 
filter 70 is placed in line 68 to remove dust and the like. 
In this connection it is also noteworthy that, when valve 58 is opened as 
described above, the pressure admitted to portion 34a will be greater than 
that in portion 34c and equal to that in portion 34b. Thus the fluid in 
portion 34a will actively sweep dust and other impurities away from seal 
46. While such fluid will not actively sweep dust away from seal 44, it 
will at least offset any tendency of such impurities to sweep through the 
latter seal from portion 34b and will thus still have a protective effect 
on both seals. 
Finally, it may at times be desirable to reduce the thrust on rotor 12 by a 
value which is even lower than that achieved by opening valve 64. For this 
purpose, a line 72 is provided communicating with line 56 and with a bore 
74 into the stator outlet 30. Stator outlet 30 is in the zone of lowest 
pressure in the turbo-expander. Thus by opening a valve 76 in line 56 
intermediate lines 72 and 50, portion 34a is placed in pressure equalizing 
communication with outlet 30 thereby greatly reducing the thrust. 
The thrust can thus be adjusted through a series of steps or increments in 
a relatively wide range as follows: a lowermost thrust may be imposed by 
opening valve 76 and closing all other valves; a slightly higher thrust 
may be imposed by opening only valve 64; an intermediate or normal thrust 
may be provided by closing all valves; a higher thrust may be provided by 
opening only valve 58; and a highest thrust may be provided by opening 
only valve 66. Furthermore, by proper throttling devices associated with 
each of the above valves, it is possible to provide further continuity of 
the adjustments over the total range, i.e. to provide in effect an 
infinite number of increments. 
It can thus be seen that the system of the present invention provides a 
precise and highly versatile means of controlling the thrust on a rotary 
fluid handling device. The system conveniently makes use of the pressures 
prevailing at various pressure zones of the device itself to accomplish 
such control. Furthermore, the system provides a means for cleaning and/or 
preventing wear of seals. 
It will also be appreciated the numerous modifications of the preferred 
embodiment described above may be made without departing from the spirit 
of the invention. By way of example only, as mentioned above, seals other 
than the labyrinth type can be employed. Furthermore, any flow restriction 
or other means sufficient to provide a substantial pressure drop 
thereacross will be considered a "seal" for purposes of this application, 
and in particular, a simple restriction may be employed in place of the 
labyrinth seal at 36. 
Also, in the embodiment shown, the seals 44 and 46 which bound the 
pressure-variable thrust control portion of the fluid-receiving space 
behind the rotor are spaced from the radial extremities of the thrust 
areas so that the fluid-receiving space is divided into three portions, 
the intermediate one being the pressure-variable one. However, in other 
embodiments, the outermost seal 44 may be placed at the outer extremity of 
the thrust areas so that the space is divided into two sealed portions. In 
another modification, seal 44 might be eliminated altogether. Then the 
fluid-receiving space would again be divided into two portions, the outer 
one being unsealed at its outer extremity, except for such rotary fluid 
vortex as may exist therein, and the inner one, bounded by first and 
second seals 46 and 36, respectively, could be the pressure-variable 
portion if bores 38 were restricted or eliminated. 
It is also noted that the type of pressure-equalizing communication 
provided between various areas in the embodiment described is open fluid 
communication. However, in other embodiments it might be possible at some 
points in the system to provide pressure equalizing communication without 
fluid communication, as by the use diaphragms. 
While the invention has been described in connection with a turbo-expander, 
it can be advantageously used with other types of fluid-handling devices 
such as turbines of various kinds, compressors, centrifugal pumps, etc. 
Also, the invention can be employed in devices in which the outer member 
is rotary and the inner member is stationary. Furthermore, the invention 
may be applied to rotary devices in which no fluid passes through the 
rotor. For example, the invention may be advantageously used with a rotary 
balancing drum sealed with respect to the surrounding housing. 
Accordingly, the "passageways" defined by the rotary and stationary 
members are not limited to openings intended to provide for substantial 
fluid flow, but may be any openings defined by said members, such as the 
clearance between the members, and in which fluid will be present. 
Finally, while the fluid passageways defined by the rotary and stationary 
members provide convenient zones of differing pressures to be selectively 
communicated with the sealed thrust control portion of the area behind the 
rotor, it is possible to utilize other sources for such pressure zones. In 
particular, suitable pressure zones may be found elsewhere in the plant in 
which the apparatus is incorporated. 
It is thus intended that the scope of the present invention be limited only 
by the claims which follow.