Liquid-vapor interface seal design for turbine rotating shafts including helical and molecular pumps and liquid cooling of mercury vapo

Bosco, G. B., Jr.

Lessley, R. L.

English

NASA Technical Reports Server

&€PLY TO 
ATTN OF G 
NATIONAL AERONAUTlCS AND SPACE AD 
WASHINGTON. D.C. 20546 
P/Office of Assistant General Counsel f o r  
a ten t  Matters 
SUBJECT: Announcement of NASA-Owned U, S ,  atents i n  STAR 
In  accordance with the procedures agreed upon by Code GP 
and Code USP, the attached NASA-owned U. S,  Patent is being 
forwarded f o r  abstracting and announcement i n  NASA STAR. 
The foblawing information is provided: - - 
U. S.  Patent No. t 
Government or  
Corporate Employee 
Supplementary Corporate 
Source ( i f  applicable) : 
Patent Case No, 
OTE - If t h i s  patent covers,an invention made by a corporate 
of a NASA Con 
Yes 
(NASA CR OR TMX O R  AD NUMBER) (CATEGORY) 
69- 
https://ntrs.nasa.gov/search.jsp?R=19710016818 2020-03-17T03:06:28+00:00Z
6 
i 
IMVENTORS 
B 
mercury vapor toward the vent is further restricted by 
means of a molecular pump in the form of a second 
helical groove extending from the vent io the slinger space 
and is adapted on rotation of the shaft to pump mercury 
molecules toward said interface. 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject 
to the provisions of section 305 of the National Aero- 
nautics and Space Act of 1958, Public Law 85-568 (72 
Stat. 435; 42 U.S.C. 2457). 
BACKGROUND O F  THE INVENTION 
Field of the invention 
This invention relates to a rotating shaft seal, and 
more specifically to an improved seal of the liquid-vapor 
inter-face type. 
More particularly, this invention relates to a rotating 
shaft seal that can be utilized in a turbine to  substan- 
tially prevent leakage from one compartment of a ma- 
chine at a given pressure to  another compartment of 
a machine at  a lower pressure. 
Description of the prior art 
The typical turbine in the art is the well known steam- 
driven type. In this type of turbine, steam is admitted 
against the blades of a rotating shaft so as to cause rota- 
tion of the shaft which is typically connected to a genera- 
tor, pump, or other driven device. In most types of tur- 
bines, it is necessary that seals be provided to prevent 
leakage along the shaft. This is particularly true where 
the turbine is used in a closed cycle or where the turbine 
fluid is toxic, corrosive, or otherwise hazardous. 
With the advent of space applications and nuclear de- 
vices and a need for different types of turbines for these 
and other applications, the problem of sealing to prevent 
leakage between the rotating shaft and the housing be- 
comes even more acute. A type of turbine, for example, 
has been developed in recent years for space use which 
utilizes mercury vapor as the working fluid rather than 
steam. 
Preventing leakage is a critical factor in turbines of 
the above type that must operate in space for long periods 
10 of a year or more. It can be seen that if there is subsian- 
tial leakage of the mercury, or of the bearing lubricating 
oil, the turbine would stop operating. Also, long-running 
A liquid-vapor interface type of seal for the rotating turbines in ground installations that must remain un- 
shaft of a turbine utilizing mercury as the working fluid attemkd and must operate for long periods of time, 
is disclosed. The seal includes three pumps extending 15 must operate without substantial leakage of the working 
between the shaft and the housing from the high-pressure fluid, or bearing lubricant. It can also be seen that where 
turbine cavity to a low-pressure vented area. The pumps the working fluid for the turbine is mercury or other ex- 
are adapted to  pump liquid or vapor upon rotation of pensive fluids, it would be very costly to  operate a turbine 
the shaft. First pump comprises a helical groove extend- where there was appreciable leakage loss. 
ing from the cavity to a slinger pump housed in a sEnger 20 In its briefest aspect, this invention provides a pump- 
space. The first pump is adapted to pump mercury vapor ing action between the rotating shaft and the housing, 
from the cavity toward the slinger space, The slinger which Pumping action is provided by a first simple helical 
pump tends to pump in the opposite direction of the groove Pump feeding to  a pump contained within a 
first pump. The mercury vapor in the first pump and the SliWer space working in oPPosition to said first pump, 
slinger space is cooled and condensed to  liquid by flowing 25 and a second simple helical groove Pump also working 
coolant liquid through a passage in the housing or by in OPPosition to said first pump and also feeding to  the 
injecting cooled mercury into the seal. A liquid-vapor slinger space. Both helical groove pumps cooperate with 
interface is formed in the slinger suace and leakage of a Cooling medium SO as to provide a common liquid- 
vapor interface. This interface is formed in the slineer 
3,468,548 
A ~ ~ i n ~ ~ a t O ~  Of *be National Aeronau- 
~ ~ ~ ~ ~ ~ n ~ ~ ~ ~ ~ ~ ~ ~ ~ e ~ ~  
QTA’p1[NG SHAFT SEAL 
8, 1966, Ser. No. 556,830 . F16k 15J40,15/54 us. el. 277- 5 Claims 
A 
30 space by the combination of the pumping action of ihe 
pumps in opposition as well as the cooling of the fluid 
between the shaft and the housing so as to provide 
this interface. 
It is therefore an object of this invention to provide 
35 a new and improved seal for sealing between a rotating 
shaft and the housing. 
Other objects and advantages of this invention will 
become apparent as this description proceeds, taken in 
conjunction with the drawings in which: 
FIG. 1 is a view partially in cross section of a portion 
of the housing, rotating shaft member and turbine disk 
employing one embodiment of this invention; and 
FIG. 2 is a view of another embodiment of this 
invention. 
Referring to FIG. 1, there is shown a housing member 
2 that is a portion of a turbine housing and a portion only 
thereof is shown for purposes of clarity. Housing 2 in- 
cludes a first portion 4 and a second portion 6. Portion 6 
is exposed to cavity 8 which includes mercury vapor 
50 which drives turbine blades on periphery of turbine disk 
10 (partially shown) which are conventional. Turbine 
disk 10 is affixed to rotating shaft member 12 which 
rotates within housing 2. The bearing support shaft 12 
within housing 2 is in the direction of arrow 14. The bear- 
55 ings and the fluid for lubricating the bearings are not 
shown. A vent 16 is provided that is vented to space or 
the like. 
Surrounding shaft 12 is a simple helical groove 18 
formed in housing 2. This groove is formed in such a way 
6o that vapor in cavity 8 is pumped i~ the direction of arrow 
20 as shaft 12 rotates in the direction of arrow 13. In a 
similar manner, helical groove 22 is formed in housing 4 
so as to pump vapor in the groove 22 between rotati% 
&aft 12 and housing 4 in the direction of arrow 24. 
40 
45 
3,468,548 
A passage 36 is formed housing 2 about rotating 
shaft 12. This passage is for the purpose of circulating 
a cooling medium such as oil so as to cool the fluid in 
the space between shaft 12 and housing 2. Alternatively, 
the housing 4 could be externally cooled in the region of 
the helical pump 18 and slinger space 24. 
A space 26 is formed by shoulder 44 of shaft 12 and 
the wall of the housing. The space is provided between 
helical grooves 18 and 22 and is known as a slinger space. 
The slinger action of the sling r pump is provided by the 
surface of the turbine shaft 2 in this space which on 
rotation operates like a centrifugal pump to throw liquid, 
that has been condensed by the cooling medium, out- 
wardly in the direction of arrow 28. 
If desired, a contact seal 30 may be provided between 
an enlarged shoulder 32 on rotating shaft 12 and a sup- 
porting member 34 which may comprise a diaphragm or 
spring so as to urge seal 30 against shoulder 32. This seal 
would function until shaft 12 begins rotating to bring 
helical grooves 18 and 22 into action. Since there is a 
contact seal it will wear away in time, so it would have 
only limited use. This seal could also be actuated to dis- 
engage the seal from the shaft after rotation is established. 
In operation, when shaft 12 is rotated relative to hous- 
ing 2 by the operation of mercury vapor in compartment 
8, a portion of this mercury vapor will be pumped by the 
action of groove 18 due to the rotating action of shaft 12 
toward slinger space 26. The mercury vapor condenses to 
a liquid 101 in the groove(s) 18 due to the housing 4 
being cooled in the region of the groove 18 and slinger 
space 26 by the cooling medium circulating in passage 36, 
and a vapor-liquid interface 102 is created in the space 
between the housing 4 and shaft 12. The action of the 
groove(s) 18 which tends to pump the liquid mercury 
101 toward the slinger space 26 is opposed by the slinger 
action of the surface of shaft 12 in slinger space 26 
which throws the liquid in the direction of arrow 28 to  
form a liquid-vapor interface 102 facing the vapor in the 
cavity 8 and a liquid-vapor interface 40 facing the vapor 
in helical groove(s) 22. 
When oil or other cooling medium, which is at a low 
temperature, is introduced into passage 36, the mercury 
vapor will be cooled to a liquid, ich forms the liquid 
of the liquid-vapor interfaces at and 40. Due to the 
presence of this liquid-vapor interface(s), a minimum 
amount of leakage of turbine operating fluid will flow 
from compartment 8 which is at a relatively high pressure 
to vent 16 which is at a much lower pressure, as will be 
noted below. 
A typical pressure in cavity 8 for a mercury vapor 
operating fluid turbine is 20 p.s.i.a. at a temperature of 
700 degrees F. The liquid mercury pressure at the outer 
periphery of the slinger space is about 25 p.s.i.a., and 
this decreases to essentially zero p.s.i.a. at the interface 
40. The actual pressure at the interface 40 is the vapor 
pressure of the mercury and depends on the liquid tem- 
perature. By the use of oil in coolant passages 34, which 
is maintained at a temperature of 225 degrees F., a liquid- 
vapor interface at 40 is formed which is typically a t  a 
pressure of 0.05 p.s.i.a. at a temperature of 310 degrees F. 
In vent 14, the pressure is 10-7 mm. of mercury. Thus 
the seal has functioned to decrease the 20 p.s.i.a. pressure 
in turbine cavity 8 to 0.05 p.s.i.a. pressure at interface 40, 
and the 0.05 p.s.i.a. pressure at interface 40 to le7 mm. 
of mercury at vent 16 to substantially reduce the amount 
of leakage. Further, since there are no parts to wear out, 
the seal will function over extremely long periods of time. 
It is pointed out that while the surface of the shaft 12 
in slinger space 26 acts as a centrifugal-type pump, shaft 
12 may have blades thereon in slinger space 26 to aid 
in pumping. It is also noted, that while housing 4 is shown 
with the helical grooves, and the surface of shaft 12 is 
smooth, that this can be reversed and the grooves pro- 
vided in shaft 12, or grooves in both housing and shaft. 
With the above simple helical grooves, it will be seen 
that it will be relatively easy to  manufacture this seal. 
All that is reauired is that threads be cut into the housing 
5 
10 
15 
20 
25 
30 
35 
40 
45 
BO 
55 
60 
G5 
70 
75 
or in the shab, or in both. This can be performed with 
such simple equipment as a lathe, for example. It also 
will be apparent to those skilled in the art that while this 
seal construction is described with respect to mercury as 
the working fluid, that it will be applicable to other fluids 
as well, such as, for example, preventing leakage of lubri- 
cating oil along a shaft. 
FIG. 2 is similar to the embodiment shown in FIG. 1 
except that the separate coolant passage for the introduc- 
tion of oil into the housing has been eliminated, and 
cooled mercury is injected into the seal so as to provide 
a liquid vapor interface. Thus, a molecular pump formed 
by groove 50 pumps from vent 52 toward working cavity 
54. Likewise, the slinger action of the shaft in slinger 
space tends to throw fluid radially outwardly to form an 
interface 56. Fluid passing in the direction of arrow 58 
will be resisted by the slinger action and the pumping 
action of groove or molecular pump 50. Mercury liquid 
at a lower temperature is introduced into the seal at point 
60 and will tend to  pass due to the slinger action in the 
direction of arrow 62. An exit port 64 is provided such 
that the mercury coolant is removed from the sea1 and 
then recirculated through means not illustrated. Thus, 
the need for a separate oil coolant passage is eliminated 
due to  the introduction of the cooled mercury and sub- 
sequent removal. A vapor-liquid interface 202 is also 
formed in slinger space 204. Alternatively a helical groove 
pump 66 may likewise be provided in a manner similar 
to that in FIG. 1, to contribute to the creation of a vapor- 
liquid interface in the helical groove pump 66. 
Thus it can be seen that by the different embodiments 
of this invention that an effective structure for sealing a 
turbine shaft or other shaft has been provided. Minimum 
leakage, as well as simple construction, is accomplished, 
thus obviating many problems of the prior art. 
Having described this invention, it is to be understood 
that it is to be limited only by the scope of the claims 
appended hereto. 
What is claimed is: 
1. In combination: 
(a)  a rotatable shaft member; 
(b) a cavity containing high pressure vapor acting an 
one area of said shaft member; 
(c) a vent to a lower pressure area communicating 
with another area of said shaft member; 
(d) a housing member surrounding said shaft member 
to form a fluid receiving seal space extending be- 
tween said cavity and vent, said housing member 
having a slinger space and a slinger pump formed 
in said space by said shaft member and said housing 
member adapted upon rotation of said shaft member 
to pump liquid from said space toward said cavity; 
(e) a first pump associated with said shaft member 
and housing member adapted upon rotation of said 
shaft member to pump vapor from said cavity to- 
ward said slinger space; 
( f )  a second pump associated with said shaft member 
and housing member adapted to pump vapor from 
said vent toward said slinger space; and 
(g) means to cool said vapor'to form a liquid within 
said first pump whereby a liquid-vapor interface is 
formed in said slinger space between said first and 
second pumps to  minimize leakage of said vapor. 
2. A combination, according to  claim 1, wherein said 
first pump comprises a helical groove in one of said 
members between said slinger space and said cavity, and 
said second pump comprises a helical groove in one of 
said members between isaid slinger space and said vent. 
3. A combination, according to claim 2, wherein said 
first pump comprises a helical groove in said housing 
member and said second pump comprising a helical 
groove in said housing member, and said first and second 
3,468,548 
pump grooves extend in opposite directions away from 
said slinger space. 
4, A combination, according to claim 1, wherein said 
means to cool said vapor comprises a passageway formed 
in said housing about said shaft member separate from 
said seal space for circulating a cooling medium to cool 
the vapor in said first pump. 
5. A combination according to claim 1, wherein said 
vapor is mercury vapor and said means to cool said 
vapor comprises cooled mercury liquid at a lower tem- 10 
perature than the mercury liquid within said first pump, 
said housing member including means to introduce said 
cooled mercury to said vapor-liquid interface, and further 
including means to remove said cooled mercury from said 
seal space. 15 
UNITED STATES PATENTS 
2,330,730 9/1943 Mosshart _ _ _ _ _ _ _ _ _ _ _ _  277-16 
3,076,656 2/1963 Hofmann _ _ _ _ _ _ _ _  277-134 X 
3,131,940 5/1964 Ertaud _ _ _ _ _ _ _ _ _ _  277-134 X 
3,150,822 9/1964 Dreyfus et al. _ _ _ _ _  277-134 X 
3,161,413 1211964 Audemar _ _ _ _ _ _ _ _ _  277-134 X 
3,355,179 11/1967 McGrew _ _ _ _ _ _ _ _ _ _ _  277-134 
945,900 1/1910 Ahlquist _ _ _ _ _ _ _ _ _ _ _ _  277-13 
SAMUEL ROTHBERG, Primary Examiner 
U.S. C1. X.R. 
277-67, 134 


Rotating shaft seal Patent

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