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Патент USA US2404022

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Filed May 26, 1945
Patented July 16, _1946
Paul Alexander, Berkhamsted, and Cecil Whiley,
London, England
Application May 26, 1945, Serial No. 596,035
In Great Britain April 21, 1945
1 claim. ( Cl. 230-101)
terminates above in the inlet 6 of the pump.
The upper annular jet l, with annular oriñce 3
of the double jet type.
is fixed on the top of the central tube 4. The
Mercury is the liquid usually vaporized in Vapor
vapor from the mercury in the boiler, passing
pumps but other liquids, such as oils, are em
up the tube 4 enters the jet 'l through holes I0
ployed. In pumps of this type mercury vapor
in the central body of the jet and issues from
from a mercury boiler ascends a central tube,
the orifice 8 into the pumping space II between
the upper jet being ñxed at the top of the tube,
the tubes 4 and 5.
while the lower jet is ñxed about halfway up the
The lower jet has its outer member I2 ñxed
tube; both jets are supplied with vapor from
to the tube 4, While its inner member i3 is fixed
the central tube, and the vapor issues from the
to the top of a tube I4 attached to the outer
jets into the annular space between the central
tube 5 at I5.
tube and the outer tube constituting the body
The mercury in the boiler is separated into
of the pump. The efficiency of the pump for a
two portions, a. central portion inside the tube 4
given vacuum depends largely on the density' of
the vapor issuing from the two jets and on the 15 and an annular portion between the tubes 4 and
5.V The two portions are in communication
downward velocity of the molecules in this vapor.
lthlrough the holes I9 in the tube 4 below the
Now it has been found that, in the described
mercury level 2, and the two portions are heated
arrangement in which the two jets are supplied
together by an electric heater in the space 3.
with vapor from the same source, it is generally
impracticable to design the two jets so as to pro 20 Mercury evaporated from the annular portion
ascends into the space I6 between the tubes Il
duce vapor jets with the desired density and
and I4 and issues from the lower jets I ï, I3.
velocity. There is necessarily a fall in vapor
The evaporation from this portion is independent
pressure from the bottom to the top of the cen
of that from the central portion, and the vapor
tral tube to produce a flow up the tube, and the
pressure at one of the jets depends on the rate 25 pressure in the tube 4 leading to the upper jet
may diiîer from that in the space i8 leading to
of ilow through the other jet. The two jets
the lower jet, any diiîerence in vapor pressure
therefore are interdependent.
being compensated by a difference of level of the
According to the invention, the two jets are
mercury inside and outside the tube 4.
supplied with vapor through two non-communi
The upper jet, therefore, operates independ
cating passages from two non-communicating 30
ently of the lower jet, and the quantity of vapor
evaporating surfaces of two communicating
issuing from each jet depends only on the di
masses of liquid. The upper jet may be sup
mensions of the jet and the temperature at
plied with vapor through a central tube de
which the mercury is maintained.
scending below the level of the liquid in the
The outer tube 5 is surrounded as is customary
boiler and separating `the liquid in the boiler 35
by a water jacket 25, and the outlet 2l of the
into a central portion within the tube and an
pump leads from the bottom of the space li to
annular portion outside the tube, and by the
the backing pump. The mercury vapor from
lower jet being supplied with vapor from the
the two jets is condensed by the cooled wall 5
annular portion of the liquid through a tube be
tween the central tube and the pumping space, 40 and falls into the space 22 between the tubes
I4 and 5. A mercury seal is formed at this point
and holes in the central tube below the level of
by the channel 23, and the condensed mercury
the liquid giving communication between the two
passes through holes 24 in the tube Ië and, over
portions. rPhe tube through which vapor is sup
flowing the channel 23, returns to the boiler.
plied to the lower jet may be connected with the
As shown in the drawing, the outer tube 5 pref ~
outer wall of the pumping space through a liquid 45
erably has parallel walls at its upper part sur
seal, through which liquid condensed in the
rounding the jet l, the annular space between
pumping space returns to the annular portion
the tube 5 and jet ‘I of width A determining in
of the liquid in the boiler.
large measure the rate of evacuation of the pump.
In the accompanying drawing, which shows in
As described and claimed in co-pending appli
a single íigure by way of example a form of pump 50
cation No. 596,034 the tube 5 diminishes in di
embodying the invention in vertical section, a
ameter by the inclusion of a conical wall just
mercury boiler I, containing mercury normally
below the jet l, which conical wall joins up with
up to the level of the dotted line 2, with heater
the parallel walls of the lower part of the tube
3, supports the central vapor tube 4 and the
outer tube 5 forming the body of the pump, which 55 5, so that the tube 5 diminishes in diameter at
rï‘his invention relates to vapor vacuum pumps
a point near jet orifice level so that the length
of vapor jet measured along a line B with angle
15 degrees from the general pumping direction,
indicated by the line C, does not exceed 2.6 times
the width A of the annular space at jet oriñce
Further as described and claimed in co-pending
application No. 596,036 a water jacket 25 may
surround, but not touch, the tube 4, for a length
just below the jet oriñce 3Y downwards, the jacket
having inlet and outlet pipes 26 by which it is
continuously supplied with cold water.
As fully explained in the aforesaid co-pending
application No. 596,036, the eñîciency of the pump
is further increased by the employment of this ~15
inner jacket since vapor molecules are thereby
prevented from striking the hot tube A and
achieving a random velocity which enables such
molecules to collide with molecules issuing from
the jet 8 and diminish the downward component 20
of their velocity,
We claim:
A vapor vacuum pump comprising a boiler for
the vapor, a central tube depending into said
boiler and having apertures in its depending part,
' an outer tube Vforming with said central tube an
annular space in said boiler, an intermediate tube
between said central and outer tubes forming
inner and outer annular spaces respectively there
between, upper and lower annular jets supplied
with vapor from the boiler respectively through
the central tube and the inner annular space, and
a liquid seal between the lower end of said in
termediate tube and said outer tube into which
seal falls condensed vapor from said jets and
from which the condensed vapor returns to said
annular boiler space.
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