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Патент USA US2404023

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July 16, 1946.
Filed May 26, 1945
C S6 IL \^//l AE'Y
Patente-d July 16, 1946
Paul Alexander, Berkhamsted, and Cecil Whiley,
London, England
Application May 26, 1945, Serial No. 596,036
In Great Britain April 21, 1945
1 Claim. (Cl. 23o-101)
Mercury is the liquid usually vaporised in vapor
pumps, but other liquids, such as oils, are em
ployed. In the usual type of mercury vapor pump,
mercury vapor from a boiler ascends a central
tube and enters an annular jet at the top of the
tube. Mercury vaporissues from the jet down
wards into the annular space between the central
tube and a water-cooled outer tube. The upper
end of the outer tube is the inlet of the pump and
the outlet is a pipe connecting the lower part of
the annular space between the central and outer
The outlet of the pump is the pipe I6 connect
ing the space I l to the usual backing pump. The
This invention relates to vapor vacuum pumps.
tube 5 is surrounded by a water jacket I1 to con
dense the mercury vapor which falls into the seal
I8, and thence returns through holes I9 into the
boiler l.
In operation the mercury vapor issuing from
the oriñce 8 into the space II causes air to be
withdrawn from the inlet 6 and is driven down
10 wards by the vapor towards the >outlet IS which
is connected with a backing pump.
As described and claimed in co-pending applica
tion No. 596,034 the tube 5 diminishes in diameter
by the inclusion of a conical wall just below the
from the jet is condensed by contact with the
15 jet 1, which conical wall joins up with the par
cooled outer tube and returns to the boiler.
allel walls of the lower part of the tube 5, so that
The molecules of mercury vapor collide with
the tube 5 diminishes in diameter at a point near
, _the air molecules in the annular space driving
jet oriiice level so that the length of vapor jet
them downwards, thus drawing air from the inlet
measured along a line B with angle l5 degrees
and driving it towards the outlet. The eñìciency
from the general pumping direction, indicated
of the pump depends on the downward velocity of
by the line I I, does not exceed 2.6 times the width
the molecules of the mercury vapor issuing from
A of the annular space at jet oriiice level.
tubes to the backing pump.
The mercury vapor .
the jet as well as on the density of the vapor.
The object of the invention is to improve the
The air pressure is a minimum in the annular
space II just below the jet oriñce and from this
point rises rapidly with increasing distance down
wards from the jet oriñce, till it reaches a pressure
above that in the outlet tube I6. The air at points
of high pressure tends to ñow backwards up the
tube over a length thereof from just below the
annular space and through the mercury vapor
jet orifice downwards.
30 to the inlet E, and any air which does so flow
In the accompanying drawing, which shows
backwards diminishes the eiiiciency of the pump.
in a single ñgure by way of example a form of
Such backward flow of the air can be prevented
pump embodying the invention, in vertical sec
only by ensuring that every air molecule is struck
tion, the mercuryboiler I, containing mercury 2
by downwardly directed molecules of mercury
with an electric heater in the space 3, supports 35 vapor and driven downwards. The efficiency of
the central vapor tube 4 and the outer tube '5,
the pump therefore (assuming adequate density
forming the body of the pump, which terminates
of the mercury vapor) depends on the downward
above the inlet 6 of the pump. The annular jet
velocity of its molecules, and the Velocity is par
1, with annular orifice 8, is mounted on the
ticularly important in the annular space from the
upper end of the tube Il. The tube 4 may either 40 neighborhood of the reference Figure 11 down
extend right up to the annular jet as illustrated
wards and past the portion of the outer tube 5
in co-pending application No. 596,035 or, as shown
which is shown conical in the drawing, because
in the embodiment illustrated in the accompany
it is over this length of space that the gradient of
ing drawing, the tube 4 terminates below the an
the air pressure is most steep.
nular jet, and the latter is fixed on a tube 9 45
It has been found that the eñiciency of the
adapted to slide over the upper end of the tube 4.
pump is increased by surrounding that portion of
The Vapor from the mercury 2, passing up the
the central tube 4 which passes through this
tube 4, enters the jet 'I through holes I0 in the
length of space by a Water jacket 25, supplied with
central body of the jet, and issues from the orifice
water by the pipes 26. The water jacket is out
8 into the annular space Il between the tubes 4 50 of contact with the tube ll, since any appreciable
and 5 in which the pumping action takes place,
cooling of the tube is disadvantageous. The rea
the pumping direction being 4indicated by the
son for the resulting increase in efficiency is that,
dotted line I2.
without the jacket 25, vapor molecules which hit
The jet is adjustable in height relatively to the
tube 5 by means of the screw I3 engaging a nut CTI Cl the hot wall of the tube lose their downward ve
locity and rebound with random velocity, equally
I4 carried by a spider l5 ñxed to the tube 5.
eíñciency of the pump by maintaining this down
ward velocity of the molecules.
According to the invention, a water-.cooled
jacket surrounds, but does not touch, the central
distributed in al1 directions. These rebounding
ascending the tube 4 to the jet 1 is appreciably
We claim:
molecules collide with the molecules of the vapor
issuing from the jet and diminish the downward
component of their velocity. Since this is the
A vapor vacuum pump comprising a central
component effective for pumping, the pumping 5 tube
and an outer tube surrounding the same and
eñìciency is diminished as the result of molecules
striking the ‘not wall of the tube 4.
forming therebetween an annular space, an an
nular jet on said central tube having a jet ori
When the molecules are prevented by the water
ñce arranged to project vapor therefrom down
jacket 25 from striking the hot wall, this harm
wardly into said annular space, and a water~
ful eiïect is avoided, and the eñiciency of the 10 cooled jacket surrounding and spaced from said
pump is increased.
central tube and extending downwardly over a
The extent of the tube 4 surrounded by the
length thereof from just below said jet oriñce.
Water jacket may be increased beyond that shown
in the drawing, but the advantage gained is small,
while some disadvantage results if the vapor 15
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