Improvements in Apparatus for the Production of High Vacua.
Year: 1895

page_text: Date of Application, 9th July, 1895
Complete. Specification Left, 8th My, 1896-Accepted, 13th J
13th June, 1896
1
: PROVISIONAL SPECIFICATION.
Improvements in Apparatus for the Production of High Vacua.
We, ARCHIBALD BARR, Professor of Engineering in the University of
Glasgow and WILLIAM STROUD Professor of Physics, the, Yorkshire College
Leeds, do hereby declare the nature of this invention to be as follows':—
The object of our invention is the provision of better means for the rapid and
efficient production of high vacua. The .apparatus is specially suitable for the
exhaustion of incandescent. electric. lamps, besides being useful for.
purposes.
many other
Our apparatus consists of two chambers (which we shall refer to as A and B)
one of which (A) is placed in communication with. the lamp or other vessel to be
exhausted, while B is the chamber into which the gas is to be passed. The
chambers are partially filled with mercury (or in some cases other liquid or liquids
may he used). Their construction is such that the mercury (or other liquid or
liquids) forms a seal between the two chambers.
:
In the interior of the apparatus there is placed..a.. part. C which is caused to
revolve about an axis. This part C. has within it a passage (or several, such)
which may conveniently have a somewhat.helical or spiral form:: These passages
are so formed and disposed that at one part of the cycle a passage comes into. open
communication with the portion of the chamber A situated above the level of the
liquid, so as to become filled with a portion of the gas contained in the chamber A.
At a later period of the revolution the aperture of the passage is brought under
the surface of the liquid in the chamber A, so. that it becomes sealed by immersion
in the liquid. The passage is further so formed and disposed: that during a
succeeding portion of a revolution the gas in the passage is..compressed, by being
carried under the level of the surface of the liquid in A and ultimately. ejected at
the outlet aperture of the passage into the chamber B, along with a current of the
liquid which moves through the passage during the revolution of the part C.
At the latter part of the exhaustion when the quantity of gas taken into the
passage during the revolution is very small, it will, when compressed become an
extremely small bubble and may not be readily removed. from contact, with the
side of the passage in C, by the sweeping action of the current of. liquid, nor by
the tendency which it possesses to rise. to the surface of the liquid. The gas
forining the bubble may nevertheless be prevented. from, again gaining access to
-the space to be evacuated by so constructing, the passage that the bubble is, when
compressed, left on a portion of the interior of the passage which is under the
surface of the liquid in the passage during the whole time that the inlet aperture
of the passage is in communication with the space.above the liquid. surface in the
chamber A.
-The chamber B may be open to the atmosphere, but in order to greatly reduce
the dimensions of the apparatus.it is preferable to have this chamber closed, and
placed in communication with a mechanical or other.pump for the production of a
partial vacuum in that chamber.

page_text: Improvements in Apparatus for the Production of High Vacua.
We, ARCHIBALD BARR, Professor of Engineering in the University of
Glasgow, and WILLIAM STROUD, Professor of Physics, the Yorkshire College,
Leeds, do hereby declare the nature of this invention and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
The object of our invention is the provision of better means for the rapid and
efficient production of high vacua. The apparatus is specially suitable for the
exhaustion of incandescent electric lamps, besides being useful for many other
purposes.
Our apparatus consists of two chambers (which we shall refer to as A and B)
one of which (A) is placed in communication with the lamp or other vessel to be
exhausted, while B is the chamber into which the gas is to be passed. The
chambers are partially filled with mercury (or in some cases other liquid or liquids
may be used). This construction is such that the mercury (or other liquid or
liquids) forms a seal between the two chambers.
In the interior of the apparatus there is placed a part or drum C which is
caused to revolve about an axis. This drum C has within it a passage (or several
such) which may conveniently have a somewhat helical or spiral form. These
passages are so formed and disposed that at one part of the cycle a passage comes
into open communication with the portion of the chamber A situated above the
level of the liquid, so as to become filled with a portion of the gas contained in the
chamber A. At a later period of the revolution the aperture of the passage
brought under the surface of the liquid in the chamber A so that it becomes sealed
by immersion in the liquid. The passage is further so formed and disposed that
during a succeeding portion of a revolution the gas in the passage is compressed
by being carried under the level of the surface of the liquid in A and ultimately
ejected at the outlet aperture of the passage into the chamber B, along with the
current of the liquid which moves through the passage during the revolution of the
part C.
At the latter part of the exhaustion when the quantity of gas taken out through
the passage during the revolution is very small, it will, when compressed, become
an extremely small bubble and may not be readily removed from contact with the
side of the passage in C by the sweeping action of the current of liquid, nor by
the tendency which it possesses to rise to the surface of the liquid. The gas
forming the bubble may nevertheless be prevented from again gaining access to
the space to be evacuated by so constructing the passage that the bubble is, when
compressed, left on a portion of the interior of the passage which is under the
surface of the liquid in the passage during the whole time that the inlet aperture
of the passage is in communication with the space above the liquid surface in the
chamber A.
The chamber B is closed and placed in communication with a mechanical or
other pump for the production of a partial vacuum in that chamber.
In order that our invention may be properly understood and readily carried
into effect, we have hereunto appended two explanatory sheets of drawings in the
several figures of which corresponding parts are marked with the same letters of
reference.
Figures 1-4 show one form of the apparatus, Figure 1 being a sectional
elevation at right angles to the axis of the rotating drum aforesaid, Figure 2 a
transverse section, Figure 3 an end-elevation and Figure 4 a plan with the
cover Y and the cap ✗ (to be hereafter described) removed.
The apparatus consists of four main parts viz. (1) An outer case Z with (2) a
•>>

page_text: removable cover Y, (3) the rotating drum C and (4) a cap A, which cap may
conveniently be supported upon shelves formed in the interior of the outer-
case Z.
The interior of the apparatus is partially filled with mercury or other liquid,
which forms a sealing between the exterior B and the interior A of the cap, the
levels of the liquid during the operation of the apparatus being somewhat as
shown, that of the liquid in the interior being higher than that outside.
X
The interior of the cap thus sealed off from the exterior forms the chamber A
above referred to, and is placed in communication with the vessel to be evacuated
by means of the tube D.
The upper portion of the casing Z exterior to the cap
forms the chamber B which communicates, by means of the tube E, with the pump
for producing the partial vacuum.
The rotating drum C has (in the example shown) three passages of a somewhat
spiral form F1, F2, F3, terminating at the periphery of the drum in the
apertures G1, G2, G3, and near the axis of the drum in apertures H1, H2, H3, as
shown by H, in Figure 2 and indicated in Figure 1 by the dot and dash outlines,
though being on the near side of the drum they cannot properly be represented in
that figure.
1
When the drum is rotated in the direction indicated by the arrows it will be
evident that the liquid contained in the passage F₁ will partially flow out by the
aperture H, into the exterior case while the passage F, will become partially filled
with gas from the chamber A. Shortly after the passage has reached the position
indicated by F, in the figure its edge I, will dip beneath the surface of the liquid,
and thus a volume of gas will be entrapped and separated from communication with
the chamber A. During the further rotation of the drum this gas will be carried
entirely under the level of the liquid and will therefore be somewhat compressed as
shown at J. After still further rotation of the drum the passage again reaches
the position indicated by F, when the bubble of gas will rise so as to reach the
aperture H, and so be ejected through that aperture into the outer chamber B; as
represented in the figure the passages are somewhat constricted in the parts in
which the bubble attains its maximum immersion so that when the liquid in the
passage begins to flow outside in virtue of the aperture G₁ rising above the level of
the liquid in the chamber A, the outflowing liquid will cause a greater sweeping
action than it would do if the passages were not so constricted. Should the
outflowing liquid fail to detach the bubble from contact with the interior of the
passage it will be evident that since the bubble is left adhering to the wall of
the passage at some such position as indicated by K, the lip of the passage I, will
be submerged, beneath the liquid before the pressure on the bubble is much
reduced and therefore should the bubble subsequently become detached as its
pressure is reduced so as again to find its way into the wider portion of the passage
it will only do so after the passage is sealed off from the chamber A. Consequently
even though the sweep of the liquid should fail to dislodge the bubble and carry it
outwards through the aperture H₁ the gas forming the bubble will not again gain
access to the chamber A. It will thus be seen that when a moderately high
vacuum has been attained in the chamber A, the apparatus may operate in any one
of three manners (1) the bubbles may rise to the aperture H in virtue of their
flotation (2) they may be swept out by the current of liquid flowing through the
passages or (3) they may be retained in the passages until by accretion with
bubbles similarly entrapped they attain such magnitude that they will be removed
in one or other of the two preceding ways.
The shaft L to which the drum C is attached is supported in suitable bearings
in the outer case Z. It may be provided with a stuffing gland or other arrangement
for preventing excessive leakage into the chamber B.
In the arrangement shown in the figure this shaft is provided with a conical
enlargement fitting into a suitable recess in the casing Z, which arrangement may
be used in lieu of a stuffing gland. M is a disc forming a part of the drum C the
object of which is to prevent any air which may leak past the cone bearing or

page_text: stuffing box of the shaft L from gaining access to the chamber A. This disc may,
as shown in the drawing, be made of such a size as to extend above the level of the
liquid in the chamber B.
The cover Y may be provided (as shown in the figures) with a projecting
edging N on its under side which rests within a channel P formed in the upper edge
of the case Z. In the bottom of this channel there may be placed a packing
piece of india-rubber or other soft material and the channel may be filled with
mercury or other liquid to further reduce the chance of leakage into the
chamber B.
The cap X may be arranged to fit around the drum C with comparatively little
clearance in order that the gas entrapped in the passages F of the drum at each gulp
may be a considerable fraction of the total volume of the chamber A. In the
arrangement shown the cap has a prolongation at R for the accommodation of the
tube D so that when the apparatus is not in use the cover Y 'may be removed then
the cap X and if necessary the drum C without disturbing the tube D or any
apparatus attached thereto. Leakage at the place where the tube D passes
through the outer case may be prevented or reduced by a stuffing gland packed
with india-rubber or other suitable packing, by cementing the tube D into the
outer case or by other means as may be found convenient in different applications
of the apparatus. Should any trouble arise from air leaking past the tubo D and
finding its way along the surface of the tube into the chamber A a piece of india-
rubber sheeting or other suitable material may be passed over the tube D in the
interior of the apparatus so as to lie between the cap X and the outer case Z and
thus to divert any bubble of air into the partial vacuum B..
The outer case Z, the cover Y, the cap X, and the drum C, may be constructed
of glass, china, vulcanite, or other suitable non-metallic material, but they can also
be conveniently constructed of iron or steel in which case they may further be
enamelled with a view to secure smoothness of the interior and air-tightness.
The mode of operation of the apparatus is as follows:-A partial vacuum say
down to a pressure represented by inch or 1 inch head of mercury having been
produced in the outer chamber B by a mechanical pump, a water jet pump or other
means, the drum is rotated by hand or by motive power in the direction indicated
by the arrow, when the gas remaining in the chamber A and any vessels placed in
communication therewith by means of the tube D is transferred step by step in the
manner described to the chamber B. The dimensions of the apparatus are such
that the liquid may stand at a height in the chamber A above the level of the
liquid in the chamber B by an amount corresponding to the excess of pressure in
the chamber B above that in the chamber A, while the level in the chamber B is
above the lower edge of the cap X so as to maintain a liquid sealing between the
two chambers.
Figures 5, 6, and 7, represent an alternative form of the apparatus. Like letters
in these figures and Figures 1 to 4 refer to corresponding parts. In the example
shown the drum C contains only one passage which in this instance has a somewhat
spiral form having apertures G and H, corresponding in function to the apertures
previously described with reference to the preceding figures. Figure 5 is a
sectional elevation of the apparatus. Figure 6, is a transverse section of the
apparatus in a direction at right angles to the axis of the drum while Figure 7 is a
projection of the apparatus upon an inclined plane parallel to the axis.
In Figure 5 the drum C is represented as being formed for convenience of
construction of two portions viz. a solid piece upon the exterior of which a groove
or recess of suitable form is provided which piece is covered by a tubular portion C₁
shown in section except for a small portion at the upper end which is shown in
external view in order to exhibit the inlet aperture G. The special construction of
the interior portion of the drum which is exhibited in the drawing may be described
as consisting of a cone having a disc at its upper end from which cone a spiral
blade projects, the diameter of the cone being small towards the upper end in
order to provide a large volume above the surface of the liquid, while at the lower

page_text: end the diameter of the cone is increased in order to minimise the quantity of liquid
(say mercury) required and further to constrict the area of the passage towards the
lower aperture H in order to increase the velocity of flow of the liquid and thus to-
increase the scouring action.
The tube E which constitutes the communication between the chamber B and
the pump producing the partial vacuum, is represented as being attached at the
bottom of a pocket formed in the upper portion of the case Z, which pocket may be
filled with mercury in order to prevent leakage of air past the joint. The exterior
case Z and the interior cap X are represented as being for the most part cylindrical
in form but as having a protuberance or pocket R towards the side as represented
in Figure 6 for the accommodation of the tube D which is carried in through a
stuffing gland and turned upwards so as to extend above the surface of the liquid
in the chamber A. The operation of this modified form of the apparatus is identical.
in its main principle with that of the apparatus shown in Figures 1 to 4.
It will be evident that in the first form of the apparatus the cover Y and the
cap X may be formed in one piece as the corresponding portions are in the case of
the second form of apparatus described, and the details of the apparatus may be-
modified in many other respects while still retaining the essential feature of our
invention, which is the use in combination with a pump producing a partial vacuum
in a chamber B of a rotating drum which during its rotation removes from a
chamber A a portion of the gas contained therein, compresses it somewhat and.
in chamber B maintained by the pump.
ejects it into the partial vacuum
aforesaid.
our invention and described the manner of
Having stated the nature of
performing the same we declare that what we claim is.:-
1. In apparatus for the production of high vacua the combination of a rotating
drum partially submerged in mercury or other liquid and containing passages of a
somewhat spiral or helical form, which drum during its rotation effects a
transference of gas from a chamber placed in communication with the vessel or
vessels to be exhausted to a chamber placed in communication with a pump
producing a partial vacuum these two chambers being sealed one from the
other by the liquid used in the apparatus, all substantially as described and
illustrated.
a
2. Apparatus for the production of high vacua consisting of a pump producing
partial vacuum in combination with apparatus, substantially as herein described
and shown in the drawings Figures 1 to 4 and Figures 5 to 7 respectively.
Dated this 7th day of May 1896.
BOTTOMLEY & LI
154, St. Vincent Street, Glasgow, Applicants' Agents..
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicants' Agents..