Year: 1894

page_text: Date of Application, 12th June, 1894
Complete Specification Left, 11th Apr., 1895-Accepted. 8th June, 1895
I, EDWIN DUNBAR CHAPLIN, of Nantick, in the State of Massachusetts,
United States of America, Engineer, do hereby declare the nature of this invention
to be as follows:-
This invention relates to vacuum pumps, it having especial reference to pumps
employed to exhaust the air from incandescent bulbs.
As the air contained in lamp bulbs always carries a certain quantity of moisture,
and as it is difficult to obtain a high vacuum in the presence of moisture, it is a
common practice to first exhaust the greater part, say ninety-five per cent.. of the air
together with a like percentage of the moisture, by a vacuum pump of ordinary
construction, and then exhaust the balance of the air, or as much of same as is
possible, by a second specially constructed pump, which, by reason of its special
construction, together with the absence of any appreciable quantity of moisture,
enables a high vacuum to be obtained.
Pumps for this second or final exhausting, as heretofore constructed, have
usually been provided with an air inlet controlled by a valve which it is necessary
to cover or flood with a liquid, usually oil, in order to form a liquid seal about the
valve to prevent possible leakage.
In practical operation, however, it has been found that, as the air valve is
opened, the scaling liquid has a tendency to cling to and to follow the valve
like the stretching of a piece of rubber and to form a thin film of liquid
stretching from and surrounding the valve seat to the open valve, which film
the rarefied air in the bulbs has not sufficient pressure to break; this film being
so strong, that, in a high vacuum, it absolutely prevents the entrance or expansion
of air from the bulbs into the pump cylinder.
To obriate this difficulty, pumps have been constructed having the air inlet
in the side of the pump cylinder, so as to be opened and closed by the piston
as it reciprocates in said cylinder, the piston fulfilling the function of a valve.
In pumps of this latter construction, that is, having the side air inlet, the tight
fitting piston which excludes any considerable quantity of oil, obviates the oil film
previously referred to, but it has heretofore been necessary to place such side air
inlet near the middle of the cylinder or near the end of the drawing-in stroke of
the piston, in order that said piston in its return or expelling stroke, may first close
or cover the inlet, and thereafter expel the air from the cylinder.
If such side inlet were located near the bottom of the cylinder, the air which
had entered and filled the cylinder during the drawing-in stroke of the piston would
simply be returned through the open inlet into the bulbs from which it had
expanded, before the moving piston could reach and cover the inlet to prevent such
return.
It has also been found that when the air inlet is placed near the middle of the
cylinder or near the end of its drawing-in stroke as described, the rarefied air
has not sufficient time between the uncovering of the inlet, as the piston reaches
the end of its stroke, and the closing of the inlet by the return movement of
the piston, to expand into and fill the cylinder; for rarefied air is sluggish in its
movements and does not readily expand to fill the cylinder, but needs to be drawn

page_text: or sucked into the cylinder by a moving piston, which cannot be done when the
inlet is not uncovered until the piston has practically reached the end of such
drawing-in stroke or sucking movement.
In my efforts to perfect vacuum pumps, I have aimed at constructing a pump
which should have, first, the air inlet in the side of the pump cylinder to avoid the
oil or liquid film surrounding the open valve referred to; secondly, the said air
inlet placed near or at the bottom of the cylinder or near the beginning of the
drawing-in stroke of the piston, in order that said inlet should be uncovered at the
very beginning of the stroke, thereby to give the longest possible time during
the stroke of the piston in which the air might expand into and fill the cylinder,
and thereby also to avail myself of the full drawing-in stroke or sucking movement
of the piston to draw or suck the rarefied air into the cylinder; and lastly, to
provide means for closing the said air inlet quickly at the end of the drawing-in
stroke of the piston, in order that none of the air drawn or expanded into the
cylinder behind the piston shall be returned or forced back into the bulbs before
the piston in its return or expelling stroke should reach and cover the said inlet to
prevent such return.
The result of my efforts is the invention forming the subject-matter of this
present application and in which the principal or distinctive feature is the employ-
ment of two pistons within the pump cylinder, one piston moving within the other,
the latter moving to open and close the air inlet and at the same time constituting
a cylinder in which the other piston, which draws in and expels the air, is
reciprocated.
These pistons, which are preferably provided with valves, may be reciprocated
relatively to each other in any suitable or desired manner; but I prefer to employ,
as a motive power, oil or other liquid under pressure. I have found that, by the
use of hydraulic pressure, I can, as I believe, better control the movements of the
pistons to facilitate the exhaustion of the air.
Two vertical pumps are erected on a suitable base, both being of the same
construction.
.
The lower cylinder heads of these vertical pump cylinders are made conical,
while the upper cylinder heads are provided at their inner sides or faces with an
annular recess; said upper cylinder heads being provided with a vertically
extended annular flange upon which is sustained and bolted the cylinder head of
the power cylinder; the latter in turn supporting at its upper end and having
secured to it a second vertical power cylinder provided with the proper cylinder
heads.
Within the cylinder I have provided, in accordance with this invention, two
independent pistons or plungers, provided with suitable packing rings; one of the
pistons being long and cup-shaped. The annular cone-shaped top of this outer
piston is fitted to enter the annular recess in the top cylinder head. The top and
sides of the piston can either be formed of independent parts bolted together or be
of one piece or member.
.
Within this cup-shaped piston, which in effect constitutes a second moving
cylinder, is placed an inner piston, shorter in length than the outer piston and
preferably box-like in construction, its under side having preferably a conical recess
to correspond with the conical cylinder head with which it contacts when at the
lower end of the stroke, the upper cone-shaped face of the said piston being formed
to enter and fit a corresponding recess in the under side of the outer piston.
The piston is provided at its under side with one or more upwardly opening
valves, its upper side being preferably perforated by ports or openings. In
practice the piston is filled with oil or other liquid. The piston and the top
cylinder-cover are respectively provided with outwardly opening valves.
The power cylinder is provided at one side with a suitable valve seat to which
passages from the upper and lower ends respectively of the power cylinder lead;
these terminating in ports in the valve seat, one towards one side and the other
below the centre thereof and substantially ninety degrees apart.

page_text: The second power cylinder is also provided with a circular valve to which
passages from the upper and lower ends respectively of the cylinder lead; the said
passages terminating in the valve seat at substantially diametrically opposite points
located vertically with relation to the valve seat. The valve seats are provided
with depressions communicating respectively with the exhaust ports leading to
one side of their respective valve seats. The valves I prefer to employ are in the
form of discs provided at their peripheries with intermeshing teeth whereby
rotation of either valve causes a like but opposite rotation of its mating valve.
The valve can be journaled loosely upon a pin or short shaft mounted in the
cylinder casing and in the face plate secured thereto.
The power fluid, preferably a liquid, as oil under pressure, is conducted to the
valve through a pipe entering the face plate, while the said power fluid for the
valve enters the said face plate at the power inlet. From the power inlet for
the upper valve, branches lead to diametrically opposite points directly over the
entrance to the ports of the cylinder.
The valve is provided at its outer face side with an arc shaped depression in
the middle of which is located a port which extends through the inner face side of
the valve. A corresponding valve is also provided at its rear side with an arc-
like exhaust depression. The valve is provided with a long arc-shaped port
extending through the valve, while said valve at its rear side is provided with an
arc-like exhaust depression.
The shaft has fast upon it a bevel wheel in gear with a second bevel wheel fust
on the upper end of a vertical shaft journaled in suitable bearings in the frame,
said shaft constituting the driving shaft of any suitable or usual rotary or centri-
fugal pump. This pump has two outlet pipes leading respectively to the two
pumps, each of its delivery pipes being divided at its end, one branch leading to
the inlet of one valve and the other branch to the inlet of the other valve.
The exhaust from the valves enters two pipes joining to form a single pipe and
leading to and constituting one of the suction pipes for the pump, said pump having
another similar suction pipe leading to the other vacuum pump.
An air-pipe connects the air-inlet of the pump-cylinder with the bulbs or other
devices which are to be exhausted. This pipe may consist of two concentric tubes
or pipes, the inner pipe constituting the air conduit proper, the space between it
and the other pipe being preferably filled with oil or other sealing fluid to prevent
possible leakage.
When the shaft is rotated, the pump maintains a constant pressure of fluid
in its delivery pipes, and the operation of the pumps may be described as
follows:-
The valves are rotated by the shaft. So soon as they have been rotated a short
distance from their position, the inlet port of the valve will be moved gradually
into position admitting fluid under pressure from the supply pipe to the said
cylinders below the pistons therein, causing the latter to rise together and thereby
move the pump pistons in the pump cylinders in unison, the said pistons at the
very beginning of their stroke uncovering the air-inlet.
The outer piston has a shorter stroke than the inner piston and reaches the end
of its stroke in contact with the top cylinder head before said piston has completed
more than half its movement. The continuous rotation of the valves at this point
brings the inlet port of the valve into position over and communicating with
another port leading to the upper end of the lower cylinder, the exhaust port of
said valve at the same time reaching a position over and in communication with a
port leading to the lower end of the cylinder, with the result that the direction of
movement of the piston is quickly changed and the said piston begins to. turn or
move downward towards the still rising piston. The two pistons thus meet and
contact with each other just before the one piston reaches the end of its downward
movement, at which time the valve in its rotation has carried its inlet port into
position over the port leading to the upper end of the upper cylinder and its exhaust
port over the port of said cylinder to change the direction of movement of the

page_text: piston in the pump cylinder, causing the latter to descend to the bottom of the
pump cylinder, preferably in unison and in contact with the piston through
the balance of the stroke of the latter, the inner piston thereafter moving down-
wards within but independently of the outer piston till the end of the stroke is
reached. The movements of the pistons are preferably timed as described, but it is
evident that they may be timed differently without affecting the scope of the
invention.
The mechanical operation having been now described, the manner in which the
air is exhausted from the bulbs will be explained.
As previously stated, both pistons begin their upward movements or strokes
together, and at the very beginning of their strokes uncover the air-inlet, so that
the retreating piston acts to draw or suck the air from the lamp-bulbs through the
pipe into the cylinder to fill the space left by the retreating piston. The outer or
what I term the cut-off piston having a shorter stroke, reaches the end of its stroke
considerably in advance of the main piston and immediately begins its downward
stroke before the other or main piston has finished its up stroke, the two pistons
meeting as described just before the cut-off piston has reached the end of its return
or downward stroke, or just as it has passed and closed the air-inlet to cut off the
cylinder from the lamp-bulbs. The two pistons now descend together through the
balance of and until the cut-off piston has reached the end of its stroke, when
the said cut-off piston stops and dwells until the inner or main piston finishes its
downward stroke and contacts with the bottom cylinder head; such downward
movement of the main piston causing the air, previously drawn into the cylinder by
its up-stroke, to be forced upwards past the valve into the oil or liquid contained
within the piston; the air rising through the latter and through the ports into the
auxiliary cylinder formed within the cut-off piston and between it and the said
inner piston. At the next up-stroke of these two pistons, this body of rarefied air
is carried bodily upwards between the two pistons until the outer or cut-off piston
reaches the end of its stroke, when further rising movement of the inner piston
within the cut-off piston in conjunction with the return or downward movement of
the said cut-off pistou, causes the rarefied air contained between the two to be
compressed until the two pistons meet; when the one piston, striking the valves,
will open the latter and cause, the air compressed between the two pistons to be
expelled past the said valves into the space between the cut-off piston and the
cylinder head in which it is compressed at the next upward stroke of the cut-off
piston and expelled from the cylinder when the said cut-off piston reaches the end
of its stroke and contacts with and holds the valves, the air thus expelled escaping
into the atmosphere through the exhaust.
The advantages of this pump are as follows:-
The air-inlet being placed at or near the bottom of the pump cylinder, is,
substantially at the very beginning of the stroke, uncovered or opened to permit
the air from the bulbs to, be sucked or drawn into the cylinder by the upward
or drawing-in movements of the pistons; said inlet remaining open until the
inner main piston has nearly or quite reached the end of its upward stroke, so
that the benefit of its full stroke is obtained in drawing in the air from the bulb.
The cut-off piston begins to cut off or close the air-inlet before the main
piston reaches the end of its up or drawing-in stroke, so that by the time the
said inner or main piston begins its down or expelling stroke, the said cut-off
piston completely closes the air-inlet, and thereby prevents the return of any air
from the cylinders to the bulbs. Consequently all the air previously drawn into
the cylinder must of necessity be expelled through the valve, rather than return to
the bulbs.
I am thus enabled to open and close the air-inlet at such times as will secure
the most effective exhaustion of air from the lamp-bulbs, and this without using
the ordinary valves, but by using the cut-off piston, which, as hereinbefore stated,
is not open to the objection of the oil film closing the inlet. The air is not required
to expand into and of itself fill the cylinder; but is, from substantially the moment

page_text: the air-inlet is opened, drawn into the pump-cylinder by the retreating piston, so
that the greatest possible quantity of air is drawn into the cylinder at each stroke.
Neither is the sluggishly moving air required to be drawn quickly into the pump-
cylinder, but is drawn in gradually throughout the rising or drawing-in stroke of
the main piston, giving ample time for the movement of the air.
By employing hydraulic pressure to move the pistons, I am enabled to better
control and govern the movements of said pistons and to give either or both of
them such proper amount of dwell at the ends of their respective strokes as will
best secure the efficiency of the pump.
Two degrees of vacuum are formed at each stroke into which the rarefied air
drawn from the lamp-bulbs is exhausted. For example, the air drawn from the
bulbs into the cylinder beneath the piston is first expelled or forced into the
vacuum chamber within the two pistons and from such vacuum chamber is again
expelled or forced into a second vacuum chamber between the piston and the top
cylinder head; the great advantage of this being that the rarefied air from the
lamp-bulbs, which is drawn into the cylinder by the piston, is more easily forced or
expanded successively into the vacuum chamber between the two pistons and
between the piston and the cylinder head, and then into the atmosphere, than
would be possible were it attempted to expel such rarefied air from the cylinder
direct into the atmosphere without the intervention of the vacuum chambers.
The pump which constitutes a pressure-creating device to store pressure with
which to actuate the power pistons, is connected with the same mechanism which
actuates the valves, so that, when once properly adjusted, the rapidity with which
the pressure is created or stored varies directly with the movements of the valves
and the consequent rapidity with which the pressure is utilized, the movements of
the piston proceeding independently.
It will also be seen that a series of pumps may be connected together, all the
valves being moved constantly with relation to each other and a single pressure-
creating device employed or provided.
A single pump cylinder, with its connected power cylinders, constituting what I
term a "single pump," fulfils the function, viz., provides different degrees of
vacuum usually fulfilled by two or more independent pumps connected together.
Thus a complete exhaust apparatus is in my invention embodied in a single pump,
whereas in the present practice a plurality of independent pumps must be coupled
together to secure different degrees of vacuum.
I have described my invention as embodied in one form of apparatus or
machine. It will however be evident that the invention is not confined to the
particular construction or form of pump described; but may be embodied in
various constructions without affecting its spirit or scope.
I have herein employed the terms upper and lower in connection with the
power cylinders, and have described the apparatus as vertically arranged; but
it will be obvious that the invention will not be departed from by laying the
apparatus on its side.
In vacuum pumps which are designed for use in creating the highest possible
vacuum, it is absolutely necessary that the piston or pistons moving within the
pump cylinder be firmly and squarely seated at each end of their respective
strokes, in order that all air, contained between the moving piston and the wall
which constitutes the end of the cylinder within which the piston moves, may
be expelled. If there be a particle of clearance at the end of the stroke, the
quantity of air contained in said clearance represents the quantity of air which can
never be expelled, and therefore never exhausted from the lamp bulb or other
article to be exhausted.
Dated this 12th day of June 1894.

page_text: I, EDWIN DUNBAR CHAPLIN, of Nantick, in the State of Massachusetts, United
States of America, Engineer, 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 :-
This invention relates to vacuum pumps.; it having especial reference to pumps
employed to exhaust the air from bulbs for incandescent electric lighting.
As the air contained in lamp bulbs always carries a certain quantity of moisture,
and as it is difficult to obtain a high vacuum in the presence of moisture, it is a
common practice to first exhaust the greater part, say ninety-five per cent., of the
air together with a like percentage of the moisture, by a vacuum pump of ordinary
construction, and then to exhaust the balance of the air, or as much of same as is
possible, by a second specially constructed pump, which, by reason of its special
construction, together with the absence of any appreciable quantity of moisture,
enables a high vacuum to be obtained.
Pumps for this second or final exhausting, as beretofore constructed, have usually
been provided with an air-inlet controlled by a valve which it is necessary to cover
or flood with a liquid, usually oil, in order to form a liquid seal about the valve to
prevent possible leakage.
In practical operation, however, it has been found that, as the air valve is opened,
the sealing liquid has a tendency to cling to and to follow the valve like the
stretching of a piece of rubber and to form a thin film of liquid stretching from
and surrounding the valve seat to the open valve, which film the rarefied air in the
bulbs has not sufficient pressure to break; this film being so strong that, in a high
vacuum, it absolutely prevents the entrance or expansion of air from the bulbs into
the pump cylinder.
To obviate this difficulty, pumps have been constructed having the air-inlet in
the side of the pump cylinder, so as to be opened and closed by the piston as it
reciprocates in said cylinder, the piston fulfilling the function of a valve.
In pumps of this latter construction, that is, having the side air-inlet, the tight
fitting piston which excludes any considerable quantity of oil, obviates the oil film
previously referred to, but it has heretofore been necessary to place such side
air-inlet near the middle of the cylinder or near the end of the drawing-in stroke
of the piston, in order that said piston in its return or expelling stroke, may first
close or cover the inlet, and thereafter expel the air from the cylinder.
If such side inlet were located near the bottom of the cylinder, the air which
had entered and filled the cylinder during the drawing-in stroke of the piston
would simply be returned through the open inlet into the bulbs from which it had
expanded, before the moving piston could reach and cover the inlet to prevent such
return.
It has also been found that when the air-inlet is placed near the middle of the
cylinder, or near the end of its drawing-in stroke as described, the rarefied air has
not sufficient time between the uncovering of the inlet, as the piston reaches the
end of its stroke, and the closing of the inlet, by the return movement of the piston,
to expand into and fill the cylinder; for rarefied air is sluggish in its movements
and does not readily expand to fill the cylinder, but needs to be drawn or sucked
into the cylinder by a moving piston, which cannot be done when the inlet is not
uncovered until the piston has practically reached the end of such drawing-in stroke
or sucking movement.
In my efforts to perfect vacuum pumps, I have aimed at constructing a pump

page_text: which should have, first, the air-inlet in the side of the pump cylinder to avoid the
oil or liquid film surrounding the open valve referred to; secondly, the said air-inlet
placed near or at the bottom of the cylinder or near the beginning of the drawing-int
stroke of the piston, in order that said inlet should be uncovered at the very
beginning of the stroke, thereby to give the longest possible time during the stroke
of the piston in which the air might expand into and fill the cylinder, and thereby
also to avail myself of the full drawing-in stroke or sucking movement of the
piston to draw or suck the rarefied air into the cylinder; and lastly, to provide
means for closing the said air-inlet quickly at the end of the drawing-in stroke of
the piston, in order that none of the air drawn or expanded into the cylinder behind
the piston shall be returned' or forced back into the bulbs before the piston, in its
return or expelling stroke, reaches and covers the said inlet to prevent such return.
The result of my efforts is the invention forming the subject-matter of the
present application and in which the principal or distinctive feature is the employ-
ment of two pistons within the pump cylinder, one piston moving within the other,
the latter moving to open and close the air-inlet, and at the same time constituting
a cylinder in which the other piston, which draws in and expels the air, is
reciprocated.
These pistons, which are preferably provided with valves, may be reciprocated
relatively to each other in any suitable or desired manner; but I prefer to employ,
as a motive power, oil or other liquid under pressure. I have found that, by the
use of hydraulic pressure, I can, as I believe, better control the movements of the
pistons to facilitate the exhaustion of the air.
The invention also comprehends various constructional features and details
hereinafter fully described.
Fig. 1 of the drawings represents, in side elevation, partially broken away,,one.
form of pump embodying this invention; Fig. 2 a vertical section of the same
taken on the dotted line - (Fig. 1);
1
Fig. 3 a vertical section taken on the dotted line '-' (Fig. 2);
Fig. 4 a top or plan view of Fig. 1;
Fig. 5 an elevation on an enlarged scale of one pair of power cylinders, the valve
chest caps being removed to expose the valves;
Fig. 6 a vertical section taken on the dotted line y-y (Fig. 5);
Fig. 7a borizontal section of one of the valves, with its valve seat, the section
being taken on the dotted line y-y¹ (Fig. 5);
Fig. 8 a cross section taken on the dotted line y-y* (Fig. 6);
Fig. 9 a section of one of the valves taken on the dotted line - (Fig. 5); and
Fig. 10 a detail view showing the form of pipes which I prefer.
Fig. 11 shows the valve h, split and opened like a clam-shell to show both sides
in perspective; Fig. 12 showing its valve seat.
Fig. 13 is a view corresponding with Fig. 11 and showing the valve ; Fig. 14
showing the valve seat therefor.
Two vertical pumps are erected on a suitable base A. These being alike in
construction, it will suffice to describe one; the corresponding parts of the other
having the same letters of reference. The lower head 6 of the pump cylinder B is
conical, while the inner face of the upper head is formed as an annular recess b..
The upper head is moreover provided with a vertically extending flange b³,
whereon is mounted the head c of the power cylinder C. The latter in turn
supports at its upper end, and has secured to it, a second power cylinder C',
provided with the proper heads e¹ and c².
Within the cylinder B are arranged two independent pistons or plungers e and f,
provided with suitable packing rings such as ; one of the pistons e being long
and cup-shaped. The annular cone-shaped top of this outer piston e is designed to
enter and fit the annular recess in the top cylinder head . The top and sides
of the piston e may either be formed as one piece or may consist of separate parts.
bolted together.

page_text: Within this cup-shaped piston e, which in effect constitutes a second moving
cylinder, is placed an inner piston f, shorter than the onter piston e and preferably
box-like in construction; its under side being conical to correspond with the conical
cylinder head b with which it contacts when at the lower end of the stroke. The
upper side of the said piston fis formed as an annular cone and enters and fits a
corresponding recess e in the under side of the piston e.
The piston is provided at its under side with one or more upwardly opening
valves, its upper side being preferably perforated by ports or openings f³ In
practice the piston is filled with oil or other liquid. The piston e and the
top cylinder head 6¹ are respectively provided with upwardly opening valves
and b¹.
The power cylinder C is provided at one side with a suitable valve seat e, shown
separately in Fig. 12 as circular, to which passages from the upper and lower ends
respectively of the power cylinder C lead; these terminating in ports e, e, in the
valve seat, the one towards one side of, and the other below, the centre, the
two being substantially ninety degrees apart.
(see
The second power cylinder C is also provided with a circular valve seat
Fig. 14), to which passages (see dotted lines Fig. 5,) from the upper and lower ends
respectively of the cylinder lead; the said passages terminating in ports c7, 8, in
the valve seat, respectively located vertically above and vertically below the centre
of the valve seat c, and therefore diametrically opposite to one another. The valve
seats and care formed with depressions c, c, which communicate respectively
with the exhaust ports cl, c¹, leading to one side of their respective valve seats, as
shown in Figs. 5, 12 and 14. The valves h and are of disc form, their peripheries
being furnished with intermeshing teeth whereby rotation of either valve causes a
like but opposite rotation of its fellow valve. Referring to Figs. 2 and 6, it will
be seen that the valve his mounted axially upon a shaft 2 journaled in the valve
chest cover; said shaft having secured to its outer end a worm wheel h*, which
meshes with and is rotated by a worm hº. This worm, as shown in Fig. 1, is
mounted on a horizontal shaft carried in suitable bearings, and is provided
with a belt pulley 8, whereby the said worm shaft may be actuated from any
convenient source of power. The valve ' may be journaled upon a stud he mounted
in the cylinder valve faces or in the valve chest cover or both.
The power fluid, preferably a liquid such as oil, under pressure, enters the valve
chest at the point in the face plate h³ (see dotted lines Fig. 1), whilst the power
fluid for the valve enters the valve chest at ". From the power inlet h¹,
branches, formed in the valve chest cover or plate, lead to diametrically
opposite points directly over the ports c, c8 of the cylinder C'.
The valve h is provided in its outer face (see Figs. 5, 7 and 11), with an
arc-shaped depression, in the centre of which is located an opening h" which
extends through to the opposite or working face of the valve; this face being also
provided with an arc-like exhaust depression 1. The valve his formed with a
long arc-shaped opening 16 extending through the valve, and is similarly provided
with an arc-like exhaust depression h¹.
Referring to Fig. 1, the shaft has fast upon it a bevel wheel i which gears
with a bevel wheelfast upon the upper end of a vertical shaft journaled in a
suitable bearing, said shaft constituting the driving shaft of a centrifugal or other
suitable pump
1. This pump has two outlet pipes leading to the power cylinders,
each of the said pipes being divided at its end, one branch leading to the inlet ¹º
and to the valve h, and the other brauch i to the inlet h" and to the valve h'.
The exhaust from the valves h and h' enters two pipes 7 and 8, which join and,
forming a single pipe, lead to the pump I; another pipe of a similar character
constituting a suction pipe from the vacuum pump to the pump I.
An air-pipe M connects the air-inlet of the pump-barrel with the bulbs or other
vessels which are to be exhausted. This pipe M may consist of two concentric
pipes m, m³, the inner pipe m¹ constituting the air conduit proper, the space between

page_text: outer pipe being prefeTUVI
prevent leakage.
When the shaft his rotated, the pump I maintains a constant pressure of fluid
in its delivery pipes i, and the operation of the pump may be described as
follows:-
The valves h and A' are rotated by the shaft in the directions of the arrows
(Fig. 5). Having been rotated a short distance from the positions shown in Fig. 5,
the inlet port of the valve h, and inlet port of the valve A arrive in position
over the ports c and c leading to the lower ends of the power cylinders Cand. C
respectively, thus admitting fluid under pressure from the supply pipe i* to the said
cylinders below the pistons and f' and causing the same to rise together and
thereby to move the pump pistons e and in the pump cylinder B in unison, the said
pistons at the very beginning of their stroke uncovering the air-inlet d..
The outer piston e has a shorter stroke than the inner piston and reaches the
end of its stroke in contact with the top cylinder head b. before the piston has
completed more than half its movement toward the head of the piston e. At this
point, the rotation of the valves brings the inlet port of the valve into position
over and communicating with the port e leading to the upper end of the lower
cylinder C the exhaust port of said valve reaching at the same time a position
over and in communication with the port c' leading to the lower end of the cylinder,
with the result that the direction of movement of the piston e is quickly changed
and the said piston begins to move downward towards the still rising piston.f. The
two pistons thus meet and contact with each other just before the piston e reaches
the end of its downward movement, at which time the valve ' in its rotation has
carried its inlet port A into position over the port leading to the upper end of
the upper cylinder C and its exhaust port " over the port of said cylinder to
change the direction of movement of the piston f in the pump cylinder, causing the
latter to descend. to the bottom of the pump cylinder, preferably in unison and in
contact with the piston e through the balance of the stroke of the latter. The inner
piston thereafter moves downwards within, but independently of, the outer piston e
till the end of the stroke is reached. The movements of the pistons are preferably
timed as described, but it is evident that they may be timed differently without
affecting the scope of the invention.
The mechanical operation having been now described, the manner in which the
air is exhausted from the bulbs will be explained.
Referring to Fig. 2, both pistons are shown at the ends of their down strokes in
contact with the bottom cylinder head b. As previously stated, both pistons, begin
their upward movements simultaneously, and at the very beginning of their strokes
uncover the air-inlet d, so that the retreating pistons act to draw or suck the air
from the lamp bulbs through the pipe M into the cylinder to fill the space left by
the retreating pistons. The outer or what I term the cut-off piston e having a
shorter stroke, reaches the end of its stroke considerably in advance of the main
piston, and immediately begins its downward stroke before the piston f has
finished its up-stroke, the two pistons meeting, as described, just before the cut-off
piston e has reached the end of its return or downward stroke, or just as it has
passed and closed the air-inlet to cut off the cylinder from the lamp bulbs. The
two pistons now descend together through the balance of and until the cut-off
piston e stops and dwells until the inner or main pisten finishes its downward stroke
and contacts with the bottom cylinder head b; such downward movement of the
main piston causing the air, previously drawn into the cylinder during the
up-stroke of the pistons to be forced upwards past the valve into the oil or liquid
contained within the piston; the air rising through the latter and through the
ports into the auxiliary cylinder formed within the cut-off piston e and between
it and the inner piston. At the next up-stroke of these two pistons, this body of
rarefied air is carried bodily upwards between the two pistons until the outer or
cut-off piston reaches the end of its stroke, when further rising movement of the
B

page_text: Γ
inner piston, within the cut-off piston, in conjunction with the return or downward
movement of the said cut-off piston, causes the rarefied air contained between the
two to be compressed until the two pistons meet; when the piston striking the
valves e, will open the latter and cause the air compressed between the two pistons
to be expelled past the said valves into the space between the cut-off pistone and
the cylinder head 6', in which space it is compressed at the next upward stroke of
the cut-off piston, and expelled from the cylinder B' when the said cut-off piston
reaches the end of its stroke and contacts with and opens the valves &, the air thus
expelled escaping into the atmosphere through the exhaust N (Fig. 3).
The advantages of this method of construction and working are as follows
The air-inlet d being placed at or near the bottom of the pump cylinder, is
substantially at the very beginning of the stroke, uncovered or opened to permit the
air from the bulbs to be sucked or drawn into the cylinder by the upward or
drawing-in movement of the pistons; said' inlet remaining open until the inner or
main piston has nearly or quite reached the end of its upward stroke, so that the
benefit of its full stroke is obtained' in drawing in the air from the bulbs.
The cut-off piston begins to cut off or close the air-inlet before the main piston
reaches the end of its up or drawing-in stroke, so that by the time the said inner or
main piston begins its down or expelling, stroke, the said cut-off piston has completely
closed the air-inlet, thereby preventing the return of any air from the cylinders to
the bulbs: Consequently all the air previously drawn into the cylinder must of
necessity be expelfed' through the valve f; rather than return to the bulbs:
I am
thins: enabled to open and close the air-inlet at such times as will secure the most
effective exhaustion of air from the lamp bulbs, aud this without using the ordinary
valves; but by using the cut-off piston e, which, as hereinliefore stated, is not open
to the objection of the oil film closing the inlet. The air is not required' to expand
into and of itself fill the cylinder but is, from substantially the moment the
air-inlet is opened; drawn into the pump cylinder by the retreating piston f; so that
the greatest possible quantity of air is drawn into the cylinder at each stroke.
Neither is the sluggishly moving air required to be drawn quickly into the pump
cylinder; but is drawn in gradually throughout the rising or drawing-in stroke of
the main piston; thus giving ample time for the movement of the air.
By employing hydraulic pressure to move the pistons e and f, I am better able
to control and govern the movements of the pistons and to give either or both of
them such amount of dwell at the ends of their respective strokes as will best secure
'the efficiency of the machine.
From the foregoing; it will be observed' that. two degrees of vacuum are formed
at each stroke, and that the rarefied air drawn from the lamp bulbs is exhausted
in two stages at corresponding degrees of vacuum. For example, the air drawn
from the bulbs into the cylinder beneath the piston is first expelled or forced into
the vacuum chamber within the two pistons and is there subjected to compression.
From this chamber it is subsequently expelled or forced into the second vacuum
chamber formed between the pistone and the top cylinder head 6"; the great
advantage of this being that the rarefied' air from the lamp bulbs, which is drawn
into the cylinder by the piston f, is more easily forced successively into the vacuum
chamber between the two pistons and into that between the piston e and the cylinder
head 6', and then into the atmosphere, tlian would be possible were it attempted to
expel such rarefied'air from the cylinder B direct into the atinosphere without the
intervention of the vacuum chambers.
The pump I which constitutes a pressure-creating device to store pressure with
which to actuate the power pistons is or may be connected with the same mechanism
which actuates the valves, so that, when once properly adjusted, the rapidity
with which the pressure is created or stored varies directly with the movements of
the valves and consequently with the rapidity with which the pressure is utilized,
the movements of the actuating pistons proceeding independently.
It will also be seen that a series of pumps may be counected together, and all the

page_text: valves. moved constantly with relation to each other'; a single, pressure-creating
device being employed for the several pistons..
66
A single pump cylinder, with its connected. power cylinders, constituting what I
term a single pump," fulfils the function of providing, different degrees of vacuum,
a duty usually fulfilled by two or more independent pumps connected together.
Thus a complete exhaust apparatus. is, under this invention, embodied in a single
pump, whereas according to the practice hitherto prevailing, in order to secure
different degrees of vacuum, a plurality of independent pumps have been coupled
together.
In practice two pumps are connected as shown in Fig. 1, and operate together in
expanding air from the lamp bulbs.
I have described my invention as embodied in one form of apparatus or machine.
It will, however, be evident that the invention is not confined to the particular
construction or form of pump described with reference to the accompanying
drawings, but that its leading principles may be applied with various types of
design.
I have employed the terms upper and lower in connection with the power
cylinders, and have described the apparatus as arranged vertically; but it will be
obvious that the nature or scope of the invention will not be affected by laying the
apparatus on its side.
In vacuum pumps which are designed for use in creating the highest possible
vacuum, it is absolutely necessary that the piston or pistons moving within the
pump cylinder be firmly and squarely seated at each end of their respective strokes,
in order that all air, contained between the moving piston and the wall which
constitutes the end of the cylinder within which the piston moves, may be expelled.
If there be a particle of clearance at the end of the stroke, the quantity of air
present in such clearance space represents the quantity of air which can never be
expelled, and therefore never exhausted from the lamp bulb or other vessel to be
exhausted. By the term "seated" is meant the contact of a piston at the end of
its stroke with the end of the cylinder, or with a co-operating piston working in
connection with it and equally serving to confine the air, it being immaterial
whether the piston contacts with a fixed or movable wall so long as it is firmly
seated against such wall so as to expel all air from between the contiguous
surfaces.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I claim :-
1. The improved vacuum pump constructed substantially as herein described and
having two pump pistons each independently actuated by its own power piston and
working one within the other, the outer piston serving to cover and uncover an
air-inlet formed in the side of the pump cylinder; the action of the pistons being
such that (a) they commence their suction stroke in unison, whereupon the inlet is
immediately uncovered by the outer piston, (b) they contact with one another upon
the completion of the stroke by the inner piston, and (c) upon the commencement
of the return stroke of the inner piston the air-inlet is immediately covered by the
outer piston, thus causing the air previously drawn into the cylinder to be forced
into the space between the two pistons.
2. The improved method of working a vacuum pump provided with two pistons
working one within the other, the outer one serving moreover as a cut-off piston,
Eubstantially as herein described and whereby the air is first drawn into the pump
cylinder, secondly is forced into the space between the two pistons, thirdly is forced
into the space between the outer piston and the cylinder head, and ultimately is
discharged to the atmosphere.
3. In a vacuum pump of the kind herein referred to, the employment of two
pistons, such as e and f, one working within the other, the outer one performing the
function of a piston, of a cylinder and of a controlling valve, substantially as herein
described.

page_text: 4. The improved vacuum pump constructed and operating substantially as
described with reference to the accompanying drawings.
Dated the 11th day of April 1895.
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Chartered Patent Agent.