An Improved Vacuum Pump.
Year: 1898

page_text: Date of Application, 6th Dec.. 1893-Accepted, 21st Jan., 1899
COMPLETE SPECIFICATION.
An Improved Vacuum Pump.
I, ADOLPH BERRENBERG, of Frederica, West Side, Wandsworth Common, Surrey,
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:-
In order to insure that the air contained in the pump, and which is to be expelled
is completely driven out of the cylinder at the end of each stroke of the piston,
which is of the utmost importance as regards the efficiency of the pump, it has
been found necessary that the piston at the end of each stroke should be left for
some little time in contact with the bottom of the cylinder. The object of his
is to insure the particles of air remaining between the piston and the cylinder
bottom sufficient time to escape. It should be noted that the inertness of motion
of these exceedingly small quantities of air increases in the ratio of their extenua-
tion, so that with a quick return of the piston it will always happen that the air
has not yet completely left the cylinder head on the completion of the piston
stroke, up to the moment when communication between the cylinder head and the
vessel or space to be emptied of air is already re-established in the next stroke.
To avoid this evil is the object of the present invention, in which as already stated
the return stroke of the piston does not commence until after it has been retained
for some little time to intimate contact with the cylinder bottom, and which, more-
over, renders it possible to adjust, at will, the duration of such retention of the
piston in its terminal positions; to the extent demanded by the existing degree
of extenuation of the air.
The enclosed drawing shows one form of execution of this invention, in longi-
tudinal section. The pumps used in working this invention consist of the lower
pump cylinder a, with the pump pistons b and c working therein, and the two
upper cylinders connected therewith, d and c, with the driving pistons f and g,
respectively working therein. The pump is worked by means of a medium, for
instance oil, introduced into the power cylinders f and g under a sufficient pressure,
after the following fashion.
If both pump pistons are in their lowest positions, as shown in drawing, the
pressure medium introduced simultaneously under both driving pistons will cause
an almost uniform upward motion of both pump pistons. The air contained
between the upper pump piston and the cylinder cover escapes through the
valves a¹ into the outer chamber q, which communicates with the open air, or may
be emptied by a special air pump.
Immediately on the commencement of the upward stroke of both pistons, the
pipe establishing communication between the cylinder and the vacuum pipe is
laid open by the upper piston, and a corresponding extenuation of air takes place,
in the further course of the travel of both pistons, in the lower part of the cylinder
and the pipe communicating therewith.
On the upper pump piston 6 reaching the end of its stroke and coming into
contact with the cylinder cover, the said piston will immediately commence to

page_text: descend, and during this downward stroke a greater extenuation of air will take
place in the upper part of the cylinder owing to the fact that the valves a¹ have
been closed.
During the commencement of this downward stroke the lower pump piston c will
still move upward for a short distance so that the upper piston will meet piston c
when on the point of commencing its downward motion; while the two pump
pistons are thus approaching each other the already extenuated air contained
between them is expelled through the valves into the upper part of the cylinder.
Both pistons then descend together for a short distance, during which movemen
the upper piston 6 closes the communication of the cylinder with the vacuum pipe,
whereupon the upper piston, having arrived at its lowest position, will stop, while
the lower piston e will continue its descent, right down to the bottom of the cylinder,
forcing the extenuated air contained in the lower part of the cylinder through
valve cand apertures into the space between the pistons e and b. The ascending
stroke of both pistons then ensues simultaneously, immediately after the lower
piston has reached the bottom of the cylinder.
Like other vacuum pumps, the one hitherto described is subject to the defect
pointed out in the commencement, namely, that the expulsion of the extenuated
air from the efficient cylinder spaces cannot be effected in a sufficiently complete
measure, on account of the two quickly succeeding reversal or return motion of the
pistons.
In order to remedy this defect and insure a practically perfect expulsion of the
air from the cylinder spaces, the following arrangement is proposed in accordance
with the present invention.
Each of the two power cylinders d and e has at its side a valve-gear governing
cylinder and respectively, containing the annular slide-valves i, which
according to their position will admit the pressure medium entering through the
channel through the aperture d' or e¹, respectively, or through aperture 62 or e²
respectively, into the power cylinders d and e. As the arrangement of both slide-
valve governing arrangements is exactly the same for both cylinders & and e, one
only is more fully described hereinafter."
The annular slide consists of a hollow cylinder enlarged at one of its ends, and
is rigidly connected, by a perforated plate inserted in the upper annular enlarge-
ment, with the piston rod of a subsidiary piston 7. This piston moves in a
cylinder adjoining the valve-gear governing cylinder 3 axially, but separated
from it, and which on its part is provided with a regulating cylinder m, with
annular slide-valve m'. The latter is constructed in the same way as the main
slide-valve or respectively, and fitted with a perforated covering plate, like the
main slide-valve i¹ generally, the arrangement comprising the piston cylinder
and the valve-gear governing cylinder, differs from the main cylinder d (e), with
its valve-gear governing cylinder h (1), in their essential features, as to size only.
The valve-gear governing cylinder m communicates with the valve-cylinder
or through a small aperture n in its bottom plate, and the size of this aperture
can be regulated at will by a screw n. The admission of the pressure medium to
the small valve-gear governing cylinders m is effected by means of a pipe r or r
respectively branched off from the main pipe k or respectively.
Both annular slides m' are provided in their outward extension with rods m³
which pass through the cylinder cover and act upon a lever of the first kind o or o'
respectively. These levers may also be worked by rod connections p p p from
the pump pistons b and c.
The mode of action of the arrangement just described is as follows:-
If the position shown in the drawing, of the various parts, is regarded as the
starting point, the pressure medium, entering the main valve-gear cylinder h¹
owing to the fact that the annular slide is in a low position will be admitted under
the pistons fg through the apertures bor respectively, and will cause the ascent
of these, and with them, of the pump bin its highest position (which owing to its
shorter travel will take place sooner than in the case of the lower pump piston c) it

page_text: will raise rod p which enters the pump cylinder through the outer chamber q and
the cylinder cover, and with it the lever of whereby the annular slide m¹ belonging
to this cylinder is brought into its lowest working position.
While the upper pump piston bis forced against the cylinder cover by the
pressure of the pressure medium acting on piston g, the pressure medium will pass
from the valve-gear governing cylinder m under the secondary piston 7 in the
cylinder thus causing a stroke of the piston and with it a reversal of the principal
annular slide 2. But as the stroke of the piston will be dependent on the
discharge of the pressure medium contained in the cylinder, above the piston, which
discharge can only take place through the upper aperture of the cylinder, the hollow.
annular slide m' and the narrow passage into the valve-gear governing cylinder
it will be apparent that some length of time is required for a complete stroke
of the piston and that of the cylinder . This time is solely determined by the
size of the discharge orifice which as already mentioned can be regulated as
required by screw n¹. When after the expiration of this time the reversal of the
annular slide has been effected the pressure medium entering the valve-gear
cylinder through tube k, is passed into the space above the piston g, whereby
the latter, and with it pump piston b are caused to make a downward stroke, in
the course of this stroke the pressure medium contained in the space underneath
piston g passes through the aperture into the valve-gear cylinder h¹ and thence
through a passage h2 and a line of piping communicating with this passage, back
to the forcing pump for the pressure medium, which will likewise be eventually
reached by the pressure medium discharged through the retarding passagen by
way of the hollow annular slide i¹.
Meanwhile the lower pump pistone and the driving piston f joined to it, have
returned to their highest working position and in doing so have turned lever o by
means of the rod projecting from the upper cylinder and the lower adjusting
ring fixed thereto, so that the small annular slide m¹ belonging to it is also moved
downward to its lowermost position. The manner in which the reversal of the
annular slide is effected is exactly the same as already described with regard to
slide. When the pressure medium contained in the space above the little piston /
has been completely forced through the retarding passage the reversal of the
annular slide will have been completed and the pressure medium can now pass
into the space above piston f, in the cylinder & so as to cause another downward
stroke of pump piston c.
Although, now, the prolonged retention of the pump piston e in its highest
position does not in the first place serve the purpose of retaining it during this
time in contact with the upper piston b (as is the case in the highest position of the
piston as regards establishing contact with the cylinder cover, and also in the
lowermost position of piston c as regards contact with the cylinder bottom) this
arrangement nevertheless insures a contact between the two pistons, by causing
them to remain in contact for some length of time during their joint descent,
which is a very material point. Unless the pump piston e is retained in its upper-
most position, the meeting of the two pistons might frequently be jeopardised.
After a short joint descent of the two pump pistons, the upper piston will
reach its lowest position in which it will remain at rest while the lower pump
piston parts company with it and continues its downward course.
As the upper
pump piston b on its arrival in its lowermost position, does not effect a reversal of
the annular slides im it will remain in this position until the lower piston e has
reached the cylinder bottom, at the same time raising the two small annular
slides m³ again to the highest position shown in drawing, by means of the piston
rod P with upper adjusting ring catch, and the lever o together with rod p¹ and
lever o¹.
In this instance also the reversal of the annular slides will not be completed
until after the pressure medium contained in the space underneath the small
piston has been forced completely through the lower cylinder aperture and the

page_text: retarding passages n, whereupon the stroke of the driving pistons f, g and with
it that of the pump pistons bc will again commence.
The protracted retention of the pump pistons in their terminal positions, caused
by the retardation of the reversal of the valve-gear, serves, as will be seen, the
purpose of insuring a protracted close contact of the pump pistons with each other
or with the cylinder cover or bottom. This is the only way to insure a complete
expulsion of the inert extenuated air from the cylinder spaces, because such air
requires a considerably longer time for its expulsion than ordinary air.
In view of the fact that the expulsion of the extenuated air from the spaces
between the piston and cylinder surfaces will be still further retarded as the degree
of its extenuation increases, the regulating screws n¹ are provided, which render it
possible to reduce, at will, the clear width of the passage-way in the channels n
and thus further retard the reversal of the annular slides i so as to insure a still
longer retention of the pistons in their terminal positions. But the screws n' also
serve at the same time for modifying the motion of the pump pistons with regard
to each other.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is
-
1. A vacuum pump with arrangement for the retention of the pistons in their
terminal positions, characterised by the combination of the principal regulating
slides of the driving cylinders de with pistons which travel in the cylinders
and are governed by hollow annular slides m¹ travelling in cylinders m which com-
municate by narrow passages with the principal slide cylinders h¹.
2. In the vacuum pump characterised under Claim 1 the connection of the
small annular slides with rods m² which are hinged to levers o o¹ and the arrange-
ment of rods p p¹² for working the levers o o as well as the arrangement of
screw m¹ for regulating the clear passage-way of channels n.
Dated this 5th day of December 1898.
J. E. EVANS-JACKSON & Co.,
Agents for the Applicant.