Improvements in Screw Pumps.
Year: 1894

page_text: Date of Application, 27th Nov.. 1894-Accepted, 5th Jan., 1895
[Communicated from abroad by WILLIAM
QUIMBY,
O au
United States of America, Mechanical Engineer.]
Improvements in Screw Pumps.
Victoria Street,
I, EDWIN MARSHALL Fox, of Connaught Mansions, 34
Westminster S.W., Gentleman 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 a screw pump of the type in which are employed two
pairs of screws with intermeshing threads which are arranged on two parallel shafts
and which rotate within a shell which closely fits the perimeters of the threads.
The space within the shells between the two pans of screws is either the induction
chamber or the eduction chainber, according to the direction in which the screws
are rotated. On one side of this chamber the screws have right-hand threads,
and on the other left-hand threads. Thus when the screws are appropriately
turned, the fluid introduced into the central chamber is drawn therefrom in opposite
directions and discharged from the ends of the screws into passages communicating
with a common outlet.
Reversing the direction of rotation of the screws reverses the direction of the
was the
currents of fluid set in motion by the screws and makes that which
induction chamber, into which the fluid was introduced in the previous case,
the eduction chamber, and makes that which was previously the outlet, the induction
chamber. In either case two equal currents of fluid are established always in
opposite directions either to or from the central chamber. These two currents
counterbalance each other and hence the screws are not subjected to any endwise
thrust in their bearings.
It is an incidental advantage of this construction and arrangement that by so
mounting the pump that the axes of the screws will be horizontal or proximately
the induction pipe can be introduced to the top of the shell and the pump can
be kept full of liquid after it has stopped working and will thus be in readiness to
be immediately started to work again whenever occasion arises.
So,
As heretofore constructed it has been necessary to make the width of the
spiral grooves considerably greater than the thickness of the spiral threads, in
This was
order to afford clearance for the threads while they intermesh.
necessary because any given point on the periphery of the screw-thread in moving
through a given number of degrees describes an arc, the chord of which is longer
than the chord of the aic described by a point on the bottom of the groove, or
It follows
upon a core of the screw in moving through a like number of degrees.
that to permit even the intermeshing of the two parallel screws, having threads
of ordinary shape, the grooves must be wider than the screw threads which they
have to contain. The resulting loose fit of the intermeshing threads greatly
increase the leakage or backward slip of the fluid, and thus diminishes the
effectiveness of the pump in operation.
By the present invention the intermeshing screws are provided with thread, the
side walls of which are hollowed out or made approximately concave, while their
faces are preferably flat, having the shape of a spiral section of a cylinder. In this
device the width of the grooves at the bottom and at their mouths is substantially

page_text: the same as the width of the faces of the threads, the difference between the two
dimensions being merely such as is required to make a sliding fit between the faces
of the threads and the bottom of the grooves respectively Thus the faces of the
intermeshed portions of each convolution completely close the bottoms of the
grooves in which they are engaged, on a line lying in the plane of the axes of
the two screws, while the hollowed out side walls of the threads afford the necessary
clearance and a sliding fit for the portions of the faces of the threads immediately
adjoining the said line
The faces of the screw-threads have the shape of spiral sections of a cylinder.
The side walls of the threads are made concave by having formed in them recesses
which gradually increase in depth from the periphery of the thread to a point
near its base, and then rapidly diminish in depth from that point to the base.
By this device during the intermeshing of the threads the outer corner on one
side of the portion of any intermeshed convolution of thread which is, say, beneath
the plane of the axes of the screws and the outer corner on the other side of the
portion of the same convolution which is, say, above the said plane are in close
proximity to the side walls of the adjacent convolutions respectively. This greatly
diminishes the slip of the fluid when the pump is at work. The screws have hollow
cores and are detachably fastened to their respective shafts.
I provide means for longitudinally adjusting the screws with relation to each
other, and a peculiarly simple and convenient combination of the screws with an
electric motor.
The accompanying drawings, illustrating the invention, are as follows:
Figure 1 is a side elevation of the pump.
Figure 2 is an end elevation with the pulley removed.
Figure 3 is an elevation of the end opposite that shown in Figure 2.
Figure 4, is a longitudinal vertical section of the shell taken through the plane
indicated by the dotted line u-u on Figure 2.
Figure 5 is a transverse section taken through the plane indicated by the dotted
line tow on Figure 1.
Figure 6 is a horizontal longitudinal section taken through the plane indicated
by the dotted line - on Figure 2.
Figure 7 is a transverse section taken through the plane indicated by the dotted
line y-y on Figure 6.
Figure 8 is a top view partly in section, illustrating the manner of driving the
pump by an electric motor.
Figure 9 is an end elevation of parts shown in Figure 8.
The drawings which represent in detail a screw pump embodying the present
improvements, also include a conventional representation of an electric motor for
driving the pump by means of a rotating armature mounted on one of the screw
shafts, which for the present purposes may be deemed the driving shaft, and which
18 geared to the other screw shaft.
The shell A of the pump has the shape in cross section of two partly intermeshing
hollow cylinders with their intersecting portions removed
At the end opposite
that at which the power is applied the shell is closed by the head B. The head, B, is
provided with a boss, B₁, in which there are two cylindrical apertures for receiving
respectively the journal boxes C and D. These journal boxes are flanged cylinders
open at their inner ends and closed at their outer ends, and are secured to the
boss, B1, by the screws C¹ C¹ and D¹ D¹ respectively. They are also centrally
perforated at their outer ends to receive the setting bolts C2 and D2 respectively.
Each setting bolt is provided with a jam nut, E, for securing it in the position to
which it may be adjusted.
The head, F, is provided with stuffing boxes F', and F2. The shell, A, is cast
integrally with or is affixed to the bed plate G. A standard, G¹, also integral with
or affixed to the bed plate, G, contains the journal boxes, G2 and G³, which
respectively afford the outer bearings for the screw shafts.

page_text: The journal boxes, G³ and G³, are provided with flanges perforated to admit the
bolts, G, by which they are secured to the standard, G¹. through which they are
inserted.
The driving shaft, a, has its bearings in the journal boxes, C and G2, and the
stuffing box F. To distinguish it the driving shaft may be regarded as the primary
screw-shaft. The secondary screw-shaft, b, has its bearing in the journal box, G³,
the stuffing box, F2, in the head, F, and the journal box, D, in the head B.
When the pump is to be driven by a belt, the diving pulley, c. may be affixed
to the end of the journal, a¹, of the driving shaft a projecting outwardly from the
standard G.
A hardened steel collar a² is pinned to the inner extremity of the journal a¹.
A washer, a³, of relatively soft metal and a washer, a, of hardened steel are
interposed between the collar, a² and the inner end of the journal box (+². The
secondary shaft, b, provided with a turned-down journal, b₁, is provided with a
similar fixed collar 6, and washers, 63 and 6, the latter bearing against the inner
end of the journal box G³.
It will be seen that by screwing in the setting bolts C², D2, the shafts, a and b,
can be forced endwise and their loose washers, a and b, forced against the inner
ends of the journal boxes G2 and G³ respectively. If necessity arise for adjusting
the shafts or either of them in the opposite direction, the adjusting screw-bolt can
be unscrewed and the journal box at the opposite end may be driven by
appropriately turning its fastening bolts G. Facility is thus afforded for the
independent end wise adjustment of the two shafts. Motion is transmitted from
the primary screw-shaft to the secondary screw-shaft by means of the intermeshing
pinions, a5 and 6, which are respectively keyed to the shafts a and b,
The portion
of the primary shaft, a, within the pump shell, A is inserted through the hollow
cores respectively of the right-hand screw, d and the left-hand screw, e, both of
which are keyed and pinned to the shaft a. Similarly, the portion of the secondary
screw-shaft, b, which is within the pump shell, is inserted through the hollow cores,
respectively, of the left-hand screw, f, and the right-hand screw. g, which are also
keyed and pinned to the shaft upon which they are mounted.
As will be seen on reference to Figure 6, the threads of the right-hand screw, d,
intermesh with the threads of the left-hand screw, f, and the threads of the left-
hand screw, e, intermesh with the threads of the right-hand screw g.
It will also be seen on reference to Figure 6, that the screw threads have flat
faces corresponding to the shape of the spiral section of a cylinder, and that the
width of the bottom and the mouth of the grooves is substancially the same as the
width of the face of the thread, and that the side walls of the thread are undercut
or hollowed out into approximately concave form. The depth and form in cross
section of the recesses in the side walls of the threads will of course vary with
threads of different pitches and different diameters. Those shown in the drawings
sufficiently illustrate the purpose of the recessed side walls and the mode of operation
of intermeshing screw threads of the character described. For convenience of
illustration the drawings represent the two screws as arranged side by side so that
their axes lie in the same horizontal plane.
Referring now to the faces of the intermeshed portions of the threads, it will be
seen that below the horizontal plane one edge, say, for example, the right-hand
edge, of each convolution of the thread of, say, the primary screw, is maintained
in close proximity to the recessed sides of the adjacent convolutions of the thread
of the secondary screw. In such case, above the horizontal plane, the left-hand
edge of each convolution of the thread of the secondary screw is maintained m
close proximity to the recessed sides of the adjacent convolutions of the threads of
the primary screw.
It will of course be seen that this mode of constructing the threads by which
5 excessive leakage or backward slip of the fluid, when the pump is in operation, is
prevented may be usefully employed not only in a screw pump having two pairs of

page_text: intermeshing right- and left-hand screws, but also in a screw pump having but one
pair of intermeshing screws.
The faces of the threads of the screw d, loosely fit the concentric wall h, of the
pump shell those of the screw e, loosely fit the concentric wall h', of the pump
shell; those of the screw f, loosely fit the concentric wall i, of the pump shell, and
those of the screw g, loosely fit the concentric wall i¹, of the pump shell.
The space between the opposed ends of the screws, d and e, f and g constitutes
what for present convenience may be called the induction chainber H, which is
surmounted by the chest H¹, cast integrally with or affixed to the top of the pump
shell A. The chest H¹, is open on opposite sides to facilitate the attachment of the
suction pipe to either side. When the driving pulley is rotated in the appropriate
direction, fluid sucked mto the chamber H, is drawn in opposite directions therefrom
and discharged into the eduction chambers, I and J, at the opposite ends of the
shell A, and thence makes its way through the channels I¹ and J¹, to the eduction
chest K, to which is connected the discharge pipe L.
Reversing the direction of rotation of the driving pulley of course reverses the
direction in which the currents of fluid are driven through the pump so that the
fluid instead of being driven in opposite directions outwardly from the central
chamber H, is forced in opposite directions into the chamber H. Hence, as will be
perceived, there will be no end thrust of the screw shafts in their bearings whichever
way the driving pulley is rotated.
The parts of the pump most subjected to wear are the screws and hence they are
preferably made with longitudinally hollow cores and are detachably fastened to
their respective shafts, so that when worn they may easily be replaced by new ones.
An especially convenient mode of driving the pump is afforded by an electric
motor, the plane of rotation of the armature of which is transverse to the axial
lines of the screw-shafts, to which end the screw-shafts may be made longer and
one or both of them may be provided with a bearing or bearings in additional
standards M M' affixed to a correspondingly elongated bed plate, as illustrated in
Figure 8, in which the field magnets, N, of the motor are shown as arranged between
the standards G¹ and M¹. The armature O, is mounted upon the extension of the
primary screw-shaft a. If a quick running armature is employed it is loosely
mounted upon the primary shaft, and intermediate speed reducing gearing is used to
transmit motion to the primary screw-shaft. Such intermediate gearing consists of
the pinion 01, fastened by the key, O2, to the armature hub, 03, and gearing with a
wheel P affixed to or formed integrally with a hub, P¹, which is loosely nounted
upon the extension of the secondary screw-shaft b. A small pinion, P2, affixed to
or formed integrally with the loose hub, P¹, is adapted to mesh into the gear Q,
affixed to the primary screw-shaft, a as shown in Figure 8.
If a slow running motor is employed, the armature may be keyed to the primary
screw-shaft, a as illustrated in Figure 9; in which case the intermediate gearing
will be dispensed with, so that the armature may drive the primary screw-shaft
directly. If intermediate gearing is used, it will of course be proportioned with
reference to effecting the required difference of speed between the arinature and the
primary screw-shaft.
It will be seen that the intermediate gearing may be thrown out of action by
simply removing the key, O2, by which the pinion 01. is fastened to the armature
hub 03.
For purposes wherein the work to be done varies from time to time, as in the
case of freight or passenger hydraulic elevators, considerable economic advantages
result from the direct application of an electric motor to drive the pump which
supplies water to the cylinder of the hydraulic elevator. Such use of a plunger
pump is however subject to the objection that the resulting pulsating movements of
This objection 18
the water impart unpleasant jerky motions to the elevator.
entirely overcome and the advantages referred to are fully realized by the employ-
ment, under the conditions stated, of the herem described pump which, when driven

page_text: directly by an electric motor, delivers a steady stream of water at practically
uniform velocity, while the motor takes more or less current according to the
pressure against which the pump has to work, or, in other words, according to the
amount of load on the elevator.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is :-
1. A screw pump having right and left hand screws constructed and arranged
substantially as herein shown and described for the purpose specified.
2. A screw pump having two pairs of right and left hand screws and a shell or
casing constructed to receive the same and provided with openings, substantially as
herein shown and described for the purpose specified.
3. A screw pump constructed substantially as described with reference to the
accompanying drawings and operating as specified.
Dated this 20th day of November 1894.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.