IMPROVEMENTS IN THE CONSTRUCTION OF ROTARY PUMPS
Year: 1867

page_text: LETTERS PATENT to Hugh Forbes, of 184, Euston Road, N.W., Parish of
St. Pancras, County of Middlesex, for the Invention of "IMPROVEMENTS
33
PROVISIONAL SPECIFICATION left by the said Hugh Forbes at the
Office of the Commissioners of Patents, with his Petition, on the
24th September 1867.
I, HUGH FORBES, of 184, Euston Road, N.W., Parish of St. Pancras,
County of Middlesex, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF ROTARY PUMPS," to be as follows:-
These improvements are additional ameliorations to those set forth in my
Specification No. 2598 of 1866, and they consist,-
Firstly. In diminishing the adverse action against the toothed drums inside
the casing by protecting to the utmost those teeth from the chief influences
inimical to the rotation of the drums in raising and forcing water (or other
fluid), that is to say, both from a portion of the pressure of water (or other
fluid) against their faces in the upper part of the casing when water is forced
to a height above the drum casing, as likewise in diminishing the drag upon
the teeth in the lower part of the casing, caused first by the vacuum and then
by the weight of the column of water thereto consequent. This I effect by so
constructing my drum casing as to continue the circle of the circumference of
the tips of the teeth both in the upper and the lower parts of the casing to (or

page_text: nearly to) the points of contact between the said circles; in the upper part
I prefer that these circles should continue quite to their points of contact over
the drum ends near the end covers, and that in the lower part of the said
drum casing below the spot where the drums gear into each other the circles
should not quite meet. This arrangement might be carried out in the upper
part of the casing without its necessarily being followed in the lower part, or
in the lower part without its being also used in the upper part, but the con-
sequence would be a diminution in the efficiency of my improvements. Instead
of an inlet and outlet of circular form direct into the interior of the casing
I construct lengthened orifices or slits above and below the point of contact of
the drums and parallel with them, and I prefer that in length the upper orifice
should run across the casing as nearly from flange to flange as may be
consistent with strength, while in breadth it should be equal (or nearly so) to
the distance across one space from pitch to pitch. The lower orifice I prefer
to make of about equal breadth with the above, because the fluid fills the
vacuum and flows quickly into the spaces of the toothed drums, as their teeth
seperate on quitting the point of contact of the drums, while on the other hand
too broad an influx would expose the teeth to the adverse action, from the
effect of which it is my wish to protect them. The water which rushes into
and fills the vacuum in the lower part of the casing I allow to flow from an
ordinary tubing into the bottom of the said casing by an oblong slit or elongated
oval, by preference rather less long than the upper orifice, leaving distinct
recesses in the bottom of the casing for reasons to be hereafter explained.
The water issuing from the upper orifice I collect in an upper chamber or
dome, whence it passes into a tube or ordinary pipe.
Secondly. I so proportion the respective diameters of the interior of the
drum casing and that of the circumference of the tips of the teeth of the drums,
and I so arrange the bearings of the axles of the latter that the tips in their
rotation pass as close to the circular inside of the casing as is possible for them
to do without scraping. From the higher part above the axles to the point of
contact of the circumferences of the tips or the edges of the upper orifice
(already described) I cause the tips of the teeth to come into very close
contact with that part of the casing, because by means of that close contact
the pressure of water from the outlet orifice is prevented from operating against
the faces of the other teeth. If this close contact be neglected at the part
described the pressure of the water from the outlet orifice may operate (more
or less, according to its ability to escape,) upon other portions of the toothed
drums, whereby rotation becomes more difficult, and water which bas once
been raised has to be raised again, so that the pump would be less efficient.

page_text: The same description of close contact may be arranged between the tips of
those teeth and the casing near the inlet orifice, but it is of less importance in
that part.
Thirdly. I prolong the inlet beyond the bottom (inside) of the drum
casing, but not so high as to touch the drums. This I do with a view to
prevent the reflux of all the water from the casing when the rotation of the
drums and raising of water is made to cease, because the fluid so retained in
the bottom of the casing may (all or portion thereof) be brought round to the
upper part so soon as rotation (in the sense of lifting) is recommenced; and
thus the water collecting above the point of contact between the teeth and
spaces of the drums acts as a water packing in procuring a vacuum, and
supersedes the necessity of "priming." An effect very similar might be pro-
duced by simply prolonging the inlet tubing itself, screwing it into the casing
till it should nearly touch the drums, or the prolongation of the circles of the
circumference of the tips protecting those tips; but it is unadvisable to allow
inexperienced persons to do this, as they might injure the teeth and spoil the
pump. On either or both sides of the inlet orifice I make recesses in the
bottom of the casing for the accumulation of water to be drawn round to the
upper part (as above described), for which reason I prefer rather to restrict
the length of the said orifice. The same effect can be produced by having two
bends (syphon like) in the inlet tubing (near to the casing), the higher-bend
of which I prefer to be above or higher than the drum casing, and in which
an air plug or other suitable opening can be' put to be opened and shut at
will; but I prefer to do without that aid, and that the tubing should be of a
larger bore between that and the drum casing, and that it be enlarged between
the first and second bends to keep water in the casing.
Fourthly. I diminish the opening at one of the ends of the drum casing by
adding thereto a thin leaf of any suitable substance and of the shape of the
segment of a circle (uearly a complete circle I prefer), so that this prolonga-
tion of the casing side (reaching to the circular plate up to the pitch line at
the ends of the drums) be made to cover the upper portions of the spaces
beyond the pitch of each drum, and I recess into the end cover this prolonga-
tion of the casing side. I would do the same at both of the ends of the casing,
but I cannot encroach upon the orifice whereby I introduce the drums,
therefore on that side I am compelled to make a water-tight addition as a sub-
stitute. The same might be done without recessing either these above-
described thin leaves, or the plates on the drum ends up to the pitch lines,
by reducing the drums the amount of the thickness of these additions. The
leaf (or leaves) above described might extend beyond the pitches of the drums

page_text: to the bottoms or roots of the spaces, or beyond that part, the plates on the
ends thereof being reduced in proportion, so that the leaf (or leaves) might
even cover the entire surface of the drum end (or ends) beyond the spindle.
Fifthly. With a view to the more perfect fitting of the teeth of one drum
into the corresponding spaces of the other drum (of the same pair) I construct
my spaces with a soft and pliant substance acting as a bed or cushion for the tip
of the corresponding tooth of each. I prefer to make this bed of prepared india-
rubber, though other substances might be adopted, and I prefer that there be
a hollow below the bed or cushion from pitch to pitch. It is however more
necessary at the root; and if there be no hollow to allow the cushion to yield
easily it is essential that the soft substance of which it is composed should be
the more thick or deep. The tips of the teeth of a pump used for forcing
should be unbending lest the pressure of water from the outlet orifice should
cause the teeth to yield and so allow an escape of fluid; therefore one drum
having teeth and spaces soft while the other one has them hard would not
answer, though they would work admirably well gearing into each other. To
prevent exterior joins in the materials of which the teeth are composed the
main portion of the drum can be made stiff, and the teeth nearly up to their
entire length the same, so that the soft substance pass or cover very thin
over the tips and deep in the spaces (more especially at the roots), though
vulcanite, which I prefer for my drums, can be made to unite the hard with
the soft.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Hugh Forbes in the Great Seal Patent Office on the
23rd March 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HUGH
FORBES, of 184, Euston Road, N.W., Parish of St. Pancras, County of
Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-fourth day of September, in the year
One thousand eight hundred and sixty-seven, in the thirty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Hugh Forbes, Her special licence that I, the said Hugh Forbes, my
executors, administrators, and assigns, or such others as I, the said Hugh
Forbes, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the

page_text: term therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN THE CON-
STRUCTION OF ROTARY PUMPS," upon the condition (amongst others) that I,
the said Hugh Forbes, my executors or administrators, by an instrument
in writing under my, or their, or one of their hands and seals, should
particularly describe and ascertain the nature of the said Invention, and in
what manner the same was to be performed, and cause the same to be filed
in the Great Seal Patent Office within six calendar months next and imme-
diately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Hugh Forbes, do hereby declare the
nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement thereof, reference being had to the accompanying Sheet of Drawings,
and to the figures and letters marked thereon, that is to say :-
These improvements have reference to an improved construction of rotary
pump for which Letters Patent have been granted to me, and bearing date
9th October 1866, No. 2598, and they consist in one part in diminishing the
adverse action against the toothed drums (by preference made or covered with
vulcanite of any suitable degree of hardness) inside the casing by protecting
to the utmost those teeth from the chief influences inimical to the rotation of
the drums in raising or forcing water or other fluid, that is to say, both from a
portion of the pressure of water or other fluid against their faces in the upper
part of the casing when water is forced to a height above the drum casing, as
also from the drag upon the teeth in the lower part of the casing, caused first
by the vacuum, and then by the weight of the column of water following the
vacuum. This I effect by so constructing the drum casing over the ends of
the drums as to continue the circle of the circumference of the tips of the
teeth both in the upper and lower parts of the casing at the ends of the drums
to or nearly to the points of contact between the said circles. The casing
may be constructed exactly or very nearly alike both in the upper and lower
parts thereof; in the upper part however I prefer that the circles should
continue quite to their points of contact over the drum ends near the end
covers, and that in the lower part of the said drum casing below the point
where the drums gear into each other the circles should not quite meet for
the sake of allowing more space for the deposit of water when the action of
pumping ceases. The before-described arrangement might be carried out in
the upper part of the casing without its necessarily being employed in the
lower part, or in the lower part without its being used in the upper part; but

page_text: this latter modification would result in a diminution in the efficiency of my
improvement. Instead of an inlet and outlet of circular form direct into the
interior of the casing I construct lengthened orifices or slits above and below
the point of contact along the drums and parallel with such contact, and I
prefer that in length the upper orifice should run across the casing as nearly
from flange to flange as may be consistent with strength, while in breadth it
should be about equal to the distance across one space from pitch to pitch
when the pump is intended to be worked with moderate speed. With a high
degree of velocity in the rotation of the drums the breadth of the orifices
(inlet and outlet) require to be increased so as to allow sufficient space for a
free flow through them. The water which rushes into and fills the vacuum
in the lower part of the casing I cause to enter an inverted dome and then to
flow into the casing, or I allow it to flow from a tubing into the bottom of the
said casing by an oblong slit or elongated oval of a similar description to the
upper one.
The water issuing from the upper orifice I collect in an upper
chamber or dome, whence it issues through a tube, and I avoid as much as
possible any sharp, angle or abrupt turn which might tend to check the easy
passage of the water; but although I say an oblong slit or elongated oval I
wish distinctly to state that I prefer that the sides of the orifice be straight
lines from end to end; allowing only such deviation therefrom as shall suffice
to round off the ends and projecting edges; and I so proportion the respective
diameters of the interior of the drum casing and that of the circumference of
the tips of the teeth of the drums, and I so arrange the bearings of the axles
of the latter that the tips in their rotation pass as close to the circular inside
surface of the casing as is possible for them to do without scraping. From the
higher part above the axles to the point of contact of the circumferences of
the tips or the edges of the upper orifice (already described) I cause the tips
of the teeth to come into very close contact with that part of the casing (which
may be lined with metal), because by means of that close contact the pressure
of water from the outlet orifice is prevented from operating against the faces
of the other teeth. In cases in which the tips of the teeth of the drums
(being made of vulcanite or other material) would be likely to become worn
those tips may be covered from pitch line to pitch line with hardened steel or
other suitable metal. In order to supply some water in the casing sufficient
to act as a water packing for the purpose of assisting to create a vacuum when
the drums are rotated for the purpose of raising water one or more small
plugged apertures may be formed in the upper part of the casing, dome, or
piping through which a sufficient quantity of water may be introduced.
not however claim the use of such apertures as part of my present Invention.
I do

page_text: On the accompanying Sheet of Drawings are shown my before-described
improvements. Figure 1 shows a transverse section of the drums, casing,
and domes; Figure 2 shows a longitudinal section of the same; Figure 3
shows a plan of the pump with the upper dome removed; Figure 4 shows a
sectional elevation of a modified arrangement of the pump. Similar letters
of reference indicate similar parts in each of the Figures.
The casing A of the pump is formed so as to surround the two drums B, B',
to such an extent both at top and at bottom as to leave only two narrow
apertures C, C', extending right across the casing, as seen in Figures 2 and 3.
The aperture C at the upper or outlet side of the casing is by preference
formed rather wider than the aperture C' at the bottom or inlet side, and the
edges of such aperture are rounded, as shown, in order to allow of an easy
flow of water from the pump, and such rounding off may if required be
effected to about the extent as shown by the dotted lines in Figure 1. The
apertures C, C, are made to widen out slightly in the transverse direction
towards the outer surface of the casing A, as shown in Figures 1 and 3, and
to narrow in slightly in the longitudinal direction, as shown at Figure 2, and
upon the outer surface of the casing covering such apertures are fixed the
domes D, D³, the passages of which are of the same configuration as the
apertures C, C', at the ends connected to the casing, from which points they
widen out transversely and narrow in longitudinally in such manner as to be
of a circular form at the other end, as shown, where they are provided either
with a screw thread, as indicated, or with flanges for the attachment of the
suction and delivery pipes thereto. The form of the sides of the upper dome
in the longitudinal direction may either be as shown in full lines in Figure 2,
or as indicated by the dotted lines. P is the driving pulley; W, driving
wheels; X, axles of drums passing through stuffing boxes Y in cover Z¹ of
casing. The other parts of the pump are of well-known construction, and
need therefore not be further described.
Figure 4 shews precisely the same construction of casing and domes as in
the previous arrangement, the only difference being that the drums B, B¹, are
arranged one above the other instead of side by side, and that consequently the
inlet aperture C¹ and the outlet aperture C with their respective domes D¹, D,
are placed in a horizontal position. My improved pump may also be placed
in any other required position without impairing its efficacy.
Having thus described the nature of my Invention, and in what manner
the same is to be performed, I wish it to be understood that I do not limit
myself to the precise proportions of the inlet and outlet apertures, nor to the
exact form of the domes as shown on the accompanying Drawing as these may

page_text: be modified without departing from the nature of my Invention; but what I'
claim is,-
First. Forming the outlet aperture of the pump casing as a narrow slit of
equal width at all points and with rounded ends, substantially as and for the
purposes herein-before set forth.
Second. Forming the inlet aperture of the pump casing as a narrow slit of
equal width at all points, substantially as and for the purposes herein-before
set forth.
Third. The employment of the dome D for conducting the water from
the long narrow outlet aperture of the pump casing to the circular discharge
tube.
In witness whereof, I, the said Hugh Forbes, have hereunto set my hand
and seal, this Twentieth day of March, in the year of our Lord One
thousand eight hundred and sixty-eight.
HUGH FORBES. (..)