Improvements in the Pistons of Rotary Pumps, Blowers, Motors, Exhausters, and Meters.
Year: 1885

page_text: Improvements in the Pistons of Rotary Pumps, Blowers, Motors,
Exhausters, and Meters.
I, FRANCIS MARION ROOTS, of Connersville, Fayette County, State of Indiana,
United States of America, at present residing at 52 Chancery Lane, London,
in the County of Middlesex, Engineer, do hereby declare the nature of iny inven-
tion for "IMPROVEMENTS IN THE PISTONS OF ROTARY PUMPS, BLOWERS, MOTORS,
EXHAUSTERS AND METERS," and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:―
The object of the invention is an improved rotary abutment that can be
constructed with less labour and with greater accuracy than those now in use, and
that will occupy less of the space within the shell and thus increase the capacity
of the machine. With these objects in view my invention consists in a method or
system by which the opposite major and minor compound convex curves of the
pistons are described from common centres, whereby the labour of handling the
abutments in finishing them for use is reduced one half, and accuracy in dressing
to the proper shape attained.
In my patent No 4583 dated 27th September 1882, the compound convex curves
or contact surfaces were all struck or described from different centres and the
abutinents when mounted between templates for dressing were made to turn around
these centres as axes as described in my patent N° 4158 dated 27th September
1881. This required a great deal of handling, and as it is difficult to have so many
holes in the templates (eight in each one) and get each hole perfectly concentric
with the points from which the major and minor curves of the pistons are described;
the slightest inaccuracy in centreing the piston in the dressing tool would of course
affect the accuracy of the abutment, and perfect contact of the pistons during their
entire revolution in the pump was not always attained especially in the larger
machines.
By my present invention I have overcome all these difficulties and am able to
produce a perfect machine having much greater capacity by reason of the
diminished ends of the abutinents, and greater strength by reason of the shortened
waist between the pistons. I will here remark that when I speak of abutment
I mean the two pistons one at each end with the waist formed by the two recesses'
which connects the two pistons, and when I speak of pistons I mean the convex
;

page_text: parts of the abutments which keep up contact with each other and the case when
the pistons are revolving. In order to distinctly point out the difference between
my present invention and that shown in my previous patent No 4583, dated
27th September 1882, upon which this invention is an improvement, I have shown
in the drawing at Fig. 2 a diagram illustrating the form of pistons of my said
former patent and the method by which they were produced, and Fig. 1, is a
diagram illustrating my newly invented piston and my new method or system for
obtaining the points from which as centres the compound curves forming the
contact surfaces of the pistons are described.
I will first describe my present invention and then by reference to Fig. 2 point
out how it is distinguished from my former inventions.
Referring now to Fig. 1, the shafts A, A, upon which the abutments are mounted
are placed the proper distance apart depending upon the size of the. machine to be
constructed. Two equal circles P, are described around the shaft centres by a
radius equal to half the distance between said centres; these are the pitch circles.
Within the pitch circles P, and from the same centres I describe two smaller
circles, marked I, by a radius equal to three fourths of the radius of the pitch
circles; these I term the inscribed circles. Both of these circles are divided into
four equal parts by the radial lines X, Y. Within the pitch circle I inscribe a
square by the lines O, which intersect the pitch circle at the same points where the
lines X and Y cut the same. Where the lines O cut the inscribed circle upon each
side of the lines X and Y, at j, are the centres from which the compound curves
of the piston are described. I now divide the inscribed square into four equal
parts by the radial lines Z, and through the centres j, I draw the lines L,
(extending them beyond the pitch circles) for the purpose of obtaining the radius
by which the minor curves of the piston are described. To obtain the radius of
the major curves I place one foot of the dividers in one of the points j, and extend
the other across the line X or Y, to the point a, where the diagonal line Z cuts the
pitch circle; with this radius all the outer or major curves of the pistons are
described. The major curve is continued through the pitch circle P, to the point k,
where it meets the line L. Now with one foot of the dividers in point j, I extend
the other to the point k; this gives me the radius by which all the minor curves are
described from the centres j. These curves meet the major curves at points k, and
extend a short distance within the inscribed circle and lines O. The major curves
extend from points k, a short distance across the lines O, at the outer end of the
pistons. The ends of the pistons instead of being left sharp at the apex or ends, as
is shown by dotted lines, may be turned off as shown by the curved lines p, p, so
as to give more bearing surface against the cylindrical part of the case; or grooves
may be planed in the ends of the pistons as shown, to be fitted with adjustable or
spring packing, as most desirable for the duty required; or the ends may be
packed as shown in Fig. 2. The spaces from the points in the major curve,
marked m, to where the ends of the pistons come in contact with the case, not
being necessary to keep up contact, are cut back as shown at e; these need not
be dressed and are left in the rough.
The recesses of the abutments are described from the points t on the minor axes
of the abutments so as to give the piston ends ample clearance; the recesses have
no part to perform in keeping up contact between the pistons; they therefore
require no dressing but may be left in the rough, as their only office is to clear the
ends of the pistons to permit them to revolve.
The construction of the case, its supports, the driving mechanism and bearings
are the same as described in my former patents above referred to, are well known
to those skilled in the art, and, therefore, need not be illustrated or described
herein.
The circles surrounding the points i, j, Fig. 1, and i2 and 4, Fig. 2, represent the
holes bored in the templates (the templates are the exact size and shape of the
ends of the abutments) to receive the centres which support the abutments in the
dressing tool, while the pistons are being finished.

page_text: It is evident from an examination of the two diagrams Figs. 1 and 2, that the
number of centres is reduced from eight in the latter to four in the former,
consequently the labour of centreing and handling is reduced one half, as when the
abutment, Fig. 1, is mounted upon one of the centres the major curve is first
dressed, and the abutment turned half way around and the minor curve upon the
opposite side dressed. This operation is repeated until all the contact surfaces are
dressed down to the templates.
The abutments may be cast or they may be stamped or rolled from any suitable
metal.
I have drawn a dotted line at Fig. 2, the form of my improved piston to clearly
show the difference in working capacity between the new and old form of piston.
The metal of the piston outside of the dotted lines being removed in the new
pistons leaves of course just so much additional space within the shell or case.
As this increased volume of water, air, or other fluid or gas, is taken in and forced
out at each revolution of the abutments, it will be readily understood that the
capacity of the machine is greatly increased.
It is evident that a good and effective pump may be made by slightly varying
the centres from the points 7, but these centres are it is believed in the exact
position to give the best results.
It is also evident that if this device instead of acting upon and forcing water,
it were used for acting on air or any other gas, it would then be an air pump or
positive rotary blower. It is further evident that if instead of acting upon and
forcing the water or air, it were acted upon by water or gas under pressure, the
abutments would turn in the reverse direction from that when acting as a pump,
and it would then be a rotary motor. And if the proper clockwork and dials were
attached for registering the quantity of fluid or gas passed through the machine,
it could be used as a water or gas meter. It is also evident that it can be used
with equal facility for a gas exhauster.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is
First. The method of forming the compound curves of rotary pistons which
consists in constructing said curves in arcs of circles of different radii, all of said
curves being described from points j, where the lines O cut the inscribed circle;
the radius of the major curves is equal to the distance from one of the points j, to
a point a, on the opposite side of the major axis where the diagonal line Z cuts the
pitch circle; and the radius of the minor curves is the distance from point j, to
point k, where the major curve meets the line L.
Second. Pistons for rotary pumps, blowers, motors, exhausters and meters
constructed substantially as hereinbefore set forth, that is having the convex
abutting surfaces composed of arcs of circles of different radii, the centres from
which said several arcs are described being the points j, which are common centres
to the major, and minor curves on the opposite sides of the major axes of the
pistons,