A Model for Educational Purposes to Illustrate the Functions and Working of Slide Valves.
Year: 1888

page_text: Date of Application, 13th Aug., 1888
Complete Specification Left, 13th May, 1889-Accepted, 22nd June, 1889
A Model for Educational Purposes to Illustrate the Functions and
Working of Slide Valves.
I, WILLIAM JOHN TENNANT of 13 Culmore Road, Peckham, in the County of
Surrey, Mechanical Draughtsman do hereby declare the nature of this invention to
be as follows :-
According to this invention a board or plate or boards or plates of any suitable
material carry a disc or discs and a pointer or pointers or any of them, capable of
receiving rotation about a centre. Other slides boards or plates upon which are
shown different forms and proportions of slide valves, ports and accessories are
attached to or are movable upon the first named board or plate or boards or plates.
The disc or discs, pointer or pointers, and the surfaces of the adjacent board and of
other parts of the apparatus are preferably provided with a facing of "blackboard"
or of such other suitable material that notes, data, and the relative positions of the
cranks and eccentrics may either be permanently indicated upon them or by them or
may be marked thereon in such a manner that they may be easily erased if desired.
Suitable scales or marks are so placed with reference to the various parts named that
the effect of alterations in the proportions and setting of the valves and accessories
may be readily deduced and graphically demonstrated.
Straightedges, cords, guide lines or other suitable means are provided and arranged
in such manner as to furnish points to aid the construction upon a suitable portion of
the model, of theoretical indicator diagrams for the various cases investigated.
Graduations, scales, or simple mechanism to ensure movement in proper corre-
spondence, of the various parts, may be provided.
Dated this Thirteenth day of Anouct 1080
COMPLETE SPECIFICATION.
A Model for Educational Purposes to Illustrate the Functions and
Working of Slide Valves.
I, WILLIAM JOHN TENNANT of 13 Culmore Road Peckham in the County of
Surrey, Mechanical Draughtsman 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 :-
The object of this Invention is to provide an educational device whereby instruction
relating to the functions and operation of the slide valves of heat engines and the like
may be conveniently and graphically imparted.
According to this Invention a board or plate or boards or plates of any suitable
material carry a disc or discs and a pointer or pointers or any of them capable of
receiving rotation about a centre. Other slides boards or plates upon which are
shown different forms and proportions of slide valves ports and accessories are attached
to or are movable upon the first-named board or plate or boards or plates. The disc
or discs pointer or pointers and the surfaces of the adjacent board and of other parts
" or of such
of the apparatus are preferably provided with a facing of "blackboard
other suitable material that notes data and the relative positions of the cranks and

page_text: eccentrics may either be permanently indicated upon them or by them or may be
marked thereon in such a manner that they may be easily erased if desired.
Suitable scales or marks are so placed with reference to the various parts named
that the effect of alterations in the proportions and setting of the valves and accessories
may be readily deduced and graphically demonstrated.
Guide lines are provided and arranged in such a manner as to furnish points to
aid the construction upon a suitable portion of the model, of theoretical indicator
diagrams for the various cases investigated.
Graduations or scales to ensure movement in proper correspondence, of the various
parts, are provided.
In order that the nature and use of this Invention may be more clearly understood
I will now proceed to describe the same with reference to the accompanying drawing
wherein Fig. 1. is a front elevation and Fig. 2. an end view of a piece of apparatus
constructed according to this invention, similar letters of reference being applied to
corresponding parts in both the Figures; the technical terms employed having
reference to valves and valve gearing will be readily understood by mechanicians and
those skilled in such matters :-
A is a blackboard, having a ledge a upon which is placed as shown a removable
board B having on opposite sides suitably drawn diagrams showing in longitudinal
sectional elevation the arrangement of steam and exhaust ports for the ordinary and
for the double-ported slide valves of the usual and well-known types, the example
chosen for illustration in Fig. 1 being that of the ordinary locomotive slide valve.
Upon this piece slides another piece or frame C₁ carrying on its opposite sides
diagrams illustrating a longitudinal section taken through each of the valves upon
which sections the "outside and inside lap" is prominently indicated, as at 1, 1,
respectively; these valve-sections correspond in scale with the port-sections before
referred to, and are placed (as in the example illustrated in Fig. 1.) to slide above
them as a valve would slide over its steam-ports, and by using either valve-section
by sliding it above its corresponding port-section the principle of the slide valve may
be readily made clear. The valve-sections and port-sections are preferably set out
with certain portions of the valves and ports coloured in a distinctive manner, as
with the laps 1, 1, and a portion b of the bridges (Fig. 1.) for example, the object
being that but a single diagram shall be needed to illustrate valves or ports of
different proportions, e.g. the diagram upon the board C₁ illustrates :-
(1.) The elementary form of slide valve, represented by the section-lined portion
alone.
(2.) A valve with outside lap only, obtained by considering the elementary valve
as having the black outside-lap pieces 7 added thereto.
(3.) A valve with outside and inside laps, obtained by considering the black
outside-lap pieces and the black inside-lap pieces as added to the elementary
valve.
Similarly the diagram shown upon the board B illustrates two dimensions of steam
ports, by considering (1) the shaded portion P only, of the said diagram, or (2) by
considering the black pieces 6 of the bridges as added thereto.
The diagram carried upon the back of B (which diagram is not illustrated in
the drawing) should be, preferably, that of a double-ported valve whose proportions
are such that it may be suitably operated with reference to one or more of the
"eccentric arms "
hereinafter referred to as being proportioned for use with the
locomotive slide valve illustrated.
"
Further a circular portion D of the blackboard below the ledge a is arranged so
that it may be rotated upon a centre-pin d and a "crank-arm line 0 may be
permanently marked upon it. Upon this disc D the user of the apparatus marks
with chalk eccentric-arm lines" indicating by their position and magnitude the
"angular advance" and "throw" respectively of the eccentric or eccentrics in the
various cases he may desire to investigate, taking either arbitrarily determined
positions or the positions proper for illustrating the normal manner of working of any
of the valves illustrated upon the diagrams carried by B; in the latter case guiding

page_text: 433
guidance these marks indicating respectively
referred to.
Forward eccentric for the elementary form of slide valve hereinbefore
Backward
Forward
Backward
"
"
وو
advanced to give lead. For the elementary form of slide
valve.
Forward Eccentrics "advanced" for a slide valve having lap (as in Fig. 1.) and
Backward giving lead.
"
Forward "virtual eccentric" } for "link motion,"
for "link motion," "linked up” slightly.
Backward
22
"Virtual eccentric" of link motion in mid-gear."
The disc D is rotated by the user of the apparatus and should be considered as a
crank shaft; its movement may be regulated in proper correspondence with the
movement of any of the valves or vice versa by means of indices or scales to be
described later, which are used in conjunction with the guiding marks z, 1, 2, 3, 4,
28; around the disc D, upon the adjacent board, taking the "crank-arm
line" C as an index finger the user notes with chalk the positions of the end of the
said "crank-arm line" at the points of "cut-off," "release" etc., with the different
valves and different eccentrics, thus getting a circular series of notes giving a graphic
comparison of the results due to their different settings and proportions and being
enabled also to demonstrate, concurrently, in what manner the interaction of individual
parts affects the results.
From the record of crank positions thus obtained, the corresponding positions of
the piston of an engine may be readily deduced assuming, to avoid complication, a
connecting-rod and eccentric-rod of infinite lengths; theoretical indicator-diagrams
may be drawn in chalk to illustrate each case, by transferring the points of "cut-off,”
releaso," etc., from their places on the scale & to the scale E, (Fig. 1.) the spacing
of the vertical lines E being obtained by projection from the scale G which has been
hereinbefore referred to and whose uses will now be further described. In order to
insure proper correspondence between the movements of the "eccentric-arms" carried
upon the disc D and the movement of the valves, or vice versa I provide scales Z Z² Z₁
upon the port-sections (such as that on B)-these scales are numbered similarly to
the scale G incised or punched upon the board adjacent to the rotating disc D (whose
diameter preferably equals the maximum travel of the valve). The scales Z, Z2, Z^,
upon the port-sections are obtained by the projection of a constant number of equi-
distant circumferential divisions (as G G) from various circles whose radii equal the
throw of the various eccentrics; consequently a division between any two numbers
upon these horizontal scales represents the linear advance of valve which should result
from an angular movement of its "eccentric arm through the correspondingly
numbered radial divisions of the scale G around the circular space in which the disc D
rotates; for convenience of reference in cases where the length of the eccentric-arm
is less than the radius of the disc D, a mark or notch is made at the edge of the said
disc at the point where such shorter "eccentric-arms" would intersect its circum-
ference if produced, in order to indicate (as in Fig. 1:) the angular position of such
shorter arms.
"
The arrowheads Z Z3 Z are the points by which the valve is adjusted to its proper
position with reference to the scales Z Z Z respectively, the scale Z being for uso
when working the elementary form of slide valve and also for "link-motion in mid-
gear" (the "travel" in each case being the same in amount but different valves being
used), while the scales Z' and Z are for use when working with a slide valve having
"outside lap" and for "link motion linked up" respectively.
Adjacent to the arrowheads Z Z³ Z are small scales & any of whose graduations
may be used as an index finger in substitution for the said arrowheads when the
maiter under consideration is the effect of working with a valve whose position at
any moment, in relation to the port face is different from the normal position by
reason of the lengthening or shortening of the eccentric-rod or by reason of the
shifting of the valve upon its spindle,

page_text: Should it be desired to illustrate the operation of a double slide valve, i.e. a slide
valve with a cut-off valve sliding upon it as in what is known as the "Meyer" valve
gear, I provide upon a plate C2 (indicated in dotted lines in the drawing) a suitable
representation of the "cut-off valve," which representation slides upon a ledge a¹ on
the board A just above the upper edge of a board which is placed in the position now
occupied by the board B and which carries a diagram of a suitably formed "lower
slide valve "the indices or scales for guidance in the operation of the said lower
slide valve remain as before described with reference to the locomotive slide valve,
and a suitable scale for guidance in the movement of the "upper slide valve" is
provided upon the board A at y and used with reference to a suitable "eccentric-arm"
which may be marked upon the disc D.
It must be understood that 1 do not confine myself in the carrying out of this
invention to arrangements of parts exactly similar to those described with reference
to the Drawings accompanying this Specification, but that I may vary the details of
my apparatus without departing from the nature of this Invention.
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 :-
Claim. The arrangement of parts in combination with suitable guiding scales,
indices and diagrams and the like, constituting an apparatus for educational purposes
to illustrate the functions and working of slide valves, substantially as hereinbefore
described and illustrated by the accompanying drawings.
Witnessed by,
EDMUND P. TENNANT,
13, Culmore Road, Peckham, S.E., London.
WM. JNO. TENNANT.