NEW OR IMPROVED INSTRUMENT FOR DETERMINING THE ANGLES OF STEAM ENGINE ECCENTRICS IN RELATION TO THE CRANKS, ALSO FOR ASSISTING IN SETTING OUT THE VALVES, AND FOR ILLUSTRATING THE RESPECTIVE AND RELATIVE POSITIONS OF THE ECCENTRICS, VALVES, CRANKS, AND PISTONS AT THE INSTANT OF THE OCCURRENCE OF THE SEVERAL EVENTS WHICH OCCUR IN THE DISTRIBUTION OF THE STEAM
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by John Newrick Coxon at the Office of
the Commissioners of Patents on the 19th June 1876.
«
JOHN NEWRICK COXON, of Hackney, in the County of Middlesex, Engineer.
A. NEW OR IMPROVED INSTRUMENT FOR DETERMINING THE ANGLES OF STEAM
ENGINE ECCENTRICS IN RELATION TO THE CRANKS, ALSO FOR ASSISTING IN SETTING
OUT THE VALVES, AND FOR ILLUSTRATING THE RESPECTIVE AND RELATIVE POSITIONS
OF THE ECCENTRICS, VALVES, CRANKS, AND PISTONS AT THE INSTANT OF THE
OCCURRENCE OF THE SEVERAL EVENTS WHICH OCCUR IN THE DISTRIBUTION OF THE
STEAM."
The Invention relates to a new or improved instrument for determining the
angles of steam engine eccentrics in relation to the cranks, also for assisting in setting
out the valves, and for illustrating the respective and relative positions of the
eccentrics, valves, cranks, and pistons at the instant of the occurrance of the
several events which occur in the distribution of the steam."
According to my Invention I take a flat piece of wood or other suitable
material A of convenient size and thickness, say half an inch thick, and of the
size and shape illustrated in the Drawings hereunto annexed, though I am not
confined to any particular dimensions. On the opposite sides of A are sliding
pieces B, C, D, E. These may all be on one side, but I prefer them arranged as
shewn. Between these opposite sliding picces is attached to the wood a thin
metal plate F, on which are inscribed various scales or divisional lines. The
circular band G represents the line of travel of some point in the crank. It is
divided into degrees, the upper half (representing the forward stroke of the piston)
being numbered 0 to 180 from right to left, and the under half (representing the
return stroke) 0 to 180 from left to right. The diameter of the inner circle of this
band should be made up of such a number of aliquot parts of an inch that each
division will also bear a decimal relation to the diameter, and so represent a per-
centage of the stroke of the piston. In the Drawing annexed the diameter of this
circle is three and an eighth inches, and is divided into fifty parts, each part thus
being a sixteenth of an inch and representing two per cent. of the stroke of the
piston. The drawing, however, is drawn to scale half full size, so that each sixteenth
represents an eighth of an inch, the percentage to the stroke remaining the same.
The horizontal diameter of the circle is thus divided, and through the points of
division vertical lines are drawn to the edges of the metal plate F missing the
Price 6d1

page_text: circular band. Circles concentric with the band G are also drawn through these
points, these circles dividing also the vertical diameter into the same divisions as
the horizontal, and on both diameters the divisions are numbered, the horizontal
scale or that marked h, d, being figured in reference to the lap and lead, and the
vertical or that marked v, d, in reference to the travel of the valve, and as the
travel of the valve is twice the throw of the eccentric the divisions are marked so
as to read off double the real distance. A projection of A. to the right in con-
tinuation of the horizontal diameter carries a plate H having marked on it a scale
of the same length and of the same divisions as the horizontal diameter h, d, of
the circle G. The purpose of this scale is to ascertain at what percentage of the
stroke of the piston any of the several events occur. The plate H is so attached
that its position in reference to its distance from the circle G may be adjusted for
the purpose herein-after described. Centred at the centre of the circular band G
are moveable pointers H, P, C, and L, P, C, joined to one another at right angles,
that one marked L, P, C, having also attached to it a quadrant marked with the
degrees from 90 to 180. These pointers represent respectively the cranks of the
high and low pressure cylinders when at right angles to one another, whilst by
means of the quadrant the position of the low-pressure crank at any angle between
90° and 180° is at once determined. Other pointers for the eccentrics are also
provided, as shewn, to each of which is a small milled nut that they may be
separately tightened up or "set" in the positions required. In Fig. 1 these
pointers are shewn in position, whilst they are omitted in Fig. 2 to render the
plan more clear. In Fig. 3 the pointers are shewn detached with an additional
one as used for the expansion valve and eccentric, when one is to be employed.
8
The action is as follows:-Supposing it be required to construct valves of the
following dimensions, vizt., high pressure valve, travel 32 inches, lap on steam
side one inch, lead 1/8 inch; low pressure valve, travel 4 inches, lap on steam side
1 inch, lead 1/8 inch. No lap or clearance on exhaust side of either valve.
Proceed as follows:-As only one slide on each side of the instrument will be
brought into use (B on the one side and on the other E being most convenient) the
other slides C and D should be fastened down by the milled screws c, d. The
slides B and E should now have attached to them strips of paper so as just to
cover them (by drawing pins or otherwise); as should also the two outer edges of
the instrument A¹, A. On these four spaces the valves and ports are to be set out.
We will first deal with the high-pressure valve; first, set the ends of the slide E
flush with the sides of the instrument, and then extend the line v, d, through as
the centre line of the valve.. On the slip A¹ set out the steam and exhaust ports
of the cylinder with v, d, as the centre line. Now on the slide E set out the
exhaust cavity of the valve without lap or clearance, then set the high-pressure
eccentric pointer (marked H, P, E,) to 31, inches (the required travel) on the
Then
travel of valve line v, d, at v, and grip it in position slightly with the nut.
from 1/8 inches (the sum of the lap and lead) on the lap and lead line h, d, at h,
follow up the vertical line and move the H, P, E, pointer to it and (after slacking
the nut) retain it there, and set the high-pressure crank pointer (marked H, P, C,)
at on the line h, d, and grip them firmly together with the nut. This gives
you the angle of the eccentric in relation to the crank. Now follow down the
same vertical line to the valve and set the centre line of the valve to it by
moving the slide (as shewn in the Drawing by dotted lines), then from the
admission of the edge of the steam port (on the right hand) set off the required
lead / inch, and from it set off the admission edge of the valve. Now bring the
H, P, C, pointer round to h on the line h, d, and following down the vertical line
indicated by the H, P, E, pointer proceed to set off the other edge of the valve in
the manner already described. The addition of the lines shewing the thickness
of the metal completes the section of the valve. Construct the low-pressure valve
on the opposite side of the instrument in a similar manner from the given
dimensions. When an expansion valve is to be used another pointer (marked E, E,
or otherwise to distinguish it from the others) must be employed, and if the valve

page_text: be of the description to work on a fixed plate it is constructed and the angle of
its eccentric determined in a manner similar to that already described in reference
to the high-pressure valve. A valve of this description is illustrated in Fig. 1,
the slides C and D being used therefor, D as the stationary piece for the ports, and
C as the slide for the valve. In Fig. 2 is illustrated an expansion valve working
on the back of the high-pressure valve. In this case only two of the sliding
pieces (D and E) are brought into requisition. After setting out the admission
edges of the high pressure valve, as in the case given, set out the admission ports
and thickness of metal. Then from the given data set the eccentric and mark
off the admission edges of the expansion valve in a similar manner to that already
described. In the above the high pressure is supposed to be the leading engine
for convenience of description. The pointer marked H, P, C, is to be taken, how-
ever, as representing the crank of the leading engine, whichever that may be.
For illustrating the respective and relative position of the several parts at the
instant of the occurrence of the several events which occur in the distribution of
the steam, that part of the instrument to which the data refer should first be set
in accordance therewith, and the remainder of the instrument then set to it. For
example, if it be desired to ascertain the position of any one of the valves, eccen-
trics, or cranks, or the relative positions of any two or more of them at a given
point of the forward stroke of the leading piston of a compound engine proceed as
follows: Having first set the pointers as previously described, adjust the position
of the plate H (Fig. 1) so that the distance between the outer extremity of its
scale and the nearest point of the horizontal diameter of the inner circle G will
bear the same proportion to the diameter of the circle G as the length of the
connecting rod of the engine in question bears to the stroke of the crank. Then
set a pair of trammel legs with one leg on the outer line of the scale and the other
on the nearest point of the horizontal diameter of the circle G. This will represent
the connecting rod. Now place one leg as far along the scale as will represent
the percentage of the stroke at which the observation is to be made, and placo
the other leg on the circumference of circle G above the horizontal diameter. To
this point set the H, P, C, pointer without alterating the positions of the eccentric
pointers relative thereto. Now set the centre lines of the several valves to the
vertical lines indicated by their respective eccentrics, and the respective and relativo
positions of the whole of the parts, namely, valves, eccentrics, cranks, and pistons
will be clearly defined. If the data to work from relate to a valve, set it in
accordance therewith, then set its eccentric thereto, then to the other eccentrics
set their valves respectively, and the trammel will shew at what percentage of
the stroke the event has taken place. Proceed similarly if the data relates to one
of the eccentrics. It will be observed that the scale on plate H is figured right to
left on the top and left to right at the bottom. The former is for the forward stroke,
the latter for the return stroke. When through the intervention of intermediate
lovers the valve of the engine has an opposite motion to the eccentric the valve
and eccentric on the instrument must be placed on the opposite sides of the vertical
diameter v, d, of circle G.