Improvements relating to the Measurement of Steam Pressure in Engine Cylinders, and to Apparatus therefor.
Year: 1893

page_text: Date of Application, 18th July, 1593-Accepted, 23th Apr.. 1891
COME DEIM DI DUTTIVATION
Improvements relating to the Measurement of Steam Pressure in
Engine Cylinders, and to Apparatus therefor.
I, WILLIAM THOMPSON HOWARD of 2015 Maryland Avenue in the City of
Baltimore and State of Maryland, United States of America, Mechanical
Engineer, 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 is based on the discovery which 1 have made, that the mean
pressure of steam acting on the piston of a steam engine for a certain period of
time may be accurately ascertained by computing or measuring the quantity or
bulk of mercury forced or discharged through a small aperture by steam in com-
munication with that acting on the piston, the capacity of discharge of the said
aperture under various constant pressures for the same period of time, being known.
The time during which the steam is allowed to act on the body of mercury is not
of vital importance. It may be a fraction of a minute or one or more minutes;
but as one minute is the unit of time used in computing horse power, that period is
best suited for the purpose. One important advantage in extending the time to at
least one minute, is that a fair average mean pressure may be obtained; as, during
that period, in nearly all cases, all the various operations of the machinery driven by
the engine will have been performed.
To apply this principle of ascertaining the mean pressure of steam acting on the
piston of a non-condensing steam engine, I employ, primarily, a mercury-holding
vessel having a small discharge aperture in communication with, or leading to, a
measuring vessel, which for the sake of convenience consists of a glass tube; and
use in connection therewith, suitable valve mechanism whereby the steam from the
two ends of the cylinder is alternately brought in communication with the said
mercury holding vessel, so as to act upon the body of mercury in the said vessel,
and thereby force or discharge a portion of it to a mercury reservoir where it
displaces a lighter liquid such as water or water and glycerine suitably colored
resting on the mercury and forces it up the measuring glass tube, by which means
the average pressure, acting on both sides of the piston during a double stroke
or series of double strokes is ascertained. I further employ in connection with the
first body of mercury a second body, a reservoir and a measuring-glass tube, to
ascertain the retarding or back pressure on the piston; the valve mechanism before
alluded to being so arranged that the forward pressure in all cases acts on one
body of mercury, while the retarding or back pressure acts on the other.
By this arrangement, I obtain two columns of mercury one representing the average
forward, and the other the average back, pressure; and by deducting the figures
indicating the latter from those representing the former, the mean effective pressure
on the piston during the time to which the mercury is subjected to the action of
the steam, is accurately ascertained.
But to make the columns of mercury with their upper stratum of light liquid
available for the purpose in view, it is necessary that scales should be prepared
whereby the quantity or bulk of mercury discharged under various pressures may
be readily computed; and to effect this, the bodies of mercury in the preparation
of the instrument for use are subjected to different constant pressures for the unit
of time fixed upon, one minute, and the heights attained by the columns of light
liquid under the various constant pressures marked.
In practice, the operation of preparing the scales is as follows: Each body of
mercury is subjected to a pressure of, say, 5 pounds, steam air or water being used,

page_text: or the space of one minute, and the height to which the colored
narked. The pressure is then removed and the mercury allowed to descend to its
original height, which brings the surface of the colored liquid to its original level
or the 0 point, and a pressure of say 10 pounds applied for the same period of time,
after which the column is again allowed to descend to the 0 point.
This operation is continued with a successive advance in pressure at each trial,
of say 10 pounds, until the maximum pressure is reached. The 10 pound spaces
are then divided into pound spaces or less, thus completing the scale.
5
It is found in practice that divisions of ten pounds, ascertained by actual
pressures, will give sufficient accuracy; but it is evident that every pound between 1
the 0 mark and the maximum pressure may be registered by actual trial or
subjecting the mercury to each different pressure for the space of one minute.
In preparing the scale, a vertical scale line is drawn on a sheet of paper, and the
heights of the pressure columns, ascertained as before described, and which represent
From these points or marks 1
pressures from, say, 0 to 80 pounds marked thereon.
are drawn horizontal lines, the first or 0 line being the base.
The base line which may be of any convenient length is then pointed off into
eight equal spaces and perpendicular lines are erected from the division points,
which are numbered to correspond with those on the scale line, or from () to 80.
A curved line is then drawn through the points where the perpendicular and
horizontal lines intersect which curved line represents in general outline a parabolic
curve.
The sub-divisions, to represent pounds, are then easily obtained by dividing the
10 pound spaces on the base line into 10 equal parts, and erecting perpendiculars
from the points to intersect the parabolic curve, and extending horizontal lines
from the intersecting points to the scale line.
In applying the invention to ascertain the horse power of condensing engines in
which a portion of the pressure of the atmosphere is added to that of the steam
acting on the engine piston, the colored liquid in the back pressure column will
descend instead of ascending, and, to compute the proportion of the atmospheric
pressure used, a second set of indicating numerals is marked on the back pressure
scale, beginning at the 0 point, the figures advancing in a downward direction.
The pressure of the steam acting on the piston not being constant, it is evident
that in the formation of a column the movement of the colored liquid in the glass
tubes will vary, its speed of rise being faster at the beginning than at the termination
of the stroke, but the bulk of mercury discharged with a varying pressure, the
mean of which is, say, 50 pounds, will be the same as that discharged in the sam
time when, in forming the scale, a constant pressure of 50 pounds was used.
For example, supposing the initial pressure on the piston be 100 pounds, and th
steam cut off at one quarter of the stroke the terminal pressure will be abou
14 pounds, and the mean pressure about 54 pounds.
At the beginning of the stroke, the discharge of mercury will be at the sam
rate as that which in the formation of the scale, carried the column to the 100 pour
mark. But as the piston advances, the rapidity of discharge will decrease until,
the termination of the stroke, it will be at the rate of that when the 14 pound ma
was ascertained. Hence the rapidity of discharge will average the 54 pound ra
and, at the termination of the minute, the colored column will have reached t
point indicated by that number on the scale.
While this result is being reached in the forward pressure tube, the average ba
pressure is recorded on the scale applied to the other; and it is evident that
value of the two records obtained by deducting the back pressure from the forw
one is the mean effective pressure acting on the piston for the space of one min
from which, the area and speed of piston being known, the horse power of the eng
may be computed.
As the exact speed of the piston is a necessary element to be taken into consid
tion in computing the horse power of an engine, a secondary part of the inven
consists in combining with the pressure-ascertaining devices before descri

page_text: improved means whereby each complete or double stroke of the piston is
so that at the termination of the minute of trial, the aggregate number may be
known, as will hereinafter appear.
In the further description of the invention which follows reference is made to the
accompanying drawings forming a part hereof and in which,-
Figure 1 is a perspective view of a steam engine provided with the improved
power measuring instrument, illustrating, principally, the means employed for
communicating motion from the crosshead of the engine to the instrument.
Fig. 2 is a front view of the instrument alone, certain parts thereof being
removed to show the interior.
Fig. 3 is an exterior side view of the invention.
Fig. 4 is a plan of Fig. 2.
Figs. 5 to 22 inclusive, are details of the instrument on an enlarged scale.
Referring to the drawings, A is the frame of the instrument, having at the
bottom two hollow bosses a and b. The boss a is in communication with one
end of the engine cylinder, and the boss b with the other end, the means of
communication being the pipes c and d, and the coupling cocks e and f, shown in
Fig. 1.
Referring more particularly to Figs. 2, 3 and 4, B and C are cylindrical steam
holding vessels supported by the frame A, and situated over the hollow bosses a and b.
Beneath the steam holding vessels B and C, is a chamber D for the cylindrical
reversing valve E, hereinafter described. The cylindrical chamber D is formed of
a fixed sleeve D2 and has ports g, h, i, j, k, and m in communication with the
exterior annular openings, n, o, p, q, r and s, see Figs. 2 and 19, the latter being an
enlarged cross section of the sleeve D².
The reversing valve E consists of a cylindrical piston having recesses t and u
formed by reducing the diameter of the piston at certain parts; and these recesses
are arranged so that they will serve, in the longitudinal movement of the valve,
effected, as hereinafter described, to connect certain of the ports g, h, i, j, k, and m.
By reference to Fig. 2 it will be seen that the annular openings o and rare
respectively in communication with the interiors of the steam holding vessels B and C
through the medium of the apertures a¹ and 6', and that the openings n and s are
connected by the channel c'; and, further, that the openings p and q are united by
the channel d.
The channels c¹ and d¹ have branch channels e¹ and f¹ leading to the outer face g¹
of the valve chamber D, which face is flat.
G is a steam chest bolted to the face g', and having a cylindrical valve chamber h¹
with its ports i, j, k', and ', leading into annular spaces m', n', o¹, and p¹. The
space m opens into the branch channel f¹, and the space o' into the branch
channel e. See Figs. 5 and 6. Within the valve chamber is a piston valve H
having two parts thereof, q' and ¹, reduced in diameter so that certain of the
ports i, j, k, and may be made to communicate as and for a purpose hereinafter
described.
Opposite the annular spaces n' and p', and in communication with them, are
(Fig. 6) hollow bosses s¹ and t¹, and these are respectively connected with the
hollow bosses a and b by pipes I and J.
KK are cylindrical mercury-holding pots which stand on raised seats u¹ in the
steam holding vessels B and C. Fig. 2.
M M represent annular plates which constitute the lids of the steam holding
vessels B and C. These plates are each held tightly in contact with the edge of its
steam holding vessel by a threaded ring N having an inner peripheral lip ' which
rests in a rebate in the lid.
OO (Figs. 16, 17 and 18) are inner mercury reservoirs, one for each steam
holding vessel, fitting loosely in central apertures in the lids M, and extending
downward into the pots K. These reservoirs have exterior flanges a² and
bottoms, and into their upper ends, which extend above the lids M, are screwed
the plugs c².

page_text: Fig. 16 is a vertical section of one of these mercury reservoirs, and Figs. 17 and 18
are, respectively, an underside, and a top view of the same.
The mercury reservoirs O are secured against upward movement by flanges dª
which rest in circular depressions in the under side of the lids.
PP (Figs. 7, 8 and 9) are circular plate valves each having a central cylindrical
projection which passes loosely through a hole in the bottom 62 of its reservoir O.
The said plate valves have each two horizontal channels f extending from their
circumferences to near the central cylindrical projections e2, and also ports 92 and h³,
leading from said channels f' to the upper faces of said valves which are in contact
with the bottoms of the reservoirs O. The adjoining faces of the plate valves and
reservoirs are true and form tight joints.
Figs. 7, 8 and 9 are respectively, a central cross section, an exterior edge, and a
top view of one of the plate valves.
The plate valves P P are threaded, and screwed into the vertical flanges of the
cylindrical blocks Q, (Figs. 10, 11 and 12); and between the blocks and the plate
valves are clamped thin spring-tempered steel diaphragms R.
Fig. 2.
Figs. 10, 11 and 12 are respectively an exterior side, a top and an underside view
of one of the blocks Q.
The horizontal channels are to connect the ports g² and h², and the reason
that they are extended to the threaded circumference is for convenience in drilling
from the outside. The portion of the channels f2 exterior of the ports 92 has
no useful office.
In the hollow projection e² of each of the plate valves P is screwed a grooved
spindle S carrying a needle T with its point entering a small aperture in the
centre of the diaphragm R. By means of the threaded spindles and their needles
the effective size of the apertures may be regulated.
The object in grooving the spindles S, as shown in Fig. 22 which is a top view
of one of them, is to form passages between the spaces above the diaphragms R
and the interiors of the reservoirs O. The adjustment of the needle points in the
apertures of the said diaphragms is effected by means of a screw driver, the flat
point of which is inserted in a cut in the upper end of the spindles S.
In the steam holding vessel B, the lower face of the plate valve P and the upper
face of the cylindrical block Q, are dished in the centre (Fig. 2) in order that a
large portion of its diaphragm R may be exposed, and to give the necessary room
for the diaphragm to bulge upward without striking the said plate valve.
This diaphragm is allowed to bulge so that as the pressure of mercury under it
increases, it will pass to a higher and larger part of the needle and thus decrease
the effective size of the aperture 2. Where the range of pressures is great, as say
from 2 pounds to 80, a hole of sufficient size to allow the mercury to pass at the
lowest pressure would or might be too large to limit the discharge so that the
colored liquid column would not be contained in the most convenient length of
measuring glass tube. In other words, an aperture which would allow the colored
column to ascend to near the top of the glass measuring tube with 80 pounds
pressure exerted for the space of one minute would be too small to allow any
mercury to pass through at the extreme low pressure of pounds. With the
bulging diaphragm as described the effective size of the aperture alters with the
pressure on the mercury tending to force it through the aperture.
In the steam holding vessel C, the diaphragm R is not intended to bulge; and
the dishing of the faces of the plate valve and the cylindrical block, is therefore
dispensed with, the said diaphragm being clamped throughout its entire surface or
nearly so.
Each of the cylindrical blocks Q has a central hole k², which extends from its
upper surface to its bottom, and serves to place the under surface of the diaphragm
in communication with the interior of the cylindrical pot K, which surrounds it.
The blocks Q are prevented from turning circumferentially by means of two
ears Q2 the upper ends of which rest between lugs Q on the under side of the
covering lids M of the steam holding vessels B and C.

page_text: U U are spiral springs situated in annular grooves m² in the blocks Q; and, as
they bear against or rest on the bottoms of the pots K, they keep the plate
valves P tightly against the faces of the reservoirs O, and also retain the flanges d
closely in contact with the recessed portions of the lids M, so as to form steam
tight joints.
The plugs are bored out (Fig. 16) to form packing boxes into which
measuring glass tubes V are inserted. The packing is held in place by the glands n².
AA (Fig. 2) are tubular protection-casings for the glass tubes V. They are
fitted tightly around the plugs c² and are closed at their upper ends by ornamental
caps B, which are bored out and provided with soft washers serving to make dust
proof joints. The protection casings are cut away at one side to expose the
ineasuring tubes, as shown in Figs. 2 and 3. The bottoms of the ornamental caps
are perforated, and the holes lead into the tubular protection casings for a purpose
hereinafter described.
By referring to Figs. 16 and 17 it will be seen that in the bottoms and the
exterior flanges of the reservoirs O, are ports o³ and p². These ports, when the said
mercury reservoirs are turned into one position register with the ports g² and h² in
the plate valves and thereby place the interiors of the reservoir and pot K of each
steam holding vessel in full communication.
The registration of the ports, as described, is effected by means of handles C',
secured to the portions of the reservoirs which project above the steam holding
vessels B and C. See Figs. 2 and 4.
Stops and on the lids M limit the circumferential movement of the
handles and the reservoirs to which they are fastened. When the handles are
brought together and come in contact with the stops 2, the ports o2 and p³
register with the ports 92 and 2, and the plate valves then offer no obstruction
to the passage of the contents of the reservoirs to the pots, or vice versa. But when
the said ports are thrown out of register, by the handles being turned towards the
stops 92, all avenues of communication between the reservoirs and ports are cut off,
except the apertures in the diaphragms R and the holes 2 in the cylindrical
blocks Q.
The holes 2 are merely supply channels to bring the underside of the perforated
diaphragms in communication with the interior of the pots, and may be of any
suitable size.
D' (Figs. 2 and 3) is a curved rocker adapted to vibrate on a stud s², projecting
backward from the frame A. The ends of this rocker have screws t2 adapted as
adjustable tappets to engage with the ends of the reversing valve E. The hub a³
of this rocker has a tail piece in which are situated and adapted to turn two
rollers c³ and d³. The lower roller is grooved at the edge, and the upper one c³
is preferably plain or only slightly grooved.
The lower roller has a fixed position with reference to the tail piece 6³ of the
rocker D1, its spindle e being in a circular hole in which it turns freely, but the
spindle of the upper and plain roller is confined in a slot g³ in order that
the roller may have some vertical adjustment. Springs h³ attached to the tail
piece, bear on the two ends of the spindle f³ of the plain vertically adjustable
roller c, which ends are slightly grooved for their reception, the springs tending to
force the upper roller towards the lower one.
E' (Figs. 1, 2, 3 and 4) is a rod which leads from some part of the engine having
a movement in common with that of the piston. By reference to Fig. 1, it will be
seen that the crosshead of the engine has an arm F', temporarily or permanently
bolted to it, and this arm, which is provided with a pin 3, is bent so as to bring the
pin directly in alignment with the space between the rollers and d³. The
rod E has a hook 3 whereby it is connected to the pin 3, of the arm F', and it
therefore moves in unison with the crosshead.
The rod E' is forced tightly into the groove of the lower roller by the resilient
action of the springs h³.
Gis a spring-supported bar hinged to the frame A at k³, and having two lugs m³

page_text: between which the end of the tail piece rests. The said lugs have screws ³ which
are so adjusted as to hold the tail piece firmly but not tightly in a vertical position
and the reversing valve E in a central one, when the bar G is at its highest point.
But the extreme end of the tail piece is somewhat reduced in width, and when the
bar is lowered or depressed so as to bring the ends of the screws n³ opposite the
narrow part, it, the tail piece, is susceptible of a slight swinging motion, but this
motion is sufficient to effect a complete forward and backward stroke of the
reversing valve E.
H' is a knob whereby the bar G¹ may be depressed by hand to allow of the
movement of the rocker and effect the reciprocating stroke of the reversing valve.
When the bar G' is depressed and the engine piston begins its stroke, the rod E
moves the rocker until the tail piece 63 comes in contact with one of the screws n³,
when all further motion in that direction is prevented, and the rod E' merely
passes on. The movement effected by the friction between the rod E¹ and the
rollers, is, however, sufficient to move the reversing valve E and admit steam from
the operative side of the piston to the interior of the steam holding vessel B, while
the steam from the back of the piston, or that which retards its stroke, is brought
in communication with the interior of the steam holding vessel C.
At the beginning of the return stroke of the engine piston, the rod E' reverses
the position of the reversing valve E, and the forward steam from the other side of
the engine piston is conducted to the vessel B and the back pressure steam to the
vessel C. The motion of the reversing valve E is accomplished when the engine
piston has moved on its stroke the distance of about one thirty-second part of an
inch, and, during the remainder of the stroke of the engine piston, the rod E' is
inoperative except that it serves to keep the said reversing valve in the position
in which it has been forced, until the beginning of the reverse stroke of the engine
piston.
The steam valve H (Fig. 5) has an operating stem I¹ with a knob o³ at the top,
and the length of the stem is such that the knob is situated immediately under the
handles C when they are brought together. Figs. 3 and 4. By this arrangement,
the knob o³ is not easily reached or touched except when the handles C¹ are
separated; and this interference of the parts is availed of to prevent the steam
valve being opened except when such opening can do no harm, as will hereinafter
appear.
J (Fig. 5) is a guiding stem leading from the bottom of the steam valve H down
through a lug p³ extending from the face of the frame A.
K' is a spiral spring coiled about the stem J¹ and confined end wise between the
lug p and a cupped collar q³, to retain the steam valve yieldingly in its highest
position, or that in which steam is cut off from the channels c¹ and d¹ which
constitutes the means of access to the ports of the reversing valve E.
The downward movement of the steam valve H is limited by a collar ³ which
comes in contact with the top of the steam chest. In order that in the depression
of the steam valve H the bar G' may also be depressed, and the rocker D' thereby
released so that the reversing valve E shall become operative, the said bar is
provided with a lateral projections with which the edge of the cupped collar 23 4
comes in contact in its downward motion. Figs. 3 and 4.
L' (Figs. 2 and 3) is a circumferentially toothed dial secured to a flanged
sleeve t adapted to turn loosely upon a fixed stud u³ projecting rearward from the
frame A.
M¹ and N¹ are pallet arms extending from the hub piece at which is passed over 5
and attached rigidly to a reduced portion at the end of the hub of the rocker D¹.
These pallet arms have spring steel pallets M2 and N2 of the shape usually
employed in escapements of clock movements, which engage with the teeth of the
dial L. The pallets and the teeth of the dial L' form the escapement which in
the oscillation of the rocker D₁ allows the dial to rotate one tooth for each double 5
stroke of the engine piston.
An ordinary clock spring O¹ (Fig. 15) is confined in a circular box d' rigidly

page_text: attached to the stationary stud u³, with its ends connected to pins on the stud and
the toothed dial.
The spring O' is wound by turning the dial L' in the direction opposite to that
in which it is intended to move in the operation of the instrument, the pallets being
formed of springs, as before stated, allowing of this winding operation.
P' is a pointer fastened to the top of the stationary spring box d with its end
bent over the toothed dial L'. Figs. 2, 3 and 4.
The tubular protection casings A¹ (Fig. 2) are each provided with a scale plate e,
which is marked to indicate the pressure figures obtained in accordance with the
theory and operation hereinbefore stated, and the teeth of the dial L' are numbered
as shown. Figs. 20 and 21 show the scale plates marked as described.
The scale plates et are forced forward and held against curved finishing pieces f*
by means of springs, one of which is shown in Fig. 2; and a slight vertical
adjustment of each scale plate is obtained by means of a rack and a pinion *.
To prepare the instrument for use after the scale plates have been marked, the
handles Care both moved in, or towards each other, until they strike the inner
stops. Fig. 4. By this movement of the handles, the ports o² and 2 are opened
or brought to register with the ports 92 and 12. The caps B' are then removed.
and mercury is poured into the glass tubes until it rises in the pots K and the inner
reservoirs O, to the dotted line =.
In the charging of the instrument, the mercury will pass around the blocks Q
and the spiral springs U, flow up through the holes k³ and come in contact with the
under side of the diaphragms R.
A lighter liquid, such as water or water and glycerine, suitably colored, is now
poured down the glass tubes onto the mercury in the reservoirs O until it rises to
the zero point on the scale plates. The caps B₁ are then replaced.
When a pot K with its reservoir and measuring glass tube is thus charged, any
depression of mercury in the pot causes a rise in the glass tube, and as the area of
the surface of mercury in the pot exterior of the reservoir is many times greater-
than the transverse area of the liquid column in the glass tube, a very slight
fall of mercury will cause a very considerable rise of the colored liquid in the
glass tube.
The rod E which for the sake of convenience and to admit of its adaptation to
engines of various sizes is in sections screwed together, is now connected to the
arm F rigidly attached to the engine crosshead, and the toothed dial turned around
until the 0 point is directly under the end of the pointer P. The instrument is
now ready for use.
Supposing the engine to be in operation, the rod E' is at first inoperative, the
tail piece being firmly held by the screws n³ in the lugs m³ of the bar G¹, and
the rod merely moves forward and backward without communicating any movement
to the rocker D¹.
At this time the ports and of the steam chest are closed by the valve H,
(see Fig. 5,) and no steam passing through the pipes c and d, hollow bosses a and b
and pipes I and J to the steam chest G, can therefore pass through said ports.
The operator now takes his watch in hand, and, at the beginning of a minute,
presses down the knob o³ which opens the ports and , and places the forward
end of the steam cylinder in communication with the exterior of the reversing
valve E by the way of the port j', annular space around the reduced part q² of the
piston valve H, the port, the space m', branch channel f¹ and channel d. The
other or back end of the steam engine cylinder is placed in communication with
the exterior of the said reversing valve E through the port 1, the annular space
around the reduced portion of the piston valve H, the port A, the space o¹, the
branch channel e¹ and the channel c'. The depression of the valve H also liberates
the tail piece of the rocker D', as before described. Now supposing the engine
piston to be at the beginning of the forward stroke, and about to move in the
direction indicated by the arrow in Fig. 1, the rod E' which moves in unison with

page_text: the engine piston, during the first one thirty second part of an inch of its stroke,
pushes over the tail piece 63 until it strikes one of the screws n³ in a lug m³ of the
spring supported bar G. In this movement, the reversing valve E is thrown in the
direction indicated by the arrow in Fig. 2, which opens the port and places
the interior of the steam holding vessel B in communication with the channel c', to
which forward or ahead steam from the back end of the steam cylinder, and behind
the piston, has been admitted, as before described, by the way of the annular
opening n, the recess in the reversing valve E, the port h, the annular opening o,
and the aperture a¹.
At the same time, the port. j is opened, and the interior of the steam holding
vessel C is brought in communication with the channel d' which receives any back
pressure or retarding steam that may be acting against the piston, as before
described, by the way of the annular opening 9, the recess u in the reversing
valve E, the port k, the annular opening and the aperture b³.
From the foregoing description it will be seen that the mercury in the steam
holding vessel B is now subjected to the forward or ahead steam, and the
mercury in the steam holding vessel C to the back pressure or retarding steam,
and this condition of things continues until the piston has completed its single
stroke.
The mercury in the pots owing to the pressure of steam on its surface, or that
portion of its surface exterior of the reservoirs, is slowly depressed and the body of
mercury in the reservoirs raised, the means of communication between the two
bodies being as before stated the small aperture 2. By the increase in volume of
mercury in the reservoirs, the light liquid (water and glycerine) standing thereon
is forced up the glass tubes.
At the beginning of the return stroke, the reversing valve is reversed in position,
and the ports and m are opened, which brings the interior of the steam holding
vessel B in communication with the channel d' which then contains forward or
ahead steam from the forward end of the steam engine cylinder, and the interior of
the steam holding vessel C is brought in communication with the channel c¹ which
then contains back_pressure or retarding steam from the back end of the steam
engine cylinder. From this it will be understood that no matter in which
direction the engine piston moves, the steam holding vessel B always receives
the forward or ahead steam, and the other vessel C, the back pressure or retarding
steam.
At the completion of the minute, the operator releases the knob o which stops
the operation of the instrument, and he then notes the heights of the two columns
of colored liquid as indicated by the figures on the scale plates. The figures
indicating the back pressure must now be deducted from those indicating the ahead
or forward pressure, and the remainder is the mean effective pressure to which the
piston has been subjected during the minute. During the displacement of the
mercury and the rise of the colored liquid colunins, the toothed dial L' has
been turning with an intermittent movement the distance of one tooth for
each double stroke of the engine piston, or complete revolution of the engine,
and when the movement of the instrument is stopped, the pointer P¹ will indicate
the number of double strokes or complete revolutions made by the engine during
the minute.
From the data furnished in figures, as described, the area of the engine piston
in inches, and the distance travelled by the piston in feet during each double
stroke, being known, the average horse power developed by the engine during
the minute may be ascertained by the well known rule used in such cases.
The operation of ascertaining the power of the engine being ended, the liquid
columns are allowed to fall by turning the seat O of the plate valves P by
means of the handles C¹, and after the handles are replaced or moved to their
original position, the instrument again ready for use. In turning the handles so
as to allow the liquid columns to recede, they are brought over the knob o³ and

page_text: thereby prevent, or render difficult, the opening of the steam valve, which should
not be opened until the ports o³ and p³, are closed or brought out of register with
the others and h².
To let off any steam left inclosed in the vessels B and C at the end of the
indicating operation and which would prevent or retard the communicating bodies
of mercury coming to a common level, the lids are each provided with a small
hole m which, as the handles are turned inward, registers with another hole n' in
the flange of each of the reservoirs, see Figs. 4 and 18.
In ascertaining the horse power of a condensing engine, the back pressure column
is lowered instead of raised, by reason of the existence of a partial vacuum on the
back of the engine piston, and in computing the effective pressure on the piston, the
number registered by this column must be added to, instead of subtracted from,
the other, as will be readily understood.
The reason for having the 0 points adjustable by means of rack and pinion, as
described, is to obviate the necessity of great accuracy in pouring in the colored
liquid in the glass tubes and also to provide for any evaporation of the said liquid
when the instrument has been in use for a great length of time.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :
1. The method of ascertaining the average pressure of steam in an engine
cylinder, herein described, which consists in subjecting a body of mercury in a
vessel having a limited discharge aperture of known capacity, to the same steam
pressure, and measuring the mercury discharged, substantially as specified.
2. The method of arriving at the average of a varying pressure of steam acting
on a moving engine piston during a given period of time, herein described, which
consists in subjecting a body of mercury in a vessel having a limited discharge
aperture, to steam in communication with that affecting the said piston, and com-
paring the quantity of mercury discharged from the said vessel with another
quantity of mercury discharged through the same or a similar aperture under a
constant pressure, for the same, or a certain proportion of the same period of time,
substantially as specified.
3. In a power measuring instrument, the combination of a mercury holding
vessel having a limited discharge opening, a pipe to convey steam to the surface of
the contained mercury, and a measuring vessel to ascertain the volume of the
discharged mercury, substantially as specified.
4. In a power measuring instrument, the combination of a mercury holding
vessel having a limited discharge aperture, a measuring vessel to ascertain the
volume of the discharged mercury, a pipe whereby pressure is applied to the surface
of the contained mercury, and valve mechanism to control the said applied pressure,
substantially as specified.
5. In a pressure measuring instrument, the combination of a mercury holding
vessel having a limited discharge aperture, a measuring vessel to ascertain the
volume of the discharged mercury, a pipe leading from the space in the mercury
holding vessel above the contained mercury to one end of an engine cylinder, a
second pipe leading from the said space above the mercury to the other end of the
said engine cylinder, and valve mechanism whereby the said vessel may be placed
alternately in communication with each end of the said steam cylinder, substantially
as specified.
6. In a pressure measuring instrument, the combination of a mercury holding
vessel having a limited discharge, a measuring vessel to ascertain the volume of
the discharged mercury, a pipe leading from the surface of the contained mercury
to one end of a steam engine cylinder, a second pipe leading from the surface of
the mercury to the other end of the said engine cylinder, valve mechanism whereby
the said mercury holding vessel may be placed alternately in communication with
each end of the said steam engine cylinder, and means whereby the said valve
B

page_text: mechanism is actuated by the piston of the steam engine and in unison with its
movement, substantially as specified.
7. In a pressure measuring instrument, the combination of two mercury holding
vessels, each one of which is provided with a limited discharge and with a measuring
vessel to ascertain the volume of the discharged mercury, a pipe leading from 5
above the surface of the mercury in the two vessels to one end of an engine
cylinder, a second pipe leading from the same place to the other end of the said
engine cylinder, and valve mechanism actuated primarily from the piston of the
engine, whereby, in the operation of the engine, the forward steam from each end
of the steam cylinder is alternately admitted to cne mercury holding vessel, and 1
the back pressure steam from each end of the steam cylinder to the other mercury
holding vessel, substantially as specified.
8. In an instrument for ascertaining the power of a steam engine, devices for
registering the mean effective pressure of steam acting on the engine piston for a
certain period of time, and devices for registering the revolutions of the engine
for the same period of time combined with mechanism whereby the two sets of
devices are simultaneously placed in operation substantially as specified.
9. In a pressure measuring instrument, consisting primarily of a mercury holding
vessel having a limited discharge leading to a measuring vessel, a valve which
controls the action of steam from the cylinder of a steam engine on the surface of
the contained mercury, and actuating mechanism for the said valve having a limited
movement less than the stroke of the engine piston, combined with a device
operated by the engine piston and having a movement in unison therewith, which
device is connected with the said valve-actuating mechanism and imparts only a
portion of its movement thereto, whereby the said controlling valve is operated at
the beginning of each single stroke of the piston, and then held in its position
until the completion of the said single stroke, substantially as specified.
10. In a pressure-measuring instrument, the combination of a valve, a valve-
operating pivoted rocker with a vibratory tail piece, a rod connected with some
part of an engine having a movement in unison with the engine piston, the
free end of which rod passes through the vibratory tail piece, and friction producing
devices or rollers forming a part of the tail piece to clamp the said rod and serve
to communicate the first part of its motion to the said valve-operating rocker,
substantially as specified.
11. In a pressure measuring instrument, the combination of a steam holding
vessel containing mercury, and a mercury reservoir inserted in the said steam
holding vessel with its end, which is immersed in the mercury, provided with a
small aperture, whereby, as pressure is applied to the surface of the mercury
exteriorly of the reservoir, the mercury is made to rise in the said reservoir,
substantially as specified.
12. In a pressure measuring instrument, the combination of a steam holding
vessel containing mercury, a mercury holding vessel having at its lower end a valve
which may be opened and closed, and also a diaphragm having a small aperture
which is at all times open, the said aperture forming a constant means of
communication between the mercury holding portion of the steam holding vessel,
and the interior of the reservoir, substantially as specified.
13. In a pressure measuring instrument, the combination of a steam holding
vessel containing mercury, a mercury holding reservoir having at its lower end a
ported plate valve which is immersed in the mercury, and also a diaphragm secured
to the plate valve having a small aperture which is never closed and forms a means
of communication between the steam holding vessel and the interior of the reservoir
substantially as specified.
14. In a pressure measuring instrument, the combination of a steam holding
vessel in which is inserted a reservoir having a controllable opening and a non-
controllable aperture, both of which serve as means of communication between the
steam holding vessel and the reservoir, and a measuring tube leading from the
upper end of the said reservoir, substantially as specified.

page_text: 15. A power measuring instrument, which consists of a steam holding vessel
having an apertured reservoir in communication with the said vessel, valve
mechanism whereby the admission of steam to the said vessel is controlled, and
means whereby a motion in unison with the engine piston is communicated to the
valve mechanism, combined with a dial and an escapement whereby, at each
complete stroke of the engine, the dial is allowed or made to perform a part of a
revolution, substantially as specified.
16. In a power measuring instrument, a reversing valve, substantially as described,
combined with an actuating pivoted rocker having a tail piece with friction rollers
therein, a rod leading from some part of an engine having a movement in common
with the engine piston, which is clamped between the friction rollers, and a holding
and releasing bar whereby the movement of the said rod may be made operative or
inoperative to communicate motion to the said rocker, substantially as specified.
17. In a power measuring instrument, the combination with a part of a steam
engine having a movement for each stroke of the engine piston, a spring wound
toothed dial, and escapement pallets connected to the said part of the engine,.
whereby at each stroke of the said engine piston, the dial is allowed to make a
partial revolution, substantially as specified.
Dated this Twenty-fourth day of June 1893.
WILLIAM THOMPSON HOWARD.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.