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Appletons' cyclopædia of applied mechanics: a dictionary of mechanical engineering and the mechanical arts .. online

. (page 111 of 153)
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of the piston, but the steam-valves are opened at the proper time and allowed to shut automatically
at some point in the early part of the stroke. The precise point at which this shutting of the steam-




ralve occurs, and consequently the volume of steam admitted into the cylinder in any given stroke,
depends on the position of the governor-balls, and the speed of the engine is regulated by the varia-
tions in the quantity of steam thus admitted.

The invention of the Corliss engine marks an era in steam-engine construction, and the history of
its introduction bears a striking analogy to that of the pumpmg engine invented by Watt Like



1450.




Watt, Mr. Corliss was contented to displace the older forms of engines by his more perfect device,
and take in payment the value of a portion of the coal saved ; and like Watt, he soon found that
proprietors of mills were unwilling to render him true accounts of the saving effected. Now that
44



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690 ENGINES, STEAM, STATIONARY (RECIPROCATING).

the patent has expired, the Corliss engine, or some modification, has been largely adopted as tbe
standard design by engine-builders in this country ; and it has displaced almost all other styles
abroad. No derice for regulating the distribution of the steam in stationary engines has been in-
▼ented that successfully supersedes the Corliss wrist-motion; and this attachment, together with

improved construction and increased pi&-
1451. ton-speed, has increased the efficiency of

the stationary engine quite as much as'lOO
per cent

The action of the Corliss wrist-motion
is plainly illustrated in Fig. 1449, whidi
shows the valres at one end of the cylin-
der, in the two extreme and middle por-
tions. The sketch will repay study, show-
ing in an admirable manner the effect of
the peculiar mode of connection. The ex-
ample is from the Corliss engine as built
by Watts, Campbell k Co. ; and Fig. 1450
is from a working drawing of one of thdr
cylinders, showing valve-motion, and de-
vice for tripping the steam-valves by the
rod connectcMl to the governor. The valre,
when tripped, is clo^ either by weights
or springs, dash-pots being ordinarily used
in connection with weights. Fig. 1451 rep-
resents the main bearing used by Wit^
Campbell & Co. on their engines;' the top
and bottom brasses not being fitted, but having a little play allowed, any adjustment required being
made on the centre brasses, as shown.

One of the finest examples of the Corliss engine ever constructed was the pair of engines bmh
by Mr. Corliss for use in Machinery Hall at the Centennial Exhibition. These engines are illustrated
in a full-page engraving, and the principal dimensions are appended :

Diameter of cylinder, inches 40

Stroke of piston, feet 10

Diameter of air-pump, inches 86

Stroke " " 24

Diameter of piston-rod (steel), inches 6.26

Length of beam between centres, feet 25

Depth of beam at centres, feet 9

Weight of beam, lbs 22,000

Length of crank-shaft, feet 12

Diameter of " inches '. 19

" " " bearings, inches 18

Length " " ** " 27

Diameter of fly-wheel at pitch-line, feet 29.7

Pitch of teeth, inches 5.183

Face of fly-wheel, inches 24

Weight of fly-wheel, lbs 11 2,000

Number of teeth in fly-wheel 216

Diameter of pinion at pitch-line, feet 9.9

Weight of pinion, lbs 17,000

Revolutions of engines per minute 86

Total revolutions during the Exhibition 2,865,800

These engines were let by Mr. Corliss, during the Exhibition, for $77,000, tbe Board of Fmanoe
building the boiler-house, making the necessary excavations, and furnishing the fuel — thus brii^ing
the whole cost up to $142,874. According to a statement made by Mr. Corliss, his expenditures
were in excess of his receipts by $40,788.10.

TTie Harris- Corliss Efigine, — Fig. 1462 represents a modified form of the Corliss engine largely
used in the United States. Fig. 1453 is a longitudinal section of the cylinder, steam-chegt, and ex-
haust-passage, with cross-sections of the valves. At A is shown one steam-port open, and at B the
other steam-port closed ; C is one exhaust open full area of port, and D the other exhaust closed.
It will be noticed in Fig. 1463 that the piston has traveled a very small part of the stroke while the
steam- and exhaust-valves A and C have been opening the full area of their ports. Fig. 1454 shows
the method of packing the valve-stems so as to obviate the use of stuffing-boxes and to cause the
thrust-collar to boar directly against the bonnet E. J) is the valve-stem, on which is shrunk the
collar F^ which fits in a recess a of the bonnet. The opposing faces are finely scraped so that they
approximate very closely, and are packed by the steam itself acting outward on an area equal to the
section of the valve-stem i>. In the hollow space in the bonnet all drip enters, and is carried off by
the pipes O^ which extend from bonnet to bonnet. (See " Economy Trials of an Automatic Engine,"
by John W. Hill, M. E., in Van Noslran^s Engineering Magaziney December, 1877.)

T?ie Wheelock Engine. — An elevation of this engine, and a modification of the Corliss valve^getr
patented by Jerome Wheelock, are shown in Figs. 1466 and 1466. In this arrangement there



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ENGINES, STEAM, STATIONARY (RECIPROCATING). 691



1459.



1463.



1456.



1464.





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698 ENGINES, STEAM, STATIONARY (RECIPROCATING).

is only one port in each end of the cylinder, an independent cut-off valve regulating the admisson
of steam. The cut-off valve is of such a form as to allow a double admission and cut-off, whidi is
an arrangement very favorable to the distribution for a given port area. The valves rotate on haitl-
ened steel bushings, which are adjustable endwise, and no stuffing-boxes are used.

The Wright Automatic Cut-off Engine is the invention of Mr. William Wright of Newburgh, N. Y.
Fig. 1467 shows the steam side with the cut-off valve gear, and Fig. 1468 the exhaust side. There

1467.



are four gridiron slide-valves, which work vertically in chests cast with the cylinder, two upon
one side of the cylinder being for induction, or cut-off, and two upon the opposite side being for
eduction, or exhaust steam. All valve-motion is derived from a single eccentric, which operates
levers, so arranged as to give a quick movement to valves when opening, and also a very elow
movement when valves are lapped. The location of all these valve- faces close to the bore of the cylin-
der insures the least possible amount of clearances. The steam valve-stems are fastened in yokes,
which have at their lower ends plungers fitted in dash-pots, the same acting as guides ; the yokes are
operated by steel slides fitted through the end of hollow rocker-arms, and which act upon the swing-
ing toes held in the yokes, the said slides having a diagonal slot in which works a feather, this featb-

1468.



er being made on a rod which has a longitudinal movement through the hollow rocker-ann, and to
which the governor is connected. By this longitudinal motion, and through the diagonal feather and
slot, the slide is automatically set, to engage more or less with the swinging toes, and which gives
the valve its proper lift, and liberates upon the chord of the arc. The governor itself stands on a
bracket or shelf, cast on the slide part of the bed-plate, and the governor-rod is connected to a le^r,
which is fastened to the governor-shaft. This same shaft carries two forked arms which take bold



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ENGINES, STEAM, STATIONARY (RECIPROCATING). 693

of the small rods running through the hollow rocker-shafts. The rods are enlarged at their other
ends, where they carry the adjustable slides mentioned before. The advantages in this arrangement
of valves and valve-gearing are easy accessibility to each valve, by the simple removal of a bonnet,
and that the whole of the valve-gear and governor connections is outside of the steam-chests, where
any derangement can be at once seen and rectified.
The Gi^ene Engine^ manufactured by the Providence Steam-Engine Company, of Providence, R. I.,

1400.



is represented in Figs. 1469, 1460, and 1461. There are four flat slide-valves, one (as shown on the
left of fig. 1460) at each end on the top to admit the steam, and one (as shown on the right of Fig.
1460) to let out the exhaust. The working of the valve-gear is as follows : The induction-valves
are connected with the rock-lever shafts i. Fig. 1469, by arms B working in slots in the valve-
stems C. Below the rock-levers D 2) is a sliding bar E^ receiving a reciprocating motion from an
eccentric on the main shaft. Behind the sliding bar is a gauge-bar F, Fig. 1461, connected with the
governor, which bar receives an up-and-down motion from a corresponding movement of the governor-
balls. The adjustable tappets O Gy Fig. 1461, in the sliding bar, are kept up in contact with the
gauge-bar F^ and are made to move up and down in unison with it by the springs ffff. As the



1461.



1460.




sliding bar moves in the direction of the arrow, one of the tappets is brought in contact with
the inner face of the toe on the rock-lever, causing it to turn on its axis, thereby opening the
steam-valve at one end of the cylinder, the other tappet meanwhile passing under the other rock-
lever without moving it. The toe and tappet are so beveled that the tappet will be forced down
against the action of this spring until it has passed by the toe, when the spring causes it to fly up to
its original position, ready to open the induction-valve at the opposite end. As a result of this
motion, the two tappets always open the steam-valves at the same period ; but, the tappet moving in
a straight line while the toe describes the arc of a drcle, the tappet will pass by, liberating the toe,



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694 ENGINES, STEAM, STATIONARY (RECIPROCATING).



1403.



which is brought back to its original position by a weight /, Fig. 1469, the steam-pressure on the
Talve-stem thus closing the valve and cutting off the steam. This liberation will take place soooer
or later, according to the elevation of the tappets ; that is, the lower the tappets are the sooner the

toes will be liberated, and vice versa ; and so, bj sim-
ply elevating or depressing the gauge-bar -F, Jlg.1461,
the period of closmg the valves can be changed while
the period of opening them remains the same. The
adjustment of the gauge-bar is effected by the gor-
emor, and the steam is cut off sooner or later accord-
ing to the amount of load. The exhaust-valves /, Fig.
1469, which lie in the bottom of the cylinder, are con-
nected at their outer ends by parallel rods K^ which
are tied together by a cross-bar on the inside. The
exhaust rock-shaft arm X is a jaw, as shown in Fig.
1469, just under the cylinder. One side of this jaw
comes in contact with a lug M on the cross-bar, tnd
moves both the exhaust-valves simultaneously, opt-
ing one and closing the other. While the exhaust-
eccentric is taking up the lost motion between the sides
of the jaw, the exhaust-valves remain at rest The
other side of the jaw coming in contact with the cross-
bar, the exhaust-valves receive a reverse motion. The
lug on the cross-bar is so shaped that it receives do
blow from the jaw Z, but takes a gradually acceler-
ated motion.

WifUtr's Cut-off, Fig. 1462.— In this the shaft D
receives a rotary motion from the eccentric-rod, the
latter being pivoted to a lever between its points of
attachment to the eccentric and shaft D, A cam on
this revolving shaft acts on the lifter ^to open the valve, through the piece E ; the duration of con-
tact, or the point of cut-off, being regulated by the position of the piece E, which can be adjusted
as shown.

T%e Brown Engine, Fig. 1468. — The cut-off mechanism in this engine is the invention of Mr. C. H.
Brown of fltohburg, Mass. Its arrangement is as follows : The cut gear-wheels shown impart a
rotary motion to the shaft Ay which operates the governor and communicates rotary motion to the
valve-shaft B. Between these two shafts is a friction device C7, which is so constructed as to permit
the shaft ^ to be operated by hand independently of the shaft A. Upon the shaft B are the eccen-
trics, the ends of the straps of which connect with the horizontal lever E ; and the latter extends
into the square slot in the slide-spindle guide to the catch of the tongue. As the shaft B revolves,
the lever ^.reciprocates vertically in the said square slot The valve-stem is attached to the guide
Fy and in the slot shown in the latter is pivoted a tongue 0, The upper end of this tongne hu a
projecting catch upon it, and beneath this catch stands the end of the arm E. The induraoD-valve
is closed when at the bottom of its travel, and the weight of the valve and stem and the pressure of
the steam (acting on an area equal to the area of the valve-stem) are, combined, always acting to




keep the valve at the bottom of its travel, that is, in its normal position ; and there it remains until
lifted for the admission of steam. The manner of effecting this admission is as follows : The end
of the arm E^ acting against the catch on the upper end of the tongue in the slot, lifts the valve and



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ENGINES, STEAM, STATIONARY (RECIPROCATING). 695



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696 ENGINES, STEAM, STATIONARY (RECIPROCATING).

holds it open so long as the tongue is not tripped. The instant, however, that the latter action takes
place, the valve, from its weight and the action of the steam upon the area above mentioned, doses,
the movement being cushioned after the valve is completely closed by means of the small dash-pot
shown beneath. By regulating the eccentrics, the valve may be given any desired amount of leid,
and the duration of the period of admission may be varied by tripping the tongue before referred to;
and this is accomplished by the engine governor in the following manner : The governor commam-
cates with the rod ^, Upon this rod, and immediately behind the induction-valve spindle^de F,



is an arm standing vertically, and canying a pin ^ standing horizontally. The tongue, which at
one end acts as a catch to the eccentric arm at the other end, protrudes from the back of the 8lid^
spindle guide, and stands directly beneath the above-mentioned pin ; so that, when the rod E lifts
(through the medium of the tongue-catch) the induction-valve, the latter continues to lift until the
tail of the catch (?, coming in contact with the pin JI^ trips the tongue, and the valve instantly
closes, returning to its normal position. The exhaust-valves lie horizontally, and are operated as
follows : Upon the shaft D are the disks /, which are provided with cam-grooves. The rocker-arm
iT carries a friction-roller extending into the cam-groove, the upper arm Z being attadied to the
exhaust-valve spindle. To compensate for the circuUr motion of the arm and the vertical more-
ment of the valve-spindle, the connection between the two is made by the eye of the spindle, contain-
ing a slot, in which is fitted a sliding die to which the pin of the arm is fitted. To regulate the
amount of compression, it is merely necessaiy to adjust the position of the disk. The governor is
of the ordinary fly-belt type, and is inclosed in a polished casing.

The Buckeye AutomoHe Cut-off Engine is represented in elevation in Fig. 1464. Fig. 1465 is a
section of the cylinder, and Fig. 1465 ▲ shows the construction of the governor used. By reference to
Fig. 1465, the main valve is seen to be a hollow box, taking steam on the inside, balanced bj the
exclusion of steam-pressure from the back, and driven in the usual way by an eccentric fast on the
shaft. Steam is admitted from the inside of the valve to the cylinder and exhausted into the chest,
the reverse of the ordinary operation. The valves are fitted up under steam at 80 lbs., insoring
freedom from leakage or cutting from distortion caused by expansion imder heat or pressure. The
cut-off mechanism consists of a light cut-off valve, working on the inner face of the main valre, the
stem passing out through the hollow steel stem of the main valve, and being driven from a loose
eccentric on the shaft with a special motioii derived from the compound rock-shaft This loose
eccentric is controlled by the governor. Fig. 1466 ▲, which is a ^ell fast upon the shaft and rerolring
with it. In this shell are pivoted two weighted levers, the outer ends of which are linked to the

1465 a.




flange on the elongated sleeve of the loose eccentric. The centrifugal force developed in the weights
throws them outward, and two well-tempered steel coil sprini:^ furnish the centripetal force. The
system being coupled is independent of gravity, and it is readily seen that the speed determines the
position of the weighted arms, which in turn determines the angular advance of the eccentric and the
consequent point of cut-off, the range of which is, we are informed, from «ro to nearly three-
quarters of the stroke.



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ENGINES, STEAM, STATIONARY (RECIPROCATING). 697

F!g. 1466 represents an indicator diagram taken from one end of the cylinder of a Buckeye auto-
matic cut-off engine ; and the following data, in relation to the engine from which the diagram was
taken, were famished by the Buckeye Engine Company :

Scale of indicator spring, ^; diameter of cylinder, 18 inches; length of stroke, 36 inches; clear-
ance in cylinder and ports at each end of cylinder, 2 per cent, of piston displacement per stroke ;
diameter of piston-rod, 8 inches ; extreme length of cylinder between heads, 44^ inches ; length of
steam-port, 17 inches; width of steam-port, 1^ inch ; rcTolutions of engine per minute, 98.

Data obtained from the Diagram, — Draw perpendiculars to the atmospheric line a b, at the eztrem-

14.7

ities of the diagrams, produce them below this line a distance equal to = 0.37 inch, and draw

40
the perfect vacuum line e d parallel to a b. Next select a point near one end of the diagram, a
little before release^ and another point near the other end, a little beyond exhaust closure. In the
diagram under consideration, these points are taken at 0.95 of the forward and return strokes re-
spectively. The length of the diagram is 8.78 inches, so that c n is 0.95 x 8.73 = 8.54 inches, as is
also d i. Erect perpendiculars to cd &% the points n and t, and draw also the perpendicular k f
through /, at which point cid^ff has apparently occurred. Make e I equal to 0.02 x 8.78 = 0.07
inch, and draw the perpendicular / m, thus increasing the length of the diagram in accordance with
the clearance. By measuring the lengths of these several perpendiculars, the absolute pressures in
pounds per square inch in the cylinder at the yarious points can be determined : Initial pressure, e e,
2.44 X 40 = 97.6 ; pressure at point of cut-off, k /, 2.28 x 40 = 91.2 ; pressure at 0.96 of forward
stroke, ng, 0.42 x 40 = 16.8 ; pressure at 0.95 of return stroke, t A, 0.44 x 40 = 17.6. The diagram

ck 0.68 Ik 0.70

also gives the cut-off in fraction of stroke, — , = — = 0.169, and the real cut-off, ; , = = 0.188.

^ 'cd 8.78 ' *ld 8.80

An annular planlmeter was used for calculating the diagram. Fig. 1466. This gave the total mean
, , ATetiefabdc 4.88

pressure in pounds per square inch = x 40 = — — x 40 = 46.48 ; the mean total back

axenehbdc 1.60 <^^ ^'^^ ^ KtetLefabh

pressure = ; x 40= x 40 = 17.16 : the mean effective pressujre = , x

^ cd 8.78 ' cd

40 = 46.43 — 17.16 =: 29.27 ; and the fraction of the total work that is due to expansion =
aieAfgbdk 2.84

^ , ~ = = 0.666.

KveAcfgbdc 4.88

The only other data needed in the calculations can be obtained from table I. in the article
Expansion of Steam and Gases. Thus, from column 10, by interpolation, it is found that the
weight of a cubic foot of steam at a pressure of 16.8 lbs. per square inch, represented on the dia-
gram by n g^ is 0.04304 lb. ; that the weight at a pressure of 17.6 lbs. per square inch, represented
by t A, is 0.04496 lb. ; and by column 6, that the latent heat in a pound of steam, at a pressure of
16.8 lbs. per square inch, is 961.8 units.

CaleukUions from the foregoing Data, — ^The effective area of piston is 260.94 square inches.
The horse-power of the engine, for 1 lb. per square inch mean pressure, and one revolution per
260.94 X 6

minute, is = 0.045626 ; so that the total horse-power is 0.045626 x 98 x 46.48 = 207.6 ;

38,000
and the indicated horse-power, 0.046626 x 98 x 29.27 = 130.87. The displacement of the piston in

260.94 X 72
cubic feet per revolution, to 0.96 stroke, including, clearance, is x 0.99 = 10.86128; so

that the number of pounds of steam used per hour, as calculated by pressure near termination of
forward stroke, is 10.85128 x 98 x 60 x 0.04804 = 2,620. The steam saved in cushion space in

260.94 X 72
cubic feet per revolution, including clearance, is x 0.09 = 0.94103 ; so that the number

of pounds of steam saved per hour by cushion is 0.94108 x 98 x 60 x 0.04496 = 249. The number of

. ^ ...., ,,, .. 207.6x0.666x1,980,000

pounds of steam condensed per hour for the total work due to expansion is =

772 X 961.8
868. From this it appears that the least possible consumption of steam in pounds per hour by the

2,734

engine = 2,734 ; corresponding to a consumption, in pounds per hour, of = 18.17 per total

2,734 207.6

horse-power, and = 20.89 per indicated horse-power. The condensing surface in the engine

under consideration is approximately 28.7 square feet, viz.: in cylinder sides, 17.6; in cylinder
heads and 2 sides of piston, 7.1 ; in piston-rod, 2.4; in ports, 1.7. Internal condensation may be
assumed at the rate of 20 lbs. per square foot of condensing surface per hour, making the total
condensation 28.7 x 20 = 574 lbs. This will give, as the probable number of pounds of steam

8,308
consumed by the engine per hour, 2,734 x 574 = 3,308 ; or at the rate, in pounds per hour, of - -

8,308 207.6

= 16.98 per total horse-power, and = 26.28 per indicated horse-power. Dividing the water

used per horse-power per hour by 9, it appears that the number of pounds of coal used per hour, in
a boiler capable of evaporating 9 lbs. of water per pound of coal, is : least possible, per total horse-
power, 1.46; probable, per total horse-power, 1.77; least possible, per indicated horse-power, 2.32;
probable, per indicated horse-power, 2.81.



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698 ENGINES, STEAM, STATIONARY (RECIPROCATING).

Tlie Rider Eng^ine^ Fig. 1467. — In short-stroke engines of this class, where the ordinary three-ported
valve is generally in use, the main slide-valve is, in its action and in the form of its face side, suni-
lar to that of the well-known slide-valve, with the exception that its ends are lengthened to admit of

steam-ports or openings being formed outside of the
valve proper. These openings or jwrta are, on the
face side of the valve, rectilinear and rectangular to
the motion of the valve ; that is, they run parallel
with the ports in the cylinder, or disposed square
across the valve-seat On the back of this main
valve, where the cut-off valve is fitted, these steam-
ports are oblique, and at opposite angles to each
other, the use of which will be presently explamed.
The cut-off valve is a sector of a cylinder, with its
ends cut off obliquely in opposite directions, so that
the extremities or acting ends of the cut-off valve
respectively conform t9 the lines of a right- and left-
hand screw of high pitch, corresponding to the obli-
quity or angle of the steam-ports in the back of the
main slide-valve. This cut-off valve just described

146S.



is fitted into a semi-cylindrical recess in the back of
the main slide-valve, and between the spiral open-
ings. It is operated lengthwise by a separate eccen-
tric, to which it is attached in the usual manner, ex-
cepting that it has a swivel-joint to permit its partial
rotation. A portion of the valve-stem is made square,
or sometimes arranged with a ** feather," and at this
place on the valve-stem is fitted a sector, engaging a rack on the lower portion of the governor-spin-
dle, so that as the governor rises or falls the cut-off valve will partly rotate. Thus the cut-off valve is
moved lengthwise by the eccentric, and at the same time has imparted to it by the governor an ad-
justing motion on its axis. As a consequence of the radial motion imparted by the governor, and



Online LibraryPark BenjaminAppletons' cyclopædia of applied mechanics: a dictionary of mechanical engineering and the mechanical arts .. → online text (page 111 of 153)