Diameter of cylinders, 3X feet; stroke, ro feet; diameter of piston rod (steel), 6 TA inches; speed, thirty-six revolutions per minute, corre sponding to a piston-speed of 72o feet per minute; length of beams, 27 feet; depth of beams at centres, 9 feet; weight of each beam, eleven tons; length of fly-wheel shaft, 12 feet; diameter of fly-wheel shaft, r foot 7 inches; diameter of fly-wheel shaft in bearings, 1Y, feet; length of fly wheel shaft in bearings, 2Y feet; diameter of fly-wheel, 3o feet; width of fly-wheel across the face, 2 feet; number of teeth on fly-wheel, two hundred and sixteen; and weight of fly-wheel, fifty-six tons.
The main line of underground shafting was 252 feet long, running north and south. The first line of shafting, by means of four trios of mitre-bevels, transmitted power to eight 6-inch shafts at right angles, leading in different directions to walled pits under heavy standard frames which carried the driven pulleys on the ends of the shafting overhead. Each of the lines of shafting was capable of transmitting a power of one hundred and eighty horses at its normal speed, and was 658 feet long, reaching from the transept to the east and west ends of the building. The larger portion of these lines ran at the rate of one hundred and twenty revolutions per minute, but the one specially devoted to wood-working machinery made as many as two hundred and forty per minute. The total weight of the main gearing, shafting, mitre-gearing, and pulleys to which these engines were attached was 365,855 pounds; the weight of the engines, underground shafting, and boilers was 1,552,18o pounds.
The boiler-house connected with these engines was located 36 feet from Machinery Hall, and contained twenty upright boilers, each having the nominal power of seventy horses. The main steam-pipe, which was located under the floor, was of wrought iron, 32o feet long and iS inches in diameter. These unparalleled engines were intended to operate a length of shafting estimated (main and subsidiary lines together) at ro,400 feet, and to answer the purpose of exhibition required by the larger portion of machines occupying a floor-space of about thirteen acres, of which machines more than eight thousand were in position on the opening day of the Ex hibition.
The Wheelock Engine, as originally constructed (15/. 92, Arr. 2), has but two ports, one at each cnd to each cylinder. Upon each of the valve scats corresponding to these ports there is an oscillating valve which admits steam at one fixed point and exhausts it at another. I;ack of or below each of these main valves is another oscillating valve, which causes cut-off by a detest motion regulated by the governor: the lighter the load, the earlier the cut-off. There is about this an elegant simplicity of design NVII1C11 leaves but little to be demanded.
The Greene Engine (pl. 91, fig. 1) has four flat valves. Those for the
exhaust have their own eccentric-rods; those for admission have each a sliding bar which has motion parallel to the centre line of the cylinder and coincident with that of the piston. This bar has two tappets adjust able vertically, so as to engage rock-shaft arms on the ends of rock-shafts attached to the valve-links inside the steam-chest. Springs hold these tappets to their work and in contact with a "gauge-bar,'' which is adjusted to various heights by the action of the governor.
The " Buckeye" Engine is one of the most successful of those which have the cut-off automatically regulated by a centrifugal governor placed on the main shaft and controlling the position of the eccentric. There are three sub-types of construction, the latest of which is shown in Fig ure 3. Figure 2 is a horizontal section through the valves and cylin der corresponding to any one of the three sub-types, and Figure 16 (N. S3) illustrates the governor employed in all. The live steam enters at A (fil. 91, fig. 2), whence it passes through passages (a, a') and the open pistons a', a' into the interior of the box slide-valve B, B, as shown by the arrows. From this box-valve it is admitted to the cylinder through ports (b, b) in its face as these ports are alternately brought to coincide with the cylinder ports. The cut-off valve, which consists of two light plates (C, C) connected by rods (C'), works on seats inside of the main valve, as shown, and alternately covers the ports leading to the cylin der. The cut-off valve-stein g works through the hollow stein G of the main valve. The exhaust takes place at the end of the valve (as shown by ,arrows on the right) into the valve-chest; thence into the exhaust-pipe F below. In the valve-seats (at e, e) are shallow recesses equal in area to the cylinder-ports, and called " relief chambers," their use being necessary at certain positions of the valve to counteract the excess of pressure tending to force the valve to its seat. In this engine the steam is within, instead of around, the slide-valve, as in most slide-valve engines, and the tendency of the steam in the ports h, b and in the cylinder is to force the valve from its seat, this being counteracted by the pressure of the entering steam in proportion to the area of the pistons or equilibrium rings Da', Da', which are proportioned to hold the valve to its seat at the moment of admission (see the left hand end of the valve in fig. 2), when the tendency to leave the scat is greatest. At other times this pressure would be too great, hence live steam is admitted to the relief chambers e, e through the holes f, f in the valve-face just after it is exhausted from the cylinders (as shown at the right-hand ends of the valve in Figure 3), and in turn is thence exhausted, as shown at the left, just after the exhaust closure.