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Title: |
1884 Images-C. H. Brown & Co., Steam Engine |
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Source: |
The Engineer's Handy Book 1884 pgs 89 & 90 |
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Insert Date: |
2/26/2011 12:58:00 PM |
The Brown Automatic Cut-Off Steam Engine.
The cuts on pages 89, 90, represent the Brown Automatic Cut-off High-pressure Engine.—The housing, which, as will be observed, is of the girder-frame pattern, somewhat resembles the Corliss, though the engine is different in every other respect. The cylinder, which contains the steam- and exhaust-ports, is encased in an ornamental cast-iron jacket, and rests on a square, tapering column, which extends nearly the full length. By a judicious distribution of the materials, every part possesses sufficient rigidity, without extra weight of metal. In its design, the evils induced by expansion, and the liability to get out of line, have been scientifically considered and practically obviated. A spur-gear on the main shaft gives motion to a shaft parallel with and below the axis of the cylinder. From this shaft the motions of the valves are derived.
There are four valves, one steam and one exhaust at each end of the cylinder, which are independent, and though slide-valves, as they have but one .function to perform for each revolution, i. e., admitting or exhausting the steam, they are necessarily of a different construction from the ordinary slide-valve. The exhaust-valves are horizontal, and travel at right angles with the cylinder; the motion being derived from cams on the longitudinal shaft, which is positive in both directions. The shape of the cam-ways is such that the motions of the valves in opening and closing are very quick, and allow of their remaining stationary during nearly the whole stroke of the piston, thus insuring a perfectly free exhaust, and preventing any possibility of back pressure.
The steam-valves, which are vertical, are of the gridiron pattern, and require very little movement to give a full port opening. They are operated by eccentrics on the cam-shaft, in connection with the following device for regulating the point of cut-off. A vibrating lifter, having the fixed centre at its outer end, is connected, at about the middle of its length, with the eccentric-rod; while the inner end engages a spring-catch or projection on the valve-stem, giving to the valve a positive motion on the left or up stroke, and allowing of its being tripped, or released for closing, when the point of cut-off is reached —jar being prevented by means of small dash-pots. On the spring-catch of the valve-stems is an inverted wedge, by means of which the valves are tripped.
The governor, which, as will be observed, is enclosed in an ornamental case or shell, is very sensitive and admirably adapted to these engines, is of the centrifugal fly-ball type, receives a positive motion from the cam-shaft, by means of bevel-gears, and causes a rod running parallel with the shaft and back of the valve-stems to oscillate. Oil this rod and opposite to each wedge is an arm, which, when the speed increases, is moved by the governor towards the wedge, thus drawing the catch away from the lifter as it rises, and allowing the valve to drop, while the lifter continues its movement to the end of the stroke and return, when it engages the catch as before.
Both steam- and exhaust-valves have ample openings, which, in connection with their quick motions, entirely obviate the evil arising from wire-drawing the steam, or choking the exhaust, thereby causing back pressure. The only unbalanced pressure on the valve is an area of about one square inch on the top, for the purpose of aiding in closing them quickly. As an evidence of the small amount of friction induced in the working of the valves of these machines, the ordinary starting-bar is dispensed with, and an eight-inch hand-wheel on the cam-shaft, which possesses sufficient leverage to work the valve by hand, substituted in its place.
The valve-gear is a most ingenious and admirable combination, of mechanical devices, being very simple, and susceptible of easy, convenient, and accurate adjustment. Its operation may be explained as follows: The shaft, A, receives its motion from a gear on the main shaft, which, in turn, imparts motion to the governor, and through the medium of the frictional device, or coupling C, to the shaft B, on which the eccentrics, D, are located, the ends of the straps of which are connected to the horizontal arms, E, which extend into the square slot provided in the slide-spindle, and to the catch of the tongue. As the shaft, B, revolves, the ends of the arms, E, will reciprocate vertically in the square slot, the valve-stem being attached to the guide, F, in the slot of which the tongue, G, is pivoted by the pin shown in the guide. The upper end of this tongue has a projecting catch upon it, beneath which stands the end of the arm, E, which lifts the valve for the admission of the steam, and holds it open until the tongue is tripped, when the valve closes, the movement being instantaneous, and rendered noiseless by means of an air-cushion dash-pot.
The governor-spindle is attached to the end of an arm which is fast upon a rod, which, being immediately back of the shaft B, is not seen in the cut; upon this rod, and immediately behind the steam-valve spindle-guide, F, is an arm standing vertically, and carrying the horizontal pin, H. The tongue which at one end acts as a catch to the eccentric arm, at the other end protrudes from the back of the slide-spindle guide, and stands directly beneath the pin, H, so that when the arm, E, lifts (through the tongue-catch) the steam-valve, the latter remains open until the tail of the catch, G, meets with the pin, H, which trips the tongue and closes the valve. The governor controls the position of the pin, H, and determines the point of cut-off. The discs, J, on the shaft, B, are provided with cam-grooves, into which a friction-roller on the rocker-arm, K, extends, the upper arm, L, being attached to the exhaust-valve spindle. To compensate for the circular motion of the arm and the vertical movement of the valve-spindle, the connection between them is made by the eye of the spindle, containing a slot in which is fitted a sliding die, to which the pin of the arm is fitted. Any change of load on the engine is instantaneously shown by the governor. Nevertheless, the valve-gear is complicated, and liable to wear out rapidly and become a source of annoyance and expense. |
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