The Improved Greene Automatic Cut-Off Engine.

The illustration represents the "Improved" Greene Automatic Cut-Off Engine, of which the Providence Steam-Engine Company,

Front View of the "Improved " Greene Automatic Cut-Off Engine.

Providence, R. I., are sole builders.

The bed-plate is of the girder pattern, symmetrical in appearance, and of ample strength. The slides are cast separate, and secured to bed-plate by I dowels and bolts. The main journal-boxes are made in four pieces, and provided with setscrews and check-nuts, which permit of convenient and accurate adjustment. The governor is of the Porter pattern, and is driven by a flat belt from the main shaft. The valvegear is detachable, and is so controlled by the governor that the cutting off may be effected from zero to threequarters of the entire stroke. The valves are four in number-two steam and two exhaust

is applied parallel to and in line with their seats, so that they cannot rock or twist-thus obviating the tendency to wear unevenly. The steam-valves when tripped, are shut by the combined action of a weight and the pressure of the steam on the large valve-stems, thereby insuring a quick cut-off, and the positive closing of the port, under all circumstances of speed and pressure. The steam-valves are operated by toes, on the inner ends of two rock-shafts that connect with the valve-stems outside the steam-chest. The outer ends of the rock-shafts are furnished with steel-tipped toes.

There is a sliding-bar carrying tappets which receive a reciprocating rectilinear motion from an eccentric on the main shaft. Below the sliding-bar is a gauge-plate connected with the governor, which receives an up and down motion from a reverse action of the governor balls.

The tappets in the sliding-bar are supported by springs, the lower ends of which rest upon the gauge-plate; the ends of the tappets projecting through the gauge-plate with nuts upon them secured by pins. As the sliding-bar moves, 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, passes under the rock-lever, without moving it,-the toe and tappet being so bevelled that the tappet will be forced down against the action of the spring, till it has passed the toe, when the spring causes it to resume its original position, prior to opening the steam-valve at the opposite end of the cylinder upon the return stroke of the bar.

As a result of this motion, the tappet always gives the valves the same lead, and as the bar moves in a straight line, while the toe describes the arc of a circle, the tappet will pass by and liberate the toe, which is brought back to its original position by a weight, and the steam pressure on the large valve-stem, which thus closes the valve and cuts off the steam. The liberation of the toes will take place sooner or later, according to the elevation of the tappet; that is, the lower the tappets are, the sooner the toes will be liberated, and vice versa. By the elevation or depression of the

gauge-plate, the period of closing the valves is changed, while the period of opening them remains the same. The adjustment of the gauge-plate is effected directly by the governor.

Both the exhaust-valves and seats are convenient of access, and removable from the outside of cylinder. These valves receive their motion from a separate eccentric, thus allowing of easy adjustment, without interference with the steam-valve mechanism. All the connections are on the outside, are few in number, and have ample bearing surfaces, insuring freedom from rapid wear and derangement.

A safety stop-motion is combined with the governor, preventing the admission of steam should the governor-belt run off or break. The cross-head gibs are directly opposite the centre of pin, thus avoiding any cross strain upon the piston-rod; a lack of attention to this point has been the cause of many serious accidents. The steam-ports are large, thus insuring the full pressure of steam to the point of cut-off. A very desirable feature of this engine, and one that will be appreciated, is the method of connecting the steam-valves with their stems, by which, if water should accumulate in the cylinder, and the engine be started without the usual precautions, the valves will lift, giving a free passage of the water through the steam-ports. The engine is extremely sensitive to the action of the governor, and is, therefore, particularly adapted to those situations where perfect regulation is required. All parts are well proportioned, made of best material, accurately fitted, and highly finished.

The Dead-Centre.

All reciprocating steam-engines have one dead-centre in each stroke and two in each revolution, and that point is the point at which the steam is exhausted, and the centre of the crank-pin is parallel with the centre of the axis of the cylinder. The centre of the cross-head, in some cases, may be above or below the centre of the cylinder; but by placing a spirit-level on the top or bottom

of the stub-end strap, the dead-centre may be easily found. The experienced engineer or machinist can generally tell by the eye when the crank is at the dead-centre; but to insure accuracy it is always better, in the case of horizontal engines, to try it with a level, and in vertical engines with a plumb-bob and line. The cranks of all engines have to be placed accurately on the centre when the valves are set.

A single reciprocating engine is completely helpless when the crank is at the dead-centre, and would stop there if it was not for the momentum of the balance-wheel. Double reciprocating engines, such as locomotives and marine engines, which have their cranks set at right angles, require no balance-wheel, as they pull each other off the dead-centre, in consequence of one crank being at its full-power point while the other is at the weakest. There are some engines, such as the rotary, which have no dead-centre in their revolution.

The Causes of Knocking in Steam-Engines.

The most frequent causes of knocking in steam-engines are lost motion in the cross-head, wrist- and crank-pin boxes; looseness in the pillow-block or main-bearing boxes; looseness of the piston-rod or follower-plate; the crank-pin or crank-shaft being out of line with the cylinder, or the wrist-pin, crank-pin, or mainbearing journal being worn oval; the slide-valve having too much or not enough lead; the exhaust opening being too soon or too late; the valve being badly proportioned, or the exhaust passage outside of the cylinder being contracted.

Other causes are shoulders being worn in each end of the cylinder, in consequence of the packing-rings not travelling over the counter-bore at each end of the stroke; or shoulders being worn on the guides, resulting from the cross-head shoes not overlapping them when the crank is at the dead-centre; the piston not having sufficient clearance at either end of the cylinder, in consequence of its being altered by taking up the lost motion in

the boxes; there not being sufficient draught in the keys to take up the lost motion in the connecting-rod boxes; the packing being screwed too tight round the piston-rod; excessive cushioning, resulting from the leaky condition of the piston, which allows the steam to occupy the space between the cylinder and piston-head, as the crank approaches the centre, thereby subjecting the engine to an enormous strain, as at this part of the stroke the fly-wheel is travelling very fast and the crank moving very slowly; or lost motion in the connection by which the slide-valve is attached to the rod. Engines out of line frequently knock sideways at the half-stroke, but most generally at the outward or inward, upper or lower dead-centre, as these are the points at which the greatest strain is thrown on the bearings, in consequence of the direction of the connecting-rod having to be reversed. The foregoing causes of knocking in engines constitute the principal ones.

The knocks arising from lost motion in any of the revolving, reciprocating, or vibrating parts of an engine may be located by placing the finger on the part, while the cross-head is being removed back and forth on the guides by the starting-bar; but knocks induced by the valve opening or closing too soon, by a contraction of the exhaust, or by the valve or valves being improperly set, are the most difficult to discover, as they are different from those induced by lost motion, the sound being a dull, heavy thud, in many instances causing the engine, building, and even the foundation to vibrate at every stroke. While an intelligent and careful search will in most cases result in successfully locating the knock, some will for a time baffle the most expert engineer. Instances are not uncommon in which weeks have been devoted, engines taken apart and put together again, to find a knock, which, when finally discovered, perhaps turned out to be caused by a loose crank-pin, follower-plate, or key in a fly-wheel. It not unfrequently happens that, after every other means have been resorted to, the indicator has to be applied, in order to determine the precise location of the knock or "thud."

From whatever causes knocking in engines may arise, they are