REVERSING AN ENGINE.
To reverse the motion of a plain Slide Valve engine, remove the cover of steam chest and place the engine on the dead center. Observe the amount of lead or opening that the valve has on the steam end, then loosen the eccentric and turn it around on the shaft, in the direction the engine is wanted to run, until the valve has exactly the same amount of lead at the other end; then turn the engine to the opposite center, to determine whether the lead at this end is the same as at the other; then place the crank at half stroke top and bottom, and see that the port openings are equal in both positions, and replace cover.
Q. What is dead center?
A. The dead center of an engine is the point where crank and piston rod are in an exact line.
Q. What is a half stroke?
A. It is the point reached by the piston after traveling exactly one-half its travel.
Q. What is the meaning of “lost motion”?
A. Lost motion is looseness of the connecting rod at crank or wrist-pin, or looseness of the link or link block, cross-head and guides, main crank shaft and pillow block, caused by friction and wearing away of the metals and the neglect to take up the wear.
The lost motion in all parts of an engine should be taken up frequently, to keep it running smoothly, but care must be taken not to tighten bearings or keys too tight.
Q. What is lap and lead?
A. Lap is the position of the valve which extends or laps over the edge of the ports when the valve is in its central position. That on the inside of the D is the inside or exhaust lap, while that at the ends of the valve is the outside lap and affects the admission and cut-off.
Lead is the amount of opening which is given to the port by the valve when the engine is on the center.
Lead on a valve is the admission of steam into the cylinder before the piston completes its stroke.
Q. How much “lead” should a valve have?
A. There is no general rule for the amount of lead that would be best suited for all makes of engines. It must be determined by the design or construction, speed and work required, to produce the best results for economy and quietness in running.
Q. What is a throttle engine?
A. A throttle engine is one in which the speed is controlled by throttling the steam with a governor, as opposed to an automatic engine in which the speed is regulated by varying the point of cut-off at the valve.
Q. What is the difference between a stroke and a revolution?
A. A stroke is the movement of the piston, from one end to the other of cylinder. A revolution takes two strokes of piston.
Q. How are steam packing rings put on the piston head?
A. Remove the back cylinder head and take the piston and rod out of the cylinder, and stand it “head up.” Then place the inside of the ring, opposite to the opening, against the side of the piston head next to you; gradually press the ring open with your hands, and it can be easily slipped over the head and put in place.
Q. How is a piston put into cylinder?
A. It is always entered from the back end in horizontal engines. The rings (if steam packing) should be carefully placed in position and compressed by the hand if piston is small, but if large, curved blocks of wood or a band of sheet iron can be used to support them until they enter cylinder. When the piston rod passes through the stuffing box, it should be supported at outer end to prevent cutting.
WATERTOWN HIGH SPEED ENGINE.
The frame of this engine is very heavy, with longitudinal and cross ribs securely bracing it. It forms the lower guide for cross-head, and contains the pillow block bearings at the front end. It also forms the front cylinder head, to which the cylinder is bolted. The working parts are placed as low in the frame as is possible, so that the strain is brought in line with the line of greatest resistance.
The double disc center crank shaft allows of two small heavy band wheels, one of which has the shaft governor attached to the inside, that operates the valve automatically to give the point of cut-off in accordance with the variation of load.
The valve is of a special design, and so constructed as to admit steam to the cylinder port through four different openings. It also exhausts steam through four different openings at once.
The engine frame rests its whole length and is securely bolted to the sub-base, which is bolted to the floor, and the smaller sizes need no elaborate foundations.
This style of engine ranges in size from 35 to 350 horse-power approximately, the speed of the smaller ones ranging from 275 to 325 revolutions, and of the larger from 160 to 185 revolutions, and are used extensively where high speed is required, and where the load is of an intermittent character.
Watertown High Speed Engine.