Piston ring

“ Two men walked around pushing the lever, and when the tool at each revolution arrived at the groove, a fresh cut was taken by moving the engine so as to raise the piston the necessary amount. It is obvious that the piston head may be steadied and held true in the bore of the cylinder by means of a few wooden wedges. Thus we see that in this operation the junk ring was made to serve as a boring bar head, the men furnishing the necessary rotative motion, the feed motion to the tool being obtained by advancing the piston toward the end of the cylinder where the work was being done. ”

“ They removed two of the piston junk-ring studs, screwed in two strong iron eye-bolts by way of handles, doubled the wire-rope, and set half a dozen men to smite with an extemporised battering-ram at the end of the piston-rod, where it peered through the piston, while the donkey-engine hauled upwards on the piston itself. After four hours of this furious work, the piston-rod suddenly slipped, and the piston rose with a jerk, knocking one or two men over into the engine-room. ”

“ Under each carriage is a vacuum chamber (Fig. 85) riding on trunnions, E E, so that it may swing a little when the brakes are applied. Inside the chamber is a cylinder, the piston of which is rendered air-tight by a rubber ring rolling between it and the cylinder walls. The piston rod works through an air-tight stuffing-box in the bottom of the casing, and when it rises operates the brake rods. It is obvious that if air is exhausted from both sides of the piston at once, the piston will sink by reason of its own weight and that of its attachments. ”

“ The Piston is another very important part in the construction of an engine, and it conveys the power of the steam to the crank. It is composed of a piston head, on which are placed the piston rings held in position by the follower plate, and is securely attached to the piston rod. Great care should be taken in the construction of the piston rings to have them fit the cylinder perfectly tight, at the same time to have the least possible friction. ”

“ When piston rings or cylinder walls are cut or scratched by running without oil, the pressure will escape into the crank case, which, while warm when the engine is running properly, will be heated to a very noticeable degree under these circumstances. The only remedy is the use of new piston rings and the reboring of the cylinder. Piston rings, being of cast iron, are brittle, and must be handled carefully. To place them in position in their grooves, thin strips of steel, like pieces of a hack-saw blade, should be bound to the piston, covering all but the lower groove. ”

“ The piston pin was locked in the piston by the usual set screw, but here no provision was made for the alternate practice of clamping the rod on the pin. This piston-pin setscrew construction had become a standard arrangement in automobile practice. The piston rings were the normal wide design of that time, with what would now be considered a low unit pressure.
Quite early in the life of this engine model the practice was initiated of incorporating shallow grooves in the surface of the more highly loaded thrust face of the piston below the piston pin to provide additional lubrication. ”

“ The follower of a piston is a plate or cover that is employed to hold the piston rings in place, and the piston rings should be so fitted that the follower should be bolted firmly up, or otherwise the bolts may come loose and work out, and getting between the piston and the cylinder cover, may cause the piston to knock the cylinder cover out. ”

“ Frequently we find steel pistons used, as they may be made lighter for the same strength, and then steel piston rings may be used; they are not much in favour for ordinary motor-car engines because the steel pistons expand at a greater rate than the cast iron of the cylinder, so that there is more liability to seizure. The crown of the piston is sometimes curved upwards and at other times curved downwards, but more often it is flat as shown in Fig. 17. The gudgeon pin is20 sometimes made of mild steel, and the surface is then case-hardened in the centre where the connecting rod end bears. ”

“ Larger plate.
[132]
Section 58.—PACKINGS, JOINTS, STUFFING BOXES, &c. PISTONS. 1089. Piston with junk ring; the packing is sometimes cast iron, steel, brass, or phosphor bronze rings, or even hemp or asbestos.
1090. Small pistons have generally two rings of steel or brass sprung into the grooves.
1091. Double-acting hydraulic piston for cold water; if single acting, one leather only is required; for hot water, rings are generally employed.
1092. Indiarubber rolling ring packing, used on Kennedy’s patent piston water meters. ”

“ Needless to say, the lubrication of the piston rings is of very vital importance, for on that depends the free working of the piston in cylinder. In single-cylinder engines, they require frequent attention, and paraffin should be squirted down the compression tap at regular intervals. ”

“ A tight joint is maintained between it and the cylinder walls by cast-iron piston rings, which are of square or rectangular cross-section, split so that they may spring open, and fitted into grooves cut around the piston. They are of such shape that their tendency to expand keeps them pressed against the cylinder walls, but being split, their elasticity prevents their binding; they fit the grooves snugly, and while they may move freely in them, they hold the pressure from escaping. ”

“ Of course it must not pass far enough to allow any steam to get through.
Self-setting piston rings are now generally used. They are kept in place by their own tension. There will always be a little leakage at the lap. The best lap is probably a broken joint rather than a diagonal one. ”

“ The two smaller balance pistons, L and M, are allowed to remain on the high-pressure end; but the largest piston, Z, is placed upon the low-pressure end of the rotor immediately behind the last ring of blades, and working inside of the supplementary cylinder W. Being backed up by the body of the spindle, there is ample stiffness to prevent warping. This balance piston, which may also be plainly seen in Fig. ”

“ This system, in which I dispensed with the packing for air-pump buckets of condensing steam-engines, I have also applied to the pistons of the steam cylinders, especially those of high-pressure engines of the smaller vertical construction, the stroke of which is generally short and rapid. Provided the cylinder is bored true, and the piston is carefully fitted, and of a considerable depth in proportion to its diameter, such pistons will be found to perform perfectly all their functions, and with a total absence of friction as a direct result of the absence of packing. ”

“ The piston is a casting, and has to be turned in the lathe to fit the cylinder, and a groove run round it to hold the greased cotton to make it steam-tight. Whilst in the lathe drill a hole in the centre, and tap it to receive the piston-rod, which you can make out of steel wire. Then pass one end through the stuffing-box on cylinder-cover and screw it on the cross-head J (Fig. 1) , having first filed it up quite square and true and finished it off with emery. ”

“ The webs, which afford at the wrist pin bearings the means for connecting the piston rod with the piston, serve to hold the head and skirt in proper relation to each other so that the air space between them retards flow of heat from the head to the skirt, undue expansion of the skirt, and the consequent increase of friction between piston and enveloping cylinder. Undue expansion of the piston is said by the patent's specifications to be avoided by the separation of the skirt by the longitudinal split in order to admit of unrestrained movement of the edges of the skirt toward each other. ”

“ An open-ended “trunk” piston, similar in principle to that used in gas engines, is employed; and the valve is of the piston type, which is less complicated than the box form of valve, though less easily made steam-tight in small sizes. The engine is single-acting, making only one power stroke per revolution.
The cylinder is a piece of brass tubing; the piston another piece of tubing, fitting the first telescopically. Provided that the fit is true enough to prevent the escape of steam, while not so close as to set up excessive friction, a packing behind the piston is not needed ”

“ The labyrinth packing of the high-pressure and intermediate pistons has a small axial and large radial clearance, whereas the labyrinth packing of the piston Z has, vice versa, a small radial and large axial clearance. Elimination of causes of trouble with the low-pressure balance piston not only makes it possible to reduce the diameter of the cylinder, and prevent distortion, but enables the entire spindle to be run with sufficiently small clearance to obviate any excessive leakage of steam. ”

“ It was far too long a job to take off the sump at the roadside—it would have meant taking the whole engine out of the frame—nearly a day's work—so I removed as many of the pieces of piston as I could get at through the inspection window. The piston-head was floating loose like a flat disc above the small end. This I removed and packed the two halves of the broken gudgeon pin [Pg 220] apart, so as to guide the small end up and down in the cylinder. ”

“ The packing of the piston now gives us little or no trouble, it goes from a fortnight to a month, opening the top now and then to screw it down, as it gets slack, which should be attended to. We use no grease or oil in packing the piston or working the engine, having found blacklead mixed with water, and poured 'a little now and then' through a hole on the top into the steam-cylinder, suits the packing of the piston much better, and is cheaper than anything else. About 1s. worth of blacklead will last our engine a week. ”

“ The cover, when bolted on, forms a part of the cylinder; the piston rod is cast solid with the piston, and is made sufficiently large at its outer end to receive the tool. These two parts constitute an engine, and with less than one fixed and one moving part it is obviously impossible to develop power in a machine by the action of an elastic fluid. ”

“ The space for the stuffing or packing is marked C. This is filled with lamp cotton, and when the gland is [134] screwed down the cotton is compressed, so that it makes a steam-tight fitting for the piston-rod to slide in. The hole for the piston-rod is shown through the centres of both sections. As before explained, the gland on the left is secured by two screws shown in the section; it is fitted into a plain cylindrical hole. The other gland is threaded to screw direct into the cylinder cover, which is tapped to receive it. The first method is the one always employed in large engines. ”