Valve gear

“ When there is no link motion, a Joy valve gear, a Marshall valve gear, or a loose eccentric may be used. A loose eccentric is one that can be moved around the shaft to reverse the engine. It may be moved around the shaft by mechanical means, or the eccentric rods may be disconnected, and the valve worked by hand, to cause the engine to run in the required direction, until a pin fast in the shaft meets a lug on the eccentric and drives it, there being two such lugs or shoulders spaced the requisite distance apart on the eccentric. ”

“ Valve gear, with single eccentric, and variable travel, adjustable by hand wheel. The eccentric drives a block to and fro in a slot, the angle of which in respect of the slide valve centre line is variable by a rocking motion controlled by a hand wheel. ”

“ A broken exhaust-valve stem or a broken or displaced spring will often be difficult to observe; a valve may have stuck open through stiffness or through something getting under its seat. The exhaust-valve gear should be carefully watched to see that all the valves work regularly and to their full extent. ”

“ The journals of the shaft, and all cylindrical wearing surfaces, are finished by grinding in a manner that leaves them perfectly round. The crank-pin and cross-head pin are hardened before being ground. The joints of the valve-gear consist of pins turning in solid ferrules in the rod-ends, both hardened and ground. After years of constant use thus, no wear occasioning lost time in the valve-movements has been detected.
High speed and short strokes are essential elements of economy. It is now well understood that all the surfaces with which the steam comes in contact condense it. ”

“ As there are so many more parts in the valve gear, in which lost motion may occur, it is manifestly preferable to take up that play by moving the driving wheel in a continuous direction, rather than to move the latter back to accommodate any play there may be in the connecting rod. ”

“ All 500 feet long. Cylinder bore, 121⁄2 inches; stroke, 24 inches; speed, 130 revolutions per minute.
“The dimensions and general form of the running gear were made from drawings sent to me by you. The valve-gear differs only in divorcing the exhaust valves from the steam valves by placing them on the opposite side of the cylinder and driving them from a separate eccentric on that side, and not from the link.
“The framing for each engine of a pair is like a Porter bed standing on end with two posts forming what would be the lower part of the bed if it were lying down. ”

“ If with the engine standing still we move the link motion from full gear forward to full gear backward and watch the valve, we shall find that the valve lead increases as the reversing lever approaches the upright position, or mid gear as it is termed, and that after passing that point it gradually diminishes again, the valve being so set that the lead is the same for full gear forward as it is for full gear backward. ”

“ A. A direct motion valve gear is one in which the valve moves in the same direction as the eccentric rod, that is doing the work, in many cases no rocker arm is used. In case a rocker arm is used, both arms point in the same direction like the letter U. An indirect motion valve gear is one in which the valve moves in an opposite direction to the eccentric rod doing the work. ”

“ Since the valves have each to act once in every two revolutions, they cannot be operated by cams or eccentrics placed directly on the crank shaft. The valve shaft D is driven at half the rate of revolution of the crank shaft C by means of the skew or worm gear E, one wheel of which is mounted on the crank shaft and the other on the valve shaft. ”

“ In either case brass or gunmetal bearings, often lined with white metal, are fitted for the shafts to revolve in, and the engine cylinders are mounted on the top of the chamber. Provision should be made39 on the sides and ends of the crankchamber for fitting the magneto and oil pump and also the water pump, if required. There must also be some form of housing or extension of the chamber to enclose the timing wheels, and sometimes the whole of the valve gear is contained within the crankchamber to ensure proper lubrication for it and stop any noise from it reaching the outside world. ”

“ Screw stopper. See No. 2544.
2461. Slotted nut and set pin for fine adjustment, or for taking up wear.
Lock nuts; usually two nuts are employed, the thickest one outermost. There are many forms of patent nuts designed to prevent loosening by vibration.
Nuts can be cast around a screw in white metal or brass.
Section 79.—SLIDE AND OTHER VALVE GEAR. (See also p. 172.)
2462. Cut-off gear. Two cut-off valves similar to No. 1456, regulated by an external hand wheel forming the valve spindle guide bush.
2463. Duplex motion for a valve, to operate it by either rod, using the other as a fulcrum. ”

“ The valves of a marine engine that are worked by hand are, the stop valves for letting on steam from the boiler, the safety valve, which is lifted to see that it is in proper working order, the Kingston valve for letting in the circulating water, the blow through or starting valve for warming the cylinders and starting the engines. The valve for adjusting the rate of boiler feed has its lift adjusting screw operated by hand. The slide valve may also be operated by hand before the engine is started, or it may be operated by a steam reversing gear. ”

“ The gear is extremely simple, and has worked without any trouble, the only setting required being the adjustment to length of the valve spindles, and the setting of one fixed centre on each side of the engine.
The springs consist of rubber pads placed between the axle-box and the horn-block. They are simple to fit, take up no room, never get out of order, and last many years. I have no steel-carrying spring on any of my stock.
The safety-valve spring is entirely within the boiler, so that it cannot be tampered with or injured by accident. ”

“ Each sleeve is operated by a connecting rod and eccentric mounted on a shaft driven by a chain or gears from the crank shaft of the motor. The eccentric replaces the cams of the poppet valve motor, and as it must maintain a certain relation with the position of the piston in order that the operation of the valves shall be timed correctly, the same care must be observed42 in replacing the eccentric shaft with the proper teeth of the sprocket or gear in mesh as has already been described in connection with the cam shaft of the poppet valve motor. ”

“ The pump is driven off a bevel gear integral with the crankshaft and is of the gear type, being without valves or moving parts other than two simple spur gears. It is entirely enclosed in a fine mesh screen through which the oil must pass to reach the pump.
Valves:
The valves have cast-iron heads reinforced with a perforated steel disc embedded in the cast iron, the whole being electrically welded to a carbon steel stem. The cam shaft is hardened and ground and cams formed integral with the shaft. The cam contour is also ground, the valve timing being exactly the same in each cylinder. ”

“ The following list will give the principal defects due to the wear of the valve mechanism.
(a) WORN CAM GEARS change timing because of play, or “back lash” in the teeth, or cause a howling or grinding noise, that will cause the owner to believe that the end of the engine is near. MISFIRING and LOSS of power are probable results of a change in the timing. If any of the teeth are stripped from the gear you may be sure that the timing is changed. Replacement with a new gear is the only cure for a worn or broken gear. ”

“ On the simple engine a piston valve is used, the seat of the valve completely surrounding it and the ports being circular openings, the result, it is claimed, being a balanced valve.
The valve reverse gear is of the Woolf pattern, the engine frame of the girder type, Waters governor, with special patent speed changer, specially balanced crank disc, patent straw burner arrangement for straw burning engines, special patent spark extinguisher, special patent gear lock, and special patents on front axle, drive wheel and loco cab. ”

“ This is all very well so far as the connecting rod and piston is concerned, and will cause them both to stand on their respective dead centers with the lost motion taken up; but, in moving the wheel back to the dead center, we have given full liberty to all the lost motion in the various parts of the valve motion or gear, as already explained, in reference to moving the eccentric upon the shaft. ”

“ In this engine the connecting rod trunk centre and the piston are made to distribute the steam as shown.
2466. Reversing movement for a valve, where the power will only move the valve to the half stroke or mid position, as in a slide valve hydraulic engine (see No. 1026) , the rolling weight then completes the movement (see also No. 1740) .
2467. Automatic or governor cut-off gear. The governor operates the sleeve, which has a screw movement on the pin fixed to the crank shaft; a parallel feather on the sleeve revolves the cut-off eccentric, and varies the travel of the cut-off valve. ”

“ To lift the dock the engine working the valve shaft is started, and with it the operating screws. These, through the levers, open the inlet valves. The rams now begin to move up: if any one has a light load it will move up ahead of the other, but in doing so it lifts the other end of the lever and closes the valve. In fact, the screws are continually opening the valves, while the motion of the rams is continually closing them, so that no ram can move ahead of its screw, and the speed of the screw determines the rate of movement of the lifting platform. ”

“ If the motor is turned but very little beyond this point, a lifting should be felt at the proper push rod or valve stem.
It is well to test the setting of the valves occasionally by means of these marks, for wear at the rocker arms, the push rods, the valve stem, or the cam travelers will result in unevenly-timed valves. It should be remembered that it is the valve itself that should open after the proper mark on the flywheel has been passed, and that the movement of a long push37 rod is not sufficient evidence that the valve is beginning to leave its seat. ”

“ As the water is incompressible, slide valves must have neither lap nor lead, and piston valves are preferable to ordinary slide valves. To prevent injurious compression from exhaust valves closing too soon in rotative engines with a fixed stroke, small self-acting relief valves are fitted to the cylinder ends, opening outwards against the pressure into the valve chest. Imprisoned water can then escape without over-straining the machines. ”

“ The outer sleeve acts really as a distributor; the inner sleeve supplies the pressure tightness required to resist compression and explosion. The idea of working exhaust and inlet by two sleeves within which the main piston operates is very daring and ingenious; and for these small engines the sleeve valve system works admirably. There are many advantages; the shape of the compression space is a most favourable one for reducing loss by cooling. All the valve ports required in ordinary lift valve engines are entirely dispensed with ”

“ The valve rod must be accurately guided so as to avoid side strains; the valve must fit accurately to its seat and to the cover plate, and the adjustment so made that the valve slides freely at first, being steam tight, and yet allowing room for lubrication to enter. When the travel of a valve, balanced by a cover plate, is varied to alter the point of cut off, the construction must be such that the ends of the valve at the shortest stroke pass over the ends of the seat and cover plate faces, or otherwise the middle of the seat and cover plate faces will wear hollow. ”

“ A thin film of the grinding compound is evenly applied to the seating face of the valve head, a screw driver or ratchet fork is set in the groove on the head of the valve, and the handle rolled between the palms of the hands, covering about one-third of the distance around the valve seat ”

“ This can be done with ordinary valves also, provided the spring has not injured the upper surface of the disc. Valve seats are generally pressed into the plates, although instances may be found where they are screwed. When pressed in they may be withdrawn by substituting a bolt having longer screw threads than the regular bolt, and provided with a nut, as shown in Fig. 188. The bolt is slipped through a yoke and screwed into the bridge. By turning the nut the seat can generally be started without difficulty. ”

“ The bolt B has a very small hole bored through it from end to end. When the vacuum is broken slowly, the pressure falls in D as fast as in the pipe; but a sudden inrush of air causes the valve A to be pulled off its seat by the diaphragm C, as the vacuum in D has not been broken to any appreciable extent. Air then rushes into the train pipe through the valve. It is thus evident that the driver controls this valve as effectively as if it were on the engine. These "emergency" valves are sometimes fitted to every vehicle of a train. ”

“ Valve body, an aluminum housing, located at the rear of the gun and mounted on the grip support by means of four screws and lock washers. The valve body has four large threaded openings. The lower opening leads into the valve grip. The side opening, which forms a Y with the main portion of the body, is connected to the fuel-hose assembly. The front opening is screwed on the barrel. The rear opening is closed by the spring retainer and plug.
(2) Valve-diaphragm assembly, which transmits and reverses the movement imparted to it by the rocker arm of the valve grip. ”