Exhaust valve

“ As the piston moves rapidly up the cylinder on the exhaust stroke it pushes the gases in front of it out through the exhaust opening, but when it gets to the top of its stroke the piston stops and then comes down again for the suction stroke, whereas the gases will tend to keep on moving if they are not unduly restricted in their passage through the exhaust system, so that we can generally obtain some slight advantage by giving the exhaust valve a small amount of lag in closing. ”

“ If the secondary circuit is proven to be in good condition, attention should be paid to the carburetor, for a poor mixture, or water in the gasoline, will cause the engine to miss. A badly fitting exhaust valve will permit the burned gases to be drawn back into the cylinder, the fresh charge thus being weakened, and as the valve will shift around on its seat, this may happen irregularly. ”

“ This maximum-capacity theory of valve operation, with its neglect of acceleration forces and seating velocities, may well have been at least partially if not largely the cause of their exhaust-valve troubles and the seemingly disproportionate amount of development they devoted to this part, as reported by Chenoweth, although it is also true that the exhaust valve continued to present a problem in the aircraft piston engine for a great many years after, even with the most scientific of cam designs. ”

“ Exhaust Piping
From each atmospheric exhaust valve, which is direct-connected to the condensing chamber at each low-pressure cylinder, is run downward a 30-inch riveted-steel exhaust pipe. At a point just under the engine-room floor the exhaust pipe is carried horizontally around the engine foundations, the two from each pair of engines uniting in a 40-inch riser to the roof. This riser is between the pair of engines and back of the high-pressure cylinder, thus passing through the so-called pipe area, where it also receives exhaust steam from the pump auxiliaries. ”

“ When the maximum power is required, the exhaust valve is not interfered with, and opens to its fullest compass. When less power is required, the exhaust valve is prevented from opening to that extent. Consequently the exhaust gases are not fully expelled, and as they partly occupy the space in the combustion chamber, a full charge of mixture cannot be admitted through the induction valve, and the explosion is weakened. ”

“ The pressure of the gases in the cylinder after the exhaust valve closes will nearly always be a little above atmospheric pressure, and therefore nothing is gained by opening the inlet valve immediately the exhaust closes—we generally allow an interval of 5 degrees, which means that the total lag of the inlet valve is 10 degrees in opening, or the inlet36 valve does not begin to open until the crank has moved 10 degrees off its top dead-centre on the downward suction stroke. ”

“ With the gas, as with any other kind of engine, the valve settings are of primary importance. On very small engines it is often the case that only the exhaust valve is operated mechanically.
Again, there are several well-known makes which operate the gas and exhaust mechanically while the air valve is opened by suction alone. Though opinions differ as to which is the best course to take, there can be little doubt that, with all three valves mechanically operated, a greater nicety of adjustment is obtainable than would be otherwise possible. ”

“ The exhaust should open when the crank lacks 30° of completing the outer end of the power stroke, that is, the crank should make an angle of 30° with the center line of the cylinder when the exhaust valve begins to open, and should be inclined AWAY from the cylinder. Some makers have the exhaust open a little later in the stroke, but little is to be gained with a later opening as the retention of the charge beyond 30° heats the cylinder and does very little towards developing power. ”

“ At the end of the working stroke the exhaust valve must liberate the gases and remain open to the end of the scavenging stroke to eliminate the residual gas while the closed inlet valve prevents the burnt gases from being forced through the inlet pipe and carburetor. ”

“ When the valves fail to seat themselves properly, there is a possibility that the springs may be weak or broken. A weak inlet spring would probably not affect the running of the engine, but weakness in the exhaust valve spring causes a very uneven action, which is difficult to locate. The symptoms area lag in the engine due to the exhaust valve not closing instantaneously, and as a result a certain percentage of the charge under compression escapes, greatly diminishing the force of the [14] explosion. ”

“ There is always an opening in the cylinder head—a relief valve, the spark-plug opening, or other—and a stiff wire may be dropped through it, with its lower end resting on the piston and its upper end projecting. As the piston is moved by cranking the engine, the wire will move with it, and is to be marked with a file at its highest and lowest positions. While no fixed rule can be laid down, it may be said that in general the exhaust valve should close when the piston has made from 1/64 to 1/32 inch of its outward stroke. ”

“ The inward movement of the piston pushes out of the open exhaust valve the gases that have not escaped through their desire to expand. The exhaust valve remains open for the entire stroke, but when the engine is running at high speed the piston moves so rapidly that the gases cannot escape fast enough to prevent their being slightly compressed. When the piston is at its inmost point, the gases are still flowing through the valve because of this slight compression, and if the valve closed, a portion would be retained. ”

“ This valve being already weighted with the pressure of the air compressed to six atmospheres by the means previously explained, a certain quantity of air is thus forced into the vessel; at this moment, another revolution of the main shaft causes the equilibrium valve at the bottom of the conducting-pipe to be shut, and at the same time opens the exhaust valve at the foot of the vertical column. ”

“ The valves, which are all of the conical-seated lift type, are four in number—charge inlet valve, gas inlet valve, igniting valve, and exhaust valve. The igniting valve is usually termed the timing valve, because it determines the time of the explosion. 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. ”

“ 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. ”

“ They are sometimes used instead of slide valves, but are objectionable because a separate admission and exhaust valve is required at each end of the cylinder, and because at quick speeds of revolution they fall to their seats with a shock or blow which wears out both the valve and the seat. When a high piston speed is obtained by great length of piston stroke, and not by high rotative speed, their use is less objectionable. ”

“ The burned gases pass out through the exhaust valve side and in so doing often deposit small pieces of carbon, which keep the valve from seating properly and let perfectly good mixture escape. If not cleaned often, the heat and constant tapping of the valve against the seat will hammer the carbon fast to the valve or seat as though it had been fused there. Carbon must be scraped off frequently and as often as necessary the valve should be reground into the seat. ”

“ BINDING GOVERNOR COLLAR, stuck with dirt or gummy oil, will cause the engine to die under load, and overspeed on light load.
INLET VALVE LOCK may be worn in such a manner as to prevent the valve from seating during the idle strokes and lose fuel, or cause overspeeding.
DETENT LEVER KNIFE EDGE may be worn, or rounded off, so that the exhaust valve is not held open for the idle stroke. This defect will cause overspeeding.
SPEED CHANGING LEVER may work loose and cause the speed to vary erratically. ”

“ Sticking valves.—With the inlet valve this trouble may be caused by oil and dirt. If this is the case it can be taken out and washed in petrol and replaced. The car may not run as it should do on account of the inlet{58} and exhaust valves being pitted and needing grinding in. To grind in use a little emery-powder and oil, and plenty of “elbow grease” until you succeed in eliminating all the little pits and making the surface quite smooth. (Be careful to clean off all traces of the emery after grinding.) ”

“ The slipping of the eccentrics is about the only cause for a valve working badly. You should therefore keep all grease and dirt away from these marks; keep the set screws well tightened, and notice them frequently to see that they do not slip. Should they slip a I/I6 part of an inch, a well educated ear can detect it in the exhaust. Should they slip a part of a turn as they will some times, the engine may stop instantly, or it may cut a few peculiar circles for a minute or two, but don't get excited, look to the eccentrics at once for the trouble. ”

“ The deterioration of piston-packing, and the rounding of valve-seats, which produce an asthmatic exhaust, may be followed in their downward course if the engineer gets into the habit of listening to the exhaust, and marking its changes. It is very important that he should do so. The man whose ear from long practice has become sensitive to a false tone of the exhaust, needs not to make experiments, by applying steam to the engine while it stands in various positions, in order to find out where a blow comes from,—whether it is in the pistons or in the valves. ”

“ The overrunning of the exhaust ports at once causes the pressure in the cylinder to fall to atmosphere, and then the pressure in the displacer overcomes the pressure in the motor cylinder and opens 499 the lift valve, when the charge flows in to the motor cylinder through the conical compression space and displaces the exhaust gases through the ports E, while it fills up the cylinder A with the inflammable charge. ”

“ Although we have spoken throughout as if the eccentrics were so set in relation to the crank, and the slide valve so proportioned that the steam was all pushed out by the piston when exhausting, it should be understood that the exhaust port is closed just before the piston reaches the end of each stroke, so that a small quantity of steam is what is called 'trapped' in the cylinder. ”