The McEwen Diesel Fuel Valve.—Another design of open type fuel valve is found on the McEwen Diesel. As outlined in Fig. 124, this valve consists of a cast-iron housing, or cage, which is bolted to the cylinder head with the axis of the fuel nozzle coincident with the axis of the cylinder, and of the neces sary atomizer and needle valve.
The fuel oil enters the valve at a and, passing around the ball check, deposits in the fuel chamber b; part of the charge also flows into the fuel valve plug. The air charge enters at c and surrounds the base of the valve stem at d. When the needle valve opens, the air passes through the valve opening and into the air port e; a part also completely fills the fuel valve nut cavity where it exerts a pressure on the oil contained in the reservoir b. The air flowing through the port e toward the cyl inder attains a high velocity with a decrease in pressure. The air`above the oil, having a fairly large volume, maintains its original pressure. This unbalanced pressure produces a flow of oil in the port F. This oil, after passing through the small chan nels G, encounters the stream of high-velocity air and. is swept into the cylinder. The oil issues from the channels G in very fine streams, which are quickly mixed with the air. The atomiza tion is further increased by the action of the atomizating plate H. This valve is one of the best yet designed. The air does not "slug" the oil, causing a poor atomizing effect. On the contrary, the channels G are of such cross-section that the oil issues from them in streams of a size that will allow a thorough breaking-up by the air. Regardless of the engine load and the volume of the fuel charge, the rate of fuel injection into the cylinder is fairly constant with any given fuel. Even a decrease of 100 lbs. in the injection air pressure apparently has but minor effect on the degree of atomization. Oils of different characteristics do not flow through the passages at identical rates. The natural consequence is a variable rate of fuel injection unless disks with different size passages are employed. A partial remedy lies in the control of the injection air pressure. Figure 125 is an early model used on the McEwen engine. It differs but slightly from Fig. 124. .
Adjustments.—The ball check valve requires some attention; especially is this true with dirty oils. In case the seat is worn, a new contact can be formed by using a hardwood stick or soft copper pin; lightly striking the pin will cause the ball to renew the curvature of the valve cage seat.
The roller, actuating the valve, is mounted on an eccentric. A lever moves the roller into and out of contact with the fuel cam. In changing the valve timing, the rocker roller can be moved by means of the adjusting pin. The adjusting pin passes through the roller pin or bearing and moves the bearing along the slots shown. The fuel valve rocker set-screw, resting on the end of the valve stem, controls the clearance between stem and rocker.
`Allis-Chalmers Diesel Fuel Valve.—The fuel valve of this engine is of the open type, Fig. 126. The body is a steel block, the'nozzle extension of which fits into the cylinder head. The oil enters the valve body at the bottom, the line having two poppet check valves. The air enters the block at the top and fills a recess behind the fuel valve. As the lever or rocker arm lifts the valve, the air rushes through the valve opening and flows into the oil cavity at the.point a. As it passes over the body of fuel, the air picks up the oil and blows it into the cylinder. The velocity of the air stream, together with the action of the atomizer, breaks up the charge into particles. The nozzle tip is flaring in contour, causing the mixture of air and oil to assume a cone shape.
Adjustments. Check Valves.—The oil check valves require regrinding at intervals, especially with dirty oils. The check valve cage is quite easily removed for valve repairs by un shipping the oil pipe line and unscrewing the cage from the fuel valve body.
Needle valve is of generous dimensions, and consequently very little regrinding is necessary.
The Atomizer atomizer, since it is exposed to the cylinder temperature, carbonizes or gums from the small amount of oil that adheres to the atomizer after the air blast ceases. A spare tip should be on hand at all times. The presence of deposits will ordinarily be indicated by the engine laboring until the injection air pressure is raised.