Two minor precautions should be observed. The check valve seat must be cleaned and ground occasionally to eliminate all danger of any blowing into the air line. The air-starter spring D must have sufficient tension to pull the stem out of contact with the cam. If the spring breaks or if the stem becomes dry and dirty, the end of the stem will continue to touch the cam nose while the engine is running. This will speedily mushroom the ends of the stem.
Primm Air Starter.—The Primm engine employs a very simple mechanism. This consists of a double-seated valve which is actuated by a push-rod. This push-rod is moved, through a bell crank arrangement, by a cam mounted on the flywheel hub. The operator follows practically the same procedure as with the starter already discussed. The only attention demanded is the grind ing of the starter valve.
Mietz and Weiss Air Starter.—On some of the Mietz and Weiss vertical engines the form of starter shown in Fig. 341 is used. The rocking or corliss type of starting valve A is actuated by an eccentric on the engine shaft. As indicated in the draw ing, it is equipped with a check valve B, as well as a disk valve C, immediately at the cylinder to shut off the air after the engine is in operation. In starting it is only necessary to bar the engine a few degrees past upper dead-center and open the hand-con trolled valve. The starter eccentric will then open and close the rocking air valve at the proper times until the air supply is cut off, and the engine begins firing.
Starting an Engine.—All engines have minor differences in the method of starting. The following is the procedure that applies to practically all of the low-pressure engines.
The engine should first be barred over to its starting position. Usually the flywheel carries a mark to indicate when this position is reached. If not, the engineer can locate the position of the crank by means of the split in the flywheel hub, if it be of this design. After locating the crank position, the wheel should be turned until the crank is about 30 degrees past the rear dead-center.
The indicator or test cock on the engine should be opened. In fact, it is better to open it before turning the engine over since it will relieve the compression. The starting torch is next ignited and the flame directed against the ignition device, whatever design be used—hot ball, hot tube or hot head. While the
torch is heating the igniter, the operator should fill up the oil and grease cups.
The fuel should next be admitted into the pump. After the torch has been burning for some minutes, the fuel pump should be operated by hand until the plunger works hard. This shows that the discharge oil line to the nozzle is filled. The pump handle should now be given about three strokes, injecting some of the fuel into the cylinder. If this results in a blue vapor issuing from the test cock, it can ,be assumed that the igniter is hot enough. The test cock is now closed, and a final stroke is given to the pump.
The air-starter mechanism is next operated, and the engine is turned over. Ordinarily the engine will not explode on the sec ond revolution, and it is generally advisable to allow at least three air charges to enter the cylinder. The engine should now ignite the fuel. If it fails to do so, the operator should discontinue his efforts to start the engine with the air and should proceed to heat the igniter to a higher temperature. A cold igniter is almost al ways the cause of a starting failure.
When the engine begins to fire the fuel, in most cases, there is a decided pound or preignition. The operator should restrain the motion of the pump plunger, preventing any great amount of fuel from being ignited. Since the governor is in its lowest posi tion, the fuel charge at starting is heavier than when fully loaded. A few strokes of the piston will allow all the fuel in the cylinder • to burn, and the stroke of the pump can be lengthened a little. Until the engine is up to full speed, the engineer should continue to restrain the stroke of the fuel pump.
The cooling water should now be turned on; it is best to open the valve slowly, thus allowing the cylinder head to cool off grad ually. If the opening of the cooling-water valve is neglected until the engine becomes thoroughly hot, a fractured head will, in most cases, occur when the water does strike it. Frequently, when starting, the connecting-rod emits a snappy or whip-like sound, while the piston slams if worn at all. This merely indi cates that the engine is coming up to speed too rapidly, and the operator should lessen the amount of fuel injected by control of the pump plunger stroke.