Before the invention of the injector, cases occasionally happened of the heater-pipe acting as an injector. Where the end of the heater pipe was carried through the feed-pipe, and pointed towards the check-valve, starting the heater under favorable conditions would carry the water into the boiler. A great many old engineers relate instances where this has happened.
SKILL AND REFLECTION NEEDED IN REPAIRING INJECTORS.
Injectors can be kept in good order with less work than is needed to keep a pump going, but the highest kind of mechanical skill is required for the injector when repairs must be done. Almost any kind of machinist can fit a new chamber or plunger into a pump. Many men who will do this job satisfactorily will get badly left when they try to put a defective injector in order. To do such work, thoughtful reflection is called for, besides the hand that can do accurate fitting. A workman who may be good on guides or cross-heads or links, takes an injector apart that will not work, and can perceive nothing wrong with it, because he has not got the philosophy of the thing through his head; and he must have that before he can have insight into the probable cause of derangement.
CARE OF INJECTORS.
When an engineer finds that an injector refuses to work, his first resort should be the strainer. That gets choked with cinders or other impurities so frequently, that no time should be lost in examining it. One day, when I was running a round-house, an engineer came in breathless, with the information that his engine was blocked in the yard, and he must dump his fire, as he could not get his injector to work. The thermometer stood at twenty degrees below zero, and an Iowa blizzard was blowing; so the prospect of a dead engine in the yard meant some distressingly cold labor. I asked, the first thing, if he had tried the strainer; and his answer was, that the strainer was all right, for the injector primed satisfactorily, but broke every time he put on a head of steam. I went out to the engine, and had the engineer try to work the injector. By watching the overflow stream, I easily perceived that the injector was not getting enough water, although it primed. An examination showed that the strainer was full of cinders, and the injector went to work all right when the obstruction to the water was removed.
THE MOST COMMON CAUSES OF DERANGEMENT.
Sand and cinders are the greatest cause of failures with injectors; as they are, indeed, with all water-feeding apparatus. I knew a case where water for a locomotive, running on a short branch, was taken out of a sandy creek with a siphon. The tank had generally about six inches of sand in the bottom. The engine had a pump and an injector; but all the feeding had to be done by the latter, for the pump never worked a gallon of water. The injector worked the water through when it seemed a quarter sand. In a short time the sand destroyed the tubes of the injector, for it acted on them the same way as a sand-blast does in cutting files or glass.
A very common cause of failure of injectors, is leakage of steam through throttle-valve or check-valve, keeping the injector so hot that no vacuum can be formed to make it prime. A great many injector-checks have been turned out too light for ordinary service, while others are made in a shape that will always leave the valve away from the seat when they stop working. Then the engineer has to run forward, and pound the check with a hammer to keep the steam from blowing back; and that soon ruins the casting. Check-valves set in a horizontal position are worthless with water that contains grit.