To preserve a good working injector, the engineer should see that all the pipes and joints are kept perfectly tight. It is hard to keep pipes and joints tight when they are subjected to the continual jars a locomotive must stand; but injectors can not be depended on where there is a possibility of air mixing with the water. Leaky joints or pipes are particularly troublesome to lifting injectors; for air passes in, and keeps the steam-jet from forming a vacuum. At first the injector will merely be difficult to start; but, as the leaks get worse, there will be no starting it at all. Then, the air mixing with the water is detrimental to the working of all injectors, as its tendency is to decrease the speed of the water. The compact molecules of water form a cohesive body, which the steam can strike upon with telling force to keep it in motion. When the water is mixed with air, it lacks the element of compactness; and the steam-jet strikes a semi-elastic body, which does not receive momentum readily. This mixture of steam and air does not act solidly on the check-valve, but makes the water pass in with a bubbling sound, as if the valve were moving up and down; and the stream of water breaks very readily when it is working in this way.
CURIOUS CASES OF TROUBLE WITH AN INJECTOR.
I ran a Sellers improved injector on a locomotive about a year, and it was an excellent feeding apparatus; but I several times had curious cases of trouble in getting it to work. Once it began drawing air; and I could not find out where the air was coming from, for the pipes seemed all tight. But the air was going through, for I could hear its mutterings; and the water kept breaking, which was an annoyance on the road. A heater-pipe was attached to the injector feed-pipe; and I afterward found out that the air was getting in at the top joint of this pipe, which did not show a leak, being above the water.
Another time I had almost a failure with this injector out in the snow. I was out with a snow-plow, opening the road through enormously deep snow-drifts. We had worked on one bank for several days; and we made water by shoveling snow into the tank, which was melted by blowing steam through the heaters and injector. Cinders were passed into the tank very freely with the snow, and presently I began to have trouble with my injector. I took it apart several times, and cleaned out cinders, when it went to work all right again. But a time came when it refused to work when there were no cinders inside, and it seemed that no amount of coaxing would make it start. It would prime all right; but, so soon as I gave it steam, the water would break. Driven to my wits’ end, I made the fireman try to work the injector, while I went down and watched its action. Everything seemed tight: I had examined the strainer, and there appeared no reason why it should not operate as well as it ever did. While watching it, I saw a drop of water oozing out at the stem of the overflow-valve; but I reasoned, “That can not affect the working of the injector, because it is ahead of where the water starts.” But, seeing that the thing would persist in not working, I put a bit of packing in the overflow-stem, thinking it will do no harm any way; and then the injector went to work all right, and I had no more trouble with it. So a defect that may seem trifling, sometimes proves serious to an injector.
COMMON DEFECTS.
As maintaining unbroken speed on the water put in motion is the first essential in keeping an injector in good working-order, any thing that has a tendency to reduce that speed will jeopardize its action. A variety of influences combine to reduce the original efficiency of an injector. Those with fixed nozzles are constructed with the orifices of a certain size, and in the proportion to each other which experiment has demonstrated to be best for feeding with the varied steam-pressures. When these orifices get worn out of the proper size, the injector will work badly; and nothing will cure it but new tubes. The tubes sometimes get loose inside the shell of the injector, and drop down out of line. The water will then strike against the side of the next tube, or on some point out of the true line, scattering it into spray, which contains no energy to force itself into the boiler. A machinist examining a defective injector, should always make sure that the tubes are not loose. Injectors that suffer from this defect will not work without a high pressure of steam. Injectors suffering from incrusted water-passages will generally work best with the steam low. Cases of the latter kind are common in calcareous districts. I have known instances where injectors got so incrusted with lime that the passages were almost closed.
Joints about injectors that are kept tight by packing must be closely watched. Many an injector that failed to work satisfactorily has been entirely cured by packing the ram-gland.
CARE OF INJECTORS IN WINTER.
During severe frosty weather, an injector can be kept in order much easier than a pump; but it needs constant watching and intelligent supervision.
To keep an injector clear of danger from frost, it should be fitted up so that all the pipes can be thoroughly drained, by frost-cocks put in for that purpose. Bends in the pipes, where water could stand, should be avoided as far as possible; and, where they can not be avoided, the lowest point should contain a frost-cock.