HOW TO KEEP AN INJECTOR IN GOOD ORDER.
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.