Rough and Tumble Engineering

by James H. Maggard

An injector must always be selected having a maximum capacity in excess of the water consumed. If the exact amount of water consumed per hour is not known, and cannot be easily determined, the proper size can be approximately determined from the nominal H. P. of the boiler. The usual custom has been to allow 7 I/2 gallons of water per hour, which is a safe rule for the ordinary type of boiler.

WHAT A GOOD INJECTOR OUGHT TO DO.

With cold feed water, a good injector with a two foot lift ought to start with 25 pounds pressure and work up to I50 pounds. With 8 foot lift, ought to start at 30 pounds and work up to I30. With feed water heated to I00 degrees Fahrenheit it should start with the same lift, that is, will say 2 foot, at 26 and work Up to I20, and at 8, from 33 up to I00. You will see by this that conditions, consisting of variation of temperature in the feed water and different lifts, change the efficiency of your injector very materially, and the water can soon get beyond the ability of your injector to work at all. The above refers more particularly to the single tube injector. The double tube injector under the same conditions as above should work from I4 pounds to 250, and from I5 to 2I0, but as this injector is not generally used on farm engines you will most likely not meet with it very often.

The injector should not be placed too near the boiler, as the heat from it will make it difficult to start the injector each time after it has been standing idle.

If the injector is so hot that it will not lift the cold water, there is no way of cooling it except by applying the water on the outside. This is most effectively done by covering the injector with a cloth and pouring water over the cloth. If, after the injector has become cool, it still refuses to work, you may be sure that there is some obstruction in it that must be removed. This can be done by taking off the cap, or plug-nut, and running a fine wire through the cone valve or cylinder valve. The automatic injector requires only the manipulation of the steam valve to start it. There are other makes that require, first: that the injector be given steam and then the water. To start an injector requires some little tact, (and you will discover that tact is the handiest tools you can have to make you a good engineer). To start an injector of the Pemberthy type; first give it sufficient steam to lift the water, allowing the water to escape at overflow for a moment or long enough to cool the injector, then with a quick turn shut off and open up the supply which requires merely a twist of the wrist.

If the injector fails to take hold at once don't get ruffled but repeat the above move a few times and you will soon start it, and if you have tact, (it is only another word for natural ability) you will need no further instructions to start your injector. But remember that no injector can work coal cinders or chaf and that all joints must be air tight. Don't forget this.

It is now time to give some attention to the heater. While the heater is no part of the pump, it is connected with it and does its work between the two horizontal check valves. Its purpose is to heat the water before it passes into the boiler. The water on its way from the pump to the boiler is forced through a coil of pipes around which the exhaust steam passes on its way from the cylinder to the exhaust nozzle in the smokestack.

The heaters are made in several different designs, but it is not necessary to describe all of them, as they require little attention and they all answer the same purpose. The most of them are made by the use of a hollow bedplate with steam fitted heads or plates. The water pipe passes through the plate at the end of the heater into the hollow chamber, and a coil of pipes is formed, and the pipe then passes back through the head or plate to the hot water check valve and into the boiler.

The steam enters the cylinder from the boiler, varying in degrees of heat from 300 to 500. After acting on the piston head, it is exhausted directly into the chamber or hollow bed-plate through which the pipes pass. The water, when it enters the heater, is as cold as when it left the tank, but the steam which surrounds the pipes has lost but little of its heat, and by the time the water passes through the coil of pipes it is heated to nearly boiling point and can be introduced into the boiler with little tendency to reduce the steam. This use of the exhaust steam is economical, as it saves fuel, and it would be injurious to pump cold water directly into a hot boiler.

If your engine is fitted with both cross head pump and injector, you use the injector for pumping water when the engine is not running. The injector heats the water almost as hot as the heater. If your engine is running and doing no work, use your injector and stop the pump, for, while the engine is running light, the small amount of exhaust steam is not sufficient to heat the water and the pressure will be reduced rapidly. You will understand, therefore, that the injector is intended principally for an emergency rather than for general use. It should always be kept in order, for, should the pump refuse to work, you have only to start your injector and use it until such time as you can remedy the trouble.