The injector is a device by which the impact of a jet of live steam may be made to force water before it into the boiler from which the steam is taken (which is apparently a paradox), or into another vessel where a pressure exists. The water forced may be lifted by the injector itself or may be supplied thereto under pressure. In either case the range and capacity of its work depend upon the proportion and position of the jets and the excellence of workmanship. Its operation is based upon the fact that a current of any fluid has a tendency to induce movement in its own direction in any body over or through which it passes; and in the injector this movement is intensified by the steam continuously condensing and producing a vacuum, to fill which the water rushes in with a momentum induced by the vacuum alone where the instrument has to lift its water, and increased thereby where the water is fed under pressure. The con densation of the steam heats the water, but some of the heat lost by the steam is converted into the mechanical force necessary to convey the water and to overcome friction, besides that which disappears through leakage, radiation, etc.
Injectors are used not only to feed the boilers which supply them with steam, but also to feed other boilers, fill tanks, put a hydrostatic-pressure test upon boilers, operate hydrostatic presses, etc. They have the advan tage over pumps in locomotive-boiler feeding that they will operate when the engine is not running. Considered merely as lifting- and as forcing pumps, their duty is not satisfactory, but as boiler-feeders there is economy in their use, because they heat the feed-water.
"Little Giant" In r (fi. 79) shows, in longitudinal ver tical section, the " Little Giant " injector, a simple type of feeding injec tor for stationary boilers which are used where the water need not be raised or "lifted," but may be fed from a tank or street-main. A is the regulating handle, I3 the steam inlet, C the water inlet, D the overflow, and E the discharge to the boiler. This injector is started by opening the water-valve (an ordinary stop-valve, not shown in the Figure). When the water shows at the overflow D, the steam-valve (not shown in the cut) is opened full. The quantity of water fed in is regulated by moving the handle A to the left or to the right. This handle, in starting, must be in a vertical or nearly vertical position, so that the " combining" tube shall not touch either the steam-nozzle or the discharge-jet.
Giffarans Giffard's injector (jig. 2) the injection of the supply of feed-water is effected by the pressure and condensation of steam from the boiler. The operation of the apparatus is as follows: steam escap ing from the boiler through the pipe a is compelled to pass through the contracted nozzle seen below ill inlet-pipe b, by which its velocity is greatly increased. The feed-water from the pipe b is drawn into the annular space surrounding the nozzle, and, mingling with the condensed steam, is driven through the pipe and valve c into the boiler.
The Automatic Injector shown in section in Figure 3 (ft1. 79) can, without the aid of any special valves or fittings, be used either to receive the water-supply under it head or to raise it a considerable height before delivering it into the boiler; besides, it does not require the adjust ment of both the water- and the steam-supply to start it either originally or after the jet breaks. The amount of \rater delivered is regulated
(whether the instrument lifts its water or is supplied raider pressure) by the water-valve operated by a screw and a hand-wheel, or by both these and the steam-plug. In the illustration A is the body or case, /1 the steam connection, C the water-supply connection (in which the water-regulating valve A' is placed), I) the water-delivery, containing a check-valve, and A' the overflow-valve. To work the apparatus when the water is lifted, the steam-spindle .5' is opened half a turn, and when the water shows at the overflow the steam-spindle is turned further until the overflow ceases. When the feed-water is under pressure, the water-regulating valve A' is opened, and then the steam-spindle is opened all the way.
The Hancock (151. 79, fig. 5) is a double apparatus practi cally composed of two injectors, one of which is constructed especially for lifting and the other for forcing when fed under pressure. The first draughts the water and delivers it to the second, which forces the feed water to the boiler. The two are combined as one instrument.
77u, Scparalor is an important addition to the ordinary boiler, as it tends to eliminate from the steam the nnevaporated globules of water which are mechanically entrained by the current of outgoing steam, and the condensed steam which is the result of loss of pressure through fric tion and radiation. It works by reason of the fact that the entrained water has a slightly greater specific gravity than the steam which carries it along. It exists in many forms, the simplest being known as a " dry pipe " separator, consisting of a horizontal pipe closed at both ends and extending into the steam-space. It connects with the steam supply-pipe by a T in its middle, and has cut or bored throughout its periphery narrow slits or snail holes which strain out the water. The separator proper is applied outside the boiler. One form (IV 79, fig. 6) consists of a vertical cylinder having an internal central pipe which forms the outlet pipe, and which extends from the top downward about half its height. The steam enters tangentially to the annular space between the inner and outer pipe at the side near the top of the apparatus. The speed of the incoming cur rent produces centrifugal action, which causes the steam to pass in a spiral line around the internal pipe down to its lower end, where it abruptly changes its direction, passing upward through it, and out at the top to the point where the steam is to he used. The entrained water thus sepa rated is thrown to the outside of the downward current and falls into a collecting-chamber below, whence it can be blown off by hand or can be automatically drawn off by a pump or trap, and returned to the boiler with little loss of temperature. A glass gauge is attached to guard against an over-accumulation of water.