The Steam Injector
A theoretical and practical treatise on the design and operation of injectors and on the flow of fluids through and the design of nozzles.

COMPOUND INJECTORS. 119 In tlie arrangement illustrated at fig. 67, the first move- ment of the handle a opens the pilot valv© b and allows steam to pass through tlie chamber c to the valve d con- trolling tlie entranoe to tlie lifting steam nozzle. By manipulating the valve d the steam supply of the lifter and therefore the quantity of water drawn into the injector are varied, but the steam supply to the forcer remains unaltered. In othe-r cases the water supply is throttled in the feed supply pipe. Some idea of the capabilities of the compound injector will be given by the following table : — Table showing capabilities of a Compound Live-steam Injector. Steam pressure, pounds per square incli.. 30 45 60-120 135-150 165-180 Lift in feet witli cold feed watei' 16| 20 16J 13 Feed water temperature permissible with water under head, deg. Fah 130 140 150 146 145 Maximum feed water temperature with 6 ft. lift, deg. Fali 120 135 140 135 130 Compound injectors should give at least an over-pres- sure or exoess of delivery pressure over steam pressure of 12 Ibs. to 15 Ibs. with steam pressures up to 60 Ibs., 20 Ibs. with steam pressures from 60 Ibs. to 120 Ibs., and about 30 Ibs. over-pressure for higher steam pressures. The temperature of the water delivered from a compound injector is on an average 80 deg. Fah. higher than the temperature of the injector supply water. Thus if the injector receives its feed water at a temperature of 140 deg. Fah., the delivery temperature will be about 220 de-g. Fah., or above boiling point. It will, of course, be under- stood that the actual increase in the temperature of the water delivered by, over that of the water supplied to, the injector depends upon the pressure of the steam. Tlie amount of the increase is less for lower pressures and some- what higher with high pressures. Fig. 61 is a general view of a compound live steam injector.