If the steam were not condensed we would have a comparatively light substance moving at a high velocity, which, as has already been explained, would have little actual energy, and would therefore not overcome the boiler pressure. QUESTION 134. _Does this involve any principle like a perpetual motion, or of work done without consumption of power?_ _Answer_. No, the steam escapes _as steam_, and is returned to the boiler _as water_ with its bulk reduced, say 1,000 times, and if it carries with it twenty times its weight of fresh feed-water, there would still be a loss of pressure or effective force in the boiler sufficient to do the work required in introducing the water. QUESTION 135. _Will the injector feed hot water?_ _Answer._ The instrument will not work when the feed-water is too hot to condense the steam, for the reasons given above, and the amount of water thrown is always the greatest when the feed-water is the coldest. Steam at a low pressure can be condensed more readily than steam of higher pressure, because it contains less heat. The feed-water may be used hotter to condense low steam than to condense high steam. In using the injector, the lower the boiler pressure the hotter may be the water within certain limits, the limit being the possible condensation of the steam. QUESTION 136. _Will a “fixed-nozzle” injector, such as has been described, answer as a boiler feeder on locomotives?_ _Answer._ It will answer at some one pressure of steam, to which pressure it may have been adapted in making the instrument, and at that pressure it will work admirably; but it will not work satisfactorily at any other pressure, either higher or lower, and has not much range in quantity of water delivered. QUESTION 137. _What is required to make an injector work at different pressures?_ _Answer._ The instrument must be so made that the water passage between the receiving tube and the combining tube can be varied in size. This is usually done by making the combining and receiving tubes conical and moving the former to or from the latter, thus contracting or enlarging the water space. Such adjustment must be made at each change of steam pressure in the boiler. If this adjustment is made _by hand_, as in some kinds of injectors, it requires constant attention, if the steam pressure varies frequently. QUESTION 138. _How has this regulation been accomplished without such attention?_ _Answer._ In the SELF-REGULATING INJECTOR, fig. 70, by using the escape water at overflow to push the combining tube towards the receiving tube and the indraught of water at the same place to pull the combining tube away from the receiving tube. This can be explained as follows: