Liquid injection apparatus having an external adjustor

Apparatus for injecting a predetermined quantity of fluid additive into a primary fluid stream comprising:

• elongated cylinder means having a bore formed therein;
• opposed head means closing opposite ends of said bore;
• means forming fluid inlet, fluid discharge and fluid bypass passages, respectively, in communication with said bore;
• respective one way valves interposed in said passages for admitting additive fluid to said bore through said inlet passage and discharging additive fluid through said discharge and bypass passages, respectively;
• an elongated piston reciprocably disposed in said bore for effecting displacement of a predetermined quantity of additive fluid;
• seal means interposed in said bore and cooperable with said piston to form opposed fluid discharge and bypass chambers in said bore, said piston including passage means formed therein and cooperative with said seal means in such a way as to bypass additive fluid from said discharge chamber to said bypass chamber during a fluid displacement stroke of said piston to control the amount of fluid discharged to said discharge passage;
• and
• means for selectively positioning said seal means in said bore to vary the effective displacement of said piston means, said means for selectively positioning said seal means comprising a plurality of annular spacers insertable in said bore in predetermined relationship to each other and to said seal means.