Dental syringe with quick disconnect tip

In a dental syringe,

• a head having a first water passage and a first air passage extending therethrough and an internally threaded cylindrical cavity in its surface having a bottom and a sidewall, the first water passage opening in the center of the bottom and the first air passage opening in the bottom adjacent the sidewall,
• a tip having inner and outer elongate, coaxial, spaced apart pipes, the inner pipe defining a second water passage and the outer pipe defining a second air passage, the forward ends of the pipes having discharge openings, the rearward portion of the outer pipe terminating short of and sealed to the rearward portion of the inner pipe and having axially spaced rearward and forward annular grooves, the rearward portion of the outer pipe further having an aperture therethrough in the rearward groove, and the rearward end of the inner pipe having an opening,
• a coupling having an externally threaded cylindrical base, the rearward portion of the base screwed into the cavity in the head, and an internally threaded cylindrical lock nut screwed over the forward portion of the base, the base and nut defining an axially extending bore therethrough adapted slidably to receive the rearward portion of the tip, the base having a first annular flange which extends radially inwardly from the rearward portion of the base and defines a hole which receives the rearward portion of the inner pipe so that the first and second water passages mate, the base further having a second annular flange which extends axially from the rearward portion of the base and defines a chamber between the second flange and the sidewall, the chamber communicating with the first air passage, and the base further having a duct extending between the bore and the chamber,
• a first elastomeric O-ring positioned between the base and the nut and seated in the forward groove when the rearward portion of the tip is fully inserted in the bore, the base and the nut confining the first O-ring and preventing sufficient deformation thereof to permit the tip to be slidably withdrawn from the bore when the nut is fully screwed over the base,
• a second elastomeric O-ring surrounding the base and deformed between the nut and the head when the nut is fully screwed over the base,
• a third elastomeric O-ring surrounding the rearward portion of the inner pipe and deformed between the first flange and the head,
• whereby when the nut is partially screwed off of the base, the rearward portion of the tip may be manually inserted and withdrawn from the coupling, and when the rearward portion of the tip is fully inserted in the coupling and the nut is fully screwed over the base the first O-ring will prevent withdrawal or ejection of the tip, and the first, second, and third O-rings will prevent water or air from escaping from the coupling except through the tip.