Abstract: An anti-float plunger for a pneumatically actuated syringe includes an inner cylindrical ring with two open ends held within a cylindrical cover having one open end and one closed end. The open end is at the backside of the plunger. The closed end is at the frontside, in contact with liquid to be forced through the syringe outlet. The cover includes an outer flexible wiper extending around the circumference. This wiper maintains an airtight seal with the syringe walls even when the walls bulge outwardly due to excessive backside pressure. The cover also includes a deformable membrane at the closed end, which deforms away from the outlet to alleviate residual pressure buildup on the liquid in the frontside. This structure eliminates air entrapment within the syringe, while also preventing residual pressure buildup within the syringe.