reverse flow of liquid a flexible sleeve valve 44 projects upwardly from the valve assembly 38 the sleeve valve 44 controls the flow of liquid from the pump chamber 16 through the liquid discharge passage 26 to the liquid outlet opening 28 and prevents the reverse flow of liquid a pump piston 46 is mounted in the pump chamber 16 for reciprocating movements between charge and discharge positions of the pump piston in the pump chamber when moved forwardly to the charge position shown in fig1 the pump piston 46 draws liquid into the pump chamber 16 when moved rearwardly to the discharge position the pump piston 46 pumps the liquid from the pump chamber 16 a vent piston 48 is connected to the pump piston 46 for reciprocating movements with the pump piston the vent piston 48 is mounted in the vent chamber 18 for reciprocating movements between vent open and vent closed positions when the pump piston 46 is moved rearwardly in the pump chamber 16 toward the discharge position the vent piston 48 is also moved in the rearward direction in the vent chamber 18 toward the vent open position in the vent open position the interior of the bottle connected to the trigger sprayer is vented through the vent chamber 18 to the exterior environment of the sprayer housing 14 when the pump piston 46 is moved forwardly in the pump chamber 16.