A hotrunner system for injecting plastics material from a plasticizer unit into an injection mold for molding plastic devices or parts, said system comprising: a hotrunner manifold having an inlet for receiving melted plastics material from said plasticizer unit and a plastics feed conduit connected to said inlet, said manifold being adapted for operation at a desired elevated temperature suitable for flow of said melted plastics material through said manifold without undesirable degradation; and at least one injection apparatus operatively connected to a downstream end of said feed conduit, the or each injection apparatus having a nozzle device having a longitudinal axis and a longitudinal injection passage extending to a nozzle tip, an elongate valve pin extending through a longitudinal guide passage (74; 216) formed in the nozzle device and movable in the passage in the direction of said longitudinal axis between an open position at which said melted plastics material can flow from the nozzle tip into the injection mold and a closed position to stop the flow of said plastics material from the nozzle tip, and a piston connected to a rear end of said valve pin, slidably mounted in an actuator chamber formed in said nozzle device, and adapted to move said valve pin between said open and closed positions by means of fluid pressure in said actuator chamber during use of the hotrunner system, the or each injection apparatus including the actuator chamber, its piston and the valve pin being mounted on or in a side of said manifold facing said injection mold, said piston and a section of the injection apparatus forming said actuator chamber being machined to close tolerances so as to form a micro gap between a peripheral wall of the piston and the adjacent wall of the actuator chamber in the range of 1 to 10 μm, thereby avoiding fluid seals between said piston and said wall of the actuator chamber, wherein the or each nozzle device and its piston provide a valve pin actuator able to operate within plastic injection temperatures ranging between 200 and 400 °C, characterized in that the or each valve pin actuator is a pneumatic actuator and gas bores (108, 110, 114) are formed in said hotrunner manifold for delivering pressurized air or gas to or from the or each actuator chamber. a hotrunner manifold having an inlet for receiving melted plastics material from said plasticizer unit and a plastics feed conduit connected to said inlet, said manifold being adapted for operation at a desired elevated temperature suitable for flow of said melted plastics material through said manifold without undesirable degradation; and at least one injection apparatus operatively connected to a downstream end of said feed conduit, the or each injection apparatus having a nozzle device having a longitudinal axis and a longitudinal injection passage extending to a nozzle tip, an elongate valve pin extending through a longitudinal guide passage (74; 216) formed in the nozzle device and movable in the passage in the direction of said longitudinal axis between an open position at which said melted plastics material can flow from the nozzle tip into the injection mold and a closed position to stop the flow of said plastics material from the nozzle tip, and a piston connected to a rear end of said valve pin, slidably mounted in an actuator chamber formed in said nozzle device, and adapted to move said valve pin between said open and closed positions by means of fluid pressure in said actuator chamber during use of the hotrunner system, the or each injection apparatus including the actuator chamber, its piston and the valve pin being mounted on or in a side of said manifold facing said injection mold, said piston and a section of the injection apparatus forming said actuator chamber being machined to close tolerances so as to form a micro gap between a peripheral wall of the piston and the adjacent wall of the actuator chamber in the range of 1 to 10 μm, thereby avoiding fluid seals between said piston and said wall of the actuator chamber, wherein the or each nozzle device and its piston provide a valve pin actuator able to operate within plastic injection temperatures ranging between 200 and 400 °C, characterized in that the or each valve pin actuator is a pneumatic actuator and gas bores (108, 110, 114) are formed in said hotrunner manifold for delivering pressurized air or gas to or from the or each actuator chamber.