A method and apparatus is provided for the efficient and controllable delivery of cryogen liquid droplets into
thin walled containers before they are sealed, the pressurization of the sealed container caused by the
evaporation of the liquid cryogen causing the walls of the container to stiffen.
Discharge of the droplets immediately upstream of the container sealing
station is facilitated using a horizontal displacement
assembly to transport metered droplets from a liquid dosing unit to the point of injection above the container. The horizontal displacement
assembly may be provided with internal heaters to prevent freeze up, and a sensor to confirm droplet
discharge. It may also be provided with a separate source of heated
nitrogen gas, which can be used to back purge the dispensing unit should it become clogged, to melt any frozen liquid occlusions which may have formed in the cryogen supply line. In one embodiment, the solenoid used to actuate the
piston regulating the opening and closing of the
needle valve, which meters the dispensing of droplets, is mounted in
thermal contact with said
piston, this placement of the solenoid serving to cool the
piston and thus prevent overheating in the case of
rapid cycling.