Controlled dosing of liquid cryogen
An aseptic liquid cryogen dosing head has a liquid cryogen reservoir in communication with a dosing outlet. An electromagnetic actuator is attached to an upper end of a dosing valve stem and is operable to move the dosing valve stem to open and close the dosing outlet. An air-tight seal extends about the dosing valve stem and separates the liquid cryogen reservoir from a cavity between the seal and the electromagnetic actuator. A controller is operable to perform a head leakage test, including pressurizing the cavity with a pressure higher than a pressure within the reservoir, to check for leakage past the seal; and pressurizing the reservoir to check for leakage from the liquid cryogen reservoir.
1 . An aseptic liquid cryogen dosing head, comprising
a liquid cryogen reservoir in communication with a dosing outlet;
an actuator operable to open and close the dosing outlet;
a seal separating the liquid cryogen reservoir from a cavity between the seal and the actuator, the seal providing an air-tight seal during operation; and
a controller operable to perform a head leakage test, including
pressurizing the cavity with a pressure higher than a pressure within the reservoir, to check for leakage past the seal; and
pressurizing the reservoir to check for leakage from the liquid cryogen reservoir.
2 . The aseptic liquid cryogen dosing head of claim 1 , wherein the controller is also operable to perform a sterilization cycle of the head, comprising introducing a pressurized sterilization fluid into the reservoir, while introducing a gas at a countering pressure into the cavity, thereby keeping the dosing outlet in a closed condition during sterilization.
3 . The aseptic liquid cryogen dosing head of claim 2 , wherein the pressurized sterilization fluid comprises steam.
4 . The aseptic liquid cryogen dosing head of claim 2 , wherein the controller is configured to perform the head leakage test both before and after performing the sterilization cycle.
5 . The aseptic liquid cryogen dosing head of claim 1 , wherein the seal comprises a diaphragm.
6 . The aseptic liquid cryogen dosing head of claim 1 , wherein the reservoir includes a tube extending from above a liquid cryogen level to below the liquid cryogen level.
7 . The aseptic liquid cryogen dosing head of claim 1 , wherein the reservoir comprises a liquid cryogen feed conduit filled with liquid cryogen in operation and extending from a primary cavity of the reservoir to the dosing outlet.
8 . The aseptic liquid cryogen dosing head of claim 1 , wherein the actuator comprises a servomotor.
9 . The aseptic liquid cryogen dosing head of claim 1 , wherein the actuator is controllable to alter a dosing valve stem displacement distance and duration.
10 . The aseptic liquid cryogen dosing head of claim 1 , wherein the actuator is controllable to alter a rest position of a dosing valve stem with respect to the dosing outlet.
11 . The aseptic liquid cryogen dosing head of claim 1 , further comprising a dosing outlet gas flow valve controllable to introduce a flow of sterile gas from a pressurized source to the dosing outlet to inhibit frost accumulation.
12 . The aseptic liquid cryogen dosing head of claim 11 , wherein the dosing outlet gas flow valve is controllable to open when the actuator is not operating to dispense a dose of liquid cryogen.
13 . The aseptic liquid cryogen dosing head of claim 11 , wherein the dosing outlet gas flow valve includes a fixed bypass orifice that allows a continuous flow of the sterile gas to the dosing outlet when the actuator is operating to dispense a dose of liquid cryogen.
14 . The aseptic liquid cryogen dosing head of claim 11 , wherein the dosing outlet gas flow valve is arranged to introduce the flow of the sterile gas to a portion of the dosing outlet open to atmospheric pressure.
15 . A method of sterilizing a liquid cryogen dosing head, comprising
performing a system leakage test by pressurizing a first cavity between a dosing valve stem seal and an electromagnetic dosing actuator, as well as a second cavity on an opposite side of the dosing valve stem seal, to check for system leakage;
testing for leakage past the seal by reducing pressure in the second cavity and, with the second cavity pressure reduced, monitoring pressure in the first cavity over a predetermined time interval; and then
in response to passing the seal leakage test, introducing a sterilization fluid to the second cavity and maintaining the sterilization fluid in the second cavity under conditions that cause sterilization of the second cavity.