Multi-piston valve actuator

An actuator for operating a valve gate to supply a flow of plastic melt intermittently into a mold cavity of a mold assembly, said actuator comprising:

• a) a stationary cylinder bounded by an end cap and a bottom wall;
• b) a movable cylinder received within the stationary cylinder, the movable cylinder having a generally cylindrical outer wall and generally flat upper end wall, intermediate wall and lower end wall, wherein the upper end wall is proximate the end cap of the stationary cylinder, such that an upper chamber is defined by the space between the upper end wall of the movable cylinder and the end cap of the stationary cylinder;
• c) a first stationary piston received between the lower end wall and intermediate wall of the movable cylinder, thereby defining (i) a first inner chamber between the lower end wall and the first stationary piston and (ii) a second inner chamber between the intermediate wall and the first stationary piston;
• d) a second stationary piston received between the upper end wall and intermediate wall of the movable cylinder, thereby defining (i) a third inner chamber between the intermediate wall and the second stationary piston and (ii) a fourth inner chamber between the upper end wall and the second stationary piston;
• e) a support post connecting the first and second stationary pistons to the end cap of the stationary cylinder;
• f) a rod attached to the lower end wall of the movable cylinder, the rod having an end portion configured to form a valve pin at a point proximate a gate to the mold cavity;
• g) a first port communicating with the upper chamber, the first inner chamber and the third inner chamber;
• and
• h) a second port communicating with the second inner chamber and the fourth inner chamber,
• such that admission of pressurized fluid through the first port generates forces acting on both end walls and the intermediate wall of the movable cylinder, thereby moving the valve pin to shut off flow to the gate, and admission of pressurized fluid through the second port generates a force acting on the upper end wall and the intermediate wall of the movable piston, thereby moving the valve pin to an open position, allowing flow through the gate and into the mold cavity.

An actuator for operating a valve gate to supply a flow of plastic melt intermittently into a mold cavity of a mold assembly, said actuator comprising:

• a) a stationary cylinder bounded by an end cap and a bottom wall;
• b) a movable cylinder received within the stationary cylinder, the movable cylinder having a generally cylindrical outer wall, generally flat upper and lower end walls, and “n” intermediate walls between the upper and lower end walls to define “n+1” cavities within the movable cylinder;
• the upper end wall of the movable cylinder being proximate the end cap of the stationary cylinder so that the space between the upper end wall of the movable cylinder and the end cap of the stationary cylinder defines an upper chamber;
• c) a stationary piston received within each cavity of the movable cylinder, thereby dividing each cavity into “a” and “b” inner chambers;
• d) a support post connecting all of the stationary pistons to the end cap of the stationary cylinder;
• e) a rod attached to the lower end wall of the movable cylinder, the rod having an end portion configured to form a valve pin at a point proximate a gate to the mold cavity;
• f) a first port communicating with the upper chamber and all of the “a” inner chambers of the movable cylinder;
• and
• g) a second port communicating with all of the “b” inner chambers of the movable cylinder,
• such that admission of pressurized fluid through the first port generates forces acting on both end walls and the intermediate walls of the movable cylinder, thereby moving the valve pin to shut off flow to the gate, and admission of pressurized fluid through the second port generates a force acting on the upper end wall and the intermediate walls of the movable piston, thereby moving the valve pin to an open position, allowing flow through the gate and into the mold cavity.