Valve system in an injection molding system

An injection molding apparatus comprising an injection molding machine, a manifold that receives injection fluid from the machine and routes the injection fluid during the course of an injection cycle from an upstream end toward a downstream end of a fluid flow channel disposed in the manifold or a nozzle communicating with the manifold, the fluid flow channel having a flow axis (AX) and a channel length, the fluid flow channel communicating at the downstream end with a gate to a cavity of a mold, the apparatus including:

• a valve pin driven by an actuator, the valve pin extending axially (AX) through at least a portion of the channel length of the fluid flow channel, the valve pin having an upstream end interconnected to the actuator and a downstream end, the valve pin being drivable by the actuator axially upstream and downstream through the fluid flow channel,
• the fluid flow channel including a throat (T) having an inner circumferential surface (TS) having a selected throat configuration and throat diameter (TD),
• the fluid flow channel and the valve pin being configured or adapted such that the valve pin is movable axially upstream and downstream between an upstream position where the downstream flow of the injection fluid is restricted by a bulbous protrusion (B) of the pin being axially aligned (AL) with the throat (T) of the channel, an intermediate position where downstream flow of injection fluid is unrestricted and a fully downstream position where downstream flow of injection fluid is stopped at both the gate and at the throat,
• wherein the valve pin is adapted to be disposed in a start of cycle or upstream flow restriction position such that a flow restriction gap (G) is formed between an outer circumferential surface (OBS) of the bulbous protrusion (B) and the inner circumferential surface (TS) of the throat (T) that is large enough to enable a predetermined small amount of flow of injection fluid through the gate that reduces a difference in fluid pressure between an upstream interior volume (UIFP) of the channel and a downstream interior volume (DIFP) of the channel.