Abstract: An automated medical fluid infusion system for delivering a bio-compatible fluid to a patient. The bio-compatible fluid is contained in a collapsible IV fluid bag having a deliver port connected by a catheter to the patient. The medical fluid infusion system utilizes an inflatable pressure bag adapted for holding the IV bag and communicating via flexible tubing with a source of compressed gas. A pressure venting device is operatively connected to the flexible tubing and resides between the pressure bag and the source of compressed gas. The pressure venting device includes a housing, a movable bleed screw located within the housing, and a chamfered bleed port. The bleed screw has a tapered end configured to selectively engage the housing at the chamfered bleed port, thereby adjustably opening and closing the bleed port to control the flow of compressed gas through the flexible tubing to the pressure bag.