A fluid displacement device, particularly for use of the device to pressurize balloon catheters, or the like. The device includes a plunger which is displaceable through a housing, and an actuating mechanism which engages the plunger. The actuating mechanism includes a nut member that is biased into engagement with a threaded portion of the plunger. The device has a press-to-release feature wherein the plunger is instantly releaseable by simply depressing a toggle lever of the nut member to overcome a restorative spring force. Subsequently, the plunger can be translated using macro movements (i.e., by pushing or pulling the plunger).