Abstract: The disclosure concerns a gravity operated infusion apparatus. A solvent container is suspended above an infusion needle. A flexible tube joins the container and needle. A tube clamp varies the cross-section of the tube for controlling the infusion rate. Between the tube clamp and the needle an additional pressing apparatus is selectively actuable for increasing the pressure within the tube and between the tube clamp and infusion needle. In one embodiment the pressing apparatus comprises an eccentric disc that cooperates with a plate for pressing the tube and in another embodiment two plates are squeezed together against the tube. In a modification embodiment one plate rocks or tumbles as it moves with respect to the other plate.