Abstract: A pressure diaphragm, wherein at least a portion of an elongate fluid channel is formed diametrically across, and is open through, a flat raised surface of a substantially rigid, disk-like body, and wherein a flexible membrane overlies the raised surface and is sealed to a surrounding flange. The fluid channel communicates with fluid inlet and outlet fittings carried by the body, which are adapted for connection with the tubes of an IV set, and the cross-sectional flow area of the fluid channel is substantially equal to or less than the cross-sectional flow area of any IV tube adapted for connection to the fluid inlet fitting.