Abstract: A method for determining if fluid is being displaced by a volumetric pump. The volumetric pump (30) includes an inlet cracking valve (46) and an outlet cracking valve (52) disposed on opposite sides of a plunger (48) used to displace fluid by compressing flexible tubing (34). During a pumping segment of a pumping cycle for the volumetric pump, the outlet cracking valve is closed with a cracking force that compresses the flexible tubing until the pressure of the fluid displaced by the plunger exceeds a cracking pressure, at which time the outlet cracking valve opens to enable fluid flow from the volumetric pump. A cracking flexure (182) provides the cracking force. As the outlet cracking valve opens in response to the fluid pressure exceeding the cracking pressure, a flow detector (54) mounted to the cracking flexure responds to the stress generated in the cracking flexure thereby, producing a signal indicative of fluid flow from the volumetric pump.

Abstract: A method and apparatus for detecting proximal and distal occlusions of flexible tubing in a positive displacement pump. A volumetric pump (30) includes a motor (146) that rotatably drives a cam assembly (142). The rotating cam assembly actuates a plunger (48), causing it to compress a pumping portion (34b) of a flexible tubing (34), compression of the tubing displaces fluid trapped within the pumping portion, causing it to flow past an outlet cracking valve (52). A proximal pressure sensor (44) and a distal pressure sensor (56) each produce signals indicative of the pressure within the proximal portion and distal portion of the flexible tubing, which are used to determine whether a proximal or distal occlusion of the flexible tubing has occurred. Both pressure sensors comprise strain gauges connected to flexures that apply a spring-biased force against the proximal and distal portions of the flexible tubing.