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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. Since a compressible gaseous fluid in the pumping portion of the flexible tubing does not develop the cracking pressure, the flow detector also provides an indication when a source of liquid (31) for the volumetric pump has run dry. The method comprises the steps of processing the signal to determine if it exceeds a predefined threshold that varies as a function of the rate at which the pump is set to deliver fluid.

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