US 5,158,437 A · Volumetric pump with spring-biased cracking valves

Abstract

A volumetric pump and method for displacing a predetermined quantity of fluid at a predefined cracking pressure, independent of supply and output pressures. The volumetric pump (30) includes an inlet cracking valve (46), an outlet cracking valve (52), and a plunger (48) for displacing fluid from a pumping portion (34b) of flexible tubing (34) that extends through the volumetric pump. The pumping portion of the flexible tube fills with liquid when the inlet cracking valve is fully opened and is urged to expand by jaws (236) on pivotally-mounted arms (234). The arms are forced to pivot, as tubing reshaper rollers (160), disposed on the plunger, roll along the inner surface (232) of each arm. During a pumpback-pressurization segment of the pumping cycle, the inlet cracking valve applies a cracking force to the flexible tubing, while the plunger compresses the pumping portion of the flexible tubing sufficiently to develop a cracking pressure that displaces excess fluid back through the inlet cracking valve toward a container (32). After the excess fluid been forced from the pumping portion of the flexible tubing, a pumping segment of the cycle begins, wherein the inlet cracking valve closes fully and the outlet cracking valve applies a cracking force to compress the flexible tubing. Fluid is then forced by the plunger from the pumping portion of the flexible tubing into a distal portion (34c). The volumetric pump compensates for variations in elasticity of the flexible tubing that would otherwise cause variations in the cracking pressure, using balance blocks (42 and 58). A volumetric pump (400) for use with a cassette (300) comprises a second embodiment of the volumetric pump, in which inlet and outlet cracking valves are defined in respect to the forces applied by actuators against a flexible membrane (340) in the cassette, while a plunger (326) displaces fluid from a pumping chamber (360) in the cassette. Volumetric pump (400) applies appropriate forces to an inlet valve actuator (318) and an outlet valve actuator (332) to achieve cracking and closure forces, just as in the first embodiment.

Claims16

Dependent claims

A method for preventing variations in fluid supply pressure from affecting a fluid delivery rate of a pump, said pump including an inlet valve and an outlet valve, and operative to displace fluid from a pumping chamber, said chamber being defined by a flexible member, the method comprising the sequential steps of:

(a) substantially filling the pumping chamber with fluid from a source by opening the inlet valve;
(b) blocking fluid flow from the pump through the outlet valve while biasing the inlet valve closed with a first force;
(c) with the inlet and outlet valves in a back-flow condition as defined in part (b), forcing fluid from the pumping chamber back through the inlet valve toward the source as fluid pressure in the pumping chamber exceeds that necessary to open the inlet valve, in opposition to the first force;
(d) closing the inlet valve with a second force substantially greater than the first force while biasing the outlet valve closed with a third force;
and
(e) with the inlet and outlet valves in a pumping condition as defined in part (d), displacing fluid from the pumping chamber through the outlet valve as fluid pressure in the pumping chamber exceeds that necessary to open the outlet valve, in opposition to the third force, whereby the pressure of fluid delivered by the pump through the outlet valve is substantially independent of variations in supply pressure.

3 more elements

Dependencies are inferred from the claim text.

Volumetric pump with spring-biased cracking valves

Life of this patent

Volumetric pump with spring-biased cracking valves

Life of this patent

Abstract

Claims16