A rotary pump assembly which reduces the volume of liquid discharged from said pump assembly on each revolution when the operating speed of said pump assembly is increased from a first operating speed to a second operating speed, said pump assembly comprising
- a rotor rotatable about its central axis,
- a rotatable drive shaft connected with said rotor for rotating said rotor at different speeds about its central axis during operation of said pump assembly at different speeds,
- a cam ring circumscribing said rotor and having a radially inner circumferential surface defining an inlet arc and an outlet arc, said outlet arc having a configuration such that the radial distance between the central axis of said rotor and said outlet arc decreases by the same amount along equal arcuate increments of said outlet arc throughout the extent of said outlet arc,
- a plurality of pumping elements connected with said rotor and extending radially outwardly of a radially outer circumferential surface of said rotor into engagement with the inner surface of said cam ring, said pumping elements being movable radially toward and away from the central axis of said rotor during rotation of said rotor relative to said cam ring,
- first and second end members disposed adjacent to opposite axial ends of said rotor, said cam ring, end members and pumping elements cooperating to at least partially define a plurality of arcuate pumping chambers disposed in a circular array between the radially outer surface of said rotor and the radially inner surface of said cam ring, each of said pumping elements being sequentially movable toward the axis of rotation of said rotor through an incremental distance which is the same for each arcuate increment of movement of each of said pumping elements along said outlet arc,
- inlet means connected in fluid communication with said inlet arc for conducting liquid to each of said pumping chambers in turn at a flow rate which is sufficient to at least substantially fill each of the pumping chambers with liquid as each pumping chamber moves along the inlet arc during operation of said pump assembly at the first speed, said inlet means including means for restricting the rate of flow of liquid to each pumping chamber in turn to a flow rate which is insufficient to fill each pumping chamber with liquid as said pumping chamber moves along the inlet arc at the second operating speed which is greater than the first operating speed,
- an arcuate array of outlets disposed in said first end member and connected in fluid communication with the outlet arc, said outlets including a plurality of recesses disposed in said first end member and having radial extents which decrease along the outlet arc from a recess which is disposed adjacent to the initial end portion of the outlet arc and has a relatively large radial extent to a recess which is disposed adjacent to the final end of the outlet arc and has a relatively small radial extent to provide a generally constant spatial relationship between radially outer edge portions of said recesses and said pumping elements as said pumping elements move along the outlet arc and move inwardly toward the central axis of said rotor, said outlets further including a plurality of passages each of which extends from one of said recesses to an outer side of said first end member,
- valve means for reducing the number of outlet passages through which fluid flow is discharged from each of said pumping chambers in turn as pump operating speed increases above a predetermined operating speed by blocking fluid flow from each of said pumping chambers in turn during movement of each of said pumping chambers along the outlet arc through an arcuate distance which increases as the operating speed of the pump assembly increases above the predetermined operating speed, said valve means including a plurality of elongated spring fingers each of which has a first end portion fixedly connected to said first end member and a free end portion movable from a closed condition blocking fluid flow through one of said outlet passages to an open condition under the influence of fluid pressure in said one of said outlet passages, and
- pressure chamber means for holding fluid at a pressure which varies as a function of variations in the pressure at which fluid is discharged from said pump assembly during operation of said pump assembly, each of said spring fingers being urged toward the closed condition under the influence of a fluid pressure corresponding to the fluid pressure in said pressure chamber means to maintain each of said spring fingers in the closed condition until the fluid pressure in one of said pumping chambers is sufficient to overcome the influence of the fluid pressure corresponding to the fluid pressure in said pressure chamber means.