Method and apparatus for controlling flow rate of fluid

DETAILED DESCRIPTION The present invention is directed to a method and apparatus for controlling the flow rate of a fluid.
The method and apparatus involve flowing a fluid through an elongated passage having a small cross-sectional area which limits the flow rate of the fluid.
The flow rate is adjusted by changing the length of the elongated passage through which the fluid is flowed.
The method and apparatus of the invention may be used, for example, for intravenous infusion of liquid solutions, for controlling the flow of gases in gas chromatography, for metering drugs into diluents, dies into foodstuffs, etc.
The flow of a fluid from an enclosed pressure vessel can be controlled by passing the fluid through a passage having a small cross-sectional area and a considerable length.
The theoretical flow rate through a tube having a cylindrical cross-section, for example, can be calculated from the following equation: ##EQU1## where: F=Flow rate r=Bore radius .
mu.
=Fluid viscosity L=Passage length dp=Pressure difference.
The method and apparatus of the present invention takes advantage of this relationship to effect a change in the controlled flow rate of a fluid through an elongated passage having a small cross-sectional area by changing the length of the elongated passage through which the fluid is flowed.
More particularly, the method of the invention for controlling the flow rate of a fluid comprises the steps of providing an elongated passage having a small cross-sectional area, supplying fluid to the elongated passage to flow the fluid through a first predetermined length of the elongated passage at a first flow rate, and changing the flow rate of fluid in the passage from the first flow rate to a second flow rate by changing the length of the elongated passage through which the fluid is flowed from the first predetermined length to a second predetermined length.
The elongated passage has a cross-sectional area of about 1.
6.
times.
10.
sup.
-4 inch.
sup.
2 or less and a predetermined length between 4