Flow rate control system

In a liquid flow system, an apparatus for controlling the rate of liquid flow through the system, said apparatus comprising:

• a venturi through which the liquid flows, said venturi comprising an inlet, a throat and a diffuser through which the liquid flows from said inlet through said throat and then through said diffuser, said throat having an internal diameter that is less than an internal diameter of said inlet;
• flow rate control valve means in fluid communication with said diffuser of said venturi for controlling the rate of liquid flow through said venturi, said flow rate control valve means having a linearly operating member;
• means for measuring a differential in pressure between the pressure of liquid flowing through said inlet and the pressure of liquid flowing through said throat;
• means for converting a signal indicative of the differential in pressure into an electrical control signal;
• linear actuator means responsive to the electrical control signal for linearly moving said linearly operating member of said flow rate control valve means to control the rate of liquid flowing through said venturi at a predetermined value;
• set point adjustment means electrically connected to said means for converting and said linear actuator means for adjusting the predetermined value at which said linear actuator means operates to control the rate of liquid flowing through said venturi;
• pressure regulator means having a flexible diaphragm extending therethrough, said pressure regulating means having a linearly acting member connected to said flexible diaphragm that linearly acts on said linearly operating member of said flow rate control valve means;
• means for transmitting a signal responsive to liquid pressure at said inlet of said venturi to one side of said flexible diaphragm;
• and
• means for transmitting a signal responsive to liquid pressure at said throat of said venturi to another side of said flexible diaphragm.

A method of controlling the rate of flow of a liquid through a liquid flow system, said method comprising the steps of:

• causing the liquid to flow through a venturi having an inlet, a restricted throat, and a diffuser in serial fluid communication with one another;
• providing a liquid flow control valve with a position adjustable member to control the rate at which liquid can flow through the venturi;
• measuring a pressure differential between the pressure of liquid flowing through the inlet and the pressure of liquid flowing through the restricted throat of the venturi;
• converting the pressure differential to an electrical signal;
• providing an actuator with a positively displaceable member for adjusting the position of the position adjustable member of the liquid flow control valve;
• using the electrical signal to control the position of the positively displaceable member of the actuator to thereby control the rate of flow of liquid through the venturi at a predetermined value;
• providing set point adjustment means for adjusting the predetermined value at which the electrical signal controls the position of the position adjustable member of the liquid flow control valve, and thereby the predetermined value at which the liquid flow control valve controls the rate of flow through the venturi;
• providing a pressure regulator with a flexible diaphragm extending thereacross and a member connected to the flexible diaphragm and movable in a linear direction on the flexing of the flexible diaphragm to assist in moving the position of the position adjustable member of the liquid flow control valve in the linear direction;
• imposing a first pressure signal indicative of the pressure of liquid flowing through the inlet of the venturi on one side of the flexible diaphragm;
• and
• imposing a second pressure signal indicative of the pressure of liquid flowing through the restricted throat of the venturi on an opposed side of the flexible diaphragm.