System for delivering liquid at a controlled flow rate

A system for delivering liquid at a controlled flow rate, the system comprising:

• first and second vessels each having an internal volume for containing a liquid and a pressurized gas and each having an outlet for delivery of the liquid, under a gas pressure from the pressurized gas, out of the vessel;
• a common outlet, connected to each of the outlets said first and said second vessels, for delivery of the liquid under the gas pressure from a respective one of said first and second vessels;
• first and second measuring means, connected to said first and said second vessels, respectively, for measuring a rate of flow of the liquid out of said first and second vessels respectively, said first and second measuring means each comprising an upper detector and a lower detector for detecting the liquid in the respective vessel at an upper level and a lower level, and producing a level signal;
• refilling means, connected to each of the outlets of said first and second vessels, for delivering an input liquid to one of said first and second vessels while the liquid continues to be delivered out of said common outlet in an uninterrupted, pulsation free stream from the other of said first and second vessels;
• switching means connected to the outlets of said first and second vessels and said common outlet;
• and
• controller means, connected to said first and second vessels, said measuring means, said refilling means, and said switching means, for controlling the gas pressure in said first vessel by using the level signal from said first measuring means to regulate the rate of flow of the liquid out of said first vessel and for controlling the gas pressure in said second vessel by using the level signal from said second measuring means to regulate the rate of flow of the liquid out of said second vessel, said controller means further controlling said refilling means by using the level signals from said first and second measuring means to start said refilling means when the liquid in a respective one of the first and second vessels is detected at the lower level by the respective lower detector, and to stop said refilling means when the liquid in a respective one of the first and second vessels is detected at the upper level by the respective upper detector, and said controller means further controlling said switching means for switching between the outlets of said first and second vessels to allow the liquid to flow from the outlet of one of said vessels to said common outlet while the other of said vessels is being refilled, and to allow the liquid to flow from the outlet of the other of said vessels to said common outlet while said one vessel is being refilled.