Proportional flow control valve

A system for dispensing fluids, said system comprising at least one dispensing outlet, tubing for flowing a fluid to said dispensing outlet, sensing means for sensing the rate of flow of said fluid through said tubing, and flow control means responsive to the sensing means and arranged to continually control at least one of the quantity and the rate of fluid dispensed through said dispensing outlet in dependence upon the sensed flow rate, said flow control means comprising valve means for controlling the flow of fluid through said dispensing outlet, and control means responsive to said sensing means and arranged to actuate said valve means, and said valve means comprising at least one flow control valve actuable to vary the flow rate of fluid through said dispensing outlet said flow control valve having

• a fluid inlet,
• a fluid outlet,
• a main valve member controlling communication between said fluid inlet and said fluid outlet, the main valve member being movable between a closed position in which communication between said fluid inlet and said fluid outlet is closed and positions in which the valve is open allowing communication between said inlet and said outlet, the fluid pressure at the fluid inlet being applied to said main valve member in a direction to open said valve,
• means for biasing said main valve member into its closed position, and
• means for moving said main valve member against the action of said biasing means to open the valve,
• the flow control valve further comprising
• a pilot chamber which is in communication with said fluid inlet, the fluid pressure within said pilot chamber being applied to said main valve member in a direction to oppose opening of said valve, and
• said main valve member being to define a flow path with said fluid outlet, the area of said flow path varying in dependence upon the position of said valve member and increasing as the valve member is moved in the valve opening direction, fluid pressure being applied to said main valve member in both opening and closing directions whereby, when the valve is open, the position of the valve member and hence the rate of flow of fluid through the valve is determined by said moving means,
• said valve further comprising an elongate tubular member having a longitudinal axis and first and second ends spaced along said longitudinal axis, said first end of the tubular member defining a tubular main valve seat, and the second end of the tubular member defining said fluid outlet, the main valve member extending within said tubular member, and
• said main valve member being elongate and having a longitudinal axis extending coaxially with the longitudinal axis of the tubular member, and having a first portion with a peripheral wall extending substantially parallel to the longitudinal axis thereof, said first portion of said main valve member extending within said tubular main valve seat in its closed position, and said main valve member having a second portion, following said first portion, having a converging cross-section, movement of the main valve member along its longitudinal axis in the valve opening direction moving the first portion out of said tubular main valve seat to open the flow path through the main valve seat, and further movement of the main valve member in the valve opening direction moving the second, converging portion of the valve member along the tubular member thereby varying the area of said flow path.