A control valve actuated by a low-pressure/low-flow-rate control fluid. The valve housing has a control-fluid channel, a second-fluid channel, and a piston which is movable between open positions and a closed limit position. The valve has a piston head seat located intermediate the control-fluid channel. The seat has a shape which compliments the piston head so that the control fluid can flow through the control-fluid channel when the piston is in an open position. The valve has a piston stem seat located intermediate the second-fluid channel. The piston stem seat has a shape which compliments the free end of the piston stem so that a fluid seal is formed in the second-fluid channel when the piston is in the closed limit position and so that a second fluid may flow through the second-fluid channel when the piston is in an open position. The valve is constructed and arranged so that a low-pressure/low-flow-rate control fluid connected to the input port of the control-fluid channel will actuate the piston from the closed limit position to an open position. The valve is also constructed and arranged so that the second-fluid channel is automatically opened when the piston is moved to an open position, and the second-fluid channel is automatically closed when the piston is moved to the closed limit position.
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