| 摘要 |
A metering valve for controlling fluid flow is provided which includes a piston assembly disposed between a fluid inlet and a fluid outlet and mounted for relative movement within a tubular unit between a first open mode, a second open mode connecting the fluid inlet and outlet and a close mode. The assembly is biased to assume the close mode and assumes the first open mode when a predetermined first external form is applied to a valve actuating element forming a component of the metering valve. The assembly assumes the second open mode when the first external force is enhanced by a predetermined second external force applied to the valve actuating element. When the external forces are released, the piston assembly automatically returns to the close mode upon successively moving through first and second segments of travel relative to the tubular unit. The rate of travel during the first segment is substantially less than the rate of travel during the second segment. During the second segment of travel the relative motion of the piston assembly is substantially instantaneous to the close mode. The valve actuating element includes an elongate member having an exposed one end portion on which the predetermined external forces are applied, and a second end portion having a first valve component mounted thereon and actuated to a first open position when the first external force is applied. A second valve component is also mounted on the second end portion of the elongate member and is actuated to a second open position when the second external force is applied.
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