| 摘要 |
Pneumatically operated throttle valve which provides both positive shutoff and precise flow control. The valve has a seat surrounding an orifice and a poppet movable between open and closed positions relative to the seat for controlling communication though the orifice. The poppet is urged toward one of the two positions by a spring, and the force for moving the poppet toward the other position is provided by a frictionless bellows. The poppet is provided with a needle valve for precise control of flow through the orifice, and internal heaters are provided for heating the poppet and the seat directly to prevent condensation from forming on them. The bellows in combination with a low friction bearing effectively eliminates stiction and permits precise control of the valve over its entire operating range. In one disclosed embodiment, the bellows serves as the spring which urges the poppet toward one of the two positions as well as an actuator which moves it toward the other position. The valve can be configured to be either normally open or normally closed.
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