| 摘要 |
A shutoff valve for installation in a gas distribution line to interrupt the flow of gas automatically upon a drop in pressure in the line due to a break or the like. The valve includes a movable valve member actuated by a piston which is disposed in a cylinder in communication with the distribution line. The top of the piston includes a calibrated aperture which admits gas into the cylinder beneath the piston so that the pressure beneath the piston in the cylinder is substantially equal to the pressure in the line. However, upon a sudden drop in pressure in the line due to a break or the like, the flow of gas through the aperture is metered so that the pressure in the cylinder beneath the piston becomes greater than the pressure in the distribution line, causing the piston to shift upwardly and move the valve member into a position where it interrupts the flow of gas. The pressure differential on the valve member retains it in the closing position. However, upon an equalization of pressure on both sides of the valve member in the line, the valve member drops by gravity out of the closing position and back into the cylinder to permit normal flow of gas through the line.
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