| 摘要 |
The device comprises a conduit 1 for introduction to a pressurised distribution system and a piston 31, 32 automatically displaceable to sealingly cooperate with seating 8 in the event of excessive pressure differential across the piston, e.g. due to a fracture in a downstream pipe. The piston is re-opened by knob 42. As shown, in the normal equilibrium position of the piston, fluid flow is established between the inlet 13 and outlet 12 via arcuate passages 33, 34 in two relatively rotatable piston parts 31, 32. Relative rotation of the latter adjusts the flow duct section at 33, 34 to set the pressure difference across the piston for normal flow conditions. Axial movement of the piston is restrained, as by the frictional grip provided by seal 6, to maintain the piston in its equilibrium position until a threshold value of the pressure difference is exceeded. Other embodiments incorporate, respectively, adjustable magnets and a diaphragm subjected to fluid pressure to provide the axial restraining means. The drive for rotating the relevant piston part may include gearing. <IMAGE> |
