| 摘要 |
<p>In a system for opening and closing a main line valve by use of high pressure hydraulic fluid which is controlled from a remote location and in which the fluid passes through a hand pump located at the site of the valve, a protective lock-out system is provided for guarding against personal injury in the event the high pressure fluid should arrive at the hand pump while it is being manually operated. The lock-out system includes a small piston located in an air passageway which is positioned outwardly of the hand pump main piston chamber. This passageway extends from the top of the hand pump main piston chamber toward the IN port which receives the high pressure hydraulic fluid. The piston is connected by a shaft to a poppet valve. The high pressure fluid is applied to the under-surface of the piston and to the seat side of the poppet valve. On the up stroke of the hand pump, the lock-out piston is forced downwardly by the increase in air pressure on the top surface of the piston which exceeds the differential hydraulic pressure applied to the underside of the lock-out piston thereby slightly opening the poppet valve and allowing a limited amount of pressure to be applied to the lower chamber of the hand pump piston.</p> |
