| 摘要 |
A controllably releasable security locking arrangement for a manhole cove r allows a manhole cover to be locked into position but allows the manhole c over to rise up in stages upon development of upward forces in an explosion to vent gases developed by the explosion. A lock body mounts a latch slide w hich has an outer end and which can be extended to prevent removal of the ma nhole cover. When a shear pin fails the lock body pivots down, to a limited extent, and a secondary shear pin can also be included allowing the cover to be blown completely free upon development of pressures of a great magnitude . A slotted skirt directs venting gas flow so as to retard the inflow of fre e air and attenuate the explosion.
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