Self-locking drop-door

Claim 1

A self-locking drop-door for a wall having an opening comprising, a door proper, hinges pivotally connecting the bottom of the door proper to the wall adjacent the bottom edge of the opening, and a support bar pivotally connected at one end to the door proper by pivot connector means at a point spaced from the bottom of the door proper, the wall having a slot through which the support bar slidably passes with the lock bar having a lower edge resting on the lower edge of the slot with the slot being adjacent the opening and at a distance from the hinges equal to the spacing from the hinges to the connection of the support bar to the door proper, the support bar being angular in shape and comprising a short locking arm having said pivot connector means on one end pivotally connected to the door proper and a long counterweight arm extending angularly from the other end of said short locking arm so that said pivot connector means is not in alignment with the axis of said counterweight arm, stop means on the end of said counterweight arm opposite said locking arm dimensioned and oriented so as to be incapable of passage through said slot, the locking arm being no longer than the distance from the pivotal connection of the locking arm to the door proper to the inside of the wall when the door proper is in raised closed position, and the angle between the locking arm and the counterweight arm being such as to position the counterweight arm at an inclined angle to said wall when the door is in its raised closed position so that the weight of said counterweight arm acts to provide a holding force on the door to hold the door in its raised closed position whereby an opposite opening force exerted on the top of the door in excess of the holding force in a door opening direction causes said counterweight arm to pivot upwardly while simultaneously sliding outwardly of said slot until said stop means engages the wall adjacent the slot to enable a full opening of movement of said door.