Gravity latch for box lid

BACKGROUND OF THE INVENTION

This invention relates to a gravity latch for preventing removal of a lid from a box, such as an underground meter box. Such latches are commonly employed in connection with meter or valve box lids in which the lid rests in a horizontal plane in a recess on the top of the box under gravity. Such lids are often removed by irresponsible persons who may tamper with the meter or valve in the box. Previous gravity latches for securing such lids (as, for example, that shown in U.S. Pat. No. 2,217,097) have been operated by simultaneously pulling a latch lever and the lid in an upward direction. While a special key is provided for the purpose, its use is easily avoided by any makeshift instrument capable of being inserted through a hole in the lid and of catching and pulling up on the lever. There is, therefore, a need for a new and improved gravity latch.

OBJECTS AND SUMMARY OF THE INVENTION

A general object of the present invention is to provide a new and improved gravity latch for box lids which will overcome the above disadvantages and limitations.

Another object of the invention is to provide a gravity latch of the above character which is positive in its operation and which requires an easily constructed key which is required to be operated in a manner which is not easily avoided with a makeshift arrangement.

Another object of the invention is to provide a gravity latch of the above character which is of simple construction and low cost.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a box and lid incorporating a gravity latch constructed according to the invention.

FIG. 2 is a cross sectional view taken along the lines 2—2 of FIG. 1.

FIG. 3 is a bottom plan view of the lid and latch mechanism of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures, there is shown a latch 10 constructed according to the invention which interlocks a meter box 12 and a lid 14 resting under gravity in a shoulder 16 of an opening or recess 18 formed through the top of the box. In general, such a box can be a concrete valve or meter box adapted to be buried with its upper surface horizontal or flush with the ground and the invention herein is designed to operate with reference to gravity although exact alignment therewith is not required.

Means are provided for securing one edge 20 of lid 14 to the adjacent wall of the box to thereby prevent it from being lifted out of recess 18 until the opposite edge 22 is first lifted clear. Such means can take any of various forms as, for example, that shown in FIG. 1 consisting of a fixed arm 24 which depends from the lowerside of the lid. Arm 24 includes a projection 26 which faces toward and engages a bearing surface 28 formed about the inner wall of the box at an angle facing away from opening 18.

Friction latch 10 releasably engages and thereby secures the opposite edge of the lid to the adjacent wall of the box. The friction latch includes portions of wall 29 consisting of an inclined bearing surface or wall 30 which faces at an angle and away from opening 18, that is to say, the normal of surface 30 is directed away from the lid.

Latch 10 also includes a lever 32 which is pivotally mounted on a pin 34 set in a yoke 36 which is secured to the lid by a screw 38 and depends downwardly therefrom. Yoke 36 mounts lever 32 for rotation in a generally vertical plane about an axis which is located below a radius line R joining edge 20 to the point of contact on surface 30. In this way, attempted upward movement of the lid cannot be effected without releasing the lever since the arc of rotation of the lid from edge 20 to the end 40 of the lever intercepts wall 30.

The end 40 of the lever is nearest the bearing surface 30 and serves to engage or cam against the same. This end is provided with a rough camming surface 42 which lies approximately on a cylinder having a center at pivot pin 34 but has a somewhat larger radius of curvature at its upper extreme than at the lower to compensate for wear and to allow for normal variations in the dimensioning of the parts. The lever is balanced so that end 40 naturally falls downwardly toward surface 30, rotating the lever clockwise (as seen in FIG. 1) and causing surface 42 to move in an expanding arc until some portion thereof comes into contact with surface 30. After surfaces 30 and 42 are in contact no further relative motion between them will take place since any movement tends to roll them on each other due to friction. In this way, the lever snubs against the wall of the box and prevents raising of the lid. This result is explained in FIG. 1 by the triangle N, P, R in which the sum of the lengths P, N is greater than the base length R. Thus, P, N would have to straighten in order to pass through R, but this is precluded by the restraining force exerted by the walls of the box.

The other end of lever 32 terminates in means for permitting selective disengagement of the latch by lifting the camming end 40 clear of wall 30. Such means consists of an upwardly facing conical receptacle 46 formed with a hole 48 at its apex for permitting selective alignment and engagement with an operating key 50.

Key 50 consists of a rod having a transversely extending handle 52 formed at its upper extreme. The lower end of the rod is provided with a pair of spaced transversely extending or cross lugs 54 and 56. A slot 58 is formed through the lid to permit the lug end of key 50 to be inserted through the top of the lid and into direct downward contact with receptacle 46. Thus, the lower end of key 50 passes through hole 48 to center the key while the lower lug 54 contacts the conical receptacle to operate the lever. When the lever is pushed into its lowermost position, as defined by a stop supplied by engagement of a shoulder 60 formed on lever 32 making contact with yoke 36, the key is turned to cause the upper lug 56 to rotate under the lowerside of the lid. The spacing between lugs 54, 56 is selected to correspond to the distance be3,530,696 tween the lid and the fully depressed position of receptacle 46. Thus, upward pull on the rotated lever lifts the lid while maintaining the operating end of the lever fully depressed and thereby effects the simultaneous pushing down on the lever while pulling up on the lid to open the same.

Installation proceeds as follows: first, edge 20 is slid into place. The other edge 22 is then merely dropped into position. As it falls the camming end 40 of the lever is pushed upwardly so that the wall 30 of the box is cleared. As the lid reaches its final position, the heavier end 40 of the lever drops and forces the rough surface 42 against surface 30. Simultaneously, arm 24 and projection 26 pivots about edge 20 until it is opposed and locked against surface 28. Obviously, the lid may be installed the other way around provided that the box and lid possesses the necessary symmetry.

In removal, the operator merely inserts the key 50, as shown in phantom lines in FIG. 2, so that the handle is transverse to slot 58 to thereby permit lugs 54, 56 to pass through the slot. The operator easily feels the lower tip of the key making contact with the conical receptacle and he merely proceeds with pushing down on the key until it can be turned which is well-defined by the spacing between the lugs. The key is then turned, for example, toward the edge 22 and lifted by handle 52 so that the upper lug 56 contacts with the lid adjacent slot 58. The lid can then be easily rotated about pivot radius R and about edge 20 to be lifted clear of the box.

From the above description it will be clear that the gravity latch of the present invention is particularly effective in providing a combined pulling and pushing motion which is not easy to defeat and which is sufficiently complex as to discourage tampering, especially by persons not familiar with its operating principle.