Manhole Cover Locking Bolt Construction

The present invention relates to a manhole cover locking bolt.

By way of background, in the past manhole covers of certain types were secured to their associated frames by means of bolts having conventional heads which could be removed by readily available wrenches. Thus, unauthorized access was available to cable-carrying tunnels by personnel who wished to install additional cables along the route of existing cables. Unauthorized access was also available to sewers for improper dumping of toxic wastes.

It is the object of the present invention to provide a manhole cover locking bolt which can be used to lock a manhole cover to its associated frame against unauthorized removal.

Another object of the present invention is to provide a manhole cover locking bolt which can be installed and removed by the use of a proper key and, further, which is protected against collecting dirt and debris which could interfere with its installation and removal. Other objects and attendant advantages of the present invention will readily be perceived hereafter.

The present invention relates to a manhole cover locking bolt comprising a shank, first threads on said shank, a head affixed to said shank, second threads on the outer periphery of said head, a top on the opposite side of said head from said shank, and a curvilinear groove in said top of said head for receiving a mating key.

The present invention also relates to an improvement to a manhole cover mounted in a frame having a threaded bolt-receiving bore therein with a first depresison in said frame and a second depression on said manhole cover proximate said bolt-receiving bore for receiving the head of a bolt, the improvement comprising a manhole cover locking bolt comprising a shank, first threads on said shank for mating engagement with said threaded bolt-receiving bore in said frame, a head affixed to said shank for entry into said adjacent depressions, a top on said head, second threads on said head, and a curvilinear groove in said top of said head for receiving a mating key.

The various aspects of the present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary plan view of a manhole cover secured to its associated frame by means of the improved locking bolts of the present invention;

FIG. 2 is an exploded view of the manhole cover bolt and its associated protective cap shown in relation to the manhole cover mounted on its associated frame;

FIG. 3 is a fragmentary cross sectional view taken substantially along line 3--3 of FIG. 1 and showing the bolt in locking relationship to the manhole cover with the protective cap mounted on the head of the bolt;

FIG. 4 is a view taken in the direction of arrows 4--4 of FIG. 2 and showing the endless curvilinear groove in the top of the head of the bolt;

FIG. 5 is a view taken in the direction of arrows 5--5 of FIG. 2 and showing the configuration of the protective cap in plan;

FIG. 6 is a side elevational view, partially broken away, showing in reduced scale, a wrench which carries a socket for mounting the protective cap on the head of the bolt and also carries a key for mating engagement with the curvilinear groove in the head of the bolt;

FIG. 7 is a view taken in the direction of arrows 7--7 of FIG. 6 and showing the curvilinear ridge in the key which mates with the curvilinear groove in the top of the head of the bolt; and

FIG. 8 is a view taken in the direction of arrows 8--8 of FIG. 6 and showing the configuration of the non-circular socket for mating engagement with a nut-like protuberance on the cap.

The improved manhole cover bolt 10 is for the purpose of locking a manhole cover 11 to its associated frame 12 which is suitably anchored in the surrounding area 13, which may be a roadway or a sidewalk or any other structure on which the frame 12 can be mounted.

The manhole cover bolt 10, which is fabricated of hardened chiselproof steel, includes an elongated threaded shank 14 and a head 15 formed integrally therewith. An annular frustoconical bevel or lip 17 is formed on the underside of head 15 for complementary mating engagement with an arcuate bevel 19 or manhole cover 11 and arcuate bevel or lip 20 on frame 12 when cover 11 is properly aligned with frame 12. The cover 11 is mounted on frame 12, the outer annular portion 21 of cover 11 rests on inner annular portion 22 of frame 12. In addition, a depression 23 in cover 11 is in alignment with a depression 24 in frame 12 to define an essentially cylindrical opening 25 for receiving head 15 of bolt 10. As can be seen from FIGS. 1 and 2, a space 27 exists between the outer edge 29 of cover 11 and the inner edge 30 of frame 12.

In order to lock manhole cover 11 to its associated frame 12, the shank 14 of bolt 10 is threaded into the tapped hole 31 in frame 12. The threading is effected by the use of wrench 32 having a body 33 and a handle 34. At one end of body 33 is a head 35 having an endless curvilinear groove 37 in the top 40 of bolt head 15. A ridge and groove of this type are fully described in U.S. Pat. Nos. 3,241,408 and 4,480,513 and other than in the present combination do not form any part of the present invention. Bolt 10 is turned by the use of wrench 32 until its annular frustoconical undersurface 17 seats on adjacent surfaces 19 and 20 of manhole cover 11 and frame 12, respectively. Surfaces 19 and 20 define a substantially annular seat which is split by space 27 at substantially diametrically opposite sides thereof. As can be seen from FIG. 1, two bolts 10 are used at diametrically opposite sides of manhole cover 11 to firmly lock it to its associated frame. Bolts 10 cannot be unscrewed without the use of a proper key comprising curvilinear ridge 37.

Since the manhole cover is on the ground, the curvilinear groove 39 can fill up with dirt, ice and other debris, which in turn, could prevent the ridge 37 from entering the groove 39 to a sufficient extent to unscrew bolt 10. Accordingly, a cap 41 is provided which has internal threads 42 for mating engagement with external threads 43 on bolt head 15. Cap 41 also includes a hexagonal nut-like protuberance 44, which may be of any other suitable configuration. Wrench 32 includes a socket 45 having a cavity 47 for mating engagement with non-circular protuberance 44. Therefore, by the use of wrench 32, cap 41 can be screwed into tight locking engagement with bolt head 15.

There is a clearance space 49 (FIG. 3) between protuberance 44 and the adjacent parts of frame 12 and cover 11 to permit entry of socket 45. Also, as can be seen from FIG. 3, there is a sufficient clearance around threaded bolt head 15 to receive the side wall 50 of cap 41, but this clearance is not sufficiently large to receive a conventional socket wrench. The wrench 32 is used to remove cap 41 and unscrew bolt 10 by following the steps in reverse to those described above for installing bolts 10.

The relative diameters of head 35 which carries key 37 and cylindrical opening 25 which receives bolt head 15 are such that opening 25 acts as a guide to center head 35 to thereby facilitate the alignment of ridge 37 with groove 39. More specifically, all that is necessary to cause ridge 37 to enter groove 39 is to insert body 35 into cylindrical opening 25 and turn wrench 32 until ridge 37 falls into groove 39.

While preferred embodiments of the present invention have been disclosed, it will be appreciated that the present invention is not limited thereto but may be otherwise embodied within the scope of the following claims.