DESCRIPTION OF THE PRIOR ART
Securing doors and other movable members against opening or other movement by means of external locking devices has been accomplished in innumerable way since, at least, as far back as Elizabethan times, if not earlier. Among the many ways this has been accomplished have been the use of staples secured to a movable or stationary member and a hasp which fits over the staple and is prevented from removal from the staple by means of some type of padlock. In addition, various bar devices have been employed where the bar members are passed through some type of looped element extending outwardly from the adjacent members, such as a door and a door jamb, the relative movement between which members it is desired to prevent. Examples of these latter arrangements may be seen in the U.S. Pat. Nos. to Foley, 1,368,711; Grodt et al., 2,794,663; Ehlers, 3,334,933; Tumbiolo, No. 3,655,229; Fazzorali, No. 4,616,493; DeForrest, 4,861,079 and Goodspeed, 4,883,294. In all of these arrangements, however, it may be possible either to remove from the member, by unscrewing or unbolting the bar-type receiving element, and in all instances, some type of pad lock is utilized to lock the bar. However, because of exposure of the U-shaped link in the padlock in most instances, such link may be cut, either by heavy wire cutters or sawed apart by some type of saw, the teeth of which can be brought against the U-shaped link.
In more recent years, there has been developed a type of cylindrical body lock which has a pair of opposed parallel faces normal to the cylinder axis in one of which faces an element receiving first passageway is provided. This first passageway extends normally to the cylinder face in which it is cut or molded and part way through the body towards the opposing cylinder face. In addition, a second passageway is bored in transversely from a side wall of the body to intersect perpendicularly, and even extend past the first passageway further into the cylindrical body. A cylindrical lock is slideably inserted into the second passageway, with this lock being provided with a co-axial plunger which, when a key is inserted in the lock member and pushed, will extend through the first passageway and in toward the end of the second passageway. Thus, if two orificed members which are to be held together are inserted in the first passageway and their orifices are co-aligned with the locked plunger, when the lock is pushed into the second passageway so that its plunger passes through the orifices, and the lock is secured in the second passageway and the key removed, it is impossible to remove the lock from the two members, short of destroying the members themselves. This type of lock is disclosed in U.S. Pat. No. 3,769,821, issued to Mortimer A. Randel, where its use is shown for securing the door of a coin operated vending machine. Locks of this type have been manufactured by American Lock Company.
While such cylindrical locks have been found to be effective for the purpose for which they have been designed, their use hitherto has been limited to securing at their ends a pair of flat bars or angle flanges which are attached to doors and frames, the relative movement between which is to be prevented. Such cylindrical locks have not heretofore been utilizable to secure bars across doors, or a door and a jamb or building frame; nor have such locks heretofore available been utilizable to secure pressure valves against tampering or other unauthorized opening, closing or valve settings.