Fig. 45
Fig. 46
The concentric cylindrical arrangement of this type of lock is shown in [Fig. 46 (a) and (b)]. Here, there is a larger cylinder encircling the key plug. This is known as the master-ring, or larger, plug, and is indicated at a. When the change key is inserted in the key plug b, the lower series of breaks in the pins comes into alinement with the outer edge of the plug, as shown at (a), and allows it to revolve in the master ring, the cam on the inner side at c actuating the lock. When the master key is inserted, the upper series of breaks comes into alinement with the outer edge of the master ring, as shown at (b), allowing the plug and the ring to rotate together with the turning of the key, and thus to produce the same result as that caused by the operation of the change key.
Fig. 47
The paracentric system, sometimes called the duplex system, consists in having two separate cylinders to each lock, as illustrated in [Fig. 47]. One of these cylinders, generally the upper one, is operated by the change key, and the lower one, by the master key. The interior construction of the lock is so devised that each key performs the necessary function of operating the same bolt, so that the individual lock may always be opened by the change key, and all locks of the series by the master key. This latter system of lock construction is more expensive than the one-cylinder type, but it possesses an advantage in that it provides greater security when a limited number of locks are grouped in one series.
41. Owners or officials of large office buildings and industrial works now avail themselves of the master-key system just explained. They are able to obtain mortise locks, rim locks, and padlocks, all arranged to operate with a master key, in one series. In fine residence work, this system is also adopted. Such a system of locking is easily recognized as convenient, especially where subordinates are held responsible for certain rooms or departments to which they, individually, have access, as all of the rooms or departments may be entered by the manager or superintendent by the aid of the master key.
A series of master-key locks may also be “submaster-keyed” by dividing it into subordinate groups. In such a case, each group is operated by a master key of its own, and all the subordinate groups are controlled by a grand master key. For example, a six-story office building could be furnished throughout with locks having non-changeable keys; the doors of each floor could be operated separately by a master key; and the doors of the entire building could be operated by a grand master key. The convenience of such a system is readily apparent in large buildings where each janitor is responsible for a certain floor, and where the head janitor, manager, or owner, has control of all the locks through the grand master key.
In some instances, for additional security and for special work, the corrugations in the keyway are changed in shape so that the manufacturers’ regular type of key will not enter the keyway, or plug, thus allowing no chance for the regular type of key to operate the lock.