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Application Schemes - Introduction

In order to lay out complicated interlock schemes, it is necessary to understand the simplest applications. On this page, the basic concepts of interlocking are outlined and discussed.

Interlocking a Single Unit in One Position

If it is desired to secure a device in the open position, an interlock is used as in Fig. 1. The possession of the key indicates hat the device is in the open position and is locked by the extension of the interlock bolt. When the key is inserted in the lock and turned to withdraw the interlock bolt, the device is free to operate to the closed position and the key is held in the lock.

When a device is to be locked only in the closed position an interlock is used as shown in Fig. 2. The possession of the key indicates that the device is locked in the closed position, as the interlock bolt has been extended to remove the key. When the key is inserted in the lock and turned to withdraw the interlock bolt, the device is free to operate to the open position and the key is held in the lock.


Interlocking a Single Unit in Two Positions

Two methods are used in interlocking a device in both open and closed position. The first method requires only one interlock as shown in Fig. 3. The interlock bolt is extended in both the open and closed positions. This is accomplished with two recesses in the device that is being interlocked - each coinciding with the locking bolt in one position.

The possession of the key indicates that the interlock bolt is extended and that the device is locked either in the open or closed position. Furthermore, the device cannot be operated until the key is inserted and turned in the lock to withdraw the locking bolt. The key cannot be removed from the lock in an intermediate position, but in the fully open or closed positions only. However, in this application, possession of the key gives no indication as to whether the device is locked closed or open.


Interlocking Two Units in Two Positions

The other method for locking in both the open and closed positions requires two interlocks as show in Fig. 4. Possession of key A-1 indicates that the device is locked open possession of key A-2 indicates that the device is locked closed. The device is shown normally open; therefore, key A-1 is free and the L-O interlock bolt is extended into its recess provided in the movable member while key A-2 is held and the L-C interlock bolt is withdrawn. To close the device, insert key A-1 in the L-O lock and turn to withdraw bolt of L-O interlock, which permits the device to be operated. Now the device can be moved to the closed position. Key A-2 can be turned to extend the bolt of the L-C interlock into its recess, which locks the device in the closed position.

This releases Key A-2 from the L-C interlock. Meanwhile, key A-1 is held in the L-O interlock since its withdrawn locking bolt cannot be extended. This method is used more often than the single two-position interlock shown in Fig. 3, due to its adaptability to sequence operations. Also, the possession of key A-1 or A-2 indicates that the device is locked open or locked closed, respectively.


Sequence Interlocking

With the fundamentals developed above, it is quite simple to extend the application to the interlocking of two or more devices in a desired sequence.

Two devices are shown in Fig. 5. In operation they are not closed at the same time. With the interlocks arranged as shown, only one key is required in the interlocking system. Both devices are shown open; therefore, the key is free. To close any one device, the key is inserted and turned in that particular lock to withdraw the interlock bolt. The key is held in this lock until the device is again locked open. This simple interlocking sequence lends itself to a multitude of applications. The procedure is the same for two devices, neither of which is to be opened at the same time.

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