Topic:
Lock cylinder:
When the correct key is inserted into a lock cylinder, the key can be turned. The operating mechanism at the back of the lock cylinder sends an open/close command to the door lock. With the wrong key, the lock cylinder cannot turn. That sounds very logical, of course. This page explains how the shape of the key bit determines whether the lock cylinder can rotate within the housing.
Situation 1: the key is in the cylinder lock:
In the image below, a lock cylinder is shown with the key bit of a key inside it. The black wafers have now taken up a certain position based on the shape of the key bit. The top and bottom are now smooth. The wafers no longer protrude at the top and bottom.
The image on the right shows the front view of the lock cylinder. The outer round section is the housing and the darker inner section is the lock cylinder. The white areas at the top and bottom are the spaces where the wafers can move when the key is removed, or when the wrong key is inserted into the cylinder. In this case, with the correct key (see the image above), the wafers are inside the cylinder lock. They do not protrude, so the lock cylinder can rotate within the housing.
Situation 2: the key has been removed from the cylinder lock:
In the image below, the key has been removed from the lock cylinder. The springs of the wafers ensure that the wafers move into a certain position.
One moves upward and the other downward. At this moment, the cylinder lock is blocked.
Because the wafers have taken on a different position after the key has been removed from the lock, the lock cylinder can no longer rotate in the housing. The black wafers in the image above have been pushed outward by the internal springs. They are now wedged between the grey walls of the housing. The lock cylinder can no longer rotate within the housing. Only when the key is reinserted into the lock cylinder will the black wafers move inward again and the cylinder can rotate within the housing.
