The provided context focuses on keyed locks, specifically those with master keys, not combination door locks. Therefore, this answer will address how keyed locks with master key capabilities work, given the available information.
Understanding Keyed Locks with Master Keys
Keyed locks, especially those found in apartment buildings or commercial settings, sometimes utilize a master key system. This means that multiple locks can be opened by a single master key, while individual locks also have their own unique keys (change keys).
Key Components
- Pins: These are small, cylindrical pieces within the lock cylinder.
- Pin Pairs: Two pins stacked on top of each other (one from the cylinder, one from the plug).
- Shear Line: The point where the cylinder can rotate and unlock the mechanism. This occurs when all pin pairs are aligned correctly.
- Change Key: A key specific to a single lock within the master key system.
- Master Key: A key that can open multiple locks within the system.
- Master Wafer (Spacer): According to the provided information, "a few of the pin pairs are separated by a third pin called a master wafer or spacer." This is the key component that allows for the master key functionality.
How They Work
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Normal Operation (Change Key): When the correct change key is inserted, it pushes the pin pairs up to the correct height, aligning the gap between the pins with the shear line. This allows the cylinder to turn, unlocking the lock.
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Master Key Operation: Locks that are part of a master key system have strategically placed master wafers (spacers) between some of the pin pairs. The master wafer creates a second shear point.
- If the change key lifts the pin pairs to its correct shear point, the lock opens.
- If the master key lifts the pin pairs to a different but also valid shear point (due to the master wafer), the lock also opens.
Example
Imagine a lock with three pin pairs. Let's say the change key needs the pin pairs to be lifted to levels 3, 5, and 2 to open the lock. A master key system could introduce master wafers in the first and third pin pairs. This means the master key might lift those pin pairs to levels 4 and 3 respectively, while still maintaining the correct shear point, and open the lock, even though the lifts are different from the change key.
Table Summarizing Key Differences
| Feature | Change Key Lock | Master Key Lock |
|---|---|---|
| Pins | Standard pin pairs | Standard pin pairs, with master wafers (spacers) separating some pairs |
| Key | Unique to a single lock | Opens multiple locks within the system |
| Shear Points | One specific shear point | Two or more possible shear points (due to master wafers) |
