Door Latch Dashpot Resists Wind Impact
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Solution Overview
Problem
Existing door latch systems with push bar exit devices fail to prevent unwanted actuation during high velocity impacts from wind-driven debris in extreme weather conditions, such as hurricanes or tornadoes, leading to potential breaches in building security.
Innovation Solution
A door latch system incorporating a dashpot, which can be a pneumatic or hydraulic damper, is mounted to the latch housing to resist instantaneous movement caused by high velocity impacts, ensuring the latch remains secured by opposing the movement of the push bar and base plate, thereby preventing unwanted unlatching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a push bar exit device is designed to meet UL specifications with an internal biasing mechanism, then the door can be easily unlocked from the interior side under normal conditions, but the device may fail to prevent unwanted actuation when the door is subjected to high velocity impacts from windborne debris
Solution Approach 1:
The dashpot provides dynamic resistance that adapts to the velocity of applied forces. Under normal operating conditions, the dashpot allows smooth operation with minimal resistance. However, during high-velocity impacts from windborne debris, the dashpot automatically increases its damping force proportionally to the impact velocity, preventing unwanted latch release while maintaining ease of operation during controlled use.
Solution Approach 2:
The dashpot changes the effective damping parameter of the system based on the velocity of the applied force. At low velocities (normal operation), the damping is minimal, allowing easy push bar operation. At high velocities (debris impact), the damping parameter increases significantly, creating sufficient resistance to prevent latch actuation. This velocity-dependent parameter change resolves the contradiction between ease of operation and resistance to unwanted actuation.
2Stability of the object's composition
If the internal biasing mechanism is strengthened to return the push bar to its extended position, then the push bar returns reliably after force is removed, but the device becomes more susceptible to unintended release during high energy impacts
Solution Approach 1:
The dashpot acts as an intermediary element between the push bar and the latch mechanism. It mediates the interaction by providing velocity-dependent damping that allows the biasing mechanism to reliably return the push bar under normal conditions while simultaneously protecting the latch from high-velocity impacts. The dashpot absorbs the harmful high-velocity energy before it can actuate the latch, while permitting normal operational movement.
3Strength
If the push bar is positioned closer to the base plate to reduce movement distance, then the latch engagement is more secure, but the relative movement during impact is reduced, causing the push bar to release the latch more easily
Solution Approach 1:
The dashpot utilizes pneumatic or hydraulic damping principles to provide velocity-dependent resistance. When a high-velocity impact occurs, the rapid movement of the push bar creates high pressure within the dashpot fluid or gas, generating substantial damping force that counteracts the impact. This pneumatic/hydraulic mechanism allows the push bar to maintain secure engagement during normal conditions while automatically resisting high-velocity impacts that would otherwise cause unintended release.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dashpot system effectively maintains the latch in a secured position during high wind and debris impacts, preventing the door from opening unintentionally while still allowing manual operation under normal conditions, thus enhancing security and compliance with safety standards.
Implementation Method 1
A dashpot is mounted to the latch housing and may be operatively connected to the driving member. The dashpot is configured to allow relatively free movement of the driving member when the distance between the push bar and base plate is reduced under normal operating conditions, and to oppose instantaneous movement of the driving member when a secure side of the door experiences a high velocity impact
Implementation Method 2
manufacturers must provide for an internal biasing mechanism, such as a spring. Thus, the internal biasing mechanism must be carefully matched to the device so as to return the push bar to its extended position after force is removed from the push bar
Data Source
AI summary
A door latch system includes an exit device having a housing mounted to an unsecured side of a door. A latch assembly is mounted in the housing and includes a latch for releasably securing the door in a door frame. An actuating assembly includes a driving member. A push bar is configured to be received within the housing. Relative movement between the push bar and base plate so as to reduce the distance between the push bar and base plate moves the driving member and latch to release the door from the door frame. A dashpot is connected to the driving member and configured to allow movement of the driving member when the push bar is manually depressed but to resist movement of the driving member when a secure side of the door experiences a high velocity impact. A method of resisting unwanted unlatching of the latch is also disclosed.