Pneumatic Fire Detector Diaphragm Minimizing Free Volume
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Solution Overview
Problem
Existing pneumatic fire detectors have a large internal free volume that reduces pressure rise and hydrogen gas reabsorption, affecting heat detection capabilities and system resetability, especially in short sensor tubes.
Innovation Solution
A pneumatic fire detector using a single deformable diaphragm to open and close two terminals, minimizing internal free volume and allowing for different alarm states at selected pressures, with the diaphragm configured to move between three positions in response to pressure changes, ensuring effective fire and integrity alarms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single deformable diaphragm is used to open and close two terminals, then the internal free volume is minimized and detection precision is improved, but the device complexity increases due to the multi-position diaphragm mechanism
Solution Approach 1:
A single deformable diaphragm performs multiple functions by moving between three distinct positions: first position (normal operation), second position (integrity alarm when pressed against second terminal), and third position (fire alarm when pressed against first terminal). This multi-functional design eliminates the need for separate integrity and fire alarm diaphragms, minimizing internal free volume while maintaining detection precision for both integrity and fire conditions.
2Measurement precision
If the internal free volume is reduced, then the pressure rise associated with inert gas expansion and hydrogen evolution is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The diaphragm is designed as a flexible thin film component that can be deformed to different positions through pressure changes. This flexible membrane approach allows for compact detector design with minimal internal free volume, enhancing pressure rise detection sensitivity while the diaphragm's elasticity provides tolerance for manufacturing variations in the rigid housing components.
3Quantity of substance
If a single diaphragm is used instead of multiple diaphragms, then the device size and weight are reduced, but the reliability requirements increase due to the diaphragm performing multiple critical functions
Solution Approach 1:
The single deformable diaphragm serves as both the integrity alarm sensor and fire alarm sensor, replacing what would traditionally require two separate diaphragms. This reduces the quantity of materials and overall detector mass while the diaphragm's ability to respond to different pressure levels ensures reliable detection of both integrity failures and fire conditions.
Solution Approach 2:
The diaphragm automatically returns to its first position after detecting an alarm condition, enabling the system to reset without manual intervention. This self-resetting capability, combined with the diaphragm's inherent elastic recovery, maintains reliability across multiple detection cycles while using a single reusable component instead of multiple disposable elements.
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 solution enhances the detection capabilities and resetability of the system by reducing internal free volume and allowing for precise pressure-based alarm activation, improving the detection of heat and integrity conditions.
Implementation Method 1
Exposure of the sensor tube to a high temperature causes the metal hydride core to evolve hydrogen.
Implementation Method 2
The pneumatic pressure detector is also configured to generate an averaging overheat alarm due to the pressure rise associated with thermal expansion of the inert gas fill.
Implementation Method 3
The deformable diaphragm is configured to be able to move between first, second and third positions within the detector
Data Source
Figure 1~2b
Figure 2c~3
AI summary
A pneumatic pressure detector 20 comprises a first electrical terminal 22, a second electrical terminal 24 and a deformable diaphragm 10 configured to deform between first, second and third positions. When the diaphragm 10 is in its first position, the first and second terminals 22, 24 are open. When the diaphragm 10 is in its second position, the first terminal 22 is open and the second terminal 24 is closed. When the diaphragm 10 is in its third position, the first and second terminals 22, 24 are both closed. The pneumatic pressure detector 20 may be connected to a sensor tube. The detector 20 may be arranged such that closure of the first terminal 22 provides a fire or overheat alarm and the opening of the second terminal 24 provides an integrity alarm. The diaphragm 10 may have a circular first portion 12 and an annular second portion 14.