Manhole Cover Latch Bolt Spring Biasing Mechanism
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Solution Overview
Problem
Manhole covers face safety hazards and high costs due to stress from gas explosions and flooding, as existing latching systems may fail to control the cover's movement effectively, potentially leading to the cover being blown free or washed away, and the height of movement is not adequately minimized for varying explosion severities.
Innovation Solution
A manhole assembly apparatus with a latch bolt and security bolt system that allows controlled movement of the manhole cover, featuring a spring-biased latch bolt, a security bolt for locking, and an extraction tool with a cam surface to override the spring bias, enabling controlled venting of gases or water while preventing the cover from being completely dislodged from the frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a latching system allows the cover to rise off the frame to relieve gas pressure during an explosion, then the vault chamber is protected from damage, but the cover may be blown free of the frame creating a safety hazard
Solution Approach 1:
The frame stop feature is pre-positioned to contact the latching lugs before the cover can be completely blown off the frame. This preliminary constraint prevents the harmful outcome (flying cover) while still allowing controlled movement to relieve gas pressure during explosions or flooding events.
2Reliability
If a clearance is provided between latching lugs and frame stop feature to allow cover movement, then gas pressure relief is enabled, but severe stress is created causing potential lug failure
Solution Approach 1:
The frame stop feature acts as a predetermined cushioning element that engages the latching lugs during pressure events. By providing this pre-positioned stop, the system allows controlled cover movement to relieve gas pressure while preventing excessive stress that would cause lug failure.
3Reliability
If a selectively releasable latching system is used to control cover removal, then unauthorized removal is prevented, but significant costs are incurred from additional latching components
Solution Approach 1:
The latching system uses the existing gravitational force and simple mechanical components (latching lugs, frame stop feature) to achieve both security functions. The cover's own weight provides the locking force when seated, eliminating the need for complex powered latching mechanisms while still preventing unauthorized removal.
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 effectively reduces the risk of the manhole cover being blown free during explosions and minimizes the height of movement, enhancing safety by allowing controlled venting and preventing secondary explosions, while also reducing costs associated with additional latching components.
Implementation Method 1
The latch bolt is biased toward the latched position by a spring
Implementation Method 2
The extraction tool engages a driven cam surface on the latch bolt to drive the latch bolt against a biasing force of the spring
Data Source
AI summary
A manhole assembly includes a manhole cover and a manhole frame. The manhole cover is received on the manhole frame. A latch bolt attached to the manhole cover is movable between a latched position and a removal position. The latch bolt is biased toward the latched position by a spring. A security bolt received in the manhole cover is movable between a locked position wherein the security bolt engages the latch bolt to lock the latch bolt in the latched position and a removal position wherein the security bolt is disengaged from the latch bolt. An extraction tool is inserted through the manhole cover to remove the manhole cover from the manhole frame. The extraction tool engages a driven cam surface on the latch bolt to drive the latch bolt against a biasing force of the spring to move the latch bolt to the removal position.