Sequencing Valve for Automatic Parking Brake Retention
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Solution Overview
Problem
Automatic parking brakes in rail cars can inadvertently release, allowing the cars to roll before a normal brake application is made, due to the lack of a system that ensures the brake remains engaged until a valid braking command is issued.
Innovation Solution
A sequencing valve that communicates with brake pipe pressure sources, exhaust, and the automatic parking brake, moving between positions to isolate or couple these ports based on brake pipe pressure levels, ensuring the parking brake is not released until the system is fully charged and a subsequent brake application is made.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the locking mechanism is made responsive to brake pipe pressure to automatically retain the brake cylinder in applied position, then the manual braking operation is eliminated and automation is improved, but the brake may inadvertently release before a normal brake application is made
Solution Approach 1:
The sequencing valve requires brake pipe pressure to be fully charged and then partially released before allowing the parking brake to release. This preliminary sequence of pressure changes ensures that a valid brake application command has been issued before the parking brake disengages, preventing inadvertent release while maintaining automation.
Solution Approach 2:
The sequencing valve acts as an intermediary between the brake pipe pressure system and the parking brake locking mechanism. It controls the pressure signal that triggers release, ensuring that only proper brake application commands can disengage the parking brake, thus resolving the reliability issue while preserving automation.
2Speed
If the brake pipe pressure is used to directly release the locking mechanism, then the system response is simplified and faster, but the brake may release into a potential rolling situation before a normal brake application is applied
Solution Approach 1:
The system requires brake pipe pressure to reach full charge and then partially release before the locking mechanism can disengage. This preliminary pressure sequence ensures that a valid brake command is present before release occurs, eliminating the rolling hazard while maintaining rapid response when proper commands are given.
Solution Approach 2:
The sequencing valve monitors brake pipe pressure changes and uses this feedback to control the locking mechanism. It only permits release when the pressure pattern indicates a valid brake application command, ensuring safety while allowing fast response to legitimate commands.
3Reliability
If a sequencing valve is added to prevent inadvertent release, then the reliability and safety are improved, but the device complexity increases
Solution Approach 1:
The sequencing valve performs multiple functions: it controls the timing of parking brake release, monitors brake pipe pressure status, and ensures proper sequencing of pressure changes. By consolidating these functions into a single component, the complexity increase is minimized while achieving the reliability improvement.
4Reliability
If the valve body is biased to isolate brake pipe pressure from the parking brake, then safety is improved by preventing premature release, but the ease of operation is reduced due to additional pressure sequencing requirements
Solution Approach 1:
The sequencing valve automatically monitors brake pipe pressure and self-actuates to permit release only when proper pressure sequencing occurs. This eliminates the need for manual intervention or complex operator procedures, maintaining ease of operation while ensuring safety through automatic pressure-based control.
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
Prevents unintended release of the automatic parking brake by maintaining engagement until a valid brake application is commanded, ensuring the rail car remains secure until a service or emergency brake is applied.
Implementation Method 1
A spring biases the valve body into the first position
Implementation Method 2
the pilot is configured to move the valve body from the first position to the second position against the bias of the spring after brake pipe pressure has been fully charged and then partially released
Implementation Method 3
The piston is interconnected to the valve body by a stem to move the valve body into the second position when the pressure on the first side of the piston exceeds the pressure on the second side of the piston
Implementation Method 4
The diaphragm opens the passage in the bead seat after brake pipe pressure has been fully charged and then partially released
Data Source
AI summary
A sequencing valve for an automatic parking brake. The sequencing valve has a housing with a first port for communication with a source of a brake pipe pressure, a second port for communication with an exhaust, and a third port for communication with a brake pipe pressure input of an automatic parking brake. A valve body in the housing is moveable to either isolate the brake pipe pressure from the input to the parking brake, or couple brake pipe pressure to the input so that the parking brake may be released. A pilot is interconnected to the valve body for moving the valve body from the first position to the second position and can be driven by a charging and partial release of brake pipe pressure, charging of brake cylinder pressure, or a pneumatic signal provided by an electrical or a pneumatic control valve.