Passive Servo Filter for Pneumatic Valve Actuator
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Solution Overview
Problem
Pneumatically actuated valves, such as butterfly valves, face performance degradation and eventual failure due to airborne contaminants like dust and sand particles accumulating in tight servo valve clearances, which impairs operation and reduces the efficiency of the servo airflow modulation.
Innovation Solution
A bleed assembly with a servo tube positioned at an angular distance of at least 10° from the top dead center position and extending a distance equal to or greater than 60% of the passage diameter upstream of the flow control member, acting as a passive particle separator to draw clean air from the main fluid passage and minimize particulate infiltration into the actuator chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the servo valve has tight operating clearances to improve modulation precision, then measurement precision is improved, but airborne contaminants accumulate in the clearances causing performance degradation and failure
Solution Approach 1:
The patent extracts the harmful contaminants from the servo air path by introducing a separate filtered air supply system. The servo tube draws air from a location upstream of the contaminant source, and a filter removes particulates before air enters the actuator chamber, effectively separating the contaminated main flow from the clean servo air path.
Solution Approach 2:
The patent introduces a filter as an intermediary component between the air source and the actuator chamber. This filter acts as a mediator that allows air to pass through while blocking contaminants, protecting the tight clearances of the servo valve without compromising the airflow modulation function.
2Productivity
If the valve operates in a closed position for most of the time, then productivity is improved, but particulate accumulation in the actuator chamber increases due to reduced airflow
Solution Approach 1:
The patent extracts servo air from a location upstream of the main flow where contaminants are present. By positioning the servo tube inlet upstream and using a separate filtered air path, the system removes contaminated air from the actuator chamber while maintaining the valve in the closed position, preventing particulate accumulation during extended closed operations.
Solution Approach 2:
The filter serves as an intermediary that enables the valve to remain closed for productivity while still providing clean air to the actuator chamber. The filtered air path acts as a mediator that maintains actuator chamber cleanliness independent of the main valve position, allowing extended closed operation without particulate buildup.
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
This configuration significantly reduces particulate intake into the actuator chamber throughout the operating range, enhancing the valve's performance and reliability by optimizing airflow and minimizing contamination, particularly in applications like gas turbine engines where the valve spends most of its time in a closed position.
Implementation Method 1
A bleed assembly with a servo tube positioned at an angular distance of at least 10° from the top dead center position and extending a distance equal to or greater than 60% of the passage diameter upstream of the flow control member, acting as a passive particle separator to draw clean air from the main fluid passage
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A bleed assembly includes a bleed valve disposed across a bleed duct. The bleed valve includes a valve housing (20), a shaft (26) connecting an actuator assembly (24) to a flow control member (66), and a servo tube (56). The actuator assembly (24) includes a linear actuator (38) disposed perpendicular to a valve centerline, so that linear motion of the actuator is transverse to a valve centerline. The member (66) is in the main fluid passage (28), rotatable between a fully closed position defined by leading (68) and trailing edges (70) abutting one or more housing walls, and a fully open position defined by the leading edge (68) at the upstream side (34A) and the trailing edge (70) at the downstream side (34B) of the main flow passage (28). A first portion (82) of a servo tube (56) extends into the main passage (28) from a distance P1 upstream of the member in a fully closed position, and angular distance A1 of at least 10° from the TDC position.