Cryogenic Rotary Valve Pressure Balancing for Lower Torque
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Solution Overview
Problem
Cryogenic refrigerators, particularly GM and pulse tube refrigerators, face issues with increased torque requirements and dust contamination due to wear from valve discs, which degrades performance and reduces efficiency, especially at low temperatures.
Innovation Solution
A rotary valve unit is developed that utilizes differential gas forces to maintain contact between the valve disc and seat, reducing torque and dust contamination by having high-pressure gas in the center of the valve disc and low-pressure gas on the outside, directing dust away from the pulse tube and reducing wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the valve disc diameter is increased to accommodate larger ports, then the gas flow capacity is improved, but the torque required to turn the valve disc increases
Solution Approach 1:
The patent changes the pressure distribution parameters by introducing a pressure equalization cavity that equalizes the pressure between the front and back sides of the valve disc. This parameter change reduces the net force differential across the disc, thereby reducing the torque required to rotate it while maintaining the larger diameter needed for gas flow capacity.
Solution Approach 2:
The pressure equalization cavity acts as an intermediary mechanism between the high-pressure and low-pressure sides of the valve disc. It mediates the pressure differential by providing a pathway for pressure equalization, reducing the net force on the disc without requiring direct mechanical intervention.
2Reliability
If high-pressure gas is used to maintain seal between valve disc and seat, then sealing reliability is improved, but dust is blown into the pulse tube causing contamination
Solution Approach 1:
The patent extracts the harmful effect of high-pressure gas blowing dust into the pulse tube by introducing a pressure equalization cavity. This cavity removes the pressure differential that causes dust contamination while preserving the sealing function through alternative pressure distribution.
Solution Approach 2:
The patent converts the harmful high-pressure differential into a beneficial pressure equalization system. The same pressure differential that previously caused dust contamination is now used to drive gas flow through the equalization cavity, reducing the net force on the valve disc and minimizing dust generation while maintaining sealing.
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 solution reduces the torque required to turn the valve disc, minimizes dust entry into the pulse tube, and extends valve disc life, improving temperature stability and performance by effectively managing gas pressures across different surfaces within the valve assembly.
Implementation Method 1
high pressure gas on the back side of the plug and low pressure gas in the cavity between the face of the plug and the central part of the back of the valve disc puts an axial load on the motor bearings, but reduces the force on the face of the valve disc
Implementation Method 2
high-pressure gas on the back side of the plug and low pressure gas in the cavity between the face of the plug and the central part of the back of the valve disc
Data Source
AI summary
A rotary valve unit which reduces the torque required to turn the valve disc, and the amount of wear dust that is blown into the cold head, using differential gas forces to keep the valve disc in contact with the valve seat, and which enables larger diameter valve discs to be utilized for multi-ported pulse tubes that have less force on the face of the valve disc, resulting in reduced torque and reduced wear rate.