Oil-Free Screw Compressor Shaft Seal Pressure Loss
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Solution Overview
Problem
Existing oil-free screw compressors face significant pressure loss issues at the annular space where the atmosphere open hole and communication hole communicate, leading to inadequate prevention of lubricant flow into the rotor chamber during unloading operations.
Innovation Solution
The design includes an inner peripheral annular space on the casing side, with a larger open cross-sectional area than the communication holes, ensuring a wider annular space in the axial direction, which reduces pressure loss and prevents lubricant ingress by satisfying the relationship S1 ≥ ∑S2i, where S1 is the open cross-sectional area of the annular space and S2 is the total area of the communication holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an annular space is formed on the outer peripheral surface of the shaft seal device, then lubricant flow prevention is improved, but pressure loss increases due to small open cross-sectional area
Solution Approach 1:
The invention relocates the annular space from the outer peripheral surface of the shaft seal device to the inner peripheral surface of the casing, utilizing the radial dimension more effectively. This dimensional relocation allows the annular space to have a significantly larger open cross-sectional area while still preventing lubricant flow into the rotor chamber, thereby resolving the contradiction between lubricant flow prevention and pressure loss reduction
2Reliability
If O-rings are disposed on both air seal and visco-seal, then sealing is improved, but axial space is restricted making it difficult to ensure adequate annular space width
Solution Approach 1:
The invention moves the annular space formation from the axial dimension (outer peripheral surface) to the radial dimension (inner peripheral surface of casing). This dimensional shift allows the annular space to be formed without consuming additional axial space, thereby maintaining adequate width for lubricant flow prevention while preserving sealing effectiveness with the O-rings
3Reliability
If communication holes are formed in the shaft seal device, then lubricant flow prevention is improved, but manufacturing complexity increases
Solution Approach 1:
The invention extracts the annular space formation from the shaft seal device and relocates it to the casing. This separation simplifies the shaft seal device manufacturing while the casing can be easily formed with the annular space through standard machining or casting operations, thereby reducing overall manufacturing complexity while maintaining lubricant flow prevention functionality
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 effectively minimizes pressure loss in the annular space, ensuring the lubricant is not drawn into the rotor chamber during unloading, thereby enhancing the sealing efficiency of the compressor.
Implementation Method 1
When the rotor chamber is brought into a negative pressure state, atmospheric air is introduced into the ventilation gap through the atmosphere open passage thus preventing the lubricant from flowing into the rotor chamber
Implementation Method 2
this configuration effectively minimizes pressure loss in the annular space, ensuring the lubricant is not drawn into the rotor chamber during unloading
Data Source
AI summary
An oil-free screw compressor includes: a casing having a rotor chamber; a bearing supporting rotary shafts of the screw rotors; a shaft seal device including an oil seal portion and an air seal portion; an atmosphere open hole formed in the shaft seal device; at least one communication hole formed in the rotary shaft; and an annular space communicating the atmosphere open hole with the at least one communication hole communicate with each other. The annular space includes an inner peripheral annular space formed on an inner peripheral side of the casing. Assuming an open cross-sectional area of the inner peripheral annular space as S1, a total open cross-sectional area of the communication holes as S2, an open cross-sectional area of the i-th communication hole out of the communication holes as S2i, and the number of communication holes as n (n being a natural number of 1 or more), a following relationship is satisfied.S1≧S2=∑i=1nS2i