Variable capacity bypass valve for screw compressor

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Solution Overview

Problem

Screw compressors face efficiency reduction at capacity reduction levels higher than 50% due to high pressures overcoming the seal between the spiral valve shutter and rotor housing window, and existing variable capacity control devices like poppet or axial slide valves experience leakage and are costly and difficult to maintain.

Innovation Solution

A variable capacity bypass valve (VCBV) with a slide valve member and actuator structure that opens a fluid pathway to a bypass chamber, using a sealing surface aligned with the rotor bore discharge face to control fluid flow and reduce leakage, integrated with a spiral valve for enhanced control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a spiral valve with shutter is used to control bypass ports, then capacity control is achieved, but leakage increases at capacity reduction levels higher than 50% due to high pressures overcoming the seal

Engineering Contradiction:

Improvecapacity control rangeVSAvoidsealing performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The invention divides the sealing function into two separate components: the spiral valve shutter controls bypass port opening, while a dedicated poppet valve with its own seal handles the high-pressure sealing requirement. This segmentation allows each component to optimize for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The poppet valve acts as an intermediary component between the high-pressure compression chamber and the bypass chamber. It mediates the pressure differential by providing a dedicated sealing surface that can withstand high pressures, preventing direct pressure exposure to the spiral valve shutter seal.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If poppet or lift valves are used for variable capacity control, then sealing performance improves, but manufacturing cost and maintenance difficulty increase

Engineering Contradiction:

Improvesealing performanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention merges the spiral valve's bypass control function with a simplified poppet valve structure. Rather than using a complex lift valve mechanism, it combines the rotational bypass control with a simple radial poppet valve that is easier to manufacture and maintain while providing reliable sealing.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If lift valves are used, then sealing may be better than spiral valves, but the valve design conflicts with rotor design due to width differences and makes precise turndown control difficult

Engineering Contradiction:

Improvesealing performanceVSAvoidvalve-rotor integration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of having the valve bridge across rotor threads perpendicular to the rotation axis (as in lift valves), the poppet valve is oriented radially with its stem extending from the compression chamber wall into the compression chamber. This inverted orientation eliminates conflict with rotor geometry and enables precise turndown control through radial movement.

Inventive Principle:

Principle #13The other way round (Inversion)

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

Improves efficiency and reduces manufacturing and maintenance costs by minimizing leakage and optimizing turndown performance, while maintaining precise control over capacity reduction.

Implementation Method 1

the valve member having a sealing surface configured to interact with a thread of a compressor screw during operation of the screw compressor

Methodology Applied

Scientific EffectMechanical Sealing: Friction

Implementation Method 2

an actuator structure coupled to the valve member and oriented to move the valve member radially along the bore to open a fluid pathway communicatively coupling the compressor chamber to a bypass chamber

Methodology Applied

Scientific EffectPressure Differential: Pressure Gradient

Data Source

PatentUS12467458B2Variable capacity bypass valve for screw compressor

Publication Date: 2025.11.11 HITACHI GLOBAL AIR POWER US LLC

AI summary

A screw compressor and a variable capacity bypass valve therefor are provided. The variable capacity bypass valve includes a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber, a slide valve member inserted into the bore to fill a cavity, the valve member having a sealing surface configured to interact with a thread of a compressor screw during operation of the screw compressor, an actuator structure coupled to the valve member and oriented to move the valve member radially along the bore to open a fluid pathway communicatively coupling the compressor chamber to a bypass chamber configured to return compressed fluid to a fluid inlet of the compression chamber.