Quimby Screw Rotor Pulsation Reduction in Vacuum Pumps
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Solution Overview
Problem
Rotary screw vacuum pumps with multi-start threads experience high pulsation frequencies, leading to inefficiencies and potential wear in exhaust valves, particularly at low suction pressures.
Innovation Solution
The use of Quimby-type screw rotors with single start threads and a non-return exhaust valve in an oil-sealed rotary screw vacuum pump design, which reduces pulsation frequency and minimizes power and noise losses by allowing only a single pulse of compressed gas per revolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-start screw rotors are used to achieve higher rotational speeds, then productivity increases, but pulsation frequency increases causing exhaust valve wear and energy losses
Solution Approach 1:
The patent changes the thread configuration parameter from multi-start to single-start screw rotors. This parameter change reduces the pulsation frequency proportionally to the reduction in starts, while maintaining the same volumetric displacement per revolution, thus achieving lower power and noise losses without sacrificing productivity
2Productivity
If multi-start screw rotors are used to increase throughput, then productivity improves, but exhaust valve reliability deteriorates due to high pulsation frequency
Solution Approach 1:
The patent modifies the thread start parameter from multiple starts to a single start, which directly reduces pulsation frequency. This reduction in pulsation frequency decreases the mechanical stress and wear on the exhaust valve, thereby improving its reliability and durability while maintaining the same throughput capability through optimized single-start geometry
3Loss of energy
If single start threads are used to reduce pulsation frequency, then power and noise losses decrease, but the number of working chambers per revolution decreases
Solution Approach 1:
The patent compensates for the reduced number of working chambers per revolution by optimizing the geometry and dimensions of the single-start thread. By increasing the thread depth, width, or axial length, the volume displacement per revolution is maintained or enhanced, thereby preserving pumping capacity while achieving the energy efficiency benefits of reduced pulsation frequency
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 design achieves lower power and noise levels, enabling effective operation at low suction pressures and higher rotational speeds, with improved throughput and reduced wear on components, allowing vacuum levels of 1 mbar to 0.01 mbar and throughputs of 40 m3/hr to 100 m3/hr.
Implementation Method 1
The housing has at least one inlet to admit a liquid into said housing to seal said working chambers
Implementation Method 2
two intermeshing screw rotors disposed in the housing and configured to cooperably rotate to compress a gas in working chambers formed between said screw rotors and said housing
Implementation Method 3
An exhaust port for receiving compressed gas from the working chambers is provided with an exhaust valve operable to prevent gas entry to the rotor chamber via the exhaust port
Data Source
AI summary
A rotary screw vacuum pump 10 comprises a housing 12 that has a lower pressure inlet region 14 and a higher pressure outlet region 16 and two intermeshing screws 18 disposed in the chamber and configured to cooperably rotate to compress a gas in working chambers formed between them and the housing while pumping the gas from the lower pressure inlet region to the higher pressure outlet region. The housing 12 has a least one liquid inlet 20 to admit a sealing liquid to seal the working chambers. The intermeshing screws 18 comprise Quimby-type screws.