Roots Vacuum Pump Unit Reducing Rough-Pump Stresses

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Solution Overview

Problem

Rough-vacuum pumps in existing pump units are prone to failure and high costs due to excessive thermal and mechanical stresses, and optimizing rotational frequencies to save energy is limited by the need to modify all pumping stages simultaneously, leading to efficiency losses.

Innovation Solution

A pump unit configuration with a Roots vacuum pump having three pumping stages and a rough-vacuum pump with a reduced compression ratio, where the first stage of the rough-vacuum pump is driven by the Roots vacuum pump's motor, allowing for a lower compression ratio and reduced stresses on the rough-vacuum pump, and enabling variable rotational frequencies without performance loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the rough-vacuum pump is designed with a high compression ratio to guarantee low ultimate vacuum pressures, then the ultimate vacuum pressure is improved, but the thermal and mechanical stresses on the rough-vacuum pump increase significantly

Engineering Contradiction:

Improveultimate vacuum pressureVSAvoidthermal and mechanical stresses

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The pumping system is segmented into two distinct pumps: a Roots vacuum pump handling the high-vacuum stage and a rough-vacuum pump handling the low-vacuum stage. This segmentation allows each pump to operate within optimized stress ranges, with the Roots pump absorbing the compression ratio demands and protecting the rough-vacuum pump from excessive thermal and mechanical stresses.

Inventive Principle:

Principle #1Segmentation

2Use of energy by moving object

If the rotational frequency of the rough-vacuum pump is reduced to save energy during waiting phases, then energy consumption is reduced, but the pumping performance is significantly lost

Engineering Contradiction:

Improveelectricity consumptionVSAvoidpumping performance

Core Design Contradiction:

Use of energy by moving objectVSProductivity

Solution Approach 1:

The system implements dynamic operational modes where the Roots vacuum pump can operate independently during waiting phases to maintain vacuum pressure without the rough-vacuum pump, enabling energy-saving idle modes. During active pumping phases, both pumps operate together to deliver full performance, thus dynamically adapting energy consumption to actual process needs.

Inventive Principle:

Principle #15Dynamics

3Stress or pressure

If the rough-vacuum pump is designed with multiple pumping stages to achieve high compression ratio, then the compression ratio is improved, but the device complexity and cost increase

Engineering Contradiction:

Improvecompression ratioVSAvoidnumber of pumping stages

Core Design Contradiction:

Stress or pressureVSDevice complexity

Solution Approach 1:

The system merges the functions of multiple rough-vacuum pump stages into a single Roots vacuum pump stage. The Roots pump's rotor design and operating principles enable it to achieve the required compression ratio in fewer stages compared to a conventional rough-vacuum pump, thereby reducing mechanical complexity while maintaining or improving performance.

Inventive Principle:

Principle #5Merging (Combining)

4Productivity

If the rough-vacuum pump operates at higher pressure to handle gas flows, then the pumping speed is improved, but the risk of corrosive attack increases

Engineering Contradiction:

Improvepumping speedVSAvoidcorrosive attack

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The Roots vacuum pump acts as an intermediary between the rough-vacuum pump and the high-vacuum environment. It accepts the higher-pressure gas flows from the rough-vacuum pump and progressively reduces the pressure in subsequent stages, thereby shielding the rough-vacuum pump from direct exposure to corrosive conditions while maintaining high pumping speed capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 extends maintenance intervals, reduces costs, enhances reliability, and allows for energy savings by enabling the rough-vacuum pump to handle higher gas flows and operate efficiently over a wide range of rotational frequencies.

Implementation Method 1

a motor to drive the rotors in rotation at a rotational frequency usually greater than the rotational frequency of the motor of the rough-vacuum pump

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Implementation Method 2

During rotation, the gas being pumped is trapped in the free space formed by the rotors and the stator, and is driven by the rotors to the following stage, then gradually to the discharge side of the vacuum pump

Methodology Applied

Scientific EffectVolumetric displacement:

Data Source

PatentUS11815096B2Pump unit

Publication Date: 2023.11.14 PFEIFFER VACUUM SAS

AI summary

A pump unit includes a rough-vacuum pump and a Roots vacuum pump connected in series and upstream of the rough-vacuum pump in the direction of flow of the pumped gases. The Roots vacuum pump has three pumping stages in which the rotors are designed to be driven simultaneously in rotation by a motor of the Roots vacuum pump. A ratio of the flow rate generated by the first pumping stage of the rough-vacuum pump in the direction of flow of the pumped gases over the flow rate generated by the last pumping stage of the rough-vacuum pump is less than or equal to four.