Liquid Ring Pump Dry-Run Detection Using Motor Current and Speed

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Solution Overview

Problem

Liquid ring pumps can operate in a dry state after shutdown, leading to excessive heat generation and potential damage to components, particularly mechanical seals, due to insufficient operating liquid, and existing methods to detect this state are unreliable.

Innovation Solution

A control system that calculates a function of electrical current and motor speed to determine if the pump is in a dry state, using a controller to output alerts or shut down the pump to prevent damage, and includes a variable frequency drive to manage motor operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If the liquid ring pump is operated in a dry state (insufficient operating liquid), then the pump can continue running, but excessive heat is generated which damages mechanical seals and other components

Engineering Contradiction:

Improvecontinuous operation capabilityVSAvoidheat damage to mechanical seals

Core Design Contradiction:

Duration of action of moving objectVSObject-affected harmful factors

Solution Approach 1:

The control system performs preliminary detection of the dry state condition before significant heat damage occurs. By monitoring the relationship between electrical current and motor speed, the system identifies dry state operation early and triggers alerts or shutdowns to prevent mechanical seal damage from excessive heat generation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors electrical current and motor speed parameters, calculates their relationship, and uses this feedback to detect dry state operation. This closed-loop feedback mechanism enables real-time detection and response to prevent heat damage while allowing continuous operation under normal conditions

Inventive Principle:

Principle #23Feedback

2Device complexity

If electrical current alone is used to detect dry state, then detection is simple, but the method is unreliable because low current also occurs during low-speed operation

Engineering Contradiction:

Improvedetection system simplicityVSAvoiddry state detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

Instead of relying on a single parameter (electrical current), the system changes to a multi-parameter approach by monitoring both electrical current and motor speed. The control system calculates the relationship between these two parameters to accurately determine dry state operation, eliminating false positives that occur with single-parameter detection

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The control system utilizes existing motor parameters (electrical current and speed) that are already available from the motor control electronics. This multi-functional use of existing sensors and data eliminates the need for additional dedicated sensors while improving detection accuracy through parameter correlation analysis

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP4295048B1Control of liquid ring pump

Publication Date: 2025.12.17 EDWARDS TECH VACUUM ENG (QINGDAO) CO LTD

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AI summary

A control system comprising: a liquid ring pump (10); a motor (12) configured to drive the liquid ring pump (10); and a controller (20) configured to: determine an electrical current within the motor (12); determine a speed of the motor (12); calculate a value of a function (F), the function (F) being a function of the determined electrical current within the motor (12) and the determined speed of the motor (12); and output one or more control signals based on the calculated value of the function (F).