Analysis of the Causes of Misoperation of Vacuum Pressure Switches

The malfunction of vacuum pressure switches may be caused by multiple factors. The following is an analysis of the possible reasons:

1. Pressure fluctuations and disturbances

System pressure fluctuation

If there are rapid and frequent fluctuations in the system pressure (such as pump start-up and shutdown, valve switching), it may cause the switch to be mistakenly triggered before reaching the set value. For example, the pressure spike causes the switch to act instantaneously and then reset.

When the water pump starts, the pressure inside the pipeline rises instantaneously, which may cause the switch to misjudge it as overpressure.

The influence of mechanical vibration

Severe vibration at the installation location (such as close to the motor or compressor) may cause mechanical shaking of the internal contacts or elastic elements of the switch, leading to incorrect operation.

Comparison: The false operation rate of the switch with shock absorption installation is significantly lower than that of the switch with direct rigid fixation.

Electromagnetic interference

Strong electromagnetic fields (such as frequency converters and high-voltage lines) may interfere with the electronic circuits of switches, causing abnormal signals. For example, electromagnetic radiation causes the output signal of the sensor to drift.

2. Problems with the switch itself

Contact adhesion or oxidation

After long-term use, the contacts may have poor contact due to arc ablation or oxidation, which is manifested as slow action or misoperation. For example, an oxide layer forms on the contact surface, increasing the contact resistance.

Aging of elastic elements

When elastic elements such as diaphragms and springs become fatigued or aged, changes in their elastic coefficients may lead to deviations in the set values. For example, the rubber diaphragm becomes sluggish in response to pressure changes after hardening.

Seal failure

Poor sealing of the switch housing or interface may allow external air or moisture to seep in, affecting the internal pressure sensing. For instance, the aging of the sealing ring leads to air leakage, causing the measured value to be lower.

Improper damping setting

If the damping time is too long, the switch may not respond to rapid pressure changes. If the damping is too short, it may amplify the interference signal. For example, when the damping time is set to 5 seconds, pressure fluctuations within 1 second cannot be filtered out.

3. Installation and maintenance issues

Problems with the pressure tapping pipeline

If the pressure tapping pipe is too long, overly bent or has accumulated liquid, it will cause delayed or distorted pressure transmission. For example, water accumulation in the pipeline may cause the switch to misjudge that the vacuum degree is insufficient.

Improper installation location

Switches installed in high-temperature, corrosive environments or directly exposed to heat source radiation may lead to a decline in performance. For example, high temperature softens the elastic element and prolongs the response time.

Insufficient maintenance

Switches that have not been calibrated or cleaned for a long time may experience unstable performance due to internal dust accumulation and contact wear. For example, dust blocks the air inlet of the pressure sensor, causing the measured value to be lower.

4. Environmental and medium factors

Temperature change

Sharp fluctuations in ambient temperature may affect the physical properties of the internal components of the switch. For example, low temperature hardens the rubber diaphragm and reduces the response speed. High temperatures may cause the performance of electronic components to drift.

Medium characteristics

If the measured medium contains corrosive components, particles or viscous substances, it may damage the internal structure of the switch. For example, corrosive gases erode the contacts, resulting in poor contact.

Altitude and Air pressure

The decrease in atmospheric pressure in high-altitude areas may affect the calibration value of the switch. For instance, at an altitude of 3.000 meters, the atmospheric pressure is only 70% of that at sea level. If not recalibrated, it may lead to malfunctions.

5. Electrical and control issues

Power supply fluctuation

Unstable power supply voltage may cause abnormal operation of the internal circuit of the switch. For example, a sudden drop in voltage may reset the microprocessor, causing a malfunction.

Signal interference

Analog signals transmitted over long distances are vulnerable to interference, resulting in distorted pressure values received in the control room. For example, when cables are laid in parallel with power lines, electromagnetic coupling may introduce noise.

Control logic defect

If the control logic in PLC or DCS does not take into account the response delay or dead time of the switch, it may lead to misjudgment. For example, a reasonable filtering time was not set to respond to instantaneous pressure fluctuations.

Suggestions for investigation and resolution

Optimize the installation environment

Avoid vibration sources and strong electromagnetic fields.

Ensure that the pressure extraction pipeline is short and straight to reduce the risk of liquid accumulation.

Regular maintenance and calibration:

Check the contact status, clean the accumulated dust and replace the aged components.

Recalibrate the switch to ensure the accuracy of the set values.

Adjust parameter Settings:

Adjust the damping time according to the working conditions to balance the response speed and anti-interference ability.

Add a dead zone setting to avoid responding to minor pressure fluctuations.

Improve system design

For systems with large pressure fluctuations, buffer tanks or pressure stabilizing devices should be added.

Replace analog switches with digital ones that have stronger anti-interference capabilities.

Environmental control

In high-temperature or corrosive environments, choose switches with a higher protection level.

Add insulation or heat dissipation measures to stabilize the working temperature.