The vacuum pressure switch has a fault of frequent starting and stopping

Vacuum pressure switches are prone to failure due to mechanical fatigue, electrical wear and the superposition of environmental stress under frequent start-stop conditions. The typical failure modes and preventive measures can be analyzed from the following dimensions:

First, mechanical structure fatigue

The diaphragm is fractured or permanently deformed

Failure manifestation: The switch malfunctions when the pressure does not reach the threshold, or there is no response after reaching the threshold.

Cause: Frequent deformation leads to fatigue cracks in metal diaphragms (for example, 316L stainless steel diaphragms may develop 0.1mm cracks after 10⁶ cycles from -90kPa to -10kPa), or rubber diaphragms undergo creep due to alternating stress.

Case: A certain vacuum packaging machine started and stopped 2.000 times a day. After three months, wrinkles appeared in the central area of the diaphragm, causing the pressure set value to drift by 15%.

Wear of the transmission mechanism

Failure manifestations: The hysteresis value gradually increases, and the action and reset pressure is unstable.

Cause: The frequent impact between the push rod and the microswitch drive arm leads to wear of the mating surface. After the lubricating grease of the lever fulcrum bearing is exhausted, the friction intensifies.

Data: After 5×10⁵ cycles of a certain semiconductor equipment switch, the hysteresis expanded from 5 kpa to 12kPa, triggering a process alarm.

Second, electrical contact failure

Contact adhesion or arc erosion

Failure manifestation: The switch cannot be disconnected, resulting in the continuous operation of the equipment or the failure of the safety interlock.

Cause: When the contacts are frequently switched on and off, an electric arc is generated between them (especially under inductive loads), and the surface of the silver alloy contacts melts to form solder joints.

Test result: Under a load of 24V DC/5A, the contacts were on and off 10 times per minute. After 200 hours, the contact resistance rose from 10mΩ to 2Ω and eventually adhered.

The electrical life is exhausted.

Failure manifestation: Poor contact of the contacts, the equipment reports "switch failure".

Cause: The electrical lifespan claimed by the manufacturer (such as 10⁵ cycles) is rapidly consumed during high-frequency starts and stops.

Comparison: A certain medical negative pressure system was originally designed to start and stop three times per minute. In actual use, due to process adjustments, it was increased to 10 times per minute, and the contact life was shortened from three years to eight months.

Third, sealing and leakage issues

The O-ring is aged or crushed

Failure manifestation: Medium seeps into the switch interior, resulting in a decline in insulation performance or corrosion of the circuit.

Cause: The pressure shock caused by frequent starts and stops accelerates the wear of O-rings, and nitrile rubber may swell under the action of vacuum grease.

Case: The vacuum switch of a certain chemical reactor suffered a short circuit due to the failure of the O-ring, allowing chlorine gas to seep into the cavity and corrode the contacts.

The edge of the diaphragm is leaking

Failure manifestations: The pressure measurement value is too low, and the switch operates prematurely.

Cause: Microcracks occur at the welding or bonding points between the diaphragm and the cavity due to alternating stress.

Detection method: Helium mass spectrometry leak detection shows that the leakage rate of a certain switch increased from 1×10⁻¹¹ Pa·m³/s to 1×10⁻⁸ Pa·m³/s after 1×10⁵ cycles.

Fourth, superposition of environmental stress

Temperature variation leads to the degradation of material properties

Failure manifestations: Changes in the elastic modulus of the diaphragm and drift of the operating pressure.

Cause: Frequent starts and stops cause the switch to switch rapidly between -20℃ and 80℃, resulting in thermal stress cracks in the metal diaphragm and hardening of the rubber diaphragm.

Experimental data: After a certain switch was cycled 100 times from -30℃ to 100℃, the deviation of the operating pressure expanded from ±1%FS to ±5%FS.

Vibration and shock damage

Failure manifestations: Loose internal components, intermittent contact of contacts.

Cause: Mechanical vibration during the start-up and shutdown of the equipment (such as the centrifuge switch being subjected to a 10g acceleration) causes the fixing screws of the microswitch to loosen.

On-site feedback: The switch of a vacuum drying oven in a certain pharmaceutical enterprise shifted its contact spring due to vibration, mistakenly triggering a high-temperature alarm.

Fifth, preventive and improvement measures

Selection optimization

Enhance mechanical life: Select models with a 30% increase in diaphragm thickness (such as from 0.2mm to 0.26mm), or adopt a dual-diaphragm redundant design.

Extend electrical life: Select gold-plated contacts (with lower contact resistance) or solid-state relay output (without contact wear), and increase the load capacity to 10⁶ on-off cycles.

Maintenance strategy

Regular calibration: Every 3 months, verify the action/reset pressure through a standard pressure source. Adjust or replace when the error exceeds ±2%FS.

Preventive replacement of seals: O-rings should be replaced every two years. Fluororubber (FKM) or perfluoroether rubber (FFKM) is preferred to resist medium erosion.

System-level improvement

Add a buffer link: Install a vacuum accumulator or damping hole before the switch to reduce the pressure pulse amplitude by more than 50%.

Optimize control logic: Achieve "soft start" through PLC programming to avoid high-frequency oscillation of pressure near the threshold. For example, the set pressure must be triggered only after the threshold is maintained for 2 seconds.

Sixth, typical industry cases

Food packaging industry

The frequent start and stop of the vacuum pump caused fatigue of the switch diaphragm, and the packaging leakage rate rose from 0.5% to 3%.

Solution: By using a switch with mechanical damping, the start-stop shock is reduced by 70%, and the diaphragm life is extended from 6 months to 2 years.

Semiconductor manufacturing

Problem: The vacuum switch contacts of the dry engraving equipment are arc eroded, with an annual failure rate of 12 times.

Solution: Upgrade to a contactless reed switch and combine it with nitrogen gas filling in the vacuum chamber for protection, reducing the annual failure rate to 0.5 times.