The diaphragm working principle of the vacuum pressure switch

The diaphragm working principle of the vacuum pressure switch is based on the deformation of the elastic diaphragm and the mechanical linkage mechanism. It realizes the on-off control of the electrical signal by sensing the pressure change. Its core structure and operation logic are as follows:

First, core structure composition

Elastic diaphragm

It is usually made of metals (such as stainless steel, Hastelloy) or elastomers (such as rubber-coated metals), and the thickness and diameter are designed according to the measurement range. For example, 0.1mm thick stainless steel diaphragms may be used in high vacuum applications, while 0.5mm thick rubber composite diaphragms can be adopted in coarse vacuum scenarios.

Pressure chamber

The diaphragm divides the cavity into a high-pressure side (measured pressure) and a low-pressure side (reference pressure, usually atmospheric or vacuum). When the measured pressure changes, a pressure difference is generated on both sides of the diaphragm, causing deformation.

Transmission mechanism

The deformation of the diaphragm is amplified by mechanical structures such as levers, ejector rods or bellows, driving the microswitch or reed switch to act. For example, a central displacement of 0.1mm of the diaphragm may be amplified to a 1mm stroke of the ejector through a lever.

Electrical contact

The microswitch is equipped with normally open (NO) and normally closed (NC) contacts and achieves on-off switching through mechanical transmission. The contact material (such as silver alloy) needs to meet the requirements of current capacity and service life.

Second, detailed explanation of the work process

Pressure perception stage

Vacuum condition: When the measured pressure is lower than the set value (such as -80 kpa), the diaphragm protrudes towards the low-pressure side (relative to the atmospheric reference pressure), and the deformation is proportional to the pressure difference.

Positive pressure condition (if supported) : When the pressure is higher than the set value, the diaphragm indents towards the high-pressure side, and the deformation direction is opposite.

Mechanical transmission stage

The deformation of the diaphragm drives the drive arm of the microswitch through the push rod. For example, when the stroke of the push rod reaches 0.5mm, the driving arm overcomes the spring force to close the contacts (NO contact) or open the contacts (NC contact).

Signal output stage

The change of contact state directly controls the on and off of the circuit, or is converted into an electrical signal (such as 4-20mA) through the internal circuit. For example, after the contacts close, the relay coil is energized, driving the external valve to open.

The hysteresis mechanism is implemented

When resetting, the diaphragm needs to overcome the elastic lag of the transmission mechanism and the friction of the contacts, resulting in the reset pressure being lower than the operating pressure. For instance, if the action pressure is -80 kpa, the reset pressure might be -85 kpa, resulting in a 5kPa hysteresis.

Third, key parameters and influencing factors

Range and sensitivity

The thickness and material of the diaphragm determine the measurement range. For example, 0.1mm thick stainless steel diaphragms are suitable for high vacuum (-10⁻³ Pa), while 0.5mm thick rubber diaphragms are suitable for coarse vacuum (-100kPa).

The larger the diaphragm diameter is, the higher the sensitivity will be, but the response speed may decrease.

Environmental adaptability

Temperature influence: High temperature causes changes in the elastic modulus of the diaphragm, which needs to be corrected through temperature compensation (such as bimetallic strips) or calibration. For example, for every 10℃ increase, the diaphragm deformation may increase by 0.5%.

Medium corrosion: If the medium contains corrosive gases, corrosion-resistant coatings (such as PTFE) or inert metal diaphragms should be adopted.

Long-term stability

The fatigue life of the diaphragm is a key indicator. For example, under a circulation pressure ranging from -90 kpa to -10 kpa, high-quality diaphragms can withstand 10⁷ cycles without leakage.

The sealing performance needs to pass the helium mass spectrometry leak detection test (such as leakage rate ≤1×10⁻⁹ Pa·m³/s).

Fourth, typical application scenarios

Vacuum packaging machine

Range: -100 kpa to 0kPa

Diaphragm material: Rubber-coated stainless steel

Action logic: When the vacuum degree reaches -90 kpa, the deformation of the diaphragm triggers the microswitch, initiating the sealing program.

Semiconductor equipment

Range: -10⁻³ Pa to 10⁵ Pa (absolute pressure)

Diaphragm material: Hastelloy + aluminum oxide coating

Accuracy requirement: ±0.1%FS. Radiation-resistant design is required to cope with the plasma environment.

Medical negative pressure system

Range: -50 kpa to 0kPa

Diaphragm material: Medical-grade silicone

Safety Certification: Certified by ISO 13485. with no biocompatibility risks.

Fifth, Fault diagnosis and maintenance

Common faults

Diaphragm leakage: It is manifested as inability to maintain pressure or malfunction of the switch. The leakage point can be located by using a helium leak detector.

Contact adhesion: Caused by arc erosion or environmental dust, the contacts need to be cleaned or the microswitch replaced.

Hysteresis drift: Caused by wear of the transmission mechanism or aging of the spring, it is necessary to readjust or replace the components.

Maintenance suggestions

Regularly check the surface of the diaphragm for scratches or corrosion. It is recommended to conduct an appearance inspection every six months.

Calibrate the action and reset the pressure through the standard pressure source every year. Adjustment is required when the error exceeds ±2%FS.

When stored for a long time, the diaphragm side should be filled with dry nitrogen (1bar) to prevent deformation.