The working principle and structure of vacuum pressure switches

The working principle and structure of vacuum pressure switches can be analyzed based on their core functions, combined with the physical process of mechanical and electrical signal conversion, as follows:

First, working principle

The core function of a vacuum pressure switch is to monitor and control the vacuum system by sensing pressure changes and converting them into electrical signals. Its working process can be divided into the following stages:

Pressure perception

Elastic element deformation: Inside the switch, elastic elements such as bellows, diaphragms or spring tubes are used. When the external pressure changes, the elements undergo elastic deformation. For instance, the diaphragm depresses inward when the vacuum degree increases (negative pressure) and protrudes outward when it is under positive pressure.

Displacement transmission: Deformation is transmitted through mechanical structures (such as levers, connecting rods) to microswitches or sensors, forming physical displacement.

Signal conversion and output

Mechanical contact type: Displacement directly drives the microswitch contacts to close or open, outgenerating a switch signal (such as AC220V/10A). For example, when the pressure reaches the set threshold, the contacts close to start the vacuum pump.

Electrical signal type: Displacement is converted into analog signals (such as 4-20mA) or digital signals (such as RS485) through potentiometers, Hall sensors or piezoresistive elements for processing by the control system.

Setting and hysteresis control

Threshold setting: Set the action pressure value through a knob, dip switch or external signal. For example, it is triggered when the vacuum degree reaches -80 kpa.

Hysteresis regulation: The built-in spring or hysteresis mechanism generates a pressure difference (such as ±5kPa), preventing the switch from frequently operating near the threshold.

Second, core structure

The structural design of vacuum pressure switches needs to take into account sealing performance, sensitivity and durability. Its typical structure includes the following parts:

Pressure-sensitive component

Diaphragm/bellows: Usually made of stainless steel, copper alloy or elastic polymer, they come into direct contact with the measured medium and sense pressure changes. For example, 316L stainless steel diaphragms can withstand corrosive gases.

Reference chamber: Some switches are equipped with a reference pressure chamber (such as atmospheric pressure or absolute vacuum) inside, achieving high-precision measurement by comparing the pressure difference between the inside and outside.

Mechanical transmission mechanism

Lever/connecting rod: Amplifies the slight deformation of the diaphragm or bellows and transmits it to the contacts or sensors. For example, when the lever ratio is 5:1. a diaphragm displacement of 0.1mm can be converted into a contact movement of 0.5mm.

Adjusting screw: It is used to adjust the action threshold and hysteresis, which is achieved by changing the spring preload or the position of the lever fulcrum.

Electrical signal conversion and output module

Microswitch: The core component of mechanical contact switches, achieving low-resistance and long-life electrical connections through silver alloy contacts. For example, the contact life can reach more than 10⁶ times.

Sensor and circuit board: The electrical signal switch integrates piezoresistive chips, ADC converters and communication interfaces to convert pressure signals into digital quantities and output them. For example, piezoresistive chips using MEMS technology can achieve an accuracy of 0.1%FS.

Shell and Interface

Protective housing: Usually made of aluminum alloy or engineering plastic, with a protection level of IP65 or above, and filled with epoxy resin or silicone inside to achieve moisture-proof and shock-proof.

Connection interface: Threaded (such as G1/4), flanged (such as DN15) or quick couplings are provided to adapt to different pipe diameters and installation methods. For instance, vacuum freeze dryers may adopt clamp-type interfaces for easy disassembly.

Adjustment and display components

Knobs/buttons: Used for on-site setting of pressure thresholds, response times and other parameters. Some models support password protection to prevent misoperation.

Indicator light/display screen: Visually shows the current pressure value, switch status and fault code. For example, the LED indicator light conveys different information through color (red/green) and flashing frequency.

Third, key technical details

Sealing design: Vacuum sealing is achieved by using O-rings, metal gaskets or laser welding, with a leakage rate as low as 10⁻⁹ Pa·m³/s.

Anti-vibration design: Reduce vibration interference through shock-absorbing rubber pads, spring buffers or contactless electronic designs (such as Hall effect sensors).

Temperature compensation: Built-in thermistors or digital algorithms correct the influence of temperature on elastic elements, for example, maintaining stable accuracy within the range of -20℃ to 80℃.

Iv. Structural Optimization in Typical Application Scenarios

Pharmaceutical equipment: It adopts an all-stainless steel structure, CIP cleaning compatible design and sterilization validation support, meeting GMP requirements.

Semiconductor equipment: Equipped with ultra-high vacuum compatible ceramic diaphragms and non-magnetic materials to prevent contamination of wafers.

Food packaging: Uses FDA-certified silicone seals and a detachable structure for easy cleaning and maintenance.

Summary

Vacuum pressure switches sense pressure through elastic elements, transmit displacement through mechanical structures, and achieve output through electrical signal modules. Their structural design needs to balance sensitivity, reliability and environmental adaptability. Understanding its working principle and structural features is helpful for matching specific application requirements during selection. For example, in pharmaceutical equipment, hygiene, corrosion resistance and verifiability should be given special attention.