In industrial automation and fluid control systems, pressure switches are indispensable components. Different types of pressure switches have their own specific features in terms of structure, performance and applicable scenarios.
Faced with a wide variety of pressure switch types, do you find it difficult to choose due to a lack of in-depth understanding? This article will give you a comprehensive overview of the various pressure switches to help you make the best choice.
What is a Pressure Switch?
A pressure switch is a device that monitors changes in fluid pressure and automatically opens or closes an electrical contact when a preset pressure value is reached. It senses pressure changes through internal pressure-sensing components and generates corresponding actions, thereby controlling the connected devices to start or stop. It converts changes in fluid pressure into electrical signals for output.
Electromechanical Pressure Switch
The electromechanical pressure switch is mainly composed of a pressure sensing element, a mechanical transmission mechanism and electrical contacts. It does not have complex electronic circuits. Instead, it converts pressure signals into electrical signals through mechanical structures.
The electromechanical pressure switch has a sturdy structure and strong anti-interference capability. It is widely used in various industrial scenarios such as hydraulic systems, pneumatic systems, refrigeration equipment, water supply pipelines, etc.
There are four types of electromechanical pressure switches depending on the pressure-sensing element.
Diaphragm Pressure Switch
Structure: The sensing element of the diaphragm pressure switch is a thin and elastic diaphragm. Depending on the medium, you can choose different types of diaphragms such as nitrile rubber, Teflon or welded metal diaphragms.
One side of the diaphragm is in contact with the medium, while the other side is connected to the driving push rod and the reset spring.
Working principle: When the pressure of the medium acts on the diaphragm, the diaphragm will undergo elastic deformation. When the pressure reaches a preset threshold, the deformation of the diaphragm is sufficient to push the ejector rod to actuate the electrical contacts. Due to the relatively large area of the diaphragm, even small pressure changes can generate sufficient thrust.
Application: The membrane can completely isolate the medium from the internal mechanism of the switch. Diaphragm pressure switches have good corrosion resistance and can be used for high viscosity, granular, or corrosive media.
You can use diaphragm pressure switches for low to medium pressure applications, such as small pneumatic equipment and low-pressure lubricant monitoring systems.
Piston Pressure Switch
Structure: The piston pressure switch uses a piston as a pressure-sensing element. The piston and seal cooperate to form a pressure-sensing chamber. One end of the piston is subjected to medium pressure, while the other end is connected to a push rod and an adjusting spring.
Working principle: After the medium pressure enters the sensing chamber, it generates axial thrust on the piston. When the thrust overcomes the preload force of the adjusting spring, the piston drives the push rod to move forward, triggering the electrical contact action.
Application: Piston pressure switches are usually used in high-pressure applications, such as hydraulic presses, injection molding machines, compressors, etc. Its structure is very sturdy and can withstand millions of cycles of impact. Therefore, piston pressure switches are also commonly used in heavy industrial equipment with high vibration.
Bourdon Tube Pressure Switch
Structure: The sensing element of a bourdon tube pressure switch is a hollow metal tube bent into a C-shape or spiral. One end of the tube is fixed and the other end is closed. The closed end is connected to the transmission mechanism through a connecting rod.
Working principle: When high-pressure fluid enters the tube, the lumen tends to expand under pressure. This causes the bent bourdon tube to deform in the straight direction, with consequent displacement of the closed end. The displacement is transmitted to the transmission mechanism through the connecting rod and then triggers the switch.
Application: Borden tube pressure switches are able to cover a wide pressure measurement range. Meanwhile, its accuracy is very high. You can use it for working conditions that require very precise pressure control points, such as refineries, steam pipeline monitoring, etc.
Bellows Pressure Switches
Structure: The bellows pressure switch senses pressure changes through a bellows-shaped metal tube. This bellows-shaped metal tube resembles the wind chest of an accordion.
The bellows will elongate or shorten along the axial direction under pressure. The bellows is usually fully welded to the interface, so it can radically avoid media leakage.
Application: Compared with the diaphragm, the bellows has a longer stroke. This allows it to drive more complex switching mechanisms while providing extremely high sensitivity.
Bellows pressure switches are used for precision monitoring of low pressures, such as HVAC control, industrial gas flow monitoring, and pharmaceutical equipment fluid pressure control. Because of its high sensitivity, it can also be used in situations where small pressure fluctuations need to be monitored.
Electronic Pressure Switch
An Electronic pressure switch is also commonly referred to as a solid-state pressure switch.
Structure: Its interior is mainly composed of pressure sensors (usually strain gauges) and electronic processing circuits (including microprocessors and signal amplifiers). The external of electronic pressure switches is usually equipped with a digital display screen and buttons for programming settings.
Working principle: When the pressure of the medium acts on the pressure sensor, the sensor will convert the pressure signal into a corresponding weak electrical signal. The microprocessor continuously collects and amplifies this signal, digitizing it into a specific pressure reading.
The processor then compares the real-time reading to your preset pressure threshold. Once the threshold is reached, the electronic circuit will immediately drive the output module to send a switch signal to complete the action.
Application: The electronic pressure switch has high precision and is programmable. It is particularly suitable for high-frequency cycling scenarios, such as robotic welding arms or high-speed injection molding machines.
It is also widely used in intelligent manufacturing lines, precision medical equipment, and semiconductor processing equipment that require real-time data feedback to PLC control systems.
Electromechanical Pressure Switch vs Electronic Pressure Switch: A Simple Comparison
| Electromechanical Pressure Switch | Electronic Pressure Switch | |
| Working Principle | Physical displacement: using pressure to push springs and mechanical elements to trigger microswitches | Signal conversion: the use of sensors to convert pressure into electrical signals, controlled by the microprocessor output |
| Programming/Adjustment | Manual mechanical adjustment | Flexible setting by digital keys or software, can set switching point, deadband, time delay, etc. |
| Precision | Low (typically ±2% to ±5%), susceptible to mechanical wear, temperature variations, and possible set point drift over long periods of use | Very high (up to ±0.5% and more), good repeatability with almost no drift |
| Cycle Life | Limited (limited by metal fatigue and seal wear, approximately a million cycles) | Very long (without mechanical moving parts, capable of over ten million cycles) |
| Power Supply Demand | No external power supply required; it is a passive component | Must be connected to an external power source |
| Deadband (Hysteresis) | Fixed or limited adjustment (usually determined by mechanical structure, narrow range of adjustment) | Fully programmable (can be set anywhere from 0-100% of range via software or keypad) |
| Switching Frequency | Medium (usually < 1 stroke/sec, too fast can cause overheating or damage to mechanical parts) | High (extremely fast response speed, suitable for high-frequency actions multiple times per second) |
| Visualization | None (external pressure gauge required for setting) | Yes (usually with a display for real-time reading) |
| Load Capacity | High | Low |
| Maintenance | Mechanical wear and tear requiring maintenance or replacement | Lower maintenance requirements, but relatively complex to repair electronic failures |
| Initial Cost | Low | High |
Deadband is also known as hysteresis. It is the difference in pressure between the set point and the reset point of the switch action.
For example, you set a switch to break when the pressure reaches 100 psi, but it does not immediately close just as the pressure drops to 99.9 psi. It may require a pressure drop to 90 psi to reset the closure. The 10 psi difference here is the deadband.
The deadband is designed to prevent the switch from shaking near the pressure value, avoid short cycles in the equipment, and improve stability.
Vacuum Pressure Switch
A vacuum pressure switch, also known as a negative pressure switch. It is a device that combines mechanical sensing with electrical control.
Structure: The vacuum pressure switch consists of a pressure-sensing element combined with a switching contact mechanism. The pressure-sensing part usually employs flexible components such as diaphragms and bellows.
Application: The vacuum pressure switches are widely used in industrial scenarios where negative pressure monitoring and control are required.
- In industrial automation, it is often used in vacuum chuck systems to monitor whether the workpiece has been successfully sucked up. If there is not enough vacuum, the workpiece is not gripped firmly. And the switch will stop the arm from moving to prevent it from falling.
- It is also used in seal testing of vacuum packaging machines and negative pressure suction control of medical devices.
Differential Pressure Switch
Structure: The differential pressure switch has two pressure interfaces, usually labeled as high-pressure side (High/+) and low-pressure side (Low/-). The sensing element is usually a diaphragm that divides the chamber in half, creating two separate pressure chambers. This dual-chamber construction makes it feel pressure from two different sources at the same time.
Working principle: When the pressure difference between the high and low pressure sides is less than the set value, the diaphragm stays in place. Once the differential pressure increases to the set point, the deformation of the diaphragm is sufficient to overcome the resistance of the spring, which pushes the contacts to switch.
Application: Differential pressure switches are widely used in scenarios such as air filter clogging detection, ventilation system flow monitoring, pump protection, and water treatment systems. It helps the system to determine if an abnormal differential pressure exists, thus triggering the appropriate control or safety measures.
Air Compressor Pressure Switch
Structure: The air compressor pressure switch includes a mechanical pressure-sensing element, a spring mechanism and an electrical contact. The pressure sensing element is installed at the position connected to the gas storage tank or compressor output pipeline.
The compressor pressure switch sets a start pressure (low pressure point) and a stop pressure (high pressure point). You can set the pressure using the adjustment mechanism.
Working principle: As the air compressor delivers air to the tank, the pressure inside the tank gradually rises. When the high pressure point is reached, the switch contacts open, cutting off power to the compressor to allow it to stop running.
As the system uses air and the pressure decreases to a low pressure point, the displacement of the pressure-sensing element prompts the contacts to reclose and the air compressor restarts.
This cyclic control makes the compressor start and stop automatically within the set pressure range.
Application: The Air compressor pressure switch is mainly used to automatically control the start and stop of the air compressor motor. It can regulate the system pressure to avoid over-pressure or under-pressure operation of the equipment.
How to Choose the Right Type of Pressure Switch?
Define the Pressure Range
First, you should confirm the pressure range in which your system will operate. Different types and models of switches have operating range limitations. When selecting, you can set your setpoint between 25% and 75% of the rated pressure range of the device.
Consider Media and Material Compatibility
Pressure switches come into direct contact with the medium. You should verify that the pressure-sensing element and sealing material are compatible with the medium.
For regular air and hydraulic fluid, you can choose from nitrile rubber seals and brass connections. For high temperature or corrosive fluids, you need to choose diaphragms and connections made of Viton or SS316.
Combine with the Work Environment
In harsh working conditions with high vibration, dust and humidity, such as construction machinery and mining equipment, you need to prioritize electromechanical pressure switches. It has no complex electronic components and is more resistant to interference and vibration.
In clean, precise automated production lines or laboratories, electronic pressure switches are more suitable. Its high precision and digital display function can meet your precise control needs.
Consider Electrical Ratings
Make sure that the electrical contact capacity, voltage and current specifications of the switch meet the requirements of the controlled equipment. Different switches vary in electrical output and durability. You should avoid overloading when choosing.
FAQs
What is the Contact Type (NO/NC/SPDT) of the Pressure Switch?
NO (Normally Open) indicates that the switching circuit is open when the set pressure is not reached.
NC (Normally Closed) indicates that the circuit is closed when the set pressure is not reached.
SPDT (Single Pole Double Throw) indicates that the switch has a common terminal (COM) and two outputs (one corresponding to NO and one corresponding to NC). The common terminal can be switched between NO and NC when the switch is actuated. In this way, a single pressure switch is capable of both behaviors or more complex control.
Is there a Requirement for the Installation Direction of Pressure Switches?
For most high-pressure piston or electronic pressure switches, the installation direction has almost no impact.
For low-pressure diaphragm or micro-pressure bellows pressure switches, gravity is a factor that cannot be ignored. If a switch originally designed for vertical installation is installed horizontally, the self-weight of the internal mechanical components may cause the setpoint to shift. So, please make sure to install according to the instructions.
Why did the Set Point of my Electromechanical Pressure Switch Change after One Year of Use?
This is a normal physical characteristic of mechanical switches and is called set point drift.
The internal spring will experience metal fatigue after a long period of compression. This will cause a change in the elasticity coefficient of the spring, resulting in a set point drift.
In addition, the seals will wear out after long-term use. At this point, the frictional resistance changes, and a greater or smaller amount of pressure is required to move the component.
Therefore, electromechanical pressure switches must be calibrated every 6-12 months. If you are unable to maintain it regularly, you can choose electronic pressure switches that have no mechanical wear and drift.
There is a Small Hole in the Electromechanical Pressure Switch Housing. Can I Plug it for Waterproofing?
No. This small hole is the breather vent. Its function is to maintain balance between the pressure chamber or spring chamber inside the switch and the external atmospheric pressure.
If you seal the hole, the pressure imbalance between the inside and outside of the switch will cause a false action. For wet environments, you should use specialized waterproof breathable plugs rather than simply sealing them.
Final Thoughts
Having read this far, I believe you are already well-versed in the various types of pressure switches. Pressure switches of all types play a crucial role in industrial control, automation equipment, fluid systems and safety protection. Similarly, it is also very important to choose the appropriate type of pressure switch.
If you need to further compare different types of pressure switches or learn about specific models, please feel free to contact us.
