What Is a Pressure Switch? Read Before Buy and Use

What Is a Pressure Switch?

A pressure switch is a specialized instrument for pressure measurement and control. Pressure switches can be electronic or mechanical. Based on a preset pressure value, they can open or close the corresponding switch contacts when the pressure is reached.

Pressure switches, like pressure transmitters, are essential instruments in industrial processes. However, the two should not be confused. Therefore, you may want to read this article before purchasing or using a pressure switch.

RFQ

Pressure Switch Working Principle

Pressure switches operate mechanically or electronically and open or close switch contacts based on the measured medium pressure.

Pressure switches typically consist of a sensing element (such as a diaphragm, bellows, etc.), a switching element (such as a microswitch, magnetic switch, etc.), and an adjustment mechanism.

The sensing element is responsible for sensing changes in external pressure and transmitting these changes to the switching element to activate it; the adjustment mechanism is used to set the pressure values for activation and deactivation.

Mechanical pressure switches are based on mechanical measurement systems such as Bourdon tubes, diaphragm elements, or diaphragm piston systems. The measuring element triggers the mechanical switch contacts in the pressure switch. Upon switching, the mechanical pressure switch sends an electrical signal.

Electronic pressure switches convert the measured pressure into an electrical signal. When the preset pressure is reached, the circuit opens or closes. Functions such as delay, switching point, reset point, and hysteresis can be programmed. The switching point and output signal can be adjusted. Electronic pressure switches can also provide a continuous pressure display for monitoring the switch output, and can therefore also be used as a digital pressure gauge.

The symbol for a pressure switch typically includes a circular or rectangular frame containing wavy lines or arrows representing pressure, and a pair of normally open (NO) or normally closed (NC) contacts. These contacts represent the electrical connection state of the pressure switch under different pressure conditions.

Specifically, the wavy lines or arrows in the symbol usually point in one direction, indicating the direction of pressure application; while the normally open and normally closed contacts are labeled “NO” and “NC” respectively, to distinguish their initial state when no pressure is applied.

Pressure switches commonly use normally open (NO) and normally closed (NC) relay contacts, and PNP output.

Relay – The contacts are passive and non-polarized. The two contact wires can be connected arbitrarily; simply select either the normally open or normally closed contact.

PNP Output – This is an active output and is polarized. When the switch is activated, it outputs 24VDC; when the switch returns to its normal state, it outputs 0V. It can be directly connected to the coil of an intermediate relay.

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What Does a Pressure Switch Do?

The main functions of a pressure switch are protection, alarm, and control. When the pressure in a system or equipment reaches a preset value, the pressure switch automatically activates, ensuring the safety of pumps, compressors, and engineering machinery.

In air conditioning systems, pressure switches monitor refrigerant pressure to ensure the system operates within a safe range.

In automotive engines, pressure switches monitor oil pressure to prevent mechanical damage caused by insufficient oil pressure.

In air compressors, air is pumped into the system. When the pressure reaches the set value, the pressure switch closes the contacts, stopping the motor. When the pressure drops below the set value, the air compressor restarts, maintaining the pressure in the tank within the desired range.

Hygienic flush diaphragm electronic pressure switch

Pressure vessels or pipelines have a maximum pressure limit. The pressure switch can act as a pressure limiting sensor, with its set point below the pressure vessel’s maximum allowable pressure. When the pressure is too high, the switch activates, opening valves or other pressure relief devices to provide protection.

Pressure switches can be used in conjunction with on-site flashing alarms. When the pressure is too high or too low, the switch activates, and the alarm alerts on-site operators.

In fire protection systems, low-pressure switches monitor the pressure in the fire pump discharge manifold, triggering pump start and stop; wet alarm valve pressure switches activate alarm devices.

Industrial equipment (such as water pumps and boilers) uses pressure switches to achieve unattended start and stop, improving system reliability.

A gas pressure switch is an important safety protection device in gas systems. It uses a pressure sensor to detect changes in gas pressure and controls the gas flow through a control circuit. By setting a reasonable pressure range, the gas pressure switch ensures the safe operation of the gas system. This makes low-pressure gas pressure switches widely used in various gas appliances and systems.

For example, household gas water heaters and industrial gas furnaces. These devices and systems all require gas pressure switches to protect their safe operation.

Pressure Switch Types

We classify and describe pressure switches based on their different operating principles and characteristics.

Based on different operating principles, pressure switches can be divided into mechanical and electronic types.

Mechanical Pressure Switches

Mechanical pressure switches sense changes in the pressure of the measured medium and use a mechanical structure to activate and deactivate the switch. They typically offer high reliability and durability, making them suitable for harsh working environments.

Electronic Pressure Switches

Electronic pressure switches use sensors to convert pressure signals into electrical signals, and then use circuitry to activate and deactivate the switch. They generally offer higher accuracy and sensitivity, making them suitable for applications requiring more precise control.

Digital Pressure Switches

Digital pressure switches are a modern type of pressure switch that utilizes digital display and control. They provide more accurate pressure measurement and more precise control.

Digital pressure switches are available in adjustable and non-adjustable formats. They offer greater flexibility and the ability to program various functions, easily adapting to the requirements of any specific application.

Based on the type of pressure measured, we have standard pressure switches, differential pressure switches, and vacuum pressure switches.

Differential Pressure Switches

Differential pressure switches are a special type of pressure switch used to measure differential pressure in fluids. They determine the differential pressure by comparing the pressure at two different locations and control the switch state accordingly.

Vacuum Pressure Switches

Vacuum pressure switches are used to sense pressure changes in a vacuum. A preset point is determined, and once this point is reached or exceeded, the vacuum switch will open or close the electrical connection.

Similar to standard pressure switches, vacuum switches can be used in a variety of industrial environments. This includes typical applications such as manufacturing, processing, and automation control, as well as pneumatic and hydraulic systems. Digital vacuum switches and adjustable vacuum switches are also available.

Based on the reset method, there are manual reset and automatic reset pressure switches.

Manual Reset Switches

Manual reset pressure switches require manual restarting after the system is shut down. This safety feature prevents the equipment from starting automatically after a pressure shutdown. You must press a button to restart the equipment.

Automatic Reset Switches

Automatic reset switches automatically return to normal operation after the pressure returns to normal, without any human intervention. Some models allow you to switch between manual reset and automatic reset modes as needed.

Common Applications of Pressure Switches

Industrial Automation: Pressure switches are widely used in industrial automation systems to monitor and control the pressure of various fluids. They can be used in hydraulic systems, pneumatic systems, water supply systems, etc.
Compressor Control: In compressor systems, pressure switches are used to detect and control the pressure range of the compressor, and to start and stop the compressor based on set values to maintain stable operation.
Oil and Gas Industry: In the oil and gas industry, pressure switches are used to monitor pressure changes in pipelines and storage tanks. They help control the transportation, storage, and processing of fluids.
Automotive Industry: In the automotive industry, pressure switches are widely used to monitor and control pressure changes in critical components such as engines, air conditioning systems, and braking systems. They help ensure the normal operation and safety of these systems.
Food and Beverage Industry: In the food and beverage industry, pressure switches are used to monitor and control pressure changes in processes. They ensure the stability of the production process and the achievement of quality standards.
Water Treatment and Wastewater Treatment: Pressure switches play an important role in water treatment and wastewater treatment. They are used to monitor and control the pressure in water pumps, valves, and piping systems to ensure the stability and safety of water supply and discharge.
Medical Equipment: In medical equipment, pressure switches are used to monitor and control the pressure of gases or liquids. This includes devices such as ventilators, blood pressure monitors, and syringes, to ensure the effectiveness and safety of patient treatment and monitoring.
HVAC Systems: In HVAC systems, pressure switches are used to monitor and control the pressure of refrigerants, compressors, and piping systems. They help maintain the stable operation of the system and provide a comfortable indoor environment.

Pressure Switch Selection

When adding or replacing a pressure switch, the following parameters need to be considered:

The pressure range: When selecting a pressure switch, you need to determine the pressure range you will be measuring to ensure it operates correctly within the intended range.
The operating temperature: Understand the temperature environment in which you will be using the pressure switch and select a product with an appropriate operating temperature range to ensure it functions correctly within the expected temperature range.
The application type: Determine your application scenario; different application scenarios may require different types of pressure switches, such as vacuum pressure or differential pressure.
The overload capacity: Select a pressure switch with sufficient overload capacity to handle potential pressure fluctuations or instantaneous pressure peaks.
The sensitivity: Choose the appropriate sensitivity based on your needs; higher sensitivity results in a faster response time of the switch.
The mounting method: Understand what type of mounting method your system requires. Common mounting methods include threaded mounting, flange mounting, and bracket mounting.
Special parameters, such as explosion-proof requirements and digital display.

FAQ

A pressure switch failure can lead to a malfunction in the system’s pressure control, or even cause the system to shut down completely. For example, if a water pump pressure switch fails, it cannot control the switching of electrical signals by sensing changes in water pressure. When the water pressure drops to a certain level, the pressure signal cannot be sent to the switching device in time, leading to a lack of water in the pump.

Here’s how to determine if your air conditioner pressure switch is faulty:

Check the AC system pressure: Use a pressure gauge to check the pressure of the air conditioning system. If the pressure is normal, the pressure switch is working correctly.
Check the pressure switch circuit: Use a multimeter to check if the pressure switch circuit is working properly. If the circuit is normal, the pressure switch is working correctly.
Check the pressure switch wiring: Check if the pressure switch wiring is loose or damaged. If the wiring is normal, the pressure switch is working correctly.
Check the pressure switch’s appearance: Check the pressure switch for any damage or corrosion. If the appearance is normal, the pressure switch is working correctly.

In short, determining whether an air conditioner pressure switch is faulty requires considering multiple factors, including pressure, circuit, wiring, and appearance. If all of these aspects are normal, the pressure switch is working correctly. If any of these aspects show a problem, the pressure switch needs to be repaired or replaced promptly.

Pressure switches provide a simple binary signal output (such as relay contacts, NPN/PNP, etc.), without continuous pressure value feedback. When the pressure reaches a preset threshold, the switch triggers an on/off signal, used to control equipment start/stop or trigger alarms.

Pressure transmitters convert the pressure value into a continuous analog or digital signal (such as 4-20mA, 0-10V, HART, RS485, etc.), transmitting pressure data in real time. The continuous output signal is linearly proportional to the pressure value, allowing for remote monitoring or participation in closed-loop control.

What Is a Pressure Switch? Read Before Buy and Use