Pressure switches
are an essential component in numerous industrial and residential systems, particularly pumping systems, compressors, and automation circuits. Despite its apparent simplicity, this device plays a crucial role in ensuring the safety, efficiency, and longevity of the system.
In this guide, we'll analyze in detail what a pressure switch is, how it works, where it's used, the most common problems, and how to adjust it correctly to avoid failures or downtime.
What is a pressure switch and what is it used for?
A pressure switch is an electromechanical device that opens or closes an electrical circuit based on the pressure of a fluid (liquid or gas). It consists of a diaphragm or piston that, deforming under the pressure, activates a microswitch. When the pressure reaches a set threshold (minimum or maximum), the pressure switch sends an electrical signal that can turn a device, such as a pump or compressor, on or off.
Where is the pressure switch used?
- Pressure tanks – to automatically control the start and stop of the water pump.
- Compressors – to maintain constant operating pressure throughout the work cycle.
- Industrial systems – to control and manage the pressure of fluids such as air, water, oil, or steam.
How does a pressure switch work?
The pressure switch operates by
deforming an elastic component
(a calibrated spring or diaphragm) as the pressure changes.
When the pressure reaches the set value, this component activates an electrical contact that closes or interrupts the power circuit of the connected machinery, ensuring that the system always operates within the established safety limits.
Difference between minimum and maximum pressure switch
There are two main types of pressure switches, distinguished based on the type of intervention on the pressure:
- Minimum pressure switch : activates when the pressure drops below a preset limit, protecting pumps from dry running, for example.
- Maximum pressure switch : activates when the pressure exceeds the safety value, interrupting the circuit to prevent damage to the system.
Pressure gauge and pressure switch: differences and complementary roles
In many systems, the
pressure gauge
and pressure switch work together to monitor and manage pressure. The pressure gauge
measures and displays
system pressure, while the pressure switch
u
ses it as a signal
to automatically activate or deactivate electrical controls.
The former provides immediate visual control, the latter automatic and safe control.
Pressure switch does not switch off: common causes
When the pressure switch doesn't respond as expected, the problem can be caused by various mechanical or electrical causes. The most common are:
- Mechanical blockage due to dirt, limescale, or wear that prevents the membrane from moving properly.
- Malfunction of the autoclave pressure switch , often caused by limescale deposits or oxidized electrical contacts.
- Pump not reaching the set pressure , due to undersizing, worn impeller, or leaks in the circuit.
- Calibration errors , which compromise the device's proper operation.
Blocked pressure switch: what to do
A stuck pressure switch requires a thorough inspection to identify the cause of the malfunction. This may include:
- Visual and instrumental diagnosis, checking for limescale, oxidation, or mechanical failures.
- Cleaning or replacing damaged components if the membrane or contacts are compromised.
- Replacing the pressure switch when adjustments fail to resolve the problem or the component is excessively worn: often a safer and more economical solution.
Compressor pressure switch: frequent problems
Even in compressors, the pressure switch is subject to failure or malfunction. Among the most common problems are:
- The pressure switch does not engage , often due to electrical defects (fuses, broken wiring) or mechanical blockages.
- Air leaks , due to loose fittings, damaged gaskets, or defective drain valves.
- Incorrect threshold values , which can be verified by periodically checking the pressure gauge to ensure the pressure switch is operating within the set parameters.
Types of pressure switches: which to choose based on the system
Choosing the right pressure switch is essential to ensure proper system operation. The main differences relate to technology, the fluid handled, and the operating environment.
Mechanical and electronic pressure switches
Mechanical pressure switches
are simple, robust, and economical, ideal for standard applications.
Electronic pressure switches
offer greater accuracy, a digital display, and advanced features such as alarms or PLC communication.
Models for water, air and oil
Each fluid requires suitable construction materials to ensure safety and durability:
- for water , brass or stainless steel are used;
- for air , galvanized steel or aluminum;
- for oil or aggressive fluids, treated steel or high-strength stainless steel.
Selection criteria
When choosing a pressure switch it is important to consider:
- the operating pressure range;
- the fluid and temperature compatibility;
- the environmental installation conditions (humidity, vibration, temperature).
How to properly adjust a pressure switch
Correct adjustment of the pressure switch is essential to ensure stable operation of the system and prevent abnormal starts or stops.
Minimum and Maximum Values
The minimum (cut-in) and maximum (cut-out) values establish the range within which the pressure must vary, ensuring efficiency and component protection.
These limits ensure that the system operates efficiently and that the components are protected from excessive stress.
Step-by-Step Adjustment Procedure
- Turn off and secure the system.
- Access the pressure switch and locate the calibration screws.
- Adjust the minimum pressure screw (cut-in).
- Adjust the maximum pressure screw (cut-out).
- Verify operation by performing several test cycles.
Common Mistakes to Avoid
During adjustment it is important to avoid some errors that can compromise the efficiency of the system:
- Setting too small a difference between minimum and maximum pressures will cause constant starting and stopping.
- Adjusting without proper pressure gauge control may result in values that are inconsistent with the system.
FAQ
- What happens if the pressure switch doesn't work?
The system won't turn on or off, with the risk of overpressure or dry running. - How do you know if a pressure switch is working?
Check it with a pressure gauge connected to the switch and verify whether the contacts click at the set values. - How much does it cost to replace a pressure switch?
The price ranges from €20–30 for simple models to over €150 for electronic industrial versions.