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Useful information about pneumatic pressure switches
Pressure switches are operated by pneumatic or hydraulic pressures and are used to monitor and control pumps, compressors and similar applications. To find out exactly how pressure switches work, what types are available and what you should pay attention to when you buy, please read our guide.
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What was pressure switch?
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Mechanical and electronic pressure switches
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Pressure switch purchase criteria – what's important?
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Our practical tip: Take maximum switching capacity into account
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FAQ – Frequently Asked Questions about Pressure Switches
What was pressure switch?
Pressure switches are an integral part of the pneumatic and hydraulic systems. It can be used to monitor the pressure or level of a medium, such as air or oil, in a pneumatic or hydraulic system. They react when the pressure of the medium changes or a defined top pressure and vacuum is reached and transmit a corresponding signal to the control unit. The top pressure unit marks the upper limit of the pressure range, while the vacuum is the lower limit. A pressure switch is used to check that both values are not exceeded or undercut. In this way, it is possible to ensure a constant pressure range in the system.
Hydraulic and pneumatic pressure switches are mainly used in industrial applications and process engineering processes. They can be found in equipment and apparatus construction as well as in plant and mechanical engineering. Pressure switches are used to control pumps or domestic water plants, are integrated in valves, compressors and are used for oil pressure monitoring, which is particularly important for internal combustion engines.
Mechanical and electronic pressure switches
Pressure switches are available in mechanical and electronic versions. Mechanical pressure switches are equipped with a diaphragm (for smaller pressures) or a piston (for larger pressures) on the pressure input side. They are similar to the design of pressure regulators. On the other side there is a pre-tensioned spring whose tension can be adjusted using a screw. A mechanical pressure switch now works as follows: While the operating pressure on the pressure input side presses against the diaphragm (or piston), the spring force on the other side counteracts the pressure force. If the operating pressure is higher than the spring force, the device moves the diaphragm and operates a microswitch that opens or closes the circuit. When the operating pressure decreases, the diaphragm and microswitch return to their initial position and the electrical signal drops.
The contacts in the pressure switch can be distinguished in terms of their function in NC, NO and CO contacts. As the name implies, an NC contact is designed to open the circuit as soon as the specified switching pressure is reached. This means that the contact is interrupted or disconnected. A normally open contact, on the other hand, closes the circuit by making the contact. A changeover contact can act both as an NC contact and as a changeover contact, thus taking over both functions.
Electronic pressure switches are opposite mechanical pressure switches. In the case of mechanical pressure switches, pressure detection and signal switching are carried out in a mechanical way, while in the case of electronic pressure switches, they are carried out in an electrical way. For this purpose, they are equipped with an electronic pushbutton (sensor) that detects the pressure or pressure change and generates a corresponding signal, which in turn is processed by the electronic microcontroller and converted into an electrical switching signal. In rare cases, electronic pressure switches are equipped with a mechanical switching element, such as a relay. Such designs can be referred to as electromechanical pressure switches.
Many electronic pressure switches have practical additional features, such as buttons for easy setting of functions or displays that indicate the measured pressure. Configurations can often be made using special software or configuration modules. The service is therefore very comfortable. Since electronic switches do not have any movable mechanical parts, they are almost wear-free and require little maintenance. They work reliably, are robust and designed for a very high number of switching cycles. Despite their advantages, electronic pressure switches have not yet displaced their mechanical equivalents. Mechanical pressure switches are more cost-effective, do not require a supply voltage and can be switched for direct and alternating current as well as for high currents, so they are still used especially for simple safety applications. However, electronic pressure switches are becoming increasingly important in the field of automation.
Pressure switch purchase criteria – what's important?
The switching pressure range of a pressure switch should first be adjusted to the respective application. There are pressure switches which are designed for a pressure range of -0.15 to 1 bar, but also those that operate in a pressure range of 0 to 20 bar. In addition, it is important that the pressure switch is suitable for the operating medium. Some switches are designed exclusively for air or compressed air, others for liquid and gaseous fluids. Depending on which function the switch is supposed to take over, also pay attention to the type of contact (opener, closer, changer).
For demanding applications, housing and membrane material as well as the maximum permissible housing pressure may be relevant. Pressure switches should ideally be shock and vibration resistant, in order to be able to function properly even in case of possible faults. In connection with the operating environment, the degree of protection should also not be ignored. For orientation: In industry, pressure switches of the protection class IP65 (dust-proof and protected against jet water from any angle) and IP67 (dust-proof and protected against temporary immersion) are often used.
Our practical tip: Take maximum switching capacity into account
It is highly recommended not to allow a pressure switch to operate permanently at maximum switching capacity, as this can have a negative effect on its life expectancy. Instead, the switching capacity should always be kept as small as possible. This helps the switch to perform its service for a long time.
FAQ – Frequently Asked Questions about Pressure Switches
What was hysteresis?
Hysteresis is the technical term for the difference between switching and switching point or switch-on and switch-off pressure. In fact, hysteresis refers to the range in which the actual value may deviate from the setpoint. It is limited upwards by a maximum value and downwards by a minimum value. With large hysteresis, the actual value may deviate more from the setpoint, which means that fewer on/off switching is required. With a small hysteresis, on the other hand, the switch must switch more frequently, since the actual value may only fluctuate in a small range.
What was actually meant by pneumatics and hydraulics?
The term pneumatics is derived from the Greek pneuma "air" and refers to the teaching of all technical applications based on air or compressed air. The hydraulics (derived from Greek hýdor “water”) must be distinguished from the pneumatics. This is the teaching of the flow behavior of liquids. Hydraulics and pneumatics are part of so-called fluid technology, which includes all processes in which forces and movements are generated by fluids (gases or liquids).