Choosing the Right Pressure Switch

WIKA electronic pressure switch

Based on the type of technology used in their construction, pressure switches can be divided into two main categories: mechanical and electronic. Each of these technologies provides various options for switching signals and adjustments.

Mechanical pressure switches

Mechanical pressure switches convert fluid pressure into mechanical movement utilizing a diaphragm or piston which, when deformed or moved, triggers the switching contact. Mechanical pressure switches offer the advantage of operating without a power supply but are limited to generating only a switching signal.

They are simple and inexpensive devices, chosen more for their robustness than their precision. They are normally used to switch high currents (for example, to control pumps) or as redundant safety devices.

Mechanical pressure switches can feature either a fixed switching point, which is factory-set, or an adjustable one. However, hysteresis, also known as differential, is typically not adjustable on most models. Hysteresis refers to the difference between the pressure value set to trigger the pressure switch (switching point) and the value required to return it to the initial position.

Electronic pressure switches

Electronic pressure switches include an electronic pressure sensor that measures the pressure and generates an output signal when the switching points are reached. Electronic pressure switches are generally more complex and therefore more expensive than mechanical ones. They have no moving parts, which makes them more reliable and longer-lasting. They are also far more accurate than mechanical models.

Electronic pressure switches can be factory-set, but they usually have a digital display and an interface that allows you to easily program the various parameters of the device (timing, switching points, hysteresis, normally open or normally closed, etc.). The digital display also allows you to see the pressure value in real-time, as well as the status of the device’s contact (open or closed). These pressure switches therefore also function as pressure sensors/transmitters.

Electronic pressure switches can offer both the possibility of programming several switching points and a greater variety of output signals. They are more suitable for automatic systems than mechanical pressure switches.

Due to their many advantages, pressure switches are currently the most widely used in industrial process control.

SUCO piston pressure switch

A mechanical pressure switch has two main components: the diaphragm and the piston.

• Diaphragm pressure switches operate by using the deformation of a diaphragm, which is subjected to the pressure being controlled on one side and the force exerted by a spring on the other side. To adjust the switching point of these pressure switches, the spring tension is adjusted. Diaphragm pressure switches can be used with pressures from 0.1 to 100 bar.

• Piston pressure switches utilize the movement of a piston, which is influenced by the monitored pressure on one side and the force exerted by a spring on the other side. As with diaphragm pressure switches, the tension of the spring sets the switching point. Piston pressure switches can be used with pressures from 10 to 400 bar.

Once you have decided which type of pressure switch you need, you can choose the most suitable model based on the following criteria:

• Factory-set or adjustable: Pressure switches with a factory-set switching point are cheaper than adjustable ones and are the ideal solution for applications where the switching point does not vary. Adjustable pressure switches are preferable if a different switching point is required. Electronic pressure switches with a digital display and interface (buttons) allow you to precisely adjust the device’s various operating parameters.
• Adjustment range: You must choose a pressure switch whose switching point corresponds to the value of the pressure to be monitored, or with an adjustment range that includes this value. The pressure at the switching point should not be confused with the maximum pressure that the pressure switch is capable of withstanding, which is much higher.

• Output signal: Pressure switches can have different types of outputs. Before choosing a model, check that it has the output you want. With mechanical pressure switches, you can only choose between a device with a Normally Open or Normally Closed contact. Electronic pressure switches offer more possibilities.

• Overpressure resistance capacity (maximum pressure): This is the maximum pressure the pressure switch can withstand. It is much higher than the switching point pressure.

• Materials used to make the pressure switch: It is important to choose the material of the part of the pressure switch that comes into contact with the fluid, as well as the housing, which will be exposed to the environment. In both cases, it is essential to choose materials that are compatible with the intended application (stainless steel for the food-processing industry, for example), the fluid, and the environmental conditions.

• Electrical connector: When choosing a pressure switch, make sure that the electrical connector is compatible with the existing system.

• Power supply: If you choose an electronic pressure switch, check that the device’s supply voltage corresponds to the voltage in the automatic process control system.

• Degree of protection, ATEX certification: The pressure switch must have a degree of protection that meets the requirements of the process.