Pressure switch


The management of technological processes in any field of activity, such as in the manufacturing or automotive industry, requires control of the pressure of the fluids that operate the system. This requires associating a particular pressure value, which is important for the system, to an electrical signal, for instance to run a machine cycle or indicate a particular situation (leaks, alarms, etc.). These operations can be controlled using a kind of pressure sensor, called a pressure switch, that is set to suit the particular application.

From an electrical point of view, there three main types:
- with two-way normally-open (NO) electrical contacts (SPST)
- with two-way normally-closed (NC) electrical contacts (SPST)
- with three-way changeover electrical contacts (SPDT)

A switch can be calibrated using a set screw which, by acting on a calibration spring, determines its load. The spring opposes the thrust of the pressure exercised by the fluid on the sensitive element (a membrane or piston), allowing the electrical contact to close or open only when the pressure setting is reached.

- In the NORMALLY OPEN (NO) version on Fig. 1, the contact is open, i.e. there is no flow of current in the absence of pressure. When the pressure setting is reached, the electrical contactcloses.

- The diagram of Fig. 2 shows a pressure switch with NORMALLY CLOSED (NC) contacts in the absence of pressure.

We can see that the contacts are closet and the signal is present on the external contacts. When the pressure setting is reached, the electrical contact rises and interrupts the signal.

- In the SWITCHING CONTACTS (SPDT) of Fig. 3 version, the presre of the fluid on the separating element (diaphram or piston) causes a microswitch to switch.
Either NC or NO contacts, or both, can be used in this version.
Pressure switch with N.O./N.C. Pressure switch SPDT contacts Vacuum switch Differential pressure