Types of pressure switches
Mechanical pressure switch
A mechanical pressure switch uses a spring and a diaphragm, or piston, to control at what pressure the micro-switch is triggered. The spring is the opposing force to the inlet pressure and the springs pretension is adjusted with a set screw or knob. The spring pretension directly correlates to the pressure at which the switch makes an electric contact. When the pressure drops, the switch resets to its original state.
The difference between the switch point and reset point is called hysteresis. Often this is expressed as a percentage of the switch point value, for example, 20%. The manufacturer defines the hysteresis, and for most mechanical switches, it is not configurable by the user.
These pressure switches usually have three different types of contact: normally open (NO), normally closed (NC), and changeover (SPDT) contacts. Changeover contacts are for both NO and NC operation.
The mechanical pressure switch is better suited for handling high voltages and amperages than an electronic pressure switch. They can be used to make a contact change for an increase or decrease in pressure.
Electronic pressure switch
An electronic pressure switch uses an electrical pressure sensor to measure the change in inlet pressure. They have digital displays to set up the switching function. The switch point can be manufacturer set or can be programmed on-site according to the application requirements. Switch point, output signals, hysteresis, delay time, etc. are some functions that can be adjusted by the user according to the requirements.
Electronic pressure switches are suitable for automated and controlled equipment systems that require programmable function, digital display, flexibility, accuracy, ingress protection, and stability.
FAQ
How to adjust a pressure switch?
For a mechanical pressure switch, turn the nut clockwise to increase and counterclockwise to decrease the switch point. An electric pressure switch has a keypad for adjustments.
How to test a pressure switch?
Unplug electric power from the pressure switch and connect the multimeter to its terminals. For a normally open switch, the multimeter should read open circuit. Turn on the circuit to let the fluid pressure into the pressure switch. If the multimeter does not read 0 ohms, replace the switch. Opposite for a normally closed switch.
What does a pressure switch do?
A pressure switch monitors the systems fluid pressure and either opens or closes an electrical connection based on a preset pressure level.
How to tell if a pressure switch is bad?
The pressure switch can have issues if the fluid is leaking, the pressure is too low, pressure changes too frequently, and incorrect initial set pressure.
How does a mechanical pressure switch work?
When the inlet pressure force is greater than the springs pre-tensioned force, it switches the electrical contact. An NC contact will open, and an NO contact will close. Once the pressure reduces, the contacts will return to their normal state.
What is the difference between a pressure switch and a pressure sensor?
Pressure switches operate electrical switches at a preset pressure level, while pressure sensors read the system pressure and convert it into an electrical signal.
