Pressure switches can be used in very many industrial and domestic applications.
For instance, the pneumatic switches can be used to switch on/off the following: the light alarms if the aircraft’s cabin pressure goes below the desired level, gas compressor and water pumps amongst others.
On the other hand, the hydraulic types can be used to switch on vehicles’ alarm light if the engines oil pressure goes below the safe level, to control automatic lock up and transmission systems among other uses.
How do they operate?
These switches exist as either normally closed or normally open. Their principle of operation is almost the same.
For a normally open pressure switch, assuming that it’s a piston type; the pressure entering through the switch’s input acts on the diaphragm or the piston (depending on the switch).
The pressure exerted results in some force which make the plunger to move alongside with the contact disks/plates which closes the switch between the contacts (open switch).
The force exerted by the pressure must be greater than the pre-loaded force of the springs. When this pressure goes down, the force reduces and as a result, the springs pull back the disks leaving the circuit open.
The reverse takes place in the normally closed switches. In some cases such as that of the micro-switch, this change over process of the normally closed and the normally open can be integrated together in one switch. This makes the micro-switch a perfect choice for very many application.
The operation principle may vary from one switch to the other. However, the bottom line is that when a given amount of pressure which is more than the preset pressure enters the switch’s input, the switch either opens or closes depending on its initial state.
Important factors to consider while dealing with pressure switches
- Hysteresis; it’s used to describe the difference between various switching points. This is mostly when the pressure is rising and wh falling. It depends majorly on the switching point.
- Switching frequency; this gives the information about the number of switching cycles/minute. It can be given as 100/minute. This will also depend on both the operating conditions and the type of switch.
- The set point tolerances; the operating temperature and pressure also determines the accuracy and lifespan of the switch. Remember, the switching points can change with time due to either the aging effects or temperature.
- Membrane; the choice of material will depend on its main application. For instance, EPDM is ideal for brake fluid,Viton® is a perfect choice for both high pressure and temperature, silicone is suitable for extensive temperature range and buna-N is the most common since it’s considered as the standard material.
- The switch’s life; diaphragm switches have a longer lifespan. The piston types are also durable. The lifespan depends on the cycle speed (the higher the speed, the shorter the lifespan), pressure levels, rate of change in pressure, the electrical load on the switch, hydraulic shock and deadband setting. A deadband refers to difference in the re-actuation and actuation of the switch.
- Switch points of a pressure switch; a switch can have more than one switching point. These may include low, high, low-low and high-high. The operator must be able to handle all these switch points. The set points must also be adjustable to suit an application.
The switch’s housing is also important since it protects it from possible hazards.
Moreover, calibrating the switch is also necessary to ensure that it operates optimally and accurately. With all these in mind, it’s possible to get a switch which suitable for a specific application.