Pressure relays have direct-acting type and pilot type, but the principle is the same. Relying on the liquid pressure and spring force to achieve force balance, the plunger or lever generates a certain displacement, and the micro switch is turned on or off. The pressure switch is usually in a state of no hydraulic pressure. When the pressure rises to a certain area value or the pressure drops to a certain area value, the internal micro switch is turned on or off, thereby sending out an electrical signal.
When the pressure relay and pressure switch are working, the setting value should be adjusted according to the actual process pressure. But the pressure relay adjusts the pressure value, and when the hydraulic pressure is equal to the adjusted spring force, it sends out an electrical signal. When the pressure switch adjusts the pressure value, the hydraulic pressure is higher than the adjusted spring force or lower than the adjusted spring force to send an electrical signal. The air filter pressure reducing valve used is similar to a pressure relay, and the electrical contact pressure gauge is similar to a pressure switch.
When the air filter pressure reducing valve is adjusted, as long as it is within its adjustable range, the output pressure is the pressure value when it is adjusted to a certain pressure point, and the pressure relay is to increase the micro switch on this basis, as long as the hydraulic pressure is equal to this pressure It is converted into an electrical signal output. For the electric contact pressure gauge, it can set the high limit and low limit, as long as the hydraulic pressure is higher than the high limit or lower than the low limit, an electrical signal is issued, as is the pressure switch. Therefore, the pressure relay can be used for a load with a small load. If it is a heavy load, it needs to be realized through an intermediate relay or a contactor, and the small load and large load of the pressure switch can be used directly.