We have seen a lot of refrigeration equipment, but what do refrigeration equipment operate on? Here we will talk about a device such as a pressure relay. However, many people may not even listen to the pressure relay. In fact, the pressure relay is When the fluid pressure reaches a predetermined value in the hydraulic system, the component that makes the electric contact actuate. The pressure relay can also be defined as a hydraulic component that converts pressure into an electrical signal. Customers can adjust the pressure relay according to their own pressure design needs to achieve the function of outputting an electrical signal at a certain set pressure. Do you want to know more about the knowledge of pressure relays?
Classification of pressure relay
1. Diaphragm pressure relay
When the pressure of the inlet reaches the setting value of the spring, the diaphragm produces convex deformation under the action of hydraulic pressure, which makes the plunger move upward. The conical surface on the plunger makes the steel ball move radially, and the steel ball pushes the lever to deflect counterclockwise around the pin shaft, causing its end to press down the micro switch to send an electrical signal to connect or disconnect a certain circuit. When the inlet pressure drops to a certain value due to oil leakage or other reasons, the spring causes the plunger to move down, and the steel ball falls back into the conical groove of the plunger, the micro switch is reset, the electrical signal is cut off, and the lever is pushed back , Disconnect or connect the circuit.
2. Single plunger pressure relay
The control port p is connected to the hydraulic system. When the system pressure rises to the setting value of the pressure relay, the hydraulic pressure acting on the plunger 5 overcomes the spring force and the ejector rod pushes up to make the contact of the micro switch turn on or off ; When the system pressure drops below the set value, under the action of the spring force, the ejector rod and plunger move down to reset, and the micro switch returns to the original position.
The plunger pressure relay has reliable operation, long life and low cost. Because of its large volume change, it is not easily affected by pressure fluctuations. However, due to the large spring stiffness, the repeat accuracy is low, and the error is 1.5-2.5 of the set pressure. In addition, the difference between opening pressure and closing pressure is large
3. Bourdon tube pressure relay
It is composed of a shell box cover, a pressure sensitive element, a pressure switch and a junction box. It is characterized in that the pressure-sensitive element is a multi-turn spiral spring tube with a metal tube. The two ends of the spring tube are respectively screwed to the oil inlet joint and the sealing plug and then welded. The oil inlet joint is fixed on the shell and the sealing plug is An adjustable contact plate is fixed, the contact plate is aligned with the contact of the pressure switch, the pressure switch is fixed on the elastic switch clamp, one end of the switch clamp is fixed on the shell, the distance between the contact plate and the contact of the pressure switch is determined by the pressure adjustment mechanism adjust.
4. Bellows pressure relay
It is mainly composed of low pressure bellows, high and low pressure rods, disc-shaped pieces, pressure difference adjustment disc, return spring, pressure adjustment disc, transmission rod and thorough switch. The high and low pressure refrigerant vapor acts on the quotient and low pressure ripples of the pressure relay through the connecting bamboo to deform it, and then the micro switch is turned on or off through the return spring and the transmission rod to control the stop and operation of the compressor , Among them, the pressure adjustment plate can adjust the elastic force of the return spring, and the pressure difference adjustment plate can adjust the pressure difference when the micro switch is opened and closed.
Selection of pressure relay
1. Determine the pressure of the hydraulic system before purchasing, and then purchase the pressure relay with the corresponding range to avoid the pressure adjustment range being too small or too large.
2. Purchasing the corresponding pressure relay according to the use of the power supply, which must meet the rated voltage in the circuit.
3. According to the pipeline caliber of the hydraulic system, choose the pressure relay with the corresponding port caliber, so as not to use it.
Performance index of pressure relay
1. The pressure regulating range refers to the ratio of the maximum pressure to the minimum pressure of the pressure relay, which becomes the pressure regulating range.
2. Sensitivity. The difference between the opening pressure and the closing pressure of the pressure relay is its sensitivity.
3. The lifting and lowering pressure action time, the time from the inlet pressure of the pressure relay to the set pressure, is the boost action time, and vice versa is the pressure drop time.
4. When the set value is determined, the pressure relay will raise and lower the pressure several times. The smaller the difference between them, the higher the repeat accuracy.