Figure 1—Structure diagram of a direct-acting relief valve
Compressed air with a pressure of P1 is input from the left end and throttled by valve port 10, and the pressure drops to P2 and output. The size of P2 can be adjusted by adjusting springs 2 and 3.Rotate the knob 1 clockwise, compress the springs 2, 3 and the diaphragm 5 to move the valve core 8 down, and increase the opening of the valve port 10 to increase P2.If the knob 1 is turned counterclockwise, the opening of the valve port 10 will decrease, and P2 will decrease accordingly.If P1 rises instantaneously, P2 will rise accordingly, causing the pressure in the diaphragm chamber 6 to rise, and the thrust generated on the diaphragm 5 will increase accordingly. This thrust destroys the balance of the original force and causes the diaphragm 5 to move upward. Moving, a small part of the airflow is discharged through the overflow hole 12 and the exhaust hole 11.As the diaphragm moves up, due to the action of the return spring 9, the spool 8 also moves upward, closing the intake valve port 10, and increasing the throttling effect, causing the output pressure to drop until a new balance is reached. The output pressure is basically Back to the original value.If the input pressure drops instantaneously, the output pressure also drops, the diaphragm 5 moves down, the spool 8 moves down accordingly, the intake valve port 10 opens, the throttling effect is reduced, and the output pressure basically returns to its original value.Turn knob 1 counterclockwise.The adjusting springs 2 and 3 are relaxed, the thrust of the gas acting on the diaphragm 5 is greater than the force of the pressure adjusting spring, the diaphragm is bent upward, and the inlet valve port 10 is closed by the action of the return spring.Turn the knob 1 again, the top of the intake valve core 8 and the overflow valve seat 4 will disengage, and the compressed air in the diaphragm air chamber 6 will be discharged through the overflow hole 12 and the exhaust hole 11, making the valve in a state of no output .
In short, the overflow pressure reducing valve relies on the throttling effect of the air inlet to reduce pressure, and relies on the balance of the force on the diaphragm and the overflow effect of the overflow hole to stabilize the pressure; the output pressure can be changed within a certain range by adjusting the spring. .In order to prevent the pollution of the surrounding environment caused by a small amount of gas from the above overflow type pressure reducing valve, a pressure reducing valve without an overflow valve (that is, an ordinary pressure reducing valve) can be used.
Figure 2—Structure diagram of internal pilot-operated pressure reducing valve
When the output pressure of the pressure reducing valve is high or the diameter is large, if the pressure is directly adjusted by the pressure adjusting spring, the spring stiffness must be too large. When the flow changes, the output pressure fluctuates greatly, and the structural size of the valve will also increase.In order to overcome these shortcomings, pilot-operated pressure reducing valves can be used.The working principle of the pilot-operated pressure reducing valve is basically the same as that of the direct-acting type.The pressure regulating gas used in the pilot pressure reducing valve is supplied by a small direct-acting pressure reducing valve.If a small direct-acting pressure reducing valve is installed inside the valve body, it is called an internal pilot pressure reducing valve; if a small direct-acting pressure reducing valve is installed outside the main valve body, it is called an external pilot pressure reducing valve .Figure 2 shows the structure of the internal pilot-operated pressure reducing valve. Compared with the direct-acting pressure reducing valve, this valve adds a nozzle composed of nozzle 4, baffle 3, fixed orifice 9 and air chamber B Baffle enlargement link.When the distance between the nozzle and the baffle changes slightly, the pressure in the B chamber will change significantly, which will cause the diaphragm 10 to have a larger displacement to control the up and down movement of the valve core 6 to make the inlet The air valve port 8 is opened or closed, which improves the sensitivity of the valve core control, that is, the accuracy of voltage stabilization is improved.
Figure 14-3 shows the main valve of the external pilot-operated pressure reducing valve, and its working principle is the same as that of the direct-acting type.There is also a small direct-acting pressure reducing valve outside the main valve body, which controls the main valve.This type of valve is suitable for occasions with a diameter of 20mm or more, long distances (within 30m), high places, dangerous places, and pressure regulation difficulties.
定值器是一种高精度的减压阀，主要用于压力定值。目前有两种压力规格的定值器：其气源压力分别为0．14MPa和0．35MPa，输出压力范围分别为0—0．1MPa和0一0．25MPa。其输出压力波动不大于最大输出压力的1％，常用于需要供给精确气源压力和信号压力的场合，如气动实验设备、气动自动装置等。
Figure 14-4 shows the working principle diagram of the fixed value device.It consists of three parts: 1 is the main closing part of the direct-acting pressure reducing valve; 2 is a constant pressure drop device, which is equivalent to a certain differencePressure reducing valve.The main function is to make the nozzle obtain a stable air flow; 3 is the nozzle baffle device and the pressure regulating part, which plays the role of pressure regulation and pressure amplification, and uses the air pressure amplified by it to control the main valve part.
Since the fixed value device has the functions of setting, comparing and amplifying, the voltage regulation accuracy is high.When the setting device is in a non-working state, the compressed air input from the air source is filtered by the filter 1 and then enters the A room and the main room.The main valve core 19 is pressed on the valve seat under the action of the spring 20 and the air source pressure, so that the A chamber is disconnected from the B chamber.The airflow entering the A chamber passes through the valve port (also called the valve) 12 to the F chamber, and then passes through the constant orifice 13 to reduce the pressure, and then enters the G chamber and the D chamber respectively.Since the diaphragm 8 has not been forced at this time, the distance between the baffle 5 and the nozzle 4 is relatively large, the airflow resistance when the gas flows out of the nozzle 4 is small, the air pressure in the G chamber and the D chamber is lower, and the diaphragm 3 and 15 Keep the original position.The trace gas entering the chamber is mainly discharged from the exhaust port through the valve port 2 through the B chamber; another part is evacuated from the output port.At this time, there is no air flow output from the output port, and the exhaust of trace gas from the nozzle is necessary to maintain the operation of the nozzle baffle device. Because it is a gas without power consumption, it is hoped that the consumption is as small as possible.
When the setter is in working condition, turn the handle 7, depress the spring 6 and push the diaphragm 8 together with the baffle 5 to move down, the distance between the baffle 5 and the nozzle 4 is reduced, the airflow resistance increases, and the G and D chambers The air pressure rises.The diaphragm 16 moves down under the action of the air pressure in the D chamber to close the valve port 2 and push the main valve core 19 downward to open the valve port. The compressed air is output from the output port through the B and H chambers.At the same time, the pressure in the H chamber rises and is fed back to the diaphragm 8. When the feedback force received by the diaphragm 8 is balanced with the spring force, the setter will output a certain pressure of gas.When the input pressure fluctuates, such as the pressure rises, the air pressures in the B and H chambers increase instantaneously, causing the diaphragm 8 to move up, which causes the distance between the baffle 5 and the nozzle 4 to increase, and the air pressures in the G and D chambers drop.As the pressure in the B chamber increases and the pressure in the D chamber drops, the diaphragm 15 moves upward under the action of the pressure difference, so that the main valve port is reduced, and the output pressure drops until it stabilizes to the set pressure.In addition, when the input pressure rises, the pressure in the E chamber and the instantaneous pressure in the F chamber also rise, and the diaphragm 3 moves upward under the action of the upper and lower differential pressures, and the pressure stabilizing valve port 12 is closed.Due to the strengthening of the throttling effect, the air pressure in the F chamber decreases, and the pressure difference between the front and rear of the throttling hole 13 is always kept constant, so the gas flow through the throttling hole 13 remains unchanged, so that the sensitivity of the nozzle baffle is improved.When the input pressure decreases, the pressures in the B and H chambers drop instantaneously, the diaphragm 8 and the baffle 5 move down due to the destruction of the force balance, the distance between the nozzle 4 and the baffle 5 is reduced, and the pressure in the G and D chambers rises , Diaphragm 3 and 15 move down.Diaphragm 15 moves downward to increase the opening of the main valve port, so that the air pressure in chamber B and chamber H rises until it is balanced with the set pressure.The diaphragm 3 moves downwards, so that the pressure stabilizing port 12 is opened, the air pressure in the F chamber rises, and the pressure difference between the front and rear of the constant orifice 13 is kept constant.In the same way, when the output pressure fluctuates, it will get the same adjustment as when the input pressure fluctuates.
Because the setter uses the feedback effect of the output pressure and the amplification effect of the nozzle baffle to control the main valve, it can respond to small pressure changes, so that the output pressure can be adjusted in time, and the outlet pressure is basically stable, that is, the fixed value The voltage regulation accuracy is higher.