Pressure relief valve principle introduction

First, the principle of pressure reducing valve Direct pressure valve pressure P1 compressed air, from the left input through the valve port 10 throttling, the pressure drop to P2 output. The size of P2 can be adjusted by pressure regulating springs 2,3. Rotating the knob 1 clockwise, the compression springs 2, 3 and the diaphragm 5 move the spool 8 downward, increasing the opening of the valve port 10 to increase P2. If the knob 1 is rotated counterclockwise, the opening of the valve port 10 decreases and P2 decreases accordingly.

If P1 rises instantaneously, P2 will increase accordingly, so that the pressure in the air chamber 6 of the diaphragm increases, and the thrust generated on the diaphragm 5 increases accordingly. This thrust destroys the balance of the original force and causes the diaphragm 5 to rise upward. Moving, a small portion of the air is discharged through the overflow hole 12 and the exhaust hole 11 . At the same time as the diaphragm moves upwards, due to the action of the return spring 9, the valve core 8 also moves upward, closes the intake valve port 10, and the throttling effect increases, so that the output pressure decreases until a new balance is reached, and the output pressure is basically It's back to its original value. If the input pressure drops momentarily, the output pressure also drops, the diaphragm 5 moves downwards, the spool 8 moves downwards, the intake valve port 10 opens large, the throttling effect decreases, and the output pressure also basically returns to the original value. Turn knob 1 counterclockwise. The adjustment springs 2 and 3 are relaxed, and the thrust force of the gas acting on the diaphragm 5 is greater than the force of the pressure adjustment spring, the diaphragm is upwardly curved, and the intake valve port 10 is closed by the action of the return spring. Turn the knob 1 again, the top of the inlet valve core 8 and the relief valve seat 4 will be released, and the compressed air in the diaphragm air chamber 6 will be discharged through the overflow hole 12 and the exhaust hole 11, so that the valve is in the state of no output. .

In short, the overflow relief valve is decompressed by the throttling action of the air inlet, and it is regulated by the balancing action of the force on the diaphragm and the overflow of the overflow hole; the output pressure can be changed within a certain range by adjusting the spring. . In order to prevent the above overflow relief valve from escaping a small amount of gas to contaminate the surrounding environment, a relief valve without a relief valve (ie, an ordinary relief valve) may be used.

Pilot-type pressure reducing valve When the output pressure of the pressure reducing valve is high or the diameter is large, adjusting the pressure directly with the pressure regulating spring will inevitably result in too large spring stiffness. When the flow rate changes, the output pressure fluctuates greatly, and the structural size of the valve It will also increase. To overcome these disadvantages, pilot-operated pressure reducing valves can be used. The working principle of pilot operated pressure reducing valve is basically the same as that of 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. . The structure diagram of the internal pilot pressure reducing valve, compared with the direct-acting pressure reducing valve, increases the number of nozzle baffles formed by the nozzle 4, the baffle 3, the fixed throttle 9 and the air chamber B. . When the distance between the nozzle and the baffle slightly changes, the pressure in the chamber B will change significantly, causing the diaphragm 10 to have a large displacement, so as to control the movement of the valve core 6 up and down. The air valve port 8 is opened or closed small, which improves the sensitivity of the valve core control, that is, improves the voltage regulation accuracy.

The main valve of the external pilot pressure reducing valve works in the same way as the direct-acting valve. Outside the main valve body there is also a small direct-acting pressure reducing valve (shown at the end of the figure) that controls the main valve. These valves are suitable for applications where the diameter is over 20mm, long distance (within 30m), height, danger, and pressure adjustment.

The setter is a high-precision pressure reducing valve and is mainly used for pressure setting. There are currently two types of pressure gauges: their air source pressures are 0.14 MPa and 0.35 MPa, and the output pressure ranges are 0-0.1 MPa and 0-0.25 MPa, respectively. Its output pressure fluctuation is not more than 1% of the maximum output pressure, and it is often used in occasions where it is necessary to supply precise gas source pressure and signal pressure, such as pneumatic test equipment, pneumatic automatic devices, etc.

The working principle of the valuer. It consists of three parts: 1 is the main closed part of the direct-acting pressure reducing valve; 2 is a constant pressure drop device, which is equivalent to a certain differential pressure reducing valve. The main role is to make the nozzle to obtain a stable flow of gas; 3 is the nozzle baffle device and pressure regulator, regulating pressure and pressure amplification, use the air pressure is amplified to control the main valve part.

Because the setter has the functions of setting, comparing, and amplifying, the precision of voltage regulation is high.

When the valuer is in the non-operating state, the compressed air input from the air source is filtered by the filter 1 and enters the chamber A and the positive chamber. The main valve element 19 is pressed against the valve seat under the action of the spring 20 and the air supply pressure so that the A chamber and the B chamber are disconnected. The flow entering chamber A passes through valve ports (also referred to as valves) 12 to F chambers, and is then reduced in pressure through constant orifice 13, and enters chambers G and D, respectively. Since no force is applied to the diaphragm 8 at this time, the distance between the baffle 5 and the nozzle 4 is relatively large, the air flow resistance when the gas flows out from the nozzle 4 is small, and the pressures in the chambers G and D are low, and the diaphragm 3 and 15 Keep the original position. The trace gas entering the chamber is mainly discharged through the valve port 2 from the exhaust port through chamber B; another part is vented from the output port. At this time, there is no air output at the output port, and the discharge of the trace gas from the nozzle is necessary to maintain the operation of the nozzle baffle device. Since it has no power consumption, it is desirable that the consumption thereof be as small as possible.

When the valuer is in the working state, the handle 7 is rotated, the spring 6 is pressed down and the diaphragm 8 is pushed down together with the baffle 5, the spacing between the baffle 5 and the nozzle 4 is reduced, the airflow resistance is increased, and the chambers G and D are Air pressure rises. Diaphragm 16 moves downward under the action of air pressure in chamber D, closes valve port 2 and pushes main valve core 19 downward, opening the valve port, and compressed air is output from the output port through chambers B and H. At the same time, the pressure in the chamber H rises and is fed back to the diaphragm 8. When the diaphragm 8 is balanced by the feedback force and the spring force, the leveler outputs a certain pressure of gas. When the input pressure fluctuates, for example, if the pressure rises, the pressures in chambers B and H increase instantaneously and the diaphragm 8 moves upward, resulting in an increase in the distance between the baffle 5 and the nozzle 4 , and the pressures in chambers G and D decrease. As the pressure in chamber B increases, the pressure in chamber D decreases, and diaphragm 15 moves upward under the effect of pressure difference, so that the main valve port decreases, and the output pressure decreases until it stabilizes to the set pressure. In addition, when the input pressure rises, the E-chamber pressure and the F-chamber instantaneous pressure also rise, and the diaphragm 3 moves up and down under the influence of the differential pressure, closing the small-pressure-regulating valve port 12 . Because the throttling function is strengthened, the pressure in the chamber F decreases, and the differential pressure between the orifice 13 and the orifice 13 is always maintained. Therefore, the flow rate of the gas through the orifice 13 is constant, so that the sensitivity of the nozzle baffle is improved. When the input pressure decreases, the pressures in chambers B and H decrease instantaneously, and the diaphragm 8 moves downward together with the baffle 5 due to the force balance failure. The gap between the nozzle 4 and the baffle 5 decreases, and the pressure in the chambers G and D rises. , Diaphragms 3 and 15 move down. The downward movement of the diaphragm 15 increases the opening of the main valve port so that the pressure in the chamber B and the chamber H can rise until it is balanced with the set pressure. The diaphragm 3 is moved downwards, so that the pressure stabilizing port 12 is opened large, and the pressure in the F room rises, and the pressure difference between the front and rear sides of the constant throttle hole 13 is always kept constant. Similarly, when the output pressure fluctuates, it will get the same adjustment as the input pressure fluctuates.

Because the setter uses the feedback action of the output pressure and the amplification effect of the nozzle baffle to control the main valve, it can react to a small pressure change, so that the output pressure can be adjusted in time to maintain the outlet pressure is basically stable, ie fixed value High precision regulator.

Second, the basic performance of the valve (1) pressure range: it refers to the pressure regulator valve output pressure P2 adjustable range, in this range required to achieve the required accuracy. The pressure regulation range is mainly related to the stiffness of the pressure regulating spring.

(2) Pressure characteristics: It refers to the characteristic that the output pressure fluctuates due to input pressure fluctuation when the flow g is constant. The smaller the output pressure fluctuations, the better the relief valve characteristics. The output pressure must be lower than the input pressure - the set value does not change substantially with the input pressure.

(3) Flow characteristics: It refers to the input pressure-timing, and the output pressure changes with the change of output flow g. When the flow g changes, the smaller the output pressure change, the better. The lower the general output pressure, the smaller it will fluctuate with the change in output flow.

Third, the choice of relief valve Select the type of pressure relief valve and pressure regulator accuracy according to the use requirements, and then select the path according to the required maximum output flow. When determining the air supply pressure of the valve, it should be greater than the maximum output pressure of 0.1 MPa. Pressure reducing valve is generally installed after the water diverter, before the lubricator or the valuer, and take care not to reverse the inlet and outlet; when the valve is not in use, the knob should be loosened to avoid the diaphragm from being deformed under pressure. Its performance.