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Pressure reducing valve works and selection
First, the working principle of the pressure reducing valve Direct acting pressure reducing valve Figure 14-1a shows the direct acting relief valve with relief valve (referred to as relief valve) structure. Pressure of P1 compressed air, the left end of the input through the valve 10 throttling, the pressure drop to P2 output. The size of P2 can be adjusted by pressure regulating springs 2 and 3. Turn the knob 1 clockwise to compress the springs 2 and 3 and the diaphragm 5 to move the valve core 8 downward and increase 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. If P1 instantaneous rise, P2 will be increased, so that the pressure diaphragm chamber 6 increased thrust on the diaphragm 5 corresponding increase in thrust to destroy the balance of the original force, the diaphragm 5 up Move, a small part of the gas flow through the overflow hole 12, the exhaust hole 11 is discharged. At the same time when the diaphragm moves up, the valve core 8 also moves upward due to the action of the return spring 9, and closes the intake valve port 10 to increase the throttling effect and reduce the output pressure 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, and the valve core 8 moves downward. The intake valve port 10 opens and the throttling effect decreases, so that the output pressure basically returns to the original value. Turn knob 1 counterclockwise. So that the adjustment spring 2, 3 relaxation, the gas pressure on the diaphragm 5 is greater than the pressure regulating spring force, diaphragm upward song, by the role of the return spring to close the intake valve port 10. Turn the knob 1, the top of the intake valve 8 and the relief valve seat 4 will be disengaged, the compressed air in the diaphragm chamber 6 is discharged through the overflow hole 12 and the exhaust hole 11, so that the valve is in a non-output state . In short, the relief valve is decompression by the throttling effect of the inlet decompression, by the balance of force on the diaphragm and the overflow hole overflow pressure regulation; adjust the spring pressure output can be changed within a certain range . In order to prevent the overflow pressure relief valve from hovering a small amount of gas pollution to the surrounding environment, can be used without pressure relief valve relief valve (ie, ordinary pressure relief valve), the symbol shown in Figure 14-1c. Pilot-type pressure reducing valve When the output pressure of the reducing valve is high or the diameter is large, the pressure is directly regulated by the pressure-adjusting spring, the spring stiffness must be too large. When the flow rate changes, the output pressure fluctuates greatly. The structure size Will also increase. To overcome these shortcomings, pilot-operated pressure relief valves can be used. Pilot operated pressure reducing valve works in the same way as direct acting. Regulated gas used in piloted pressure reducing valves is supplied by a small, direct acting pressure reducing valve. If the small direct-acting valve installed in the valve body, then known as the internal pilot-style valve; if the small direct-acting valve mounted on the outside of the main body, known as the external pilot-style valve . Figure 14-2 shows the internal pilot relief valve structure, compared with the direct-acting relief valve, the valve increased by the nozzle 4, the baffle 3, the fixed orifice 9 and the gas chamber B Nozzle bezel amplification. When there is a small change in the distance between the nozzle and the baffle, a significant change in pressure in chamber B occurs, causing a greater displacement of diaphragm 10 to control the up and down movement of spool 6 Valve opening 8 large or small, increased control of the spool sensitivity, which increased the regulator accuracy. Figure 14-3 shows the main pilot of the external pilot pressure reducing valve, which works the same as the direct acting type. Outside the main valve body there is a small direct acting pressure reducing valve (not shown), which controls the main valve. Such valves for more than 20mm in diameter, long distance (30m or less), height, dangerous place, pressure regulator difficult situations. The set-point setter is a high-precision relief valve, mainly used for pressure setting. There are currently two pressure gauge setters: the gas pressure is 0.14MPa and 0.35MPa, the output pressure range of 0-0.1MPa and 0 a 0.25MPa. The output pressure fluctuations of not more than 1% of the maximum output pressure, commonly used in the need to supply accurate air pressure and signal pressure of the occasion, such as pneumatic laboratory equipment, pneumatic automatic devices. Figure 14-4 shows the operation of the setter. It is composed of three parts: 1 is the main closed part of the direct acting pressure reducing valve; 2 is the constant pressure drop device, equivalent to a certain differential pressure reducing valve. The main role is to make the nozzle to obtain a stable gas source flow; 3 is the nozzle baffle device and pressure regulating part, from the regulator and pressure amplification, the use of it amplified by the pressure to control the main valve part. As the setter has set, compare and enlarge the function, so the voltage regulation accuracy. When the calibrator is in non-working state, the compressed air input by the air source is filtered by the filter 1 and enters into the A chamber and the positive chamber. The main spool 19 presses against the valve seat under the pressure of the spring 20 and the air source to disconnect the A and B chambers. The air entering chamber A flows through ports 12 to F through the valve ports (aka valves), and then depressurizes through the constant orifice 13 to enter compartments G and D, respectively. Since the diaphragm 8 is not yet energized, the distance between the baffle plate 5 and the nozzle 4 is large, the flow resistance of the gas flowing out of the nozzle 4 is small, the pressures in the G and D chambers are low, and the diaphragm 3 and 15 Keep the original position. The trace gases entering the chamber are mainly discharged from the exhaust port through the valve chamber 2 through chamber B and the other portion is exhausted from the output port. At this moment, there is no air flow output at the output port. It is necessary for the nozzle baffle device to work to purge the micro gas by flowing out of the nozzle. Because it is a reactive gas consumption, it is desirable that the consumption is as small as possible. When the calibrator is in the working state, the handle 7 is rotated, the spring 6 is pushed down and the diaphragm 8 is pushed down together with the baffle 5, the distance between the baffle 5 and the nozzle 4 is reduced, and the airflow resistance is increased, Pressure increased. The diaphragm 16 is moved down by the atmospheric pressure of chamber D, closes the valve port 2, and pushes the main valve 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, H chamber pressure rise and feedback to the diaphragm 8, when the diaphragm 8 by the feedback force and spring force balance, the value of the device will output a certain pressure gas. When the input pressure fluctuates, if the pressure rises, the air pressure in chamber B and chamber H increases instantaneously, causing the diaphragm 8 to move upward, resulting in an increase in the distance between the baffle 5 and the nozzle 4, and a decrease in the pressures in chambers G and D. As chamber B pressure increases, chamber D pressure drops, diaphragm 15 moves upward under pressure differential, reducing the main valve port and reducing the output pressure until it settles to the set pressure. In addition, when the input pressure rises, the pressure in chamber E and the instantaneous pressure in chamber F also rise. The diaphragm 3 moves up and down under the pressure difference up and down, and closes the valve port 12. Due to the throttling effect, F chamber pressure drop, and always maintain the orifice 13 before and after the pressure difference is constant, so through the orifice 13 of the gas flow rate unchanged, the nozzle baffle sensitivity is improved. When the input pressure decreases, the pressure in chamber B and chamber H instantaneously drops. The diaphragm 8 together with the baffle 5 descends due to the force balance failure, the distance between the nozzle 4 and the baffle 5 decreases, and the pressures in chamber G and chamber D increase , The diaphragm 3 and 15 down. Diaphragm 15 down to make the main valve opening increased, so that B and H room pressure rise until the pressure balance and set. While the diaphragm 3 down, so that the pressure port 12 open large, F room pressure rise, and always maintain constant orifice 13 before and after the pressure difference is constant. Similarly, when the output pressure fluctuates, the same adjustment will be obtained as the input pressure fluctuates. Because the setter uses the feedback effect of the output pressure and the enlargement of the nozzle baffle to control the main valve so that it can react to smaller pressure changes so that the output pressure can be timely adjusted and the outlet pressure can be kept stable, Regulator accuracy. Second, the basic performance of the valve (1) pressure regulating range: It refers to the output pressure of the pressure reducing valve P2 adjustable range, within the scope of this requirement to achieve the required accuracy. Regulating the pressure range and the main spring stiffness. (2) Pressure characteristics: It refers to the flow rate g is set value, due to input pressure fluctuations caused by the output pressure fluctuations. The smaller the output pressure fluctuation, the better the characteristics of the pressure reducing valve. The output pressure must be lower than the input pressure - the setting will not substantially change with the input pressure. (3) flow characteristics: It refers to the input pressure - timing, the output pressure with the output flow g changes in the holding capacity. When the flow rate g changes, the output pressure changes as small as possible. The lower the general output pressure, the smaller it fluctuates as the output flow changes. Third, the selection of pressure reducing valve selected according to the requirements of the type of pressure reducing valve and pressure regulator accuracy, and then select the maximum output flow according to the required diameter. When determining the air pressure of the valve, it should be greater than the maximum output pressure 0.1MPa. Pressure reducing valve is generally installed in the water after the scrubber, mist eliminator or setter before, and be careful not to import, export reverse; valve knob should be relaxed when not in use, in order to avoid the diaphragm often affected by compression deformation Its performance.