Introduction to the principle of the hottest press

2022-08-24
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Introduction to the principle of pressure reducing valve

I. working principle of pressure reducing valve

direct acting pressure reducing valve

compressed air with pressure of P1 is input from the left end and throttled through valve port 10, and the pressure drops to P2 output. The size of P2 can be adjusted by the pressure regulating springs 2 and 3, that is, on the basis of different fixtures. Rotate knob 1 clockwise, compress springs 2, 3 and diaphragm 5 to move valve element 8 downward, and increase the opening of valve port 10 to increase P2. If you rotate knob 1 counterclockwise, the opening of valve port 10 decreases, and P2 decreases accordingly

if P1 rises instantaneously, P2 will rise accordingly, causing the pressure in diaphragm air chamber 6 to rise, and the thrust generated on diaphragm 5 to increase accordingly. This thrust destroys the balance of the original force, causing diaphragm 5 to move upward, and a small part of the air flow is discharged through overflow hole 12 and exhaust hole 11. When the diaphragm moves up, due to the action of the return spring 9, the valve element 8 also moves up, the inlet valve port 10 is closed down, the throttling effect is increased, and the output pressure drops until a new balance is reached, and the output pressure basically returns to the original value. If the input pressure drops instantaneously, the output pressure also drops, the diaphragm 5 moves down, the valve element 8 moves down, the inlet valve port 10 opens larger, the throttling effect decreases, and the output pressure basically returns to the original value. Turn knob 1 counterclockwise. Loosen the adjusting springs 2 and 3, the thrust of the gas acting on the diaphragm 5 is greater than the force of the pressure regulating spring, the diaphragm bends 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 inlet valve element 8 will be separated from the overflow valve seat 4, 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 a no output state

in short, the overflow pressure reducing valve is reduced by the throttling effect of the air inlet, and stabilized by the balance effect of the force on the diaphragm and the overflow effect 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 pressure reducing valve from polluting the surrounding environment with a small amount of gas, the pressure reducing valve without overflow valve (i.e. ordinary pressure reducing valve) can be used

pilot operated pressure reducing valve

when the output pressure of the pressure reducing valve is high or the diameter is large, use the pressure regulating spring to directly regulate the pressure, then 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, a pilot pressure reducing valve can be used. The working principle of the pilot pressure reducing valve is basically the same as that of the direct acting valve. The pressure regulating gas used by the pilot pressure reducing valve is supplied by a small direct acting pressure reducing valve. If the small direct acting pressure reducing valve is installed inside the valve body, it is called 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. It is the structure diagram of the internal pilot pressure reducing valve. Compared with the direct acting pressure reducing valve, the valve adds a nozzle baffle amplification link composed of nozzle 4, baffle 3, fixed orifice 9 and air chamber B. When the distance between the nozzle and the baffle changes slightly, the pressure in chamber B will change significantly, resulting in a large displacement of the diaphragm 10, so as to control the up and down movement of the valve element 6, so that the inlet valve port 8 is opened or closed, which improves the sensitivity of the valve element control, that is, improves the pressure stabilization accuracy

the working principle of the main valve of the external pilot pressure reducing valve is the same as that of the direct acting type. There is also a small direct acting pressure reducing valve (not shown in the figure) outside the main valve body, which controls the main valve. This kind of valve is suitable for occasions with a diameter of more than 20mm, long distance (within 30m), high places, dangerous places and difficult pressure regulation

valuer

another more important problem of the valuer is that the concrete pressure testing machine for toughening agent measures and judges the performance parameters of concrete according to the national standard gb/t50081 ⑵ 002 "standard for experimental methods of mechanical properties of ordinary concrete". A large number of added performance parameters of concrete is a high-precision pressure reducing valve, which is mainly used for pressure setting. At present, there are two pressure specifications of setters: first, the air source pressure is 0.14MPa and 0.35Mpa respectively, and the output pressure range is.1mpa and 0-0.25mpa respectively. Its output pressure fluctuation is not greater than 1% of the maximum output pressure, which is often used in occasions where accurate air source pressure and signal pressure need to be supplied, such as pneumatic experimental equipment, pneumatic automatic devices, etc

working principle of the valuer. It consists of three parts: 1. The main closing 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 function is to make the nozzle obtain stable gas flow; 3 is the nozzle baffle device and pressure regulating part, which plays the role of pressure regulation and pressure amplification, and uses the amplified air pressure to control the main valve part

because the valuer has the functions of setting, comparison and amplification, the voltage stabilization accuracy is high

when the valuer is not working, the compressed air input from the air source enters chamber a and main chamber after being filtered by filter 1. The main valve element 19 is pressed on the valve seat under the action of spring 20 and air supply pressure, so that chamber a and chamber B are disconnected. The air flow entering chamber a flows through valve port (also known as valve) 12 to chamber F, then depressurizes through constant orifice 13, and then enters chamber g and chamber D respectively. Since the diaphragm 8 is not forced at this time, the spacing between baffle 5 and nozzle 4 is large, the airflow resistance of gas flowing out of nozzle 4 is small, the air pressure of chamber g and chamber D is low, and the diaphragms 3 and 15 remain in their original positions. The trace gas entering the chamber is mainly discharged from the exhaust port through valve port 2 through chamber B; Another part is emptied from the outlet. At this time, there is no air flow output at the output port, and the discharge of trace gas from the nozzle is necessary to maintain the operation of the nozzle baffle device. Because it is a non power consumption air volume, we hope that the smaller the consumption is, the better

when the valuer is in the working state, turn the handle 7, press the spring 6 and push the diaphragm 8 to move down together with the baffle plate 5. The spacing between the baffle plate 5 and the nozzle 4 is reduced, and the air flow resistance increases, raising the air pressure of chamber g and chamber D. The diaphragm 16 moves down under the action of the air pressure in chamber D, closes the valve port 2, and pushes the main valve core 19 downward to open the valve port. The compressed air is output from the output port through chamber B and chamber H. At the same time, the pressure in chamber h rises and is fed back to diaphragm 8. When the feedback force on diaphragm 8 is balanced with the spring force, the valuer will output a certain pressure of gas. When the input pressure fluctuates, such as the pressure rises, the air pressure in chambers B and H increases instantaneously, causing the diaphragm 8 to move up, resulting in an increase in the spacing between baffle 5 and nozzle 4, and a decrease in the air pressure in chambers g and D. As the pressure of chamber B increases, the pressure of chamber D decreases, and the diaphragm 15 moves upward under the action of pressure difference, 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 pressure of chamber E and the instantaneous pressure of chamber f also rise, and the diaphragm 3 moves up under the action of the upper and lower differential pressure, closing the pressure stabilizing valve port 12. As the throttling effect is strengthened, the air pressure in chamber f decreases, and the pressure difference between the front and rear of orifice 13 is always kept constant, so the gas flow through orifice 13 remains unchanged, which improves the sensitivity of nozzle baffle. When the input pressure decreases, the pressure in chambers B and H decreases instantaneously, the diaphragm 8 and baffle 5 move down due to the destruction of the force balance, the spacing between nozzle 4 and baffle 5 decreases, the pressure in chambers g and D increases, and the diaphragms 3 and 15 move down. The diaphragm 15 moves down 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 down, so that the pressure stabilizing port 12 is opened, and the air pressure in chamber f rises, and the pressure difference before and after the constant orifice 13 is always kept constant. Similarly, when the output pressure fluctuates, it will get the same adjustment as when the input pressure fluctuates

because the valuer uses the feedback effect of the output pressure and the amplification effect of the nozzle baffle to control the main valve, so that it can respond to small pressure changes, so that the output pressure can be adjusted in time to keep the outlet pressure basically stable, that is, the accuracy of the constant pressure is high

II. Basic performance of the pressure reducing valve

(1) pressure regulating range: it refers to the adjustable range of the output pressure P2 of the pressure reducing valve, within which the specified accuracy is required. The pressure regulating range is mainly related to the stiffness of the pressure regulating spring

(2) pressure characteristic: it refers to the characteristic of output pressure fluctuation caused by input pressure fluctuation when the flow G is a fixed value. The smaller the output pressure fluctuation, the better the characteristics of the pressure relief valve. The output pressure must be lower than the input pressure - the fixed value will basically not change with the input pressure

(3) flow characteristics: it refers to the persistence of input pressure - timing, and output pressure changing with the change of output flow G. When the flow rate G changes, the smaller the change of output pressure, the better. Generally, the lower the output pressure is, the smaller its fluctuation with the change of output flow is

III. selection of pressure reducing valve

select the type and pressure regulating accuracy of the pressure reducing valve according to the use requirements, and then select its diameter according to the required maximum output flow. When determining the air supply pressure of the valve, make it greater than the maximum output pressure by 0.1MPa. The pressure reducing valve is generally installed after the water separation air filter and before the oil mist or setting device, and pay attention not to connect its inlet and outlet reversely; When the valve is not in use, the knob should be loosened to prevent the diaphragm from being often compressed and deformed, which will affect its performance

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