The establishment of piston gas flow device

Abstract: The information on the establishment of the piston gas flow device is provided by the excellent flowmeter and flowmeter production and quotation manufacturers. Keywords: piston type, gas flow, mass transfer system 1. Characteristics of gas piston device Accurate standard volume value: The standard volume is only related to the descending distance of the piston and the diameter of the cylinder, and there are few related influencing factors. Good repeatability: In principle, it repeats. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the establishment of the piston gas flow device. Keywords: piston type, gas flow, mass transfer system 1. Characteristics of gas piston device The standard volume value is accurate: the standard volume is only related to the distance of the piston and the diameter of the cylinder, and there are few related factors. Good repeatability: In principle, the repeatability is only related to the change of the cylinder area, the repeatability of the grating measurement and the deformation of the sealing ring, and these factors are very small. Large internal pressure: The balance pressure in the cylinder can be adjusted by filling the cylinder with compressed air. The maximum internal pressure of this device can reach 200kPa (gauge pressure 100kPa). Stable flow: Since the flow value is the product of the piston running speed and the cross-sectional area of ​​the cylinder, the piston is driven by the servo motor, and the rotation speed of the servo motor is easy to adjust and control, so during the test, the flow can be easily achieved and stabilized at Set the flow point on. Pressure stability: The flowmeter that has a proportional relationship between the flow rate and the pressure difference can achieve pressure stability in a short period of time by relying on the self-leveling relationship between the flow rate and the pressure difference during the test. Second, the working principle 1. The working principle is shown in the figure, when the device is working, the piston moves downward, and the gas in the cylinder is discharged through the pipeline and the flow meter. When the piston moves downward at a constant speed, the pressure in the cylinder gradually reaches a stable value after a rising process. It is considered that the temperature, pressure and volume of the gas do not change during this process. Since the inner diameter of the cylinder is known, the volume value of the gas exhausted by the piston running a certain distance can be calculated. Take this as the standard volume flow and compare it with the indicated value of the flowmeter to detect the flowmeter. 2. System composition The piston gas flow device is mainly composed of servo motor, reduction mechanism, ball screw, grating, piston cylinder, piston, temperature measurement system, pressure measurement system, pipeline and inlet and outlet valves, computer data acquisition and control system etc. composition. 3. Volume flow calculation method Calculate the volume value of the gas discharged by the piston descending: Vs=A*h (1) In the formula: A——Cylinder block area, m2;h——The effective descending height of the piston, m; it is considered that the temperature and pressure of the gas in the cylinder remain unchanged, so the volume of gas discharged by the piston is the cumulative flow value of the gas passing through the flowmeter. That is: Vp=Vs (2) The instantaneous volume flow of gas through the flowmeter is: qs=Vp/t (3) In the formula: qs——Mass flow given by standard device, kg/s;t——Test time, s; 3. Mechanical structure The core parts of the piston gas flow device are the piston and the cylinder. It is the piston cylinder and the piston that form the closed space in the cylinder to provide an accurate volume for flow measurement. The piston translates along the cylinder axis in the cylinder during operation. On the premise of ensuring sealing, the inner cross-sectional area of ​​the piston cylinder is the same as the piston The product of the moving distance is the standard cumulative flow given by the device. Therefore, the design of the device is mainly centered on ensuring the seal between the piston and the piston cylinder, the geometrical tolerance of the piston cylinder, and the dimensional tolerance indicators, combined with factors such as the performance-price ratio under domestic machining conditions. The mechanical structure of the device is mainly composed of cylinder block, piston, stroke measurement system, deceleration and lead screw system, sealing system, base and reinforcing rod, inlet and outlet pipelines and valves, etc. 1. Stability and rationality of the overall structure According to the structure and operation process of similar devices, the piston cylinder should be placed vertically, which has the following characteristics: a. The cylinder is uniformly stressed and not easily deformed. b If the oil used for sealing in the cylinder leaks and accumulates, it will not affect the standard volume value. c. The weight of the piston will increase the pressure in the cylinder to a certain extent. d is conducive to the smooth operation of the piston, and is not easy to cause crawling at low speed. Since the motor and transmission system are located on the piston cylinder, three additional rods are added to increase the stability and system rigidity. The upper rod is connected with the tray, and the bottom is connected with the base. 2. The total volume of the piston cylinder is calculated by the design flow rate, and the diameter-height ratio of the piston cylinder is considered, and the size of the piston cylinder is set as: Ф200mm×800mm, of which the upper and lower 100mm of the cylinder is the non-working area. During processing, it is mainly to ensure the shape and position tolerance of the non-cylindrical degree of the inner circle of the cylinder within 600mm in the middle of the cylinder. ①Determination of the wall thickness of the cylinder The wall thickness of the cylinder should be able to meet the requirements for the strength and rigidity of the cylinder under normal working conditions. The wall thickness of the cylinder is calculated from the radial and circumferential allowable stresses and strains of the cylinder. Get the cylinder wall thicknessδ=8.6mm. Therefore, the wall thickness of the cylinder block is selected to be 10mm.

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