Measuring principle of throttling device in industrial gas
Throttling device in the field of industry has been widely used in gas measurement, not only can measure the general gas flow, and is suitable for containing various impurities (dust, suspension, precipitation, etc.) of the fluid, such as a variety of hot gas, flue gas, natural gas, blast furnace gas, etc. Throttling device has many advantages, but large pressure pipeline laying in propaganda work, also easy to leak, congestion and other issues. Differential pressure transducer made by leaps and bounds in recent years of development, not only small volume, and more stable, adjustment is convenient, in use process basically don't need to adjust the zero point. These merits a normal size throttle flowmeter (orifice, circular orifice, nozzle flowmeter, balance meter) of the development and application. SIKE measurement and control technology co., LTD. In this article in view of the high pressure gas circuit of the throttle device is analyzed, combining with the working principle of the throttle device and and the summary of the usage, and throttling device in the design of a brief introduction. Through the analysis to the principle of the throttle device design and practical application has certain help.
In engineering use, often as a power source, high pressure gas colleagues on some special occasions, high pressure gas refrigeration air as a product. Throttling device as can adjust the pressure device, has been widely applied in the pneumatic system.
Throttling device is actual gas resistance. Is refers to the small volume, big circulation resistance components, the form a lot, such as capillary can make it, also can make the adjustable flow device. Constant throttling device refers to when a certain amount of pressure drop and flow rate, the ratio of two to fixed value, cannot be adjusted.
Throttling device is divided into adjustable and not adjustable, an adjusting flow device generally used to change the gas flow, the use of pressure can be high, single purity have certain requirements for gas path; Adjustable throttle device is not easy to jam, the traffic is not stable, is generally used in low pressure situations. Both throttling principle is consistent, main number here the application of fixed throttle device.
Throttling principle, in the gas path, excellent throttling device is used to control the flow and pressure, the general is through the change of ventilation in the pipeline of the throttle device realizes the paint, divided into holes meter aperture throttling device, often used in pipeline for holes, cracks commonly used in the valve. Design using the throttle device is in the gas path, should follow the proportion requirements, based on the Bernoulli equation, the throttle device at the ends of the flow and pressure difference in any of the following relationships:
Q = KAT Δ PM type of q - flow through the throttle device; K - determined by the hole shape, length and gas coefficient; Δ p - before and after the orifice differential pressure; M - hole length to diameter ratio coefficient of the decision.
The practical application of the throttle device:
The throttle device can be used in the regulation of gas flow and pressure, can also be used for the stability of the gas circuit to avoid overshoot. In the standard meter, flowmeter throttle device is the typical differential pressure flowmeter, the principle is the throttle principle of throttling device. Here introduces the application of non-standard throttling device measuring gas.
Strength design:
(1) the throttle device throttling device first need to consider the strength requirement, for the throttle device can refer to the full container in pressure vessel design, for the application and the throttle device of high-pressure situations, generally will not be able to produce plastic deformation caused by insufficient sealing. Work under different temperature, if the throttle device requires the use of harsh conditions of material strength calculation. The design pressure of the throttle device should be to maximize the pressure calculation.
(2) the throttle device design: the throttle device of flow calculation, through the throttle device of pressure and flow calculation is required before and after the throttle coefficient. Under normal circumstances before and after the orifice tube diameter is greater than the throttle aperture, orifice at the same time is short, can not consider in the design of throttle hole length.
(3) the throttle device in the application of gas path flow test: test the product work flow, in conditions allow direct use of flowmeter is more convenient, the flow of products can be directly on the meter reading, when the choice, but in the flowmeter to estimate in advance the product flow, avoid the flow of traffic injury. In actual use, also can use processing of throttling device is installed in the product testing line in terms of product flow test. In the flow test, using the throttle device installed in front of the throttle device filtering device, to ensure the purity of gas medium, avoid congestion occurs.
(4) for the larger flow throttling device layout: when the flow of work product is bigger, when designing the throttle device products need to be taken into account the needs of work pressure and throttling device in front of the line pressure, and considering the accuracy of measurement. Test, can make use of the throttle device is determined, for the same kind of the characteristics of the throttle coefficient of dielectric constant, flowmeter measurement. It's important to note that in order to avoid the throttle device for pressure measuring accuracy, the influence of the throttle device to gauge the distance of the branch at least not less than 5 times the pipe diameter, pressure regulating valve exported to gauge the distance of the branch at least not less than 10 times the pipe diameter.
Before use, should according to the product flow range of throttling device in differential pressure flow calibration, calibration, replaced the above products for precision meter with regulating valve. Before throttling pressure regulating valve to the input pressure gauges for pressure value and stability, and ensure the valve 1 open, then open valve and control valve to gradually adjust the flow meter with the 2 stable output pressure, so that you can get a in the input pressure under certain conditions, the output pressure gauge and a corresponding relation between the output flow, according to the measuring accuracy requirement, can increase the number of calibration points, could discern a fragment of differential pressure flow diagram as follows:
The precision of measuring way depends on the degree of density calibration point, at the same time and the precision of the pressure gauge and the throttle device of throttling capability. Throttling ability in general, the throttle device, the better, then the same flow conditions, the greater the differential value of throttling device segment, but should consider the pressure of product measurement needs.
(5) the flow is small throttling device layout: when the medium very hour work flow, using the previous method of flow measurement is not accurate, the main principle of the pressure difference between two pressure gauge is very small, so reading error caused by a lot. By this time the medium can be used as a cylinder, by measuring a period of time within the pipeline pressure drop method to measure the average of the medium flow. The diagram below:
In the gas path calibration, are also replaced the product media for regulating valve of flow meter, then open the valve and valve 2 1, adjust the pressure regulating valve and pressure gauge pressure to the need to stress and stability, then the throttle flowmeter flow for a certain, then close the valve timing starts 2, to a certain time, it can be concluded that under a certain flow pressure gauge pressure value. Then also can undertake other flow condition of pressure calibration, it is important to note each initial pressure calibration of pressure gauge should be certain; Another connection flow time, the line capacity and connection line of the real product medium capacity as consistent as possible, in order to improve the calibration results.
(6) the throttling device in the application of gas path stability: in general gas path, used in the stability of airflow is air capacity, but the capacity is to hero the quickness of gas circuit work. So is considering rapid oil to reduce the overshoot of the airflow occasions to consider using the throttle device. Here it is important to note that the application of throttle device and the relief valve is not the same, the throttle device in air pressure, the air consumption, but stress hour consumption is small.
In throttling device measurement system design, using the high pressure gas after reducing valve to drive the piston movement, tests, to measure to air missile cylinder piston movement to a certain position of time, and on the job requirements of the working pressure is certain. Using pressure regulating valve can be starting from scratch. The diagram below: