Correct installation and selection of orifice flowmeter
Correct Installation And Selection Of Orifice Flowmeter
Orifice flowmeter is a throttling device and a differential pressure sensing element for measuring flow.Combined with differential pressure transmitter and realistic, recording, integrating and adjusting instruments, it can be used to measure, integrate and control the instantaneous and cumulative flow of liquid, steam and gas.
The throttle device has the advantages of simple structure, convenient installation, reliable use, low price, convenient maintenance and wide selection range (the pipe diameter measured by the standard throttle device can range from 50mm to 1200mm, and the pipe diameter applicable to the non-standard throttle device can be as small as 6mm or as large as 3000mm;Measuring temperature can be as high as 555 ℃;Pressure resistance up to 42MPa), and the standard throttling device has the advantages of no separate calibration, is the flow meter in the most widely used, the most mature one of the products, so widely used in electric power, chemical, metallurgy, petroleum, textile, military and other fields.
Throttling device consists of throttling device, pressure extraction device (including pressure outlet, pressure guide pipe and valve, etc.), supporting flange, sometimes including the front and rear straight pipe section in line with the standards.Standard throttle device has standard orifice plate, standard nozzle, standard venturi pipe.Standard orifice plate is divided into angular joint (ring chamber or drilling hole) for pressure taking, flange for pressure taking, diameter distance for pressure taking;Standard nozzles are divided into formal nozzles and long-diameter nozzles.The standard venturi pipe is in the form of a venturi nozzle, venturi pipe (roughcast or machined or rolled).Non-standard throttle devices include small-diameter orifice plate, 1/4 round orifice plate, round orifice plate, round hole plate, eccentric orifice plate, double orifice plate, inner orifice plate, tapered inlet orifice plate, etc.Other forms of throttling devices include pitot tube, equal-velocity tube, wedge, cone, etc.
When using a standard throttling device, the properties and state of the fluid must meet the following conditions:
(1) the fluid must be filled with pipes and throttling devices and continuously flow through the pipe;
(2) the fluid flow does not change with time or changes very slowly;
(3) no intersections occur when the fluid flows through the throttle;
(4) the fluid must be Newtonian, that is, physically and thermodynamically uniform, single-phase, or can be considered to be single-phase, including mixed gas, solution and dispersible particles less than o.1 m of colloid.In the gas has not more than 2% (mass component) uniform dispersion of solid particles, or liquid has not more than 5% (volume component) uniform dispersion of bubbles, can also be considered as a single-phase fluid, but its density should take the average density;
(5) before the fluid flows through the throttle, the flow beam is non-swirl flow parallel to the pipe axis.
Standard throttling devices are not suitable for dynamic and critical flow measurements.Throttle device is artificially caused in the medium flow pipe throttling, when the measured media flow through the throttling device, resulting in a local contraction, flow beam concentration, flow rate increase, static pressure reduction, so in the upper and lower reaches of the throttle parts on both sides of a static pressure difference.There is a certain functional relationship between the static pressure difference and the flow rate. The larger the flow rate is, the greater the static pressure difference will be. Therefore, the flow rate can be measured by measuring the differential pressure.
Orifice plate flowmeter is different from other flowmeters is orifice plate flowmeter is designed according to the parameters drawings, the final processing production, only according to the measurement of the media to choose the quality of the orifice plate on the line.
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