Correct Selection And Installation Method Of Orifice Flowmeter
Author:vacorda Source:www.vacorda.com Date: 2020-05-12 09:38:44
The orifice flowmeter is a high-range ratio differential pressure flow device composed of a standard orifice plate and a multi-parameter differential pressure transmitter (or differential pressure transmission, temperature transmitter and pressure transmitter), which can measure gas and steam , Liquid and natural gas flow.
The throttling device of the orifice flowmeter includes an annular orifice plate, a nozzle and the like. The throttling device (orifice flowmeter) is a collection of flow, temperature, and pressure detection functions. It has strong functions, compact structure, simple operation, and easy to use.
The orifice flowmeter throttling device produced by Sichuan Huikeda Instruments is used in conjunction with the differential pressure transmitter to measure the flow of liquid, steam, and gas. The orifice flowmeter is widely used in petroleum, chemical, "gold, power, light Industry.
The throttling device is composed of a throttling piece, a pressure taking device (including a pressure taking port, an impulse pipe and a valve, etc.), a matching flange, and sometimes includes straight front and rear pipe sections that meet the standard. Standard throttle devices include standard orifice plates, standard nozzles, and standard venturi tubes. The standard orifice plate is divided into angle connection (ring chamber or drilling), flange pressure and radial pressure according to the pressure taking method; standard nozzles are divided into nozzles and long-diameter nozzles according to the form; standard Venturi tubes are divided into Venturi according to the form Nozzle, Venturi tube (rough casting or machining or coiling). Non-standard throttling devices include small-diameter orifice plates, 1/4 round orifice plates, round orifice plates, round missing orifice plates, eccentric orifice plates, double orifice plates, internal orifice plates, conical inlet orifice plates, etc. Other forms of throttling devices include pitot tubes, uniform velocity tubes, wedges, and cones.
Notes on installation of orifice flowmeter:
(1) The straight pipe sections before and after the throttle must be straight, with no visible bends.
(2) The straight pipe section of the device throttle should be lubricated. If it is not lubricated, the flow coefficient should be multiplied by the roughness correction sparse.
(3) In order to ensure that the fluid activity is at the 1D in front of the throttle, it forms a full spread of turbulent velocity, and makes this dispersion into an average axis symmetry, so
1) The straight pipe section must be round, and for the 2D range in front of the throttle, its roundness requirements are strict, and there is a certain roundness goal. Detailed trade-offs:
(A) On the OD, D / 2, D, and 2D of the four vertical pipe sections before the throttle, at most equal angular intervals, at most, the single measurement values of the inner diameters of the four pipes are discriminated and the uniform value D is taken. The difference between the single measured value and the uniform value of the arbitrary inner diameter shall not exceed ±0.3%
(B) After the throttling device, 8 single measurements of inner diameter were measured in the OD and 2D positions by the above method. If the single measurement is compared with D, the maximum deviation shall not exceed±2%
2) Before and after the throttle piece, a straight pipe section of sufficient length is required. This straight pipe section of sufficient length is related to the mode of the partial resistance piece in front of the throttle piece and the diameter ratio β, see Table 1 (β = d / D, d is The diameter of the orifice opening, D is the inner diameter of the pipe).
(4) The length of the straight pipe section between the first resistance member and the second resistance member on the downstream side of the throttle member can be in the manner of the second resistance member and β = 0. 1/2 of the value.
(5) When the downstream side of the throttle is a closed space or a large container with a diameter ≥ 2D, the length of the straight pipe between the closed space or the large container and the throttle should not be less than 30D (15D) if the throttle and the closed space are large When there are other partial resistance parts between the containers, except for the minimum straight pipe length 1 of the rules in Table 1 between the throttling part and the partial resistance part, the straight from the closed space to the throttling part The total length of the pipe section should not be less than 30D (15D).
1. The above table is only for the standard throttle installation, and it can be used for special throttle installation
2. The number of columns is a multiple of the inner diameter D of the tube.
3. The numbers outside the brackets in the above table are the values of "the additional absolute limit error is zero", and the numbers in the brackets are the values of the "additional absolute limit error is ± 0.5%". That is, when one of the straight pipe lengths adopts the value in parentheses, the limit absolute error of flow measurement is τQ / Q. The arithmetic addition should be 0.5%, which is (τQ / Q + 0.5)%
4. If the length of the straight pipe section in practice is greater than the value in the brackets and less than the value outside the brackets, it shall be handled as "the absolute error of the additional limit is 0.5%".
(1) The direct current device is installed in the pipeline, and its front end surface must be perpendicular to the axis of the pipeline, and the maximum allowable non-vertical degree should not exceed ± 1 °.
(2) After the throttling device is installed in the pipeline, its opening must be concentric with the pipeline, and its maximum allowable eccentricity ε must not exceed the following formula to calculate the consequences: ε≤0.015D (1 / β-1).
(3) All the gaskets should not use too thick materials, it is better not to exceed 0.5mm, the gaskets cannot protrude inside the pipe wall, otherwise it will cause a large measurement error.
(4) Whereas the valve for regulating flow should be installed beyond the minimum pipe length after the throttle
(5) Throttling devices installed on process pipes must be stopped after pipe cleaning and purging.
(6) Pressure-taking method for installation of throttling in degree or inclined piping.