Corner joint pressure tapping eight slot orifice plate (nozzle) throttling device Applicable pressure: PN ≤ 10MPa Range: 50mm ≤ DN ≤ 400mm Ring chamber pressure tapping throttling device, flange pressure tapping throttling device, drilling pressure tapping throttling device Introduction: 1. Working principle of throttling device: Orifice plate is the most traditional and long-standing flow measurement method, with a series of advantages such as strong adaptability to measuring media, high temperature and high pressure resistance, highest standardization degree, and no need for real flow calibration. It is still the national standard for flow measurement in some developed countries and occupies a dominant position in flow measurement. When the fluid (Newtonian fluid) enters the throttling device through a straight pipe section, due to the action of the throttling element, the flow cross-section of the pipeline is reduced, and some of the potential energy of the fluid is converted into kinetic energy. The fluid flow velocity at the contraction cross-section increases, and the static pressure decreases. Therefore, a static pressure difference is generated before and after the throttling element. The larger the fluid flow velocity, the greater the change in fluid flow velocity at the contraction cross-section, resulting in a larger static pressure difference before and after the throttling element. By measuring the static pressure difference (i.e. differential pressure) before and after the throttling element, the fluid flow rate in the pipeline can be measured When the fluid flows through the throttling device, it satisfies the fluid continuity equation and Bernoulli equation, and thus derives the fluid flow equation: qm=[C/(1- β 4)] × ε× A0 × (2 × ρ 1 × Δ p) 0. In equation 5: qm - fluid flow rate; C - outflow coefficient; β=ratio of d20/D20 orifice plate aperture to pipeline inner diameter (aperture ratio); ε - coefficient of beam expansion (for liquid, ε=1); A0=π d2/4 flow area of orifice plate; ρ 1- fluid density in front of the orifice plate; Δ p - static pressure difference before and after the orifice plate. There are various ways to measure the pressure difference before and after the orifice plate, including the ring chamber pressure measuring and throttling device, flange pressure measuring and throttling device, and drilling pressure measuring and throttling device, which have been widely used for a long time. 2. Structural form: 1. Ring chamber pressure measurement: (Figure 1) Ring chamber pressure measurement throttling device, also known as corner joint ring chamber pressure measurement throttling device. Structure as shown in the figure: The positive ring chamber is installed on the upstream side of the orifice plate to measure the static pressure upstream of the orifice plate. The negative ring chamber is installed on the downstream side of the orifice plate to measure the static pressure downstream of the orifice plate. The pressure measured upstream and downstream is input into the differential pressure transmitter to obtain the differential pressure of the orifice plate. Input the measured differential pressure into electronic instruments such as square root calculators and flow integrators to obtain the flow value. The characteristic is that the pressure tapping holes are located on both sides of the orifice plate close to the orifice plate (so it is called corner tapping). Due to the average effect of the pressure tapping rings on both sides of the orifice plate on the pressure entering it, the measured differential pressure is relatively accurate, which is very suitable for situations where the measuring medium is single, clean, and requires high measurement accuracy. Mainly used for measuring relatively clean steam, water, and gas. Widely used in industries such as chemical, power, petroleum, cotton textile, steel, etc. The processing requirements for the ring chamber: Generally, the inner diameter of the ring chamber should be equal to the inner diameter of the pipeline, but the standard stipulates that D ≤ D1 ≤ 1.04D, which means that the inner diameter of the ring chamber can be slightly larger than the inner diameter of the pipeline, but must not be smaller than the inner diameter of the pipeline. If it is smaller than the inner diameter of the pipeline, it will introduce significant measurement errors. The pressure ring should be smooth and free of burrs, and the two sealing end faces of the ring chamber should be parallel, ensuring that the plane of the orifice plate is perpendicular to the axis of the pipeline and that the axis of the hole in the orifice plate is basically aligned with the axis of the pipeline. At the same time, the sealing gasket between the positive and negative ring chambers and the flange shall not protrude into the pipeline, and the sealing gasket between the orifice plate and the negative ring chamber shall not protrude into the negative ring chamber groove. Disadvantages of the pressure throttling device in the ring chamber: a. Medium requirements: ① The measured medium must not contain impurities, such as dust in gas or steam media, or small amounts of solid particles in liquid media, which may accumulate in the pressure chamber and affect measurement accuracy. Therefore, regular maintenance is required. Increase maintenance costs. ② The viscosity of the medium should not be too high. When the viscosity of the medium is too high, the delay effect of the pressure ring chamber on the fluid may cause instability in pressure measurement. b， Not suitable for larger pipelines, such as when D ≥ 450mm, the production cost of the pressure ring chamber is high, and installation and maintenance are difficult. c， When the pressure is not too high, such as P>10Mpa, it is difficult to solve the sealing problem. 2. Flange pressure tapping: (Figure 2) The flange pressure tapping throttling device, also known as one inch flange pressure tapping, has pressure tapping holes located one inch (25.4mm) on both sides of the orifice plate. The structure is as shown in the figure: one pressure tapping hole is drilled on each one inch position of the flange on both sides of the orifice plate to obtain differential pressure. The structure is simple and easy to maintain. The characteristics are: 1. The pressure level can be made very high, with a pressure range of P=1.6Mpa to 42.0Mpa. 2. The requirements for the medium are slightly looser than those for the ring chamber pressure measurement. When there are slight impurities in the fluid medium, the pressure tube is also less likely to block and affect the measurement. 3. Suitable for fluid media with high viscosity. 4. Easy installation and maintenance. Mainly used in industries such as chemical, oil refining, and petroleum. The processing requirements for flange pressure tapping: 1. The sealing surface of the flange should have a high degree of smoothness; 2. The flange end face should be perpendicular to the flange center axis; 3. The flange pressure hole should be free of burrs. The disadvantage of the flange pressure throttling device is that its measurement accuracy is slightly lower compared to the ring chamber pressure. b， The processing cost of the device is relatively high. C， Not suitable for larger pipelines, such as when D ≥ 450mm, the production cost is high and installation and maintenance are difficult. 3. Drilling pressure throttling device Drilling pressure throttling device, also known as corner drilling pressure throttling device, has a structure of drilling one pressure hole on each flange or throttling element near the orifice plate to obtain pipeline pressure, with a simple structure. Characteristics: 1. Suitable for larger pipe diameters, with a diameter of D=6-3000 and above. 2. The pressure can be very high, with a pressure range of P=0.25-32.0Mpa. Mainly used for flow measurement in chemical engineering (small pipe diameter 250 ≤ D (Figure 4)), steel (large pipe diameter D ≥ 350 (Figure 3)), central heating pipelines, etc. 3. Easy installation and maintenance four Installation requirements: 1. Pay attention to the flow direction of the medium. The medium should flow from the right angle side of the hole in the orifice plate to the side with a 45 degree angle. 2. Generally, all fasteners of the throttling device should be tightened before connecting the throttling device as a whole to the pipeline to ensure the sealing performance of the throttling device. 3. Do not damage the throttle component during installation.