1 thematic content and scope of application
This standard specifies the pump flow measurement method.
This standard applies to centrifugal pumps, mixed flow pumps, axial flow pumps and vortex pumps and other pump flow measurement. Other pumps can also refer to use.
2 reference standard
GB2624 flow rate throttling device The first part: throttling pieces for the angle access pressure, flange standard pressure plate and take standard pressure nozzle.
GB3216 centrifugal pump, mixed flow pump, axial flow pump and vortex pump test methods
JJG198 turbine flow transmitter verification procedures
3 Name, symbols, definitions and units
This standard uses the amount of name, symbols, definitions and units in Table 1 ~ Table 3.
4 standard orifice, standard nozzle and standard venturi nozzle
4.1 standard orifice, the standard nozzle
The use of orifice and nozzle flow measurement, should be used in line with the provisions of GB2624 standard orifice and standard nozzle.
4.1.1 The inner surface of the measuring tube shall be clean, free of potholes and deposits and shall not be fouled to at least 10D upstream and 4D downstream.
4.1.2 When measuring the temperature of the fluid outside the normal temperature range, the measuring pipe section and the flange shall be insulated at least for the entire straight pipe section required.
4.1.3 In addition to 2D from the throttle, the pipe between the throttle and the first upstream drag or spoiler may consist of one pipe segment or several pipe segments.
As long as the misalignment y between any two pipe sections does not exceed 0.3% D, the flow coefficient has no additional uncertainty.
If the misalignment y between any two pipe sections exceeds 0.3% D, the uncertainty of the flow coefficient should be arithmetically added ± 0.2% of the additional uncertainty if the relationship of (1) or (2) is satisfied. If the misalignment Greater than (1) or (2) given the limit, that is, the installation does not meet the requirements of this standard.
Y / D ≤ 0.002 · j / D + 0.4 / 0.1 + 2.3β 4 (1)
Y / D ≤ 0.05 (2)
The diameter of the downstream straight pipe section shall be within ± 3% of the average diameter of the upstream straight pipe section, at least along the length of the upstream end face 2D of the throttle member.
4.1.4 Ducts shall be provided with vents, but no fluid should flow through these vents during the flow measurement. Exhaust vents shall not be located near the throttle, and if they have to be located near the throttle, the diameter of these vents should be less than 0.08D and their straight line from the orifice on the same side of the throttle The distance should be greater than 0.5D.
4.1.5 Throttle and pressure ring outdoor installation location should meet the following requirements:
Throttling pieces should be perpendicular to the center line of the pipe, the deviation should be within ± 1.0 °.
b. Throttling pieces should be concentric with the pipe. If using pressure ring, it should be concentric with the pressure ring. The distance ex between the centerline of the hole and the pipe centerline upstream and downstream should satisfy the relation of (3)
ex ≦ 0.0005D / 0.1 + 2.3β4 (3)
If ex is the relationship of (4), the uncertainty of flow coefficient a should be arithmetically added with additional uncertainty of ± 0.3%. If ex is the relationship of (5), it is beyond this standard:
0.0005D / 0.1 + 2.3β4 <ex ≦ 0.005D / 0.1 + 2.3β4 (4)
ex> 0.005D / 0.1 + 2.3β4 (5)
c. When using the pressure ring, should take pressure ring does not protrude into the tube.
4.1.6 Clamping methods and gaskets shall meet the following requirements:
a. Throttling pieces installed in place, should remain intact. When the throttle is fixed between the flange should be free to thermal expansion to avoid buckling and deformation;
b. When using the gasket, the gasket should not protrude into the tube at any point. When using the corner access pressure, it should not block the access hole or pressure trough. Gasket should be as thin as possible, in no case more than 0.03D;
c. If gaskets are used between the restrictor and the pressure ring, the gaskets must not protrude into the ring chamber.
4.1.7 Uncertainty of Flow Coefficient of Standard Orifices: The relative uncertainty of a is shown in Table 4, assuming that β, D, Re and k / D are known and have no error.
Uncertainty of the standard nozzle flow coefficient: Assuming that β, D, Re and k / D are known and have no error, the relative uncertainty of a is:
0.8% when β≤0.6;
When β> 0.6, it is (2β-0.4)%.
4.1.8 Pipeline conditions and installation requirements shall comply with the provisions of Chapter 4 GB 2624.
Flow regulation, it is recommended to set the throttle on the downstream side of the valve to carry out. Rectifier can be used when it is necessary to regulate the flow with the upstream side of the throttle.
4.1.8.1 The rectifier is installed on the straight pipe between the throttle and the upstream regulating valve. The length of the straight pipe between the valve and the inlet of the rectifier shall be at least equal to 20D and the length between the outlet of the rectifier and the throttle shall be equal to at least 22D. And only when the rectifier choke tube around the smallest gap, so that there is no bypass flow can interfere with the correct role, the rectifier is fully effective. Using a rectifier that meets the above installation conditions does not require any additional uncertainty.
4.1.8.2 Rectifier standard form points A, B, C three, as shown in Figure 1. These rectifiers result in pressure losses that are approximately 5 (1/2 · pu2) for type A rectifiers, approximately 15 (1/2 · pu2) for type B, and approximately 5 (1/2 · pu2) for type C.
A type, ZanKer type rectifier. Is composed of a perforated sheet having a circular hole of a predetermined size and a channel (each having a slot) formed by crossing a number of flat plates behind it. The major dimensions are given in Figure 1, and the plates should be of adequate strength but not unnecessarily thick.
B type, Sprenkle type rectifier. Is composed of three perforated metal plate in series, the distance between two adjacent plates is double the diameter. Preferably the chamfer is on the upstream face of the hole, and the total area of ​​the openings in each plate should be greater than 40% of the cross-sectional area of ​​the tube. The thickness of the plate to the aperture ratio of at least 1.0, the diameter of the hole should be less than 1/20 diameter. The three plates should be connected together with rods or bolts that should be analyzed on the inner circumference of the tube and, as much as possible, of the diameter of the holes, with the required strength.
C-type, tube-type rectifier. Is composed of a number of parallel tubes that are fixed together and rigidly fixed inside the tube. It is important to ensure that the individual tubes are parallel to one another and therefore parallel to the tube axis. If this requirement is not met, the rectifier itself may cause flow disturbances. At a minimum, there are 19 tubes of length greater than or equal to 20d. The tubes should be connected together and the tube bundle tangential to the tube.
Note: To reduce pressure loss, the entrance of the hole can be made as a bevel of 45 °.
4.1.9 The method of estimating the uncertainty of the flow measurement shall be carried out according to the provisions of Article 4.3 of this standard.
4.2 Standard Venturi nozzle
The standard Venturi nozzle consists of an inlet nozzle section consisting of two arcuate surfaces, a cylindrical throat and a conical diffuser tube. Standard Venturi nozzles for different diameters are geometrically similar.
4.2.1 Standard Venturi nozzle inlet nozzle size and technical requirements should be consistent with the relevant provisions of GB2624 3.3.2.
4.2.2 take the pressure drilling center to the beginning of the tapered end of the cylindrical portion e 'of the length of 0.40 ~ 0.45d, this part of the cylindrical nozzle and the cylindrical throat together determine the diameter d The total length of the cylindrical throat. This part of the inner surface processing requirements should be consistent with GB2624 standard 3.3.2 of the provisions.
4.2.3 Conical diffuser pipe directly connected with the cylindrical throat, without arc transition, the maximum diffusion angle φ up to 30 °. The length of the diffuser tube has virtually no effect on the flow coefficient, however, associated with the diffusion angle, has an impact on the residual pressure loss.
4.2.4 pressure way to take only access pressure law, the pressure device structure and technical requirements according to GB2624 standard 2.4 provisions.
4.2.5 When the diameter D is 0.065 ~ 0.500m, the diameter ratio β is 0.32 ~ 0.77 and the Reynolds number Re is 1.5 × 105 ~ 2 × 106, the standard venturi nozzle in a smooth pipe In Table 5, the table lists the relationship between the value of β4 and the flow coefficient a.
4.2.6 The outer surface of the flow-through part shall be marked with the symbol (+, -) indicating the installation direction of the standard Venturi nozzle, the manufacturing serial number, the installation direction, the designed dimension value of the pipe inner diameter D and the diameter of the cylindrical throat d Actual size value.
4.2.7 Pipeline conditions and installation requirements shall comply with the provisions of 4.1.8 of this standard.
4.2.8 Test Method According to the provisions of Chapter 5 GB 2624 standard.
4.2.9 Standard venturi nozzle flow coefficient of uncertainty, when the scope of application within the limits of 4.2.5, assuming that β is known and without error, the relative uncertainty of the flow coefficient a value by the formula 6) Calculation:
δa / a = ± (1.2 + 1.5β4)% (6)
4.3 Estimation of the uncertainty of flow measurement
4.3.1 Definition of uncertainty
Uncertainty when measuring flow with a standard orifice, a standard nozzle and a standard Venturi nozzle is that 95% of the estimated value falls within this range of true values, that is, 95% confidence.
The uncertainty of flow measurement can be expressed in terms of absolute terms or relative terms:
a. For volume flow
Flow = Q ± δQ or Flow = Q (1 ± e);
b. For mass flow
Flow = q ± δq or Flow = q (1 ± e).
Wherein the uncertainty δQ, δq should be the same as that of Q, q, then e is dimensionless when e = δQ / Q or e = δq / q.
The flow uncertainty defined in this way equals twice the standard deviation of statistical terms. The standard deviation is synthesized from the uncertainty in the quantities used to calculate the flow rate (assuming these uncertainties are relatively small and many are independent of each other). Although some of these uncertainties may actually be the result of systematic errors (where only their estimates of the maximum absolute value are known) for a single measurement device and the coefficients used for one measurement, However, if they are treated as accidental errors that conform to the Laplace-Gaussian normal distribution, they are also allowed to be synthesized.
4.3.2 Uncertainty of practical calculation method The actual calculation formula of the uncertainty of flow is as follows:
δQ / Q = ± [(δa / a) 2 + 4 (β4 / a) 2 (δD / D) 2 + 4 (1+ β4 / a) 2 (δd / d) 2 + 1/4 · (δΔP / ΔP) 2 + 1/4 · (δP1 / P1) 2] ½ (7)
Where: δa / a - flow coefficient of uncertainty, in the standard 4.1.7 and 4.2.9 are given;
δD / D - the pipe diameter of the uncertainty, by the GB2624 standard 4.3.2.1 given given maximum;
δd / d - Throttle orifice diameter uncertainty, by the provisions of 2.2.2.7 and 3.3.2.5 GB2624 standard derived maximum;
δΔP / ΔP - the uncertainty of differential pressure, depending on the measurement method;
δP1 / P1 - the density of uncertainty, according to the measurement method.
4.4 differential pressure measurement
The differential pressure ΔP for standard orifice plates, standard nozzles and standard venturi nozzles can be measured with a differential pressure gauge. The measurement uncertainty of ΔP (δΔP / ΔP) is determined according to the differential pressure meter used. If liquid column differential pressure meter is used, it should be:
a. liquid column differential pressure glass tube diameter 6 ~ 12mm;
b. The pressure in the pressure conduit and the liquid column differential pressure gauge must be completely vented;
c. Pressure catheters are generally available with an inner diameter of 6 ~ 12mm connecting pipe, the connecting pipe can be selected according to different system pressure stainless steel pipe, copper pipe, hose, transparent plastic pipe;
d. The uncertainty of differential pressure ΔP measurement of liquid column differential pressure gauge should be within ± 1.0%.
4.5 standard orifice, the standard nozzle, the standard Venturi nozzle calibration
Where the standard orifice, standard fountain nozzle and standard venturi nozzle manufactured in accordance with GB2624 and this standard shall be regularly checked for size or calibrated on a device with a high degree of uncertainty (normally one year).
5 water weir
5.1 water weir structure
Water weir by the weir and weir tank form.
5.1.1.1 Weir mouth at right angles to the medial side, lip thickness 2mm. 45 ° tilt to the outside surface, burr should be removed clean.
5.1.1.2 Weir ridge edge to be trimmed into sharp edges, not circular. The inner side of the slice should be smooth, especially from the top to 100mm area.
5.1.1.3 weir should be used stainless steel and corrosion-resistant materials.
5.1.1.4 weir plate installation must be vertical. Weir mouth should be located in the middle of the weir width, at right angles to both sides of the weir slot.
5.1.1.5 weir of various weirs as shown in Figure 5. Right angle triangle weir perpendicular bisector should be vertical, right angle tolerance of ± 5 '. The width of the weir of the full width weir and the rectangular weir shall be at a level of ± 5 ° at right angles to the weir and ± 0.001 b at the weir width.
5.1.2 weir slot by the import part of the rectifier device and rectifier parts.
5.1.2.1 weir tank (including the support plate) to be strong and not easily deformed, can be made of steel or concrete.
5.1.2.2 In the weir upstream should set the rectifier (4-5 rectifier grid), in order to reduce the fluctuations of the water surface, the recommended grid size shown in Figure 6. The width of the rectifying portion is equal to the width of the lead-in portion.
5.1.2.3 Weir groove bottom and sides should be flat, side and bottom should be vertical.
5.1.2.4 Full width Weir slot on both sides should be extended outward, shown in Figure 5. The extension of the wall should be as flat as both sides, perpendicular to the edge of the weir, with a tolerance of ± 5 ° at right angles. Extend the wall should be set up vents, vents should be close to the weir and head below, in order to ensure measurement of air inside the head smooth, vents area.
A ≧ Bhmax / 140 (8)
Where: hmax - maximum weir head, that is, the maximum water surface water to the weir bottom (right triangular weir) or weir lower edge (rectangular weir, full width weir) vertical distance, m.
5.1.2.5 The capacity of the lead-in part should be large, the width and depth of this part should not be less than the width and depth downstream of the fairing, and the conduit should be buried in water.
5.1.2.6 weir slot length shown in Figure 7, the size shown in Table 6.
5.2 weir head measuring device
5.2.1 There is a small hole in the side wall of the weir groove communicating with another small bucket to measure the water level in the bucket. Barrel and weir connection pipe length should be adapted to ensure easy and accurate measurement, diameter 10 ~ 30mm.
5.2.2 The location of the hole is from the weir (4 ~ 5) hmax, the size of the lower edge of the weir and the bottom of the weir shall not be less than 50mm. There should be no burr in the hole. The axis of the hole should be perpendicular to the weir wall .
5.3 weir head measurement method
5.3.1 Measurements shall be made of the flow of water flowing down the weir and the absence of the weir.
5.3.2 weir weir weir to weir outside the pool height of not less than 100mm.
5.3.3 You can use the crochet level gauge or buoy level gauge (shown in Figure 9) to measure the water level, but when the water level is not stable, you can not use the crochet level, you should sink the needle into the water and then put on the level to Eliminate the effects of surface tension. In addition to the above water level gauge, water level measurement accuracy can also be used not less than these two water level gauge of the other water level gauge.
5.3.4 head of the water level gauge to determine the zero point, the error should be within 0.2mm.
5.3.4.1 rectangular weir, full width weir to determine the method:
a. The first temporary measurement with a special crochet water level gauge stuck in the weir, and level with leveling, read the figure "G" value;
b. Put the water into the weir tank and make the water level lower than the weir;
c. Lower the crochet hook of the specially designed crochet hook gauge and immerse it in the water. Lift the crochet hook so that the tip is flush with the water surface. Read the difference between the "F" value and the reading G, F (" GF ") is the distance between weir mouth and weir groove surface;
d. Lower the crochet of the water level gauge, which is pre-installed at the measurement cross-section hmax to the weir (4 ~ 5) or in a small bucket, so as to level the tip with the water surface and read out the scale value. The reading minus the "GF" value, the resulting value is the head of the permanent water level gauge zero value.
5.3.4.2 right triangle weir to determine the method
a. Place a special round rod of diameter D parallel to the long axis of the weir slot on the weir, and level with a level gauge;
b. Place a special crocheted water level measuring instrument for temporary measurement on the round rod with the tip of the crochet in contact with the bottom line of the axial section of the round rod, and then follow the rectangular weir and full width weir measurement methods b, c, d get on. Subtract the value of "GF" from the reading value of the permanent water level gauge minus the value of 0.2071D, which is the zero value of the permanent water level gauge.
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