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Nanjing Jinnuo Instrument Co., Ltd
Differential pressure flowmeter standard orifice plate
NegotiableUpdate on 01/05
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Overview
The throttling device, also known as the throttling differential pressure flowmeter, is a type of flowmeter with a long history and the largest usage. It is divided into two categories: standard throttling devices and non-standard throttling devices. Any design, installation, and use that complies with the international standard IS05167 and/or the national standard GB/T2624 are called standard throttling devices, while others are non-standard throttling devices. Standard orifice plate is a product with a simple structure, easy installation, and strong adaptability in standard throttling devices. Differential pressure flowmeter standard orifice plate
Product Details
1、 Purpose, characteristics, and scope of applicationDifferential pressure flowmeter standard orifice plate
1. Purpose: The throttling differential pressure flowmeter consists of three parts: throttling device, differential pressure transmitter, and flow accumulator. The throttling device is a primary element directly installed on the pipeline, and the differential pressure transmitter and integrator are secondary elements. It is mainly used for the flow of various gases (pure or dusty), steam (saturated or superheated), and liquids (conductive or non-conductive; highly corrosive; viscous or containing tiny particles of dirt) through pipelines. It can directly measure volumetric flow rate or mass flow rate.
2. Differential pressure flowmeter（standardOrifice plate)The conditions for useCharacteristics and Scope of Application
a、Terms of Use：
1) In the measurement section,The fluid must fill the circular tube continuously and continuouslylandFlow through the throttling device;
2)The fluid must be a homogeneous single-phase fluid both physically and thermodynamically;
3)The fluid measured by the throttling device must be a stable flow, or can be regarded as a stable slowly changing fluid, and is not suitable for pulsating flow and critical flow measurement;
b、 Characteristics and scope of application:
1) The standard throttling device does not require real flow calibration to ensure its measurement accuracy.
2) It is widely applicable to the measured medium and can be used for flow measurement of almost all gases, vapors, and liquids;
3) Applicable diameter ratio β is 0.22-0.75, Reynolds number ReD ≥ 5000, pipeline diameter DN50~1000mm, allowing extrapolation to 5000mm. β=d/D, d - orifice plate opening diameter; D - Actual inner diameter of pipeline
4) The pressure can reach up to 32MPa and can also be used for negative pressure;
5) Medium temperature range: -30 ℃ to+650 ℃;
6) The intelligent differential pressure flowmeter adopts an intelligent differential pressure transmitter, which can set the differential pressure value (within the specified range) on site through buttons or communication methods according to the changes in the flow rate of the measured object, thereby changing the flow range and greatly expanding the system flow range;
7) No movable parts, the mechanism is safe and reliable, easy to use and operate, easy to master, and maintenance free;
According to the national standards of the People's Republic of ChinaGB/T2624-93 and international standard ISO5167-1 stipulate that the flow range ratio applicable to throttling devices is 3 (i.e. the ratio of maximum and minimum applicable flow rates), and in some cases, a range ratio of 4 is allowed. If the range ratio is greater than the above value, the measurement error at low flow rates using the same differential pressure meter will be significant
2、 Working principle
The principle of measuring flow rate with a throttling device is based on the famous Bernoulli fluid dynamics principle. As shown in the picture（1) When a throttling element is placed in the pipeline as shown, a pressure difference (differential pressure P) will be generated on both sides of the throttling element when fluid flows through it. At this time, the flow rate is proportional to the square root of the differential pressure, that is:
Volume flow rate:
In the formula: A: constant;C: Outflow coefficient;β: Diameter ratio (=d/D)；d: Throttle element aperture (mm);ε: Coefficient of expandability;△ P: Differential pressure before and after the throttle element (Pa);ρ: Fluid density under working conditions (kg/m)3）；
3、 ClassificationAnd structural diagram
1. Classification
① Classified by flange clamping method
(1) Welding type (2) flange clamping type
② Classified by pressure collection method
(1) Corner drilling for pressure measurement; (2) Pressure measurement of corner joint chamber
(3) Flange pressure measurement; (4) Radial pressure measurement;
2. Structure and schematic diagram
① Figure 2 Structure diagram of standard annular orifice plate throttling device
1. Flange 2, pressure pipe
3. Front chamber 4, throttling element
5. Rear chamber 6, sealing gasket
7. Bolt 8, Nut
4、 Structure and schematic diagram
② Various standard orifice plate structures, as shown in Figure 3
Figure 3
5、 Installation and use precautions: Differential pressure typeFlow meter standard orifice plate
1. Approval parameters: Before installation, it is necessary to verify the on-site working conditions and confirm that all parameters in the throttling device calculation sheet are the same as the installation point working condition parameters * * before installation can proceed,Otherwise, necessary corrections or compensation must be made.
2. Direction: There are "+" and "-" marks on the orifice plate handle or flange outer surface of the throttling device, respectively, with "+" indicating the upstream side（Facing the direction of the fluid）Do not reverse.
3. Insertion depth: The pressure tapping hole plate in the ring chamber is inserted at a depth of 2-5mm between the pipeline and the ring chamber, but the pipeline cannot be pushed into the ring chamber, otherwise the pipeline will expand due to heat and damage the ring chamber. Drill a pressure tapping hole plate, and the pipeline protruding into the hole plate must not block the pressure tapping hole at any point.
4. System blowing: After the installation of the throttling device is completed, it should be blown. At this time, the throttling element (orifice plate) should be removed first to prevent debris in the pipeline from scratching the orifice plate or blocking the pressure pipe. After the blowing is completed, it should be installed in the same direction as the arrow on the orifice plate and the direction of fluid flow. Pay attention to tightening to ensure sealing.
5. Zero adjustment: After the purging and installation are completed, open the middle valve of the three valve group. At this time, the differential pressure value should be zero. If it is not, it must be reset to zero. The method is to hold down the button in the lower left corner for 20 seconds and release it.
6. Finally, slowly close the middle valve of the three valve group (it must be tightly closed), open all the shut-off valves on the upper part of the positive and negative pressure pipes, and the orifice plate can work normally.
7. Installation coaxiality requirements:The throttle element and the pipeline must be concentric, with an eccentric distance not greater than0.0025DUsers should pay attention to or take necessary measures during welding operations.
8Orifice plates generally need to be matched with differential pressure transmittersmakeWhen connecting the pressure pipe to the differential pressure transmitter, be careful not to install the positive and negative pressures in reverse,'H' is positive, 'L' is negative;
9The pressure pipes led out from the positive and negative pressure ports must be kept parallel in any situation;
10. If a regulating valve must be installed, it is recommended to install the regulating valve after the required length of the straight pipe section on the downstream calculation sheet.
11. When the measured medium is gas or steam and there are significant fluctuations in temperature and/or pressure, temperature and/or pressure compensation should be performed. The pressure transmitter is installed at 1D upstream, and the thermocouple is installed at 1D downstream.
12. There should be no bag shaped space on the differential pressure signal pipeline where liquid or gas may accumulate. If unavoidable, a gas collector (or exhaust valve) and a settling device (or drain) should be installed.
13Zero drift of the transmitter can also cause measurement errorsDuring use, the differential pressure transmitter should be calibrated regularly.
14. In addition to regularly inspecting the pressure pipes to prevent blockage, outdoor pressure pipes should be properly insulated to prevent solidification or freezing. If the pipeline (vertical section) is quite long, false pressure difference caused by temperature difference should be avoided. At this time, it is recommended to lay two differential pressure pipelines close to each other and wrap them together in the insulation layer.
15. Differential pressure pipelines should have brackets to prevent vibration and strong forces from acting on the differential pressure gauge.
16When hoisting the throttling device on site, it is strictly prohibited to use iron wire, steel wire, or hook to penetrate the throat hole of the throttling element to prevent sharp mouth damage and affect accuracy;
17After using the throttling device for a period of time, due to the presence of solid particles in the liquid and gasIf there are liquid droplets or other impurities, the sharp inlet will be blunted, thereby increasing the outflow coefficient and causing additional errors. At this time, it is necessary to consider replacing the throttling element; In addition, after long-term use of the throttling device,It is easy to accumulate dirt at the lower corner of the upstream side of the orifice plate, which will cause changes in the outflow coefficient. Therefore, regular inspections should be carried out to eliminate dirt.
18. Pressure tube: The material of the pressure tube should be determined according to the properties and parameters of the measured medium. If the inner diameter is too small or the length is too long, it will cause serious signal lag or distortion. It is recommended to refer to Table (1) for determination.
Table (1) Inner diameter and length of pressure conduit
|
<16000（mm） |
<16000～45000（mm） |
<45000～90000（mm） |
Water, steam, dry gas |
7~9 |
10 |
13 |
Wet gas |
13 |
13 |
13 |
Low and medium viscosity oil products |
13 |
19 |
25 |
Dirty liquid or gas |
25 |
25 |
38 |
19. Requirements for straight pipe sections
Regulations and requirements for the length of straight pipe sections upstream and downstream of throttling devices:
The required length of the straight pipe section between the orifice plate and the flow blocking component in the IS05167 standardcompareRelated to β (β=d/D, where d is the diameter of the orifice plate and D is the inner diameter of the pipeline)The specific length is shown in Table (2) below:
Table (2) Minimum straight pipe length on the upstream and downstream sides of the throttling element
|
diameter compareβ ≤ |
The form of upstream flow blocking element and the shortest straight pipe length of the throttling element |
Downstream of throttling component Shortest straight pipe section Length (including In this table All flow blocking components |
||||||
|
single90O bend Head or three-way connector (Fluid only) From a branch Pipe outflow) |
On the same level The two on the surface One or more 90° elbow |
On different levels The two on the surface One or more 90° elbow |
reducing pipe (In)1.5D to3D long Within the degree2D change intoD） |
reducing pipe (In)1D to Length of 2D From within0.5D change intoD） |
Ball valve fully open |
Full hole ball Fully open the valve |
||
0.20 |
10（6） |
14（7） |
34（17） |
5 |
16（8） |
18（9） |
12（6） |
4（2） |
0.25 |
10（6） |
14（7） |
34（17） |
5 |
16（8） |
18（9） |
12（6） |
4（2） |
0.30 |
10（6） |
16（8） |
34（17） |
5 |
16（8） |
18（9） |
12（6） |
5（2.5） |
0.35 |
12（6） |
16（8） |
36（18） |
5 |
16（8） |
18（9） |
12（6） |
5（2.5） |
0.40 |
14（7） |
18（9） |
36（18） |
5 |
16（8） |
20（10） |
12（6） |
6（3） |
0.45 |
14（7） |
18（9） |
38（19） |
5 |
17（9） |
20（10） |
12（6） |
6（3） |
0.50 |
14（7） |
20（10） |
40（20） |
6（5） |
18（9） |
22（11） |
12（6） |
6（3） |
0.55 |
16（8） |
22（11） |
44（22） |
8（5） |
20（10） |
24（12） |
14（7） |
7（3.5） |
0.60 |
18（9） |
26（13） |
48（24） |
9（5） |
22（11） |
26（13） |
14（7） |
7（3.5） |
0.65 |
22（11） |
32（16） |
54（27） |
11（6） |
25（13） |
28（14） |
16（8） |
7（3.5） |
0.70 |
28（14） |
36（18） |
62（31） |
14（7） |
30（15） |
32（16） |
20（10） |
7（3.5） |
0.75 |
36（18） |
42（21） |
70（35） |
22（11） |
38（19） |
26（18） |
24（12） |
8（4） |
0.80 |
46（23） |
50（25） |
80（40 |
30（15） |
54（27） |
44（22） |
30（15） |
8（4） |
Note:1) The length of the straight pipe section in the table is expressed as a multiple of the nominal diameter DN of the actual pipeline.
2) The unsigned value is the value of 'zero additional uncertainty'.
3) The signed value is the value of '0.5% additional uncertainty'.
4) When the user's process pipeline layout cannot meet the requirements of Table 2, a rectifier (flow regulator) can be installed. Otherwise, the measurement accuracy will be reduced.
20. Selection of installation locations for different media:
The gas pressure tapping port is preferably located at the upper part of the pipeline; The liquid pressure tap is located on the sidefollowing,But don't be directly below, sediment particles will block itblockPressure tapping port; The pressure tap for steam is located on the side of the pipeline;As shown in the figure below:
1) Installation requirements on horizontal pipelines
①As shown in the figureAs shown in Figures 4 and 5: When measuring the flow rate of liquid and water vapor media, the optimal installation angles for the pressure tapping tube are 0 ° and 180 °; If installation is not possible at 0 ° and 180 °, it can be selected within the range of 0 ° to 60 ° and 120 ° to 180 °. But the differential pressure transmitter must be installed vertically on the vertical end face of the three valve group.
②As shown in the figureAs shown in Figure 6: When measuring the flow rate of gas medium, the optimal installation angle for the pressure tapping tube is 270 °. If it is impossible to install at 270 °, it can be installed within the range of 210 ° -270 ° and 270 ° -330 °. But the differential pressure transmitter must be installed horizontally on the top horizontal plane of the three valve group.
2) Installation requirements on vertical pipelines
①imageAs shown in Figure 7: When measuring the flow rate of water vapor and liquid media, the differential pressure transmitter is installed on one side of the pressure tap at the lower end of the vertical pipeline, and is vertically installed on the vertical end face of the three valve group plate below the pressure tap.
②As shown in the figureAs shown in Figure 8: When measuring the flow rate of gas medium, the differential pressure transmitter is installed at a height of the vertical pipelinelOn one side of the pressure port, and horizontally installed on the horizontal end face of the three valve group plate higher than the pressure port.
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