HQWG Elbow Flow Meter

Elbow Flow Meter

I. Main Characteristics of the Bent Pipe Flowmeter
The HQ-WG bent pipe flowmeter is a typical energy-saving differential pressure flow measurement device, widely used in metallurgy, chemical industry, petrochemical industry, thermal power, textile, papermaking, pharmaceutical, food processing, and heating sectors for measuring the flow rate of liquids, gases, and steam.  It can be used as a flow metering instrument for long-term continuous flow monitoring and accumulation, and its excellent repeatability accuracy makes it suitable for use as a flow measurement device in flow control units. Its application range is very broad.
The HQ-WG bent pipe flowmeter can adapt to various complex field conditions, and its characteristics in terms of installation conditions and methods are increasingly attracting attention and recognition from industry professionals and relevant users. As a newcomer to the flowmeter market, the bent pipe flowmeter has seen significant improvements in market coverage and growth rate in recent years.
II. Components of the Bent Pipe Flowmeter
The bent pipe flowmeter mainly consists of a bent pipe sensor, an intelligent flow totalizer, a differential pressure transmitter, and some supporting pipe valve components. When density compensation (temperature and pressure compensation) of the medium is required for flow measurement, a pressure transmitter, temperature components, and other accessories should also be included.

III. Working Principle of the Bent Pipe Flowmeter
When the fluid flows through the bent pipe sensor, it is constrained by the sensor and forced to move in a circular motion (i.e., forced swirling flow). The centrifugal force generated by the fluid creates a pressure difference △P (P1-P2) between the inner and outer walls of the sensor. The magnitude of this centrifugal force is related to factors such as the fluid velocity v, density ρ, and the radius of curvature R of the circular motion, i.e.,
△P = F(V, ρ, R)
This differential pressure value is led out through pressure-sensing tubes installed at 45° on the inner and outer sides of the bent pipe sensor and sent to a differential pressure transmitter. The differential pressure transmitter converts it into a 4-20mA current signal, which is then sent to a secondary instrument for further processing. The functional expression between the average fluid velocity and the differential pressure value is:

Where: V: Average flow velocity of the medium (m/s)
Cf: Flow coefficient (related to the structural form of the bend sensor, the Reynolds number of the fluid, dynamic viscosity, compressibility coefficient, pipe roughness, and other parameters);
△P: Pressure difference between the inner and outer sides of the bend sensor;
△P = P1 - P2 (Pa); ρ: Density of the measured medium (kg/m³).
IV. Main Characteristics of the Bend Flowmeter
1. Simple Structure
No additional resistance loss – The bend sensor is a 90° elbow with definite geometric dimensions, either circular or rectangular.  It has no internal inserts, throttling devices, or flow restrictors, resulting in a simple structure and no additional resistance loss. It is an energy-saving flow measurement device.
2. Good Repeatability
The repeatability of the bend flowmeter is better than ±0.2%, which is the basis for achieving high-precision measurement results.
3. Good Wear Resistance and Long Service Life
The service life of the bend sensor is equivalent to that of the standard elbow it replaces. It is wear-resistant, and the slight wear of the pipe diameter during long-term operation has minimal impact on the measurement accuracy of the bend sensor, ensuring stable operation over a long period.
4. Simple Direct Welding Installation
The bend sensor can be installed by direct welding, solving problems such as leakage and greatly reducing on-site maintenance workload and costs.
5. Strong Adaptability and Wide Measurement Range
The bend flowmeter is unaffected by adverse factors such as high temperature, dust, humidity, vibration, and electromagnetic fields, and can operate in any complex environment. The measurement pipe diameter is suitable for DN15~2000mm, and various sizes of rectangular pipes, with liquid flow velocity not less than 0.5 m/s, and steam or gas flow velocity not less than 5 m/s.
6. Low Straight Pipe Section Requirements
The bend sensor has relatively low requirements for the straight pipe section; sufficient measurement accuracy can be obtained as long as the requirements of 5D before and 2D after the bend are met.

V. Specifications and types of bent tube flowmeters

(1) This sample does not include selection information for transmitters; please contact your local distributor or manufacturer directly if needed. (2) Other special media options are available; please contact the manufacturer for details.
VI. Selection Table for Elbow Flow Meters
Elbow Flow Meter Selection Code Table

*Integrated type includes welded pressure tapping valve, three-valve manifold, and pressure tapping short pipe, all welded together with the flow meter body and supplied as a complete set. The material of the pressure tapping short pipe/pressure tapping valve/three-valve manifold is the same as the pressure tapping port (according to on-site process requirements, the pressure tapping valve can be a socket-welded globe valve, socket-welded gate valve, or other types and materials of valves). The mating flange material is the same as the on-site pipeline material. The transmitter is supplied according to user requirements.
**Separated type does not include all installation accessories.  These are supplied according to user requirements at the time of ordering. The mating flange material is the same as the on-site pipeline material. Separated type is recommended for steam measurement.
***When the pipeline is rectangular, the nominal diameter specification is selected according to the wider dimension.
****The selection code for nominal diameter DN32 is 0D.

VII. Structural Dimensions of ElbowTube Flowmeters
(1) HQ-WG-L Series Products
Outline Drawing

Structural dimensions table

(2) HQ-WG-S Series Products
Outline Structure Diagram

Structural dimensions table

(3) HQ-WG-H Series Products
Outline Structure Diagram

Structural dimensions table

(4) HQ-WG-P Series Products
Outline Structure Diagram

Structural dimensions table

(5) HQ-WG-X Series Products
Outline Structure Diagram

VIII. Installation Requirements for Elbow Flow Meters
1. Straight Pipe Section Requirements
The HQ-WGL type elbow sensor flow measurement point should be selected at a natural bend in the measured pipeline. The VCFS type elbow sensor flow measurement point can be selected on any straight pipe section, and the length of the straight pipe sections before and after should meet the requirements of 5D and 2D respectively.
2. Installation Space and Position Selection
The HQ-WG-H type elbow sensor can be installed at the bend of the measuring pipeline using flange connection or welding.  Its spatial installation state can, in principle, be arbitrary.  Generally, there are three installation states to choose from:
a. Horizontal to horizontal (as shown in the attached figure);
b. Horizontal to vertically upward or vertically downward to horizontal (as shown in the attached figure);
c. Vertically downward or vertically upward to horizontal (as shown in the attached figure);
The S-type elbow sensor can be installed on a straight pipe line in any state (vertical or horizontal), and is basically not limited by site conditions.

3. Installation precautions for pressure taps on HQ-WG-P type bent pipe flow meters

(A) For measuring general liquid media, the bent tube sensor can be installed in any orientation:
Because the liquid in the pipe and the liquid in the pressure sensing tube are under almost the same operating conditions, no offset or compensation is required for the differential pressure transmitter, regardless of the position of the two pressure taps of the bent tube sensor.
(B) For systems measuring hot or cold water, it is best to choose a horizontal-to-horizontal installation: If the bent tube sensor is installed vertically, there will be a height difference H between the two pressure taps of the bent tube sensor (as shown in the right figure).  Since the liquid in the pipe and the liquid in the pressure sensing tube are at different temperatures, their densities will differ. To improve the measurement accuracy of the system, it is necessary to compensate for the deviation of the differential pressure transmitter caused by this height difference and temperature difference. The offset can be calculated using the following formula:
△P = H (ρ1 - ρ2) × 9.81
Where: △P – Offset of the differential pressure transmitter, Pa;
H – Height difference between the two pressure taps, m;
ρ1 – Density of the liquid in the pressure sensing tube, kg/m³;
ρ2 – Density of the liquid in the pipe, kg/m³.
(C) For measuring steam or other condensable gases, the bent tube sensor is best installed horizontally:
When the bent tube sensor is installed vertically, the pressure sensing tube will eventually fill with liquid, and it is necessary to compensate for the height difference of the liquid columns in the two pressure sensing tubes. To avoid additional measurement errors caused by improper compensation, if site conditions permit, the bent tube sensor should be installed horizontally, or an S-shaped bent tube sensor should be selected, so that the two pressure taps of the bent tube sensor are on the same horizontal plane, thus fundamentally eliminating the need for compensation of the differential pressure transmitter.

4. Installation of pressure sensing lines

IX. On-site installation diagram of the bent pipe flow meter

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