Adjustable Flow Meter

Adjustable Flow Meter
I. Main Characteristics of the Adjustable Flow Meter
The adjustable flow meter is a new type of differential pressure flow meter.  It not only inherits the advantages of traditional differential pressure flow meters, such as simple structure, safety and reliability, and ease of maintenance, but also significantly improves upon traditional throttling devices with a central opening. Based on fluid mechanics equations, the throttling device features four equally distributed and symmetrical openings. The aperture ratio and hole distribution are optimized through extensive experimental data to achieve the best measurement results.
The operating principle of the adjustable flow meter is the same as other types of differential pressure flow meters. However, the adjustable flow meter uses a throttling element with four equally sized throttling holes. The distribution of these holes is based on years of experimental data. The evenly distributed throttling holes reshape the flow velocity curve and immediately create a low-pressure zone downstream of the throttling element. There is a pressure difference between the positive pressure upstream of the pipe and the negative pressure downstream after throttling. This pressure difference is measured using pressure taps, and the flow rate of the medium in the pipe can be calculated using Bernoulli's equation. Because the throttling element optimizes the flow velocity curve of the measured medium, it offers high measurement accuracy and requires shorter straight pipe sections upstream and downstream of the instrument.

II. Components of Adjustable Flow Meters
The HQ-TZ series of adjustable flow meters comes in two configurations: integrated and split. The integrated type consists of a primary flow restriction (sensing) element, a transmitter, and a valve assembly. The split type includes these components plus additional pressure sensing lines.

III. Working Principle of Adjustable Flow Meters
Adjustable flow meters are a type of differential pressure flow meter.  Flow meters designed based on the differential pressure principle have been in use for over a hundred years. The differential pressure principle is based on the energy conversion principle in sealed pipes, meaning that for a stable fluid, the flow rate is proportional to the square root of the pressure difference across the pipe. We know that pressure decreases as velocity increases. When the fluid approaches the throttling element, its pressure is P1. As the fluid passes through the throttling area, the flow velocity increases due to the reduced flow area, and the pressure decreases to P2. Both P1 and P2 are connected to a differential pressure transmitter through the pressure taps of the flow meter. When the flow rate changes, the differential pressure value between the two pressure taps of the flow meter will increase or decrease. For the same flow rate, a larger throttling area will result in a larger differential pressure value.

Q: Volumetric flow rate  Ɛ: Gas compressibility factor  d: Orifice diameter  β: Equivalent orifice ratio  c: Discharge coefficient  ρ: Fluid density  △P: Differential pressure value

IV. Main Characteristics of Adjustable Flowmeters
1. High Accuracy and Good Repeatability
The accuracy of adjustable flowmeters can reach ±0.5% of the measured value, and the calibration accuracy can reach ±0.25%, with repeatability better than 0.1%. The unique rectification structure design of the adjustable flowmeter allows the fluid to form small and symmetrically distributed vortices after passing through the throttling element. These equivalently and uniformly distributed small vortices not only stabilize the output differential pressure signal but also enable the fluid to maintain high measurement accuracy even at very small differential pressure values, thus resulting in high measurement accuracy and good repeatability.
2. Low Straight Pipe Section Requirements
The multi-hole flow equalization design of the adjustable flowmeter can redistribute the velocity curve of the upstream fluid, making it closer to an ideal fluid, ensuring high measurement accuracy under harsh conditions. In most cases, leaving a 2D straight pipe section before and after installation is sufficient to meet the measurement requirements.
3. Wear-Resistant and Good Long-Term Stability
The four holes of the adjustable flowmeter are processed using a CNC machining center. The throttling element has no sharp edges, making it less prone to wear, thus resulting in good wear resistance and high long-term stability.
4. Measurement of Bidirectional Flow and Redundant Output of Transmitters
Due to the geometrically symmetrical structure of the balanced flowmeter, a single flowmeter can be used to measure bidirectional fluid flow.  Furthermore, because of its geometrically symmetrical structure in the circumferential direction, one flowmeter can provide up to 3 differential pressure signal outputs, meeting the redundancy requirements for transmitters in ESD systems that require a two-out-of-three voting method.

V.Installation of pressure sensing lines