Advantages and disadvantages of various gas meters

1.Diaphragm Gas Meter

The measured gas enters from the inlet of the meter, fills the space inside the meter, and enters measuring chambers 2 and 4 through the open slide valve seat hole. It relies on the gas pressure difference on both sides of the membrane to push the membrane movement of the measuring chamber, forcing the gas in measuring chambers 1 and 3 to flow out from the outlet through the slide valve and distribution chamber. When the film reaches its end, it relies on the inertia of the rotating mechanism to make the slide valve cover move in the opposite direction. Measurement chambers 1 and 3 are connected to the inlet, and chambers 2 and 4 are connected to the outlet. The membrane moves back and forth once, completing one revolution. At this time, the reading value of the meter should be the flow rate of one revolution (i.e. the effective volume of the measurement chamber). The accumulated flow rate value of the membrane meter is the product of the flow rate of one revolution and the number of revolutions.

※ Advantages

There are many advantages to membrane meters. Firstly, the range is relatively wide, reaching 1:160, which is particularly suitable for users with large flow changes. This is also the reason why they are widely used in application scenarios such as hotels, restaurants, and canteens. Low cost, high precision, safety and reliability, and durability are all its advantages.

※ Disadvantages

Membrane gas meters can only be used for low-pressure metering, and generally Pmax (ZUI high working pressure) cannot exceed 50kPa.

2、 Differential pressure flowmeter

Differential pressure flowmeter is based on Bernoulli equation and fluid continuity equation. According to the throttling principle, when the fluid flows through the throttling element (such as standard orifice plate, standard nozzle, long diameter nozzle, classical Venturi nozzle, Venturi nozzle, etc.), a pressure difference is generated before and after it, and this differential pressure value is proportional to the square of the flow rate. In differential pressure flow meters, the standard orifice plate throttling device has been widely used due to its simple structure, low manufacturing cost, thorough research, and standardization.

Differential pressure flow meters generally consist of throttling devices (throttling elements, measuring tubes, straight pipe sections, flow regulators, pressure measuring pipelines) and differential pressure gauges. In situations where high accuracy is required due to changes in operating conditions, pressure gauges (sensors or transmitters), thermometers (sensors or transmitters), flow computers, etc. are required. When the components are unstable, online density gauges (or chromatographs) are also required.

※ Advantages:

(1) The most widely used orifice plate flowmeter has a simple and sturdy structure, stable and reliable performance, long service life, and low price.

(2) The application range is extremely wide, and there is currently no type of flow meter that can compare with it. All single-phase fluids, including liquid, gas, and steam, can be measured, and some mixed phase flows can be measured.

(3) The detection components, transmitters, and display instruments are produced by different manufacturers, which facilitates economic production.

(4) The standard throttling DPF does not require real flow calibration and can be put into use.

※ Disadvantages:

(1) The measurement repeatability and accuracy are generally low.

(2) Narrow range, due to the square relationship between differential pressure signal and flow rate, the general range is only 3:1~4:1.

(3) The on-site installation requirements are high, requiring a long straight pipe section.

(4) High pressure loss (referring to orifice plates, nozzles, etc.).

Application Overview:

Differential pressure flowmeter has a wide range of applications, including flow measurement in closed pipelines for various objects such as fluids: single-phase, mixed phase, clean, dirty, viscous flow, etc; In terms of working conditions: normal pressure, high pressure, vacuum, normal temperature, high temperature, low temperature, etc; In terms of pipe diameter: from a few millimeters to a few meters; In terms of flow conditions: subsonic, sonic, pulsating flow, etc. It accounts for approximately 1/4 to 1/3 of the total usage of flow meters in various industrial sectors.

3、 Vortex flowmeter

Place a non streamlined vortex generator in the fluid, and the fluid alternately separates and releases two rows of regularly arranged vortex streets on both sides of the vortex generator. Within a certain range of flow rates (Reynolds number), the separation frequency of vortices is proportional to the volumetric flow rate of the fluid passing through the vortex flow sensor.

※ Advantages:

(1) The structure is simple and sturdy, easy to maintain, and requires minimal maintenance.

(2) Suitable for various types of fluids, such as liquids, gases, vapors, and partially miscible fluids.

(3) High accuracy, generally within ± 1% R~± 2% R

(4) Wide range, up to 20:1~10:1

(5) The pressure loss is small, about 1/4~1/2 of the orifice plate.

(6) Output pulse frequency signal, suitable for total quantity measurement and computer connection, without zero drift

(7) Within a certain Reynolds number range, the output frequency signal is not affected by fluid properties (density, viscosity) and composition, that is, the instrument coefficient is only related to the shape and size of the vortex generator and pipeline, and only needs to be verified in a typical medium to be applicable to various media. VSF is a type of flowmeter that is more likely to become a dry calibration only flowmeter.

※ Disadvantages:

(1) Not suitable for low Reynolds number measurements (ReD ≥ 2 × 104), limited in application under high viscosity, low flow rate, and small aperture conditions.

(2) The stability of vortex separation is affected by flow velocity distribution distortion and rotational flow, requiring a longer straight pipe section.

(3) VSF is sensitive to mechanical vibrations in pipelines and should not be used in areas with strong vibrations.

(4) The instrument coefficient is relatively low (compared to turbine flow meters), the resolution is low, and the larger the diameter, the lower the resolution. It is generally used for DN300 and below.

(5) The instrument still lacks application experience in pulsating flow and multiphase flow.

4、 Spiral vortex flowmeter

When the fluid passes through the vortex generator composed of spiral guide vanes, it is forced to strongly rotate around the centerline to form a vortex flow. When passing through the enlarged tube, the vortex center precesses along a conical spiral shape. Within a certain range of flow rates (Reynolds number), the precession frequency of vortex flow is proportional to the volumetric flow rate of the fluid passing through the vortex flow sensor.

The characteristics of a vortex flowmeter are basically the same as those of a vortex street, with three differences: first, the pressure loss of the flowmeter is much greater, about 3-4 times that of a vortex street; Secondly, it has strong anti-interference ability, and the necessary length of the straight pipe section is short, generally 5D for upstream and 1D for downstream; The third reason is that the initial flow is relatively large.