# Double-Venturi Gas Flowmeters

> Custom low-loss measurement for large gas ducts. Application-engineered internal and insertion differential-pressure assemblies for low-velocity gas in large circular and rectangular ducts.

## Overview

Shizhong Double-Venturi Gas Flowmeters address large-duct duties where low gas density, low velocity, limited pressure-loss allowance and restricted retrofit access must be solved together. The manufacturer-specific sensing geometry produces a usable differential-pressure signal without the size and process penalty of a conventional full-bore restriction. Internal, insertion, integrated round-duct and rectangular-duct configurations are engineered around the actual process, duct, disturbance layout, maintenance plan and validation objective. This product is not the classical Venturi tube defined by ISO 5167-4; its coefficient and performance belong to the approved Shizhong geometry and project evidence basis.

## Product class and standards boundary

The Shizhong Double-Venturi Gas Flowmeter is a manufacturer-specific, custom-engineered differential-pressure device for large, low-velocity gas ducts. It is **not** the classical Venturi tube defined by ISO 5167-4. Do not apply ISO 5167-4 geometry, discharge coefficients, accuracy values or straight-run tables to this product.

ISO 3966, ISO 16911-1/-2, ISO 14164, ISO 15259, ISO 10780 or an agreed site reference method may support measurement planning, velocity-area comparison, automated-system assessment and site correlation where their scope is applicable. These references do not provide one universal coefficient for the Double-Venturi family.

## Measurement model

The supplied sensing geometry creates a differential pressure related to gas velocity. A project model can be represented as:

`v = K_v × sqrt(2 × Δp / ρ)`

Section flow additionally requires the measured duct area and an approved profile/area factor. The coefficient belongs to the supplied geometry, insertion depth, pressure circuit, duct and validation basis; it is not transferred from another device or installation.

## Application-engineering rules

- Provide minimum, normal and maximum flow, pressure, temperature and gas composition.
- State dust, droplets, condensation, corrosion and purge/cleaning requirements.
- Provide measured round-duct diameter or rectangular clear W × H plus the complete upstream/downstream disturbance layout.
- Confirm allowable pressure loss, required output and reference conditions.
- Select internal, insertion, integrated or rectangular-duct configuration before fixing the coefficient basis.
- Agree representative calibration, velocity-area comparison or site correlation before fabrication.

## Selection caution

Accuracy, turndown, straight run and permanent pressure loss are project-specific. Two-phase, strongly pulsating or strongly swirling flow requires a separate feasibility study. Regulated emissions reporting or commercial settlement also requires the applicable local approval and traceability route.


## Technical specifications

| Parameter | Specification |
|---|---|
| Size range | Round DN500–DN4000; rectangular 600 × 600 to 3600 × 3600 mm typical family envelope |
| Measurement geometry | Not applicable—manufacturer-specific Double-Venturi sensing geometry |
| Reynolds-number range | Project-specific; minimum usable velocity is confirmed from DP signal, density, profile stability and validation basis |
| Pressure taps | Engineered high/low pressure connections; G3/4, M20 × 1.5 or 1/2 NPT typical |
| Accuracy | Project-specific; stated after representative calibration or approved site correlation |
| Turndown ratio | Engineered from minimum usable DP, gas density, transmitter rangeability and validated operating envelope |
| Permanent pressure loss | Low-loss design objective; confirmed during sizing for the selected geometry and operating points |
| Discharge coefficient | Device- and installation-specific coefficient established by the approved validation route |
| Temperature range | Below +400°C typical; higher temperature by material, support and instrumentation review |
| Pressure rating | Up to PN6.4 MPa within the typical family; final rating per mechanical design and project code |
| Materials | Stainless steel, carbon steel, Hastelloy and project-specific alloys |
| Straight-run requirement | Project-specific; determined from actual disturbances, profile assessment and the approved validation basis |

## Standards

Manufacturer-specific device; not ISO 5167-4. ISO 3966, ISO 16911 and ISO 14164 may support reference measurement and validation where applicable

## Applications

- Blast-furnace, coke-oven, converter and mixed-gas ducts
- Boiler primary air, secondary air and combustion air
- Flue gas and large process-exhaust ducts
- Low-pressure, low-velocity industrial gas measurement

## Features

- More usable differential-pressure signal for low-velocity gas
- Low-loss internal or insertion configurations for large ducts
- Round and rectangular duct engineering
- Project-specific calibration, velocity-area comparison or site correlation

## Contact and source links

- Product page: https://www.shizhongflow.com/products/double-venturi-flow-meters
- Product catalog API: https://www.shizhongflow.com/api/products
- Selection API: https://www.shizhongflow.com/api/select
- Request an engineering review: https://www.shizhongflow.com/contact
- Email: info@shizhongflow.com
- Phone/WhatsApp: +86-188-0531-6689

Final sizing, materials, pressure-boundary design, calibration and compliance are confirmed against the complete process data sheet and project requirements.