Current position > Product detail
『How Does a Venturi Flow Meter Work: Differential Pressure Sizing Formulas』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
Venturi Flow Meter Working Principle and Differential Pressure Sizing Formulas
Quick Answer: A venturi flow meter creates a controlled pressure drop between a pipe inlet section and a reduced throat. Flow rate is proportional to the square root of that differential pressure. Silver Instruments supplies venturi meters with matched 4-20 mA HART differential pressure transmitters for DN25 to DN600 lines.
How a Venturi Flow Meter Works
A venturi flow meter has three sections. The inlet cone converges to a throat. The throat has a smaller diameter than the pipe. The outlet cone diverges back to the pipe diameter. When fluid enters the throat, velocity increases and static pressure decreases. That pressure difference is measured between the upstream pipe and the throat.
In practice, the venturi meter follows Bernoulli equation and continuity equation. The differential pressure transmitter reads high side from the upstream tap and low side from the throat tap. The flow computer or PLC calculates flow from the square root of DP. Most engineers skip this part because the DP transmitter does the square root extraction internally.
Differential Pressure Sizing Formula
The general mass flow formula for a venturi meter is:
Qm = C / sqrt(1 - beta^4) * epsilon * pi/4 * d^2 * sqrt(2 * delta P * rho)
Qm is mass flow in kg/s. C is discharge coefficient. Beta is throat diameter divided by pipe diameter. Epsilon is expansion factor for gas or steam. d is throat diameter in meters. Delta P is differential pressure in Pascal. Rho is fluid density in kg/m³.
For liquid water at 25 Celsius and a cast stainless steel venturi, C is often 0.995 to 1.005. Epsilon is 1 for liquids. For gas applications, use the expansion factor based on pipe pressure and beta ratio. Beta values from 0.4 to 0.75 keep permanent pressure loss low.
Step by Step Sizing Example
A water utility in Vietnam asked for a venturi flow meter on a DN100 carbon steel line. Actual pipe ID was 102.3 mm. Target flow range was 20 to 80 m3/h. We selected a throat diameter of 51.1 mm so beta was 0.5. For 80 m3/h, water density 998 kg/m3, and C 1.0, the calculated DP was about 0.48 bar. The permanent pressure loss was around 0.08 bar. That is much lower than an orifice plate on the same line.
Then we set the DP transmitter span to 0 to 0.6 bar. The transmitter had 4-20 mA HART output and a PT100 input for temperature correction. The customer installed the meter with 10D upstream straight run and 5D downstream straight run. The signal matched a portable ultrasonic flow meter within 0.8 percent.
Materials and Installation Notes
Choose the venturi material for the fluid. Sea water and desalination plants need 316L stainless steel or duplex. Wastewater with solids needs a smooth throat to reduce buildup. Chemical plants use PTFE lined venturi meters for acids. For steam flow, use a 4-20 mA HART DP transmitter with an integrated PT100 temperature sensor. The
_600x400.jpg)
Install the venturi meter with enough straight pipe. Upstream 10D and downstream 5D is a common start. If the upstream has an elbow after a pump, add a flow straightener. Mount the DP transmitter below the taps for gas. For liquid, mount above so bubbles do not collect inside impulse lines. A three valve manifold makes commissioning faster.
Common Applications and Customer Sites
We have seen venturi meters on customer sites in many places. A paint manufacturer in Southeast Asia uses a DN50 venturi meter for solvent flow. The solvent has low conductivity so an electromagnetic flow meter was not suitable. A diesel terminal in Australia measures fuel loading with a DN80 venturi meter. The DP transmitter has ATEX Zone 1 approval. A desalination plant in Saudi Arabia uses a 316L venturi meter on brine recirculation. The flow range is 60 to 120 m3/h with a DP span of 0 to 0.4 bar.
Because the venturi meter has no moving parts, it survives dirty gas and high temperature steam better than a turbine meter. That is why many oil and gas process engineers still specify venturi meters for flare gas and produced water injection.
Model Selection and Silver Instruments Offering
Silver Instruments supplies venturi flow meters in DN25 to DN600 sizes. Body materials include carbon steel, 304 stainless steel, 316L stainless steel, and duplex. Process connections include flanges or wafer style. We pair each venturi with a differential pressure transmitter from 0 to 0.1 bar up to 0 to 25 bar. The transmitter outputs 4-20 mA HART with optional ATEX Zone 1 approval.
We also supply matching pressure transmitters and no paper recorders. Send us your pressure in bar, temperature in Celsius, pipe size in DN, and flow range in m3/h or kg/h. We return a sizing sheet and quote within one working day.
Contact Silver Automation Instruments. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610. Website: flow-meter.com.au
FAQ: Venturi Flow Meter Sizing
What is the minimum pipe size for a venturi flow meter? We supply DN25 as standard. Smaller sizes are possible but machining the throat becomes expensive.
Can a venturi meter handle gas and steam? Yes. Use the expansion factor epsilon in the formula. Add pressure and temperature compensation for mass flow.
What is the permanent pressure loss of a venturi meter? Usually 5 to 20 percent of the differential pressure. An orifice plate often loses 40 to 60 percent. Venturi meters save pump energy.
What straight run length is required? Try 10D upstream and 5D downstream. If the flow profile is disturbed, install a straightening vane.
Can Silver Instruments supply the complete package with transmitter? Yes. We ship the venturi body, DP transmitter, three valve manifold, impulse tubes, and calibration report as one package.