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Venturi Type Flow Meter: Differential Pressure High-Velocity Fluid Sizing
Quick Answer: A Venturi type flow meter handles high velocity gas, steam, and liquid lines with low permanent pressure loss. Size the meter by inner pipe diameter, differential pressure range, fluid density, temperature, and Reynolds number. Silver Automation Instruments supplies Venturi type differential pressure flow meters from DN25 to DN1200 with 4-20 mA HART output.
Most engineers choose a Venturi tube when line velocity exceeds 25 m/s for gas or 10 m/s for liquid. The short version is this. You get reliable flow measurement without high permanent pressure loss. A paint manufacturer in Vietnam asked us last year about a 150 mm steam line running at 42 m/s. A standard orifice plate would have wasted too much pressure. We sized a Venturi type meter instead.
When a Venturi Meter Makes Sense
Venturi type flow meters use a smooth contraction and expansion section. This creates a differential pressure between the inlet and the throat. The dp transmitter converts that signal to flow rate. Because the recovery cone is long, permanent pressure loss stays around 5 to 10 percent of the generated differential. For high velocity fluids this matters a lot.
An LNG terminal in Indonesia runs natural gas at 35 m/s in a DN200 header. Orifice plates caused excessive noise and vibration. Silver Instruments supplied a Venturi tube with a 250 mbar dp cell. The site reports stable readings and lower compressor load.
Sizing Inputs You Need to Send Us
We need five values to size a Venturi type flow meter. These are pipe size, fluid name, operating pressure, operating temperature, and flow range. Density and viscosity help but we can calculate those from pressure and temperature. For gas or steam, include molecular weight if you have it. Without complete data, the sizing output is a guess. In practice, most engineers skip the full viscosity check for gas lines above 5 bar. We only ask for viscosity on heavy oil or slurries.
Send us your pressure in bar, temperature in degrees Celsius, pipe size DN, and flow range in kg/h or m3/h. Our engineers return a sizing sheet within one working day. This applies to oil and gas, chemical, water and wastewater, and food and beverage lines.
Recommended Models and Ranges
Silver Automation Instruments offers Venturi type primary elements in carbon steel, 304 stainless steel, and 316L stainless steel. Standard line sizes run from DN25 to DN1200. Flange ratings cover PN16, PN40, ANSI 150, and ANSI 300. Higher ratings are available on request. The matching differential pressure transmitter outputs 4-20 mA HART with optional ATEX Zone 1 appro
For high velocity gas and steam we normally specify a 0 to 250 mbar or 0 to 1000 mbar dp range. For liquid lines with solids, a Venturi with a single pressure tap on each side avoids clogging. This is common in wastewater plants in Australia and desalination plants in the Middle East.
Installation Notes for High Velocity Service
Straight pipe requirements are shorter than an orifice plate but still matter. We recommend 10D upstream and 5D downstream for most Venturi meters. In tight skids, a flow straightener can reduce the upstream run to 5D. Mount the dp transmitter below the pipe for gas or steam. Use a manifold valve for zero checks.
High velocity flow can produce acoustic noise and vibration. So the pressure taps must be welded or flanged, never threaded in small sizes. A customer in Chile replaced threaded taps after a steam leak. We now supply welded tap connections as standard for steam lines above 10 bar.
FAQ
What is the accuracy of a Venturi type flow meter?
Typical accuracy is plus or minus 1.0 to 1.5 percent of actual flow with a calibrated dp transmitter. Without flow calibration, expect plus or minus 1.5 to 2.0 percent.
What is the minimum Reynolds number for Venturi sizing?
We recommend Reynolds number above 100,000 at the throat for stable discharge coefficient. Below 50,000, uncertainty increases quickly.
Can a Venturi meter handle slurry or dirty liquid?
Yes. The smooth bore resists solids buildup. Use single pressure taps and a remote seal transmitter if solids are present.
How much straight pipe does a Venturi meter need?
10D upstream and 5D downstream covers most installations. Add a flow straightener if you have less than 5D upstream.
What dp transmitter do you pair with the Venturi tube?
Silver Instruments supplies a 4-20 mA HART dp transmitter with LCD display. Options include ATEX, SIL, and remote diaphragm seals.
Get a Venturi Type Flow Meter Quote
Tell us your fluid, pressure bar, temperature degrees Celsius, pipe size DN, and flow range. Email us at [email protected] or call Tel: +86-135-1213-1526. WhatsApp: 86-135-12131526. WeChat: +86 13512131526. Silver Automation Instruments serves customers in Southeast Asia, Oceania, Latin America, Africa, and the Middle East.
We respond to sizing requests within 24 hours. Because we manufacture the Venturi primary element and supply the dp transmitter from one factory, you get one calibration report and one warranty. That matters when your process runs at high velocity and you cannot afford a bad flow reading. See flow-meter.com.au for the full product range.
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