Company Profile

Venturi Meters and Orifice Plates: Heavy-Duty Differential Pressure Flow Measurement Systems

Quick Answer: Venturi meters and orifice plates are heavy-duty differential pressure flow devices for dirty, high temperature, and high pressure lines. A Venturi tube handles slurries and raw water with low permanent pressure loss. An orifice plate offers a lower cost option for steam, gas, and clean liquid lines where some pressure loss is acceptable.

What Is a Venturi Meter?

A Venturi meter uses a smooth reduction in pipe diameter to create a pressure drop. Pressure taps at the inlet and throat measure this drop. The flow rate is calculated from the differential pressure. Silver Automation Instruments supplies Venturi tubes from DN50 to DN1200 for water, wastewater, chemical, and slurry service. Most engineers choose a Venturi when the process needs high accuracy plus low permanent pressure loss. The smooth cone shape also resists wear better than a sharp orifice edge in abrasive flows. A copper mine in Peru runs a DN400 Venturi on slurry at 1.8 bar and 45 deg C with stable readings.

What Is an Orifice Plate?

An orifice plate is a thin metal disk with a machined bore. The plate bolts between two flanges. Fluid passes through the bore and creates a pressure drop across the plate. Corner taps or flange taps transmit this differential pressure to a DP transmitter. Orifice plates work well on steam, natural gas, compressed air, and clean water. The initial cost is low and the plate can be replaced quickly during a shutdown. A paint manufacturer in Southeast Asia runs a DN80 orifice plate on a steam header at 10 bar and 185 deg C. The plant replaces the plate every two years because of wet steam erosion. The replacement takes less than one shift.

Venturi or Orifice: Which One Fits Your Plant?

Choose a Venturi meter when the fluid contains solids, sludge, or abrasives. Choose a Venturi when permanent pressure loss matters. Choose an orifice plate when the line is clean and budget is the main concern. In practice, many plants use both. A wastewater plant may put a Venturi on raw sewage and orifice plates on clean air and biogas lines. A food and beverage plant can use orifice plates on CIP water and a Venturi on mash transfer. The decision depends on fluid condition, pipe size, pressure loss allowance, and maintenance access.

Heavy-Duty Applications We See

We quote these flow measurement systems for oil and gas, water and wastewater, chemical, food and beverage, and marine projects. For seawater intake, a DN600 Venturi with Hastelloy C276 taps works for a desalination plant in Oman. For high pressure natural gas, a DN100 orifice plate with a 4-20 mA HART transmitter and ATEX Zone 1 housing is typical. On live crude lines, a Venturi meter avoids moving parts and handles rapid pressure changes. A customer in Nigeria ordered a Venturi meter on a DN250 crude oil transfer line at 22 bar and 70 deg C. Last year a customer in Vietnam asked for a DN50 orifice plate on a superheated steam line at 16 bar and 320 deg C. We supplied the meter body, pressure taps, 3-valve manifold, and a DP transmitter calibrated to the kg/h range.

Pressure Taps and Transmitters

A differential pressure flow system includes a primary element and a secondary element. The Venturi tube or orifice plate is the primary element. The DP transmitter is the secondary element. The transmitter converts the pressure drop into a 4-20 mA signal, often with HART. For hazardous areas we offer ATEX and IECEx certified transmitters. For remote sites, a solar powered loop with wireless telemetry is common. The tubing, manifolds, and root valves matter as much as the meter body. We have seen incorrect tap orientation cause a false reading on a steam line in a Philippine food plant. The transmitter was in good condition. The taps were not level and condensa