Primary element flow meter for gas, steam and liquid

In fluid mechanics, a depressurizer is a device used to restrict the flow of a fluid while measuring the pressure difference. The main application is flow measurement using a differentialpressure transmitter . This measures the pressure on both sides of the orifice to calculate the flow rate. Orifice plates, nozzles, venturis and V-cones are used as depressurizers. Their installation conditions are described in ISO 5167.


Flow measurement with differential pressure transmitters and orifice :

Flow measurement using differential pressure transmitters is one of the most common solutions used in industry to accurately monitor the flow of liquids, gases and steam. This method is based on the installation of a cross-section-reducing device - such as an orifice plate, Venturi tube or Pitot tube - directly integrated into the pipe. As the fluid passes through this restriction, a pressure drop is generated. The transmitter then measures the pressure difference between upstream and downstream, directly related to the fluid's flow velocity.

This physical principle enables reliable calculation of volume or mass flow, guaranteeing continuous monitoring and precise regulation of industrial processes. Pitot tubes, on the other hand, are particularly well-suited to local spot velocity measurements in pipes, useful for diagnostics or performance checks.

This technology is robust and easy to integrate, with low maintenance costs. It is widely used in hot water and cooling circuits, and for measuring high-pressure steam or high-temperature condensates.

Differential pressure flow measurement complies with international standards, includingISO 5167, and is easily integrated into industrial supervision systems, making it a popular solution in theenergy, chemical,food andprocess industries.

flow measurement using differential pressure and primary element

Advantages of flow measurement using depressors


Measurement principle

Depressurization measurement is based on Bernoulli's theorem, which establishes a relationship between the velocity of a fluid and the pressure difference observed before and after a restriction in the pipe. As the fluid passes through the restrictor, its velocity increases, while the pressure drops. By measuring this pressure difference (ΔP = P1 - P2) and knowing the density of the fluid (ρ), it is possible to calculate its flow velocity (V) according to the following formula:
V = √[(P1 - P2) / (0.5 × ρ)]
where:

What is the output signal of a differential pressure sensor?

V is the flow velocity.
This velocity, multiplied by the flow cross-section, is used to deduce the fluid's volume or mass flow rate. This measurement method is suitable for a wide range of industrial applications, and requires no power supply.

P1 is the pressure measured upstream (high-pressure side),

P2 downstream pressure (low-pressure side),

ρ the density of the fluid,

fuji electric guides you in choosing the most suitable technology

Guide to choosing depressants

Depressant organs
Orifice plate and
corner taps

Integrated orifice placeVenturis and NozzlesAverage Pitot tubesV-ConeTM flow meter
orifice plates diaphragmsflow meters with integral orificeNozzlesmedium pitot tubesv cone flow meters
Diameter mini.DN501/2′ NPTDN50DN50DN15
Diameter max.DN10001/2′ NPTDN800DN1500DN3000
Static pressure max.500 bar160 barAll50 bar689 bar
Temperature max.200 °C120 °CAll350 °C450 °C
Reynolds numbers>2 500>2 500>20 000>12 000>4 000
Rangeability5:15:15:110:110:1
Straight lengths
(upstream/downstream)
3D/5D3D/5D5D/3D7D/4D0D/3D
Accuracy± 1,5 %± 2 %± 1 %± 1 %± 0,5 %
Load lossAverageAverageAverageLowLow
Applications             Gases, vapors, corrosive and non-corrosive fluids

Primary element : essential for accurate, reliable fluid measurement!

Opt for industrial performance

/ Depressurizers are essential for reliable, accurate flow measurement in line with industrial requirements, whether for liquids, gases or steam. Their robust, standardized design (orifice plate, venturi, nozzle) ensures perfect compatibility with critical environments and industrial automation systems.

At Fuji Electric, we offer you a complete range of differential measuring devices, perfectly adapted to the most demanding applications in the energy, chemical, oil & gas, nuclear and hydrogen sectors. Combined with our high-precision pressure transmitters, these devices enable you to optimize your process control while controlling your operating costs.

Need technical advice or customized sizing?
Our experts can help you choose and integrate the solution best suited to your needs.

Request a customized study today and enter a new dimension of industrial flow control with Fuji Electric.