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EMCO Controls

How to select a suitable thermowell

EMCO Controls manufactured its first venturi tube in 1987, which was also the first delivery to an international customer. The Venturi tube therefore paved the way for our international endeavours and has been a core product ever since. In this article, we will offer you a surface-level understanding of this important piece of flow instrumentation. 


A venturi tube is a short pipe with an inner constriction that can be used to measure fluid. The Venturi tube is designed by and named after the 18th–19th-century Italian physicist Giovanni Battista Venturi, who noted the effects that constricted channels have on fluid flow. Based on his observations, he designed a device with a narrow throat in the middle, causing a phenomenon known as the Venturi effect. 

The Venturi effect states that the pressure will drop when a fluid passes through the tube and enters the narrow throat, which is the opposite of what one would immediately think. This relationship between pressure and velocity can be used to mix certain substances such as gasses or fluid with air at a continuous rate.

The natural design of the Venturi makes it suitable for applications requiring a low permanent pressure drop. 


The Venturi effect is widely used in industry and everyday products to mix different substances at controlled rates. Here are some examples of where it is used:

  • in barbecues, gas stoves, bunsen burners and airbrushes
  • the choke on a car engine
  • the air pump on a fish tank
  • atomizers that disperse perfume or spray paint
  • foam firefighting extinguishers nozzles
  • sand blasters – draw sand in and mix it with air


There are two different types of Venturi tubes which each have their own specific advantages. The 2 types differ in such a way that the body of the Venturi tube can either be welded from rolled sheet or machined from solid bar. This results in a difference in accuracy, with the machined process ensuring a more precise internal diameter which gives it an accuracy of 1% as opposed to 1,5% for welded sheet Venturies. 

The machined Venturi tube allows us to make a Venturi body with large wall thickness and is well-suited for: 

  • High pressure applications i.e., high pressure steam from boiler process or high-pressure gas applications i.e. LNG process.
  • Producing quite small Venturi tubes i.e. 2” to 4”, where fabrication processes are less time consuming and therefore more cost effective.

The welded sheet Venturi is welded together in sections thus making it suitable for larger Venturi diameters in low pressure applications. Welded sheet Venturi tubes are ideal for:

  • air flow intakes i.e. primary and secondary air intakes in boiler applications.
  • flue gas or exhaust gas going to chimney/stack
  • low pressure water application i.e. feed water process
  • low pressure steam applications i.e. industrial applications

Related Products

Classical Venturi Tube Machined

Graphic model of machined venturi tube

Classical Venturi Tube Welded Sheet