• Classical Venturi Tubes
  
• Venturi Nozzles
  
• Calculation, Design and Manufacture to
  
• BS EN ISO 5167:1
  
• Fabricated from Plate or Machined from
  
• Bar/Forgings
  
• Flanged or Weld-In Construction
  
• Range of Material Grades
  
• Pipe Sizes from 50 mm to 1200 mm
  
• Calibration Service on Request

General Description
There are two common types of Venturi tube - the Venturi Nozzle, and the Classical (Herschel) Venturi. Both feature a convergent inlet section and a divergent outlet section. The classical Venturi convergent section is a simple truncated cone, whereas for the Venturi nozzle, the inlet contour matches that of the ISA 1932 flow nozzle.

The major advantage of the Venturi over orifice plates and flow nozzles is in the area of pressure recovery. Typically, unrecovered pressure is in the region of 10 - 30% of measured DP as opposed to 40 - 90% for an orifice plate (depending on beta ratio). Although the cost of a Venturi can be comparatively high, where pumping costs are important the initial outlay can be warranted.

Another advantage of the Classical Venturi over the other differential pressure producers is that the requirements for upstream and downstream straight pipe lengths are somewhat less onerous.

Materials
Venturi tubes and Venturi nozzles can be supplied in a wide range of material grades.

Machined devices can be manufactured from barstock, or forgings. Standard materials include ASTM A182 F316 & F304 Stainless Steels, ASTM A182 F11 & F22 Chromium Steels and ASTM A105 Carbon Steel Standard materials for fabricated devices are ASTM A240 316/L Stainless Steel and Carbon Steel.

We are experienced in machining and welding exotic materials, including Hastelloy®, Inconel®, Incoloy® and Duplex Stainless Steels.

Incoloy, Inconel and Monel and are trademarks of INCO Alloys International Inc.
Hastelloy is a trademark of Haynes International Inc.

Pressure Tappings
Venturis can be supplied with a wide variety of pressure tappings, including threaded connections, socket weld connections and welding nipples.

We can also supply isolation valves, condensate chambers and manifolds, as the application demands.

Required Straight Lengths
Upstream straight pipe requirements for classical Venturi tubes are less than those required for orifice plates, flow nozzles and Venturi nozzles - the convergent portion of the classical Venturi is designed to obtain a more uniform velocity profile at the throat of the device.

Fittings located more than four throat diameters downstream of the plane of the throat tapping do not affect the accuracy of the measurement.

British Rototherm Company Limited,
Kenfig Industrial Estate, Margam,
Port Talbot   SA13 2PW
United Kingdom

Telephone: +44 (0) 1656 740 551
Facsimile: +44 (0) 1656 745 915
E-mail: rototherm@rototherm.co.uk

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