• Liquid, Gas and Steam Flow Measurement
  
• Low Installation Costs
  
• Long Term Accuracy
  
• Minimal Unrecovered Pressure Loss
  
• Suitable for Large Pipes and Ducts
  
• ‘Hot-Tap’ Versions Available
  
• Optional Integral Manifold
  
• Flow Transmitters Fitted
  
• Mass Flow Measurement

General Description
The Averaging Pitot Tube is a differential pressure producer suitable for liquid, gas and steam flow measurement. It offers simple, low cost installation into pipes and ducts, and high energy savings due to its low unrecovered pressure loss. There are no moving parts or sharp edges to wear, so long term accuracy can be maintained.

‘Hot-Tap’ versions are available which allow the Averaging Pitot Tube to be withdrawn from the process whilst still under pressure.

Versions fitted with an optional manifold allow close mounting of differential pressure transmitters. For true mass flow measurement, a multivariable transmitter may be fitted.

Specification

Pipe Sizes
Standard Averaging Pitot Tubes can be provided to suit pipe sizes from 80 mm up to several metres in diameter. Flow in square and rectangular ducts may also be measured by Averaging Pitot Tubes. For small pipe sizes, in-line Pitot devices are available.

Probe Diameter
Depending on pipe size and process conditions, probe diameters may be 13 mm, 25 mm or 60 mm (nominal).

Materials
Averaging Pitot Tubes are provided in 316L Stainless Steel as standard. Other material grades are available to special order, including Duplex Stainless Steel , Monel® 400 and Hastelloy® C-276.

Process Connection
Connections to the pipe may be either flanged or screwed. A wide choice of sizes and ratings are available.

Impulse Connection
Averaging Pitot Tubes may be specified with a variety of impulse connections including threaded, socket weld or flanged. Primary isolation valves may also be supplied, appropriate to the process temperature and pressure.

Opposite Supports
When fluid flows past an Averaging Pitot Tube, vortices form at both sides of the probe. These vortices detach, first from one side, and then from the other. This phenomenon is known as the Von Karmann effect. The frequency of shedding of these vortices is a function of the diameter of the Pitot Tube, the fluid velocity and, to a lesser extent, the Reynolds number. The vortex shedding subjects the Pitot Tube to a periodic transverse force. As the vortex shedding frequency approaches the natural frequency of
the Pitot Tube, it will oscillate, and is liable to snap off. This effect is taken into account when designing the Pitot Tube.

When the natural frequency of the Averaging Pitot Tube coincides with the vortex shedding frequency a lower support may be used to counteract these effects. Opposite supports can be provided in any material in line with the pipe specification.

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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