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Straight Run Requirements for Flow Meters

Why are Straight Pipe Runs for Flow Meters Necessary?

Why do straight piping requirements for flow meters even matter? The answer to this question is surprisingly simple. For many flow technologies, turbulent and swirling media within a pipe is hard to measure in a reliable and accurate manner. There are many obstructions and details within a piping system that case cause a flow profile to become turbulent. If this occurs relatively close to flow meters, it can lead to significant errors as high as 50% of the reading.

There are many types of variables and configurations that can lead to an undesirable flow profile. Some common examples are bends in the pipes from elbow joints, control valves, pressure taps, T-joints, other instrumentation, thermowells, reducers, and more. Anything that can cause the flow to move in a non-linear way needs to be properly accommodated for to ensure the accuracy of your flow meter readings.

Straight Runs for Flow Meters Explained

What are the Straight Run Requirements for the Different Flow Meter Types?

Different flow meter technologies have different straight run requirements, based on the inherent principle of operation being used. The requirements are usually expressed in terms of the distance away from the flow meter in a multiplication factor of the pipe diameter. They are also expressed as being either upstream (from the instrument) or downstream (from the instrument). It is important to consider straight run requirements ahead of time to ensure that the flow meter you select will fit in the space that the current system already has to offer.

While there are some general ballpark rules of thumb that can be used in reference to the straight run requirement for the flow meter technology type, each application may have its own special unique considerations that will need to be accounted for when choosing a flow meter.

Always consult the manual that came with your flow meter for exact straight run requirements as the following information below is only a general reference. If you are unsure, you can always contact our expert engineers for fast and free flow meter selection help.

What are the Straight Run Requirements for Magnetic Flow Meters?

  • Usually, 5x upstream and 3x downstream straight run requirement
  • Minimal requirements compared to many other technology types

What are the Straight Run Requirements for Differential Pressure Orifice Plate Flow Meters?

  • Difficult to give a general range for DP flow meters
  • Helpful to use impulse lines on either side
  • Actual requirement depends on the type of upstream elements and the beta ratio
  • Beta ratio is defined as the diameter of the pipe orifice divided by the pipe diameter

What are the Straight Run Requirements for Vortex Flow Meters?

  • Require a stable and symmetrical flow profile
  • Requirement depends on the obstruction
  • Usually, 30x downstream of control valves
  • Usually, pressure taps must be 3x-4x downstream
  • Any temperature elements must be 5x-6x downstream

What are the Straight Run Requirements for Coriolis Mass Flow Meters?

  • Generally, do not have any straight run requirements
  • Operating principle is insensitive to disruptions in the flow profile

What are the Straight Run Requirements for Ultrasonic Flow Meters?

  • Install upstream of any flow obstacles
  • Provide as much space between obstructions and the flow meter
  • Can go as close as 5x, but it results in an additional 1% inaccuracy in the reading
  • Example: KOBOLD DUK requires 10x upstream and downstream straight run requirement

What are the Straight Run Requirements for Thermal Mass Flow Meters?

  • Usually, 5x upstream and downstream straight run requirement recommended

What are the Straight Run Requirements for Insertion Flow Meters?

  • Due to the nature of the measuring probe protruding into the media and creating its own obstacle of sorts, the straight run requirements for insertion flow meters is high
  • Usually, 20x to 50X upstream straight run requirement recommended

What are the Straight Run Requirements for Rotameter Variable Area Flow Meters?

  • No straight run requirements necessary

What are the Straight Run Requirements for a Turbine Flow Meter?

  • Usually 10x-15x upstream and 5x downstream straight run requirements
  • Certain obstructions can increase the requirements
  • 20x for 90-degree elbow or T, etc.
  • 25x for partially open valves
  • 50x for 2 elbows or any spiraling flow

What are the Straight Run Requirements for a Paddle Type Flow Meter?

  • Usually, 5x upstream and downstream straight run recommended

What are the Straight Run Requirements for Paddle Wheel Flow Meters?

  • Depends on the flow meter
  • Can be anywhere from no requirement to 20x

What are the Straight Run Requirements for Positive Displacement Flow Meters?

  • No straight run requirements
Straight Pipe Requirements for All Flow Meter Types

Choosing a Flow Meter for Your Application

Still confused about which flow meter technology may be best for your application? Learn more about choosing a flow meter in our in-depth article or call one of our knowledgeable engineers now for fast and free assistance.

Learn more about why you should partner with KOBOLD for your application.

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KOBOLD USA is a subsidiary of KOBOLD Messring GmbH, a world-leading instrumentation engineering business founded in Germany in 1980 by Klaus J. Kobold. With patented technology and superior service, the company quickly established itself as one of the global leaders in sensor and control systems with high quality products. The KOBOLD brand name became synonymous with superior quality and technological advancement in instrumentation engineering.

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