Tuesday, October 10, 2017

Applying Turbine Flow Meters With Clean Liquids and Gases

turbine flowmeter flow meter with flange connections
Turbine flow meter
Image courtesy Hoffer Flow Controls
A turbine flow meter provides a volumetric measurement of liquid or gas flow through the use of a vaned rotor (turbine) inserted in the fluid flow path. Fluid movement causes the turbine to rotate at an angular velocity proportional to the flow rate. A pickup senses the passage of the rotor vanes, producing a sine wave electrical signal output which is detected by the unit electronics. The frequency of the signal relates directly to the turbine rotation and fluid flow rate.

Generally, a turbine flow meter is applied to measure unidirectional flow. Some turbine flow meters, through the use of two pickups, have the capability to measure flow in both directions.

There are a number of considerations when selecting a turbine flow meter:
  • Material of construction: Numerous material options are available for the housing and internal parts. Proper selection considers media characteristics and cost.
  • Bearing selection: The combination of bearing type and material will likely be selected by the device manufacturer, based upon a comprehensive application information set.
  • Pickup selection: Several pickup options may be available, with the manufacturer making a recommendation that best suits the application parameters.
Here are a few other things to consider about applying turbine flow meters:

  • Turbine flow meters are precision instruments and will not tolerate debris well. An installation should include a strainer configured to trap debris that may damage the instrument or hinder its operation.
  • For longevity, it is advisable to size the flow meter to avoid extended operation near the upper end of its rotational range. Excessive rotational speeds can accelerate wear on bearings.
  • Lower rotor mass will provide more rapid response to changes in flow, allowing use of the device in applications with flow pulsations.
  • Maintain sufficient downstream pressure to prevent flashing or cavitation. This condition will cause the instrument to produce readings higher than the actual flow rate.
  • Sufficient straight pipe length should be installed at the inlet and outlet of the flow meter to provide flow conditioning necessary for accurate readings. In some cases, a flow staightener may be needed on the upstream side.
  • The output signal from the pickup may need amplification or other signal conditioning. Electrically noisy environments or long cable lengths may require special treatment.

Careful consideration of what is necessary for proper operation will pay off with reliable and accurate performance, low maintenance, and a long service life. Share your flow measurement challenges with product application experts, combining your process knowledge with their product application expertise to develop effective solutions.