Range Overview: Positive Displacement Flow Meters

Macnaught’s Positive Displacement Flow Meters are suitable for a wide range of industrial applications including fuel and oil distribution, corrosive chemical, solvent measurement and high pressure applications to name a few. Macnaught offers Positive Displacement Flow Meters featuring Oval Gear technology. The measuring principle includes two high precision toothed oval gears, which are driven by the flow of the medium and mesh with each other: in presence of a flow, defined volumes of fluid are transported through the meter for each rotation of oval gears pair. As the flow rate increases, so does the rotational speed of the rotors. The number of gear rotations is a measure of the amount of fluid that has passed through the meter; each rotation is detected by a sensor and the volume is calculated using a conversion factor (K factor). Figure 1: Macnaught Positive Displacement Flow Meter operation.

A key distinction of positive displacement flow meters is that they offer direct measurement of the volumetric flow rate. Positive displacement flow meters are frequently specified as they offer high accuracy and repeatability. They readily provide measurement accuracy within +/-0.5% of the true value. Additionally, positive displacement flow meters require no power to drive the gear operation with no special fluid conditioning (e.g. straight lengths of pipe) and are capable of handling high pressure, large flow variations and plant equipment vibration due to their robust design.


  • High accuracy and repeatability
  • High accuracy and repeatability
  • Suitable for viscous fluids
  • Cost-effective
  • Accuracy unaffected by changes in viscosity
  • Requires minimal maintenance
  • Ease of installation
  • Exceptional turn-down ratio

Precision engineering and manufacturing methods are used by Macnaught using cutting edge CNC machining technology and mill certified materials to deliver highly repeatable accuracy and durability. All critical components are machined in-house with astute quality control monitoring the production process continuously.*

As a result of over 50 years experience with Positive Displacement Flow Meter technology, Macnaught offers two comprehensive ranges that cater for the ever changing market needs. The latest innovation with the MX-SERIES range to the original M-SERIES range, Macnaught flow meters are designed to insist upon durability, reliability and excellence.

The MX-SERIES is the latest innovation featuring:

  • High precision billet construction for enhanced material integrity and process reliability
  • High precision billet construction for enhanced material integrity and process reliability
  • Programmable digital display and Pulse output options• Unique bayonet assembly for added versatility and flexibility


The M-SERIES is Macnaught’s original range of meters featuring:

  • Established design and cast construction for proven performance
  • Mechanical and pulse output options