Independent technical reference. Not affiliated with, endorsed by, or a distributor for Macnaught or any manufacturer. The name is used only to describe a class of oval-gear meter.
Macnaught is well known for compact, rugged oval-gear flow meters aimed at oils, fuels, lubricants and chemicals — the kind of small-to-mid-line positive-displacement instrument found on workshop reels, dosing skids and transfer lines. This page covers the technology those meters represent.
Compact Oval-Gear Metering
These are oval-gear meters: two meshing rotors carry a fixed volume per revolution, measuring liquid directly rather than inferring it from velocity. The appeal is a small, self-contained package that combines the accuracy of positive displacement with a built-in digital display, often with both a resettable batch total and a cumulative total. Because oval-gear meters need no straight run, they drop straight into tight plumbing on a lubrication reel or a mobile fuel rig.
Sizes and Duty
Compact oval-gear meters of this type typically span 1/2 inch to 3 inch (DN15–DN80), handling anything from precise additive dosing to diesel transfer at tens of litres per minute. A representative small-line size is described on our 1-inch DN25 and 2-inch DN50 reference pages. Accuracy sits in the usual oval-gear band of about ±0.5% of reading, improving with viscosity.
Ruggedness and Care
The design's strength is durability — an aluminium or engineered-polymer body, few components and a simple, serviceable rotor set. As with every PD meter, a strainer upstream is essential to keep grit out of the fine rotor clearances, vapour should be excluded, and the meter should be sized so normal flow lands in the accurate middle of its range. Follow those rules and a compact oval-gear meter is a reliable, low-fuss instrument.
For broader mechanical-measurement practice, the American Society of Mechanical Engineers (ASME) publishes useful independent guidance.
Related Reading
See the general oval-gear technology page, the underlying PD principle, and the selection guide for sizing.