Do you want to know how an oval gear works?

Do you want to know how an oval gear works?

Oval gear flowmeters are categorized as positive displacement flow technology. They are considered as direct volume meters. Their measuring element includes two toothed precision oval wheels. They are used to measure the volume flow rate of liquids and liquefied gases in the chemical and petrochemical industry, in the food and beverage industry and also in the mineral oil industry.


It is a flow meter that provide precise volumetric ¬ flow measurement of clean fuels and lubricants in industries which including automotive, transport, aviation, mining, agriculture, earthmoving & construction.

Wants to know more about positive displacement here is the link to it: Positive Displacement flowmeters

Construction of oval gear

The meter should be installed in a position that prevents it from draining down as on start-up serious damage could result by “impacting” an empty flowmeter with a high velocity fluid stream.

The flowmeter must be mounted so that the rotor shafts are in a horizontal plane. The rotar shafts will be in horizontal plane if the flowmeters are mounted. So by mounting the meter, the terminal cover or integral instrument display, whichever is fitted, will be facing in a horizontal direction. The pipe-work will be designed in such a way so as to eliminate the reverse flow.


  1. Body assembly
  2. Rotor assembly set
  3. Body-o-ring
  4. Meter cap
  5. Cap screw
  6. Pulse output broad
  7. Output broad screw
  8. Terminal cover o-ring
  9. Terminal cover
  10. Terminal cover screw
  11. Flange portion o-ring
  12. Flange portion screw
  13. Flange portion

Working principle

Fluid passing through the meter causes the rotors to turn. Oval gear meters are displacement-type volume meters that transport defined incremental volumes in individual measuring chambers. The measuring element consists of two high precision toothed oval gears, which are driven by the flow of the medium and mesh with each other.

In this way, a defined volume is transported for each rotation of the pair of oval gears. The number of rotations is a measure of the amount of fluid that has passed through the meter. The rotations are detected by a sensor element.

How does oval gears measures?

When liquid flows through this type of positive displacement flowmeter, two oval geared rotors measure a constant volume per rotation within a precisely machined measuring chamber. With each rotation, a constant volume of liquid is measured.

The rotation of the oval gears is detected through magnets embedded inside the rotors. These magnets transmit a high resolution pulse output. The output signal can be processed externally through a remote display controller or PLC or through a variety of output / display options available as accessories connected to the flow meters.


There are two types of outputs available in each meter, the open collector of the Hall effect sensors or the switch contact of the reed switch. Each type of output is linearly proportional to the volumetric flow and each pulse is representative of an equal volume of liquid.

Pulse output from the Hall effect sensor The Hall effect sensor is a 3-wire solid state device that provides an open collector output NPN. It requires a DC voltage between 5 ~ 24Vdc to operate and is the recommended pulse output for power-hungry installations, such as local or remote batches. The pulse output between the signal and -0V is a square wave of voltage with the high level being the DC voltage available in the open collector and the low level of -0V.

The receiving instrument must incorporate an extraction resistance (typically greater than 10K ohms in most instruments) that links the open collector to the available DC voltage level when the Hall sensor is not energized. When activated, the open collector output is grounded through the emitter (-0 V).

Latch switch pulse output The Latch switch output is a normally open two-wire SPST non-voltage contact ideal for non-energized installations or for use in hazardous area locations.


The oval gears are designed and specified for standard fuel and oil applications including:

• Distribution and dispensing of fuels, fuel oils, lubricants

• Blending of bio & ethanol fuels and lubricating oils

• Fuel consumption monitoring for boilers, generators and vehicles

• Pumped or gravity fed applications

Suitable for viscous, non-abrasive, clean liquids like Petroleum, Oil, Chemicals, Grease, Fuels, Ink, Pastes etc.

Performance features

• Positive displacement meter for volumetric flow rate or total flow measurement.

• Applicable for fluids such as lubrication oils, mineral oils, hydraulic oils, fuels, liquified gases and others.

• No inlet or outlet section required.

• High-quality construction for long service life and high reliability.

• Long-term stability.

• High measurement accuracy and repeatability.

• Easy installation


• The positive displacement flow technology allows for precise flow measurement of most clean liquids regardless of the media’s conductivity.

• Other liquid properties also have a minimal effect on the performance of this type of meter

• The unit is manufactured in a choice of materials and pressure ratings to suit most applications and as with all positive displacement flowmeters, the performance improves with increasing viscosity achieving an accuracy of ±0.1% of reading with higher viscosities.

• These flowmeters can be installed within hazardous areas by using the reed switch pulse output in Intrinsically Safe loops or fitting Intrinsically Safe certified Instruments. Please consult the factory for the availability of flameproof models.


• The standard meters can be used up to 1000 cP; above this viscosity specially profiled gears must be used.