Guide To Choosing The Correct Fuel Flow Meter

Guide To Choosing The Correct Fuel Flow Meter

What is a fuel flow meter ?

During the process of transferring fuel from one place to another, perhaps from a tank to a vehicle, a fuel flow meter is often used to check the quantity of fluid or fuel that has been moved. These meters usually have a numerical display but these can have either digital or mechanical faces. In some cases though they may not have a local display, but work by sending an electrical pulse to a remote display. Because of the many different fluids and transfer applications there are lots of options in flow meter styles. These can be turbine, oval gear or nutating disk style meters. Although different in the way they work they all do the same thing.

Types of fuel flow meter

turbine fuel flow meter
A turbine fuel flow meter

Turbine Fuel Flow Meters

A rotating turbine is the main feature of a turbine fuel flow meter. A turbine rotates on an axis and the flow rate is recorded as the fluid passes over it.  The fluid’s velocity will be proportional to the rotation speed once it becomes constant. In the case of a digital turbine fuel flow meter one of the blades of the turbine would have a magnet or sensor on it that passes a pulse to the computer on each rotation. A good example of digital turbine meter is the GPI G2 digital turbine flow meter range.

Oval Gear Flow Meter
Oval Gear Flow Meter

Oval Gear Fuel Flow Meters

Two gears within the an oval gear flow meter rotate at right angles to each other in a t-shape. Therefore the centre point of the flow meter will be the point at which the two gears teeth will mesh. As a result this ensures no fluid can pass through this point. The gears rotate as the fluid pushes against them, moving the fluid in the measuring chamber to the meter’s outlet port. At the same time, as the fluid entering the flow meters inlet port, the gears will then drive it into other measuring chamber. As one measuring chamber opens the second chamber closes, this continues to alternate as the gears rotate. Measured by magnets in the rotating gears as they pass an electric reed switch they transmit a signal which then calculates the flow, based on the speed of the rotation.

nutating disk flow meter
A Nutating Disk Flow Meter

Nutating Disk Fuel Flow Meter

This type of meter contains only one essential moving part and is relatively inexpensive and accurate. Its operating principle is very simple, but it may be difficult to understand its operation without actually inspecting the device firsthand. The device consists of a metering chamber with spherical sides and conical top and bottom. A disk passes through a central sphere and divides the chamber into two portions. The disk is constrained to be at an angle not normal to the axis of symmetry of the chamber.

A radial plate (diaphragm) divides the chamber so that the entering fluid causes the disk to wobble (nutate), with fluid flowing alternately above or below the disk. The fluid exits the chamber after the disk has completed one wobble. This wobble corresponds to a specific volume of fluid passing through the chamber. During each wobble of the disk, the pin attached to the tip of the center sphere, normal to the disk, completes one circle. The volume of fluid that has passed through the meter can be obtained by counting the number of revolutions completed.

Selecting the correct fuel flow meter for your application

When considering the use of a fuel flow meter within a diesel dispensing system, the flow meter will count the amount of fuel in that transaction as it’s being dispensed. This would be called the batch total, this total is usually resettable before each transaction. Consequently there are two totals on most flow meters, the other is a cumulative total which is a total amount of fuel transferred over the lifetime of the flow meter and is normal non resettable. This would be almost the same for an Adblue flow meter. With the exception of the internal parts that are chemically compatible with Adblue. Due to the slow consumption rate of heating oil it is measured over a period of time.

Most fuel flow meters will either be mechanical or digital.  A battery powered flow meter will usually have a digital display.  Alternatively a tick over digit display fuel flow meter will be mechanical.  Accuracy is another factor to consider when selecting a fuel flow meter. The stated accuracy rating for a fuel flow meter will depend on the meters flow rate range. For example the flow rate of the fuel will need to meet the minimum flow to maintain accuracy.

Therefore the flow rate must be another consideration when selecting the right flow meter. Litres per minute is the most common flow rate when it comes to fuel flow meters. A meter checking heating oil would be measuring in litres per hour because of the low consumption rate. Diesel has a general flow rate maximum of 120lpm as this would cover the flow rate range expected for refuelling. Consequently you should expect higher flow rates when performing a bulk transfer of fuel and therefore would require a meter capable of measuring higher flow rates up to 500lpm.

What is a pulse meter ?

Whilst still the component that measures the flow in a system, a pulse fuel flow meter has no display to show the amount of fuel transferred. As the name suggests instead of visually displaying a pulse meter sends an electronic signal to a remote receiver unit.  The setting on a pulse meter will usually be one pulse per litre or part litre.

Third party fuel management systems or larger building management systems sometimes require an electronic link to the fuel dispensing system. An ideal job of the pulse meter is to send the quantity dispensed in an electronic format to these other systems.  Furthermore a pulse meter can send a reading to a remote location. Perhaps in a fleet manager’s office rather than at the refuelling point of a transport company.


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