How Does A Petrol Pump Work?

Flow meters are used in many applications in both domestic and industrial environments. And if you own a car you’ll use a flow meter every time you fill up the car with a tank of fuel. The flow meter isn’t in the car… it’s in the fuel pump at the petrol station.

When you are filling up your car with a tank of petrol you’ll likely be considering how long it’ll take to fill up the tank and if you’ll be able to stop at the amount you require without going over this by the obligatory extra penny. The petrol station owner needs to know how much petrol you’ve put in the tank so he can accurately charge you for this amount … and this is where the flow meter comes in.

As fuel travels through the petrol pump when you depress the filling nozzle handle it passes through a flow control valve which regulates how fast the fuel enters the tank. This is done using a small plastic diaphragm which is squeezed when the flow of petrol increases so only the exact amount of petrol flows through it.

The fuel is stored in huge tanks underneath the service station which can hold around in excess of two thousand gallons of fuel. Being at a level lower than the petrol pump itself poses a problem as the fuel cannot flow to your car using gravity, so a submersible pump sits in the liquid which uses an impeller to push the petrol over the long vertical distance it has to travel when required.

To measure the amount of fuel used the petrol pump will also contain a flow meter which is usually a small chamber which contains a simple rotor or series of gears. This ‘counts’ the units of petrol as it flows past the meter. The petrol flow is monitored by a computer connected to the dispenser which displays how much petrol you’ve pumped at the pump and at the petrol station owner’s digital display screen.

To maintain accuracy of the flow meter so that you are paying the right amount for the petrol you’ve pumped, the petrol companies will regularly inspect the pumps for volume accuracy. To do this they will typically use a container of a known volume and fill this with petrol. They will then compare the volume of petrol in the container to the volume reading on the pump.

David Forsyth wrote this article about components such as flow meters and pressure switches on behalf of

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