Powering Machines with "a"
In Portuguese, when you want to describe how a machine, tool, or device is powered or operated, use the preposition a followed directly by the power source. This simple construction is the equivalent of the English suffixes "-powered", "-driven", or the prefix "hand-".
Notice that no article (like o or a) is used after the preposition in these phrases.
Fuels and Elements
You will frequently see this pattern used with traditional fuels and elements, especially when talking about vintage machinery. Common examples include a vapor (steam-powered), a gás (gas-powered), and a petróleo (oil-powered).
| The steam pump needs more water. | A bomba a vapor precisa de mais água. |
| We do not have a gas oven, but we have an oil lamp. | Não temos um forno a gás, mas temos um candeeiro a petróleo. |
Manual and Mechanical Power
This exact same rule applies to physical mechanisms, whether they require human effort or an internal engine. You can use it with mechanisms like uma manivela (a crank) or um pedal (a pedal) to describe how the gears (a engrenagem) are turned.
| I bought a hand-cranked gramophone at the flea market. | Comprei um gramofone a manivela na feira da ladra. |
| The pedal pump has a broken gear. | A bomba a pedal tem uma engrenagem avariada. |
| The motor-driven fan broke down ten years ago. | O ventilador a motor avariou há dez anos. |