Fuel is only pumped to the carburettor as required and depending on the fuel level in the carburettor bowl, with integral valves controlling the flow and pressure, despite the continuous action of the pump arm. Air leakage on the inlet-side can cause the air to be drawn into the pump and make the pump less efficient. Mechanical pumps are generally placed below the petrol tank to avoid the inlet pipe emptying back into the tank in case of air leakage, which can make any direct signs of leakage invisible and cause the pump to work harder than usual; as such, it is recommended to have periodic checks on the inlet side of the fuel pump in case of any problems.