A combined air vent and pressure switch are provided at the inlet of a liquid pump. The air vent is adapted to exhaust air from a supply line, such as a garden hose, and thereby substantially prevent the pump from running dry before water from the hose reaches the inlet. The pressure switch is connected to the motor of the pump and is adapted to signal the motor to stop if the pressure switch senses a low pressure condition at the pump inlet, such as when there is inadequate liquid or no liquid at the pump inlet. The features of the air vent and pressure switch combine to prevent the pump from being damaged by running the pump without adequate liquid supply.