Final answer:
Pressing the BOOST PUMP switches increases fuel pressure by activating an auxiliary pump that supports the fuel system, especially if low pressure is detected.
Step-by-step explanation:
When the BOOST PUMP switches are pressed on an aircraft's fuel system, it increases fuel pressure. The boost pump is an auxiliary pump that helps maintain fuel pressure in the system, ensuring that the engines receive a constant flow of fuel under varying conditions. It does not deactivate the fuel system or reduce fuel flow; instead, it provides an additional pressure source to support the fuel system. If low pressure is sensed at either main ejector switch, activating the boost pumps ensures the proper functioning of the system and prevents fuel starvation to the engines. Regarding thermodynamics, the work done by a gas in a system will increase if a large amount of energy is added to or extracted from the system, resulting in an increase in the gas's volume, pressure, or both.