How are the hydraulic systems powered on a 737-800?

The hydraulic systems on a Boeing 737-800 are powered primarily by engine-driven pumps, which are typically connected to the aircraft's engines. These pumps provide the necessary hydraulic pressure for operating the aircraft's various systems, including flight control surfaces, landing gear, and brakes. In addition to the engine-driven pumps, the 737-800 is equipped with an AC electric motor-driven pump that serves as a backup in case of an engine pump failure or during engine start-up when hydraulic pressure is needed prior to engine operation. This combination of engine-driven pumps and an electric motor-driven pump ensures a reliable hydraulic system, capable of maintaining performance under various operating conditions.

The other options would not provide the necessary hydraulic pressure for the systems onboard. Gravity feed from fuel tanks is not a mechanism used to power hydraulic systems; it is primarily a method for fuel delivery. Standby batteries are not designed to power hydraulic systems directly, as their primary use is to provide power for electrical systems when the main power source fails. Relying solely on electrical pumps would not meet the demands of hydraulic systems effectively, particularly in terms of pressure and reliability during flight operations.