What type of pump does the standby hydraulic system use on a 737-800?

The standby hydraulic system on the Boeing 737-800 utilizes an electric motor-driven pump, which is designed to provide hydraulic pressure in the event of a failure in the primary hydraulic system. This type of pump is advantageous because it offers reliability and responsiveness. It allows for the electric motor to be controlled and operated independently, thereby ensuring that essential hydraulic functions can be maintained without the need for manual intervention or physical effort.

Electric motor-driven pumps are specifically engineered to supply hydraulic fluid on demand, improving the efficiency and performance of the hydraulic system. In critical situations where hydraulic power is imperative for safe operations, such as flight control systems or landing gear, having an electric pump ensures that the standby system can quickly assume responsibility and maintain functionality.

In contrast, manually-operated or hand-cranked pumps may require additional effort and could introduce human error or delay in emergency situations, while pneumatic pumps rely on compressed air, which might not be as readily available or effective in maintaining hydraulic pressure during specific scenarios. Hence, the electric motor-driven pump is the most effective choice for maintaining the reliability of the standby hydraulic system on the 737-800.