Tech. Sgt Christopher Shields, 28th Munitions Squadron trailer maintenance NCO in charge, releases a valve to empty brake fluid from a munitions trailer at Ellsworth Air Force Base, S.D., Feb. 7, 2013. Each drum must be bled of brake fluid to ensure all air is removed from the lines which guarantees constant pressure in the hydraulic system. (U.S. Air Force photo by Airman 1st Class Alystria Maurer/Released)