Hydraulically, servo-operated, automatic, change over valves, utilized in a two ram hydraulic steering gear, serve to .
A.
allow an alternate main pump to start in the fully loaded condition thus developing immediate full torque
B.
prevent either main pump from being hydraulically motored when idle by cross pressure flow
C.
prevent both units from operating simultaneously which could result in doubling the flow of oil and pressure leading to over pressurization of the system
【简答题】镁在空气中燃烧除生成氧化镁外,还会生成氮化镁Mg 3 N 2 .写出镁与氮气反应生成氮化镁的化学方程式:______.已知24g镁在空气中完全燃烧,所得生成物总质量______(填“<”“=”或“>”)40g.已知氮化镁是黄绿色固体,根据镁在空气中燃烧的实验现象,可知在这样的条件下,镁更容易与______(填“氧气”或“氮气”)反应,因为______.