Figure 9-6. Jack Hydraulic Schematic Diagram
into the cylinder. As more fluid is pumped into the
cylinder, the fluid pushes the rams upward. By opening
the release valve, pressure is released and the rams
retract. The safety valve becomes operative when the
load to the rams exceeds the maximum allowable load
of the jack.
Types. Aircraft jacks vary by weight lifting
capacity, style of assembly, and intended use. Two
common styles of jacks are tripod and flat base. Aircraft
jacks with weight lifting capacities from 3 to 12 tons will
be described in the following paragraphs.
Tripod jack, 12-ton. The 12-ton
tripod jack, shown in figure 9-7, will lift 24,000 pounds
vertically. It has a closed height of 14 inches and a lift
of 23 inches. The casters depress and the jack rests on
3 feet when a load is applied.
Tripod jack, 5-ton. The 5-ton tripod
jack, shown in figure 9-8, will lift 10,000 pounds
vertically. The jack is designed to provide 5 tons of
lifting effort through a range of 23-9/16 inches collapsed
to approximately 75-9/16 inches when fully extended.
The spring-loaded casters retract when under a load.
Tripod jack, 3-ton. The 3-ton
tripped jack, shown in figure 9-9, will lift 6,000 pounds
vertically. It has a closed height of 14 inches. The tripod
legs are equipped with swivel castered wheels. Until a
load is applied to the jack, a spring-loaded yoke and
spindle keeps the base of the jack foot assembly about
2 inches from the grounds.
Aircraft landing gear jack. The
aircraft landing gear jack, shown in figure 9-10, will lift
10,000 pounds vertically. It has a collapsed height of 5
1/2 inches and a lift of 9 inches from the rams. When
fully extended, the extension screwlift provides another
3 inches of lift.
Figure 9-7. Tripod Jack, 12 -Ton