will also cause a change in pH number.) Normal values
for the viscosity and pH number of the unused fluid are
Viscosity (fluid temp. 100ºF): 185 to 210 SSU
pH number: 8.8 to 9.8
fluid, NAEC P/N
217768-3 is nontoxic and requires no special
clothing or handling procedures. If splashed
into eyes, flush with water.
Accumulator and Air Flasks
The accumulator receives the hydraulic fluid
delivered to the system by the hydraulic pumps and
delivers it to the retraction engine cylinder, bridle
tensioner, and other components of the catapult where
high-pressure fluid is required.
The two 50-cubic-foot air flasks are installed in the
base of the retraction engine. The air flasks contain no
moving parts. Drain valves are provided for
maintenance. Figure 4-47 illustrates the two types of
accumulators used with linear retraction engines.
Main Hydraulic Pumps
The main pump sets (figs. 4-44 and 4-45) deliver
hydraulic fluid to the retraction engine accumulator.
The hydraulic pumps are connected in parallel. The
intake line to each pump is provided with a strainer.
Each pump discharge line is fitted with a delivery
control unit, which has a built-in relief valve. When the
hydraulic fluid leaves the pumps, the delivery control
unit directs it either through the bypass line back to the
gravity tank (pump offstroke), or through the pressure
line to the main accumulator. This pressure line is
equipped with one-way check valves to prevent the
backing up of fluid from the accumulator when the
pumps are offstroke.
The gravity tank is designed to fit the individual
installation. Baffles are installed to minimize entrapment
of air in the hydraulic fluid.
The fluid stored in the gravity tank enters the
pumps through the pump intake screen, which filters
out any large particles of foreign matter that may be in
the fluid. The fluid goes into the main pumps, which
are connected in parallel. The intake line to each pump
is fitted with a shutoff valve and a strainer.
The strainer assists in removing dirt from the
hydraulic fluid. The fluid then passes through the
pumps, which generate a pressure in the fluid. As it
leaves the pumps, the fluid is fed through the delivery
control unit, which incorporates adjustable relief valves.
The fluid then passes through the pressure line, which
carries it to the retraction engine accumulator.
The retraction engine accumulator operates to
maintain the pressure of the fluid within the required
pressure range (2700 psi on C-7/C-11, 2500 psi on
Hydraulic fluid under pressure from the pumps is
forced into the main accumulator. This fluid pushes a
piston against preset air pressure. The force of the air
against the piston keeps a constant pressure in the
Normally, the pumps operate automatically. For the
C-7 and C-11 catapults, this is accomplished through
the action of a tailrod switch. When the hydraulic fluid
chamber is filled to maximum capacity, the tailrod is
withdrawn into the accumulator, and the cam trips the
lever on the tailrod switch, de-energizing the solenoids
on the delivery control unit. This stops the flow of fluid
to the accumulator and directs fluid from the pumps to
the gravity tank. When a hydraulic component is
operated, air pressure in the accumulator pushes the
piston toward the hydraulic-end cover, forcing hydraulic
fluid to the component. As the hydraulic fluid is used,
the tailrod is extended from the accumulator until the
cam on a second guide trips the switch lever, energizing
the solenoids on the delivery control unit to direct fluid
to the accumulator. Fluid is then pumped to the
accumulator until the cam on the first guide trips the
The two cams on the tailrod guide are
spaced far enough apart to prevent the pumps
from going onstroke every time a small amount
of hydraulic fluid is discharged from the main
accumulator. In addition, a hydraulic volume
normal limit switch is installed to maintain an
adequate amount of fluid to complete a launch