C. Reservoir, Quantity Gage and Fluid Replenishment:
The left system hydraulic reservoir is located on the left side of the aft
equipment bay. The reservoir is a cylindrical container divided internally
into two compartments, one for left system fluid and the other for AUX
pump fluid. Centered within the cylinder is a spool shaped piston that slides
within the reservoir cylinder. Each end of the piston terminates in a plate-
like divider connected with a central shaft. The central shaft penetrates the
internal cylinder wall separating the left and AUX fluid supplies. The larger
plate on the aft end of the shaft defines the volume of the fluid within the
reservoir. When fluid is added to the reservoir, the fluid forces the large
plate of the spool to the end of the reservoir cylinder when the reservoir is
full. The smaller plate at the opposite end of the shaft is surrounded by an
extension of the reservoir cylinder with a smaller cross section. The design
of the reservoir enables system return fluid, ported into the smaller cylinder
extension, to exert a force on the smaller plate end of the central shaft thus
pulling the larger plate against the left and AUX system fluid within the
reservoir. This action, called bootstrap pressure, pressurizes the contents
of the reservoir to approximately thirty to forty (30 - 40) psi., promoting fluid
flow to the engine-driven or AUX pump.
The total capacity of the left hydraulic system, including the fluid in system
lines is twenty point six (20.6) gallons, with the reservoir containing five
point seven (5.7) gallons, of which three point seven (3.7) gallons are
available to the left system and two (2) gallons reserved for use by theAUX
pump. The internal wall separating the two quantities is perforated by a
baffle so that servicing the reservoir fills both compartments of the
container. If left system fluid is depleted by a leak, the large end of the
central spool is pulled toward the wall separating left and AUX fluid, with
the baffle opening in the wall continually admitting left system fluid into the
AUX compartment to ensure the integrity of theAUX fluid supply. If all three
point seven (3.7) gallons of left fluid is lost, the large end of the spool
bottoms out at wall dividing the compartments, preserving the AUX pump
fluid.
The fluid quantity within the reservoir is displayed in two locations:
(1) A direct reading circular gage, mounted on the side of the reservoir,
has a needle pointer and colored bands to indicate quantity. The
gage is illustrated in Figure 4. A green band arcs between the FULL
and REFILL marks and a red band arcs between the REFILL mark
and the EMPTY mark.
(2) An electrically powered float within the reservoir provides quantity
data to the cockpit. The float moves with fluid quantity, with float
displacement measured by a Linear Variable Displacement
Transducer (LVDT). The LVDT is powered by twenty-eight volt direct
current (28v DC) from the left essential bus or the ground service
bus. Quantity information is derived from the displacement
measured by the LVDT, and transmitted electrically to Modular
Avionics Unit (MAU) #1 where it is converted from analog to digital
format and forwarded to the Monitor and Warning System (MWS) for
presentation on cockpit Hydraulics Synoptic, Summary, Secondary
Engine, Engine Start and Ground Service system window displays.
The quantity interface is shown in Figure 5.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-29-00
Page 7
August 14/03
