FED-STD-791D
two different widths. The narrow test gear is used for rating purposes. The mating gear
is wider in order to maintain a constant contact width between the two gears at different
tooth loads. Both sides of the test gear are used for testing. The "A" side of the gear
refers to the side obtained by installing the tests gears with the serial numbers facing the
end cover as shown in Figure 5. The "B" side is obtained by reversing the gear (serial
numbers facing away from the end cover). Test gears can be used once only on each side
and then discarded.
4.1.3 Support and load-oil system. The support and load-oil system, shown in
Figure 6, serves two purposes: to provide lubrication to all parts except the test gears and
to apply load to the test gears. The system is charged with approximately 30 L (8 gal) of
lubricating oil, SAE J1966. It is recommended that the oil be changed every 200 h of
running time under normal circumstances. A support oil pressure pump and a relief valve
furnish oil to the distributing manifold at a specified support oil pressure of 758 69
gage kPa (110 10 psig). The support oil temperature, also measured at the distributing
manifold, is maintained at a specified value of 73.9 2.5C (165 5F) by electric
heaters located in the sump and by a water cooler located after the pump, through the
action of thermoswitches. Pressure lines from the distributing manifold lubricate the
bearings and helical gears of the machine as well as the adapter housing and the stepup
gear box. The pressure to the latter is reduced to 172 to 207 kPa gage (25 to 30 psig) by a
throttle valve. Three scavenge pumps scavenge oil from the machine, the adapter
housing, and the step-up gear box, back to the support oil sump. The action of the load
oil circuit can be seen in Figures 3 and 6. Oil from the distributing manifold (Figure 6)
enters the Ryder gear machine at points W and X (Figures 3 and 6). After lubricating the
bearings and slave gears, the oil enters the load chambers Y and Z (Figure 3). For a
given pressure in the distributing manifold, the pressure in the load chambers is
dependent on the flow restriction offered by the circuit downstream of the load chambers.
Figure 6 shows that the oil, upon leaving the load chambers at J and J, must pass through
a control in the load oil circuit before returning to the support oil sump. Two pressure
gages (a low range and a high range) located near the outlet points J and J, read the so
called "load oil pressure", i.e. the pressure in the load chambers. The load oil circuit
contains three valves. Of these the load bypass valve is an open or shut valve which is
closed during the test run. The load oil pressure is controlled by regulating the load oil
adjusting valve. The bleeder valve is normally slightly open, its function being to
decrease the sensitivity of the load adjusting valve, thus facilitating the control of load oil
pressure. The load bypass valve is opened when it is desired to quickly release the load
on pressure, such as at the end of a test run.
4.1.4 Test oil system. A schematic diagram of the test oil system is shown in
Figure 7. The capacity is 500 mL. Test oil is supplied to the test gears by a pressure
pump through a jet located on the unmeshing side of the gears. Oil temperature to test
gears is maintained at 73.9 2.5C(165 5F) by a line heater actuated by a thermo
switch and controlled by a thermocouple close to the oil jet. The bypass circuit is
arranged to permit the use of the graduated sump for the determination of the test oil flow
rate. The bypass circuit also facilitates inspection of the narrow test gear without
stopping test oil circulation.
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