The bypass return flow from the fuel control is passed back to the inlet of the gear elements through a
pressure regulating valve which maintains the bypass flow pressure above inlet pressure. By means of
passages, leading to auxiliary filling ports on the periphery of the gear elements, a portion of the bypass
flow is used to fill the gear teeth when vapor-liquid conditions exist at the inlet to the gear elements.
A 5-micron paper filter is located inside the fuel pump assembly upstream of the gear elements. It is
retained by a threaded cover, distinguished by a hex, which can be found on the lower side of the pump
assembly. A container should be used to catch undrained fuel when the filter cover is removed.
PC Air Filter. The Pc air filter is a 10 micron filter located in the Pc air supply line leading
from the diffuser scroll to the power turbine governor. It incorporates a permanent type, wire mesh,
cleanable element and prevents the governor and fuel control pneumatic components from being con-
taminated with foreign particles by filtering Pc air flow to the governor and control.
1-18. Lubrication System. The lubrication system (fig. 1-9) is a dry sump type with an external reser-
voir and heat exchanger. A gear type pressure and scavenge pump assembly is mounted within the Power and
accessory gearbox. oil fiter, bypass valve (fig. 1.9), and pressure regulating valve are in a unit
which is located in the upper right-hand side of the power and accessory gearbox housing and are accessible
from the top of the engine. A check valve is located between the housing and the filter unit. Indicating
type magnetic chip detectors are installed at the bottom of the power and accessory gearbox, snd at the
engine oil outlet connection. All engine oil system lines and connections are internal with the exception
of pressure and scavenge lines to the front compressor support, the gas producer turbine support, and the
power turbine support.