Wafer Screen Filter
operation of the aircraft engine. The engine-driven
fuel pumps must be capable of delivering the
maximum needed flow at high pressure to obtain
The wafer screen filter, shown in figure 4-25,
satisfactory nozzle spray and accurate fuel
has a replacement element made of layers of
regulation.
screen discs of bronze, brass, and steel. This type
of filter can remove minute particles. It also has
the strength to withstand high pressure.
Fuel pumps for engines are generally positive
displacement gear, piston, or rotary vane types.
The term positive displacement means that the
Plain Screen Mesh Filter
pump will supply a fixed quantity of fuel to the
engine.
The plain screen mesh filter is the most
These pump types may be divided into two
common type. It has long been used in internal-
combustion engines of all types for fuel and oil
groups--constant displacement and variable
strainers. In present-day turbojet engines, it is
displacement. Their use depends on the fuel
used in units where filtering action is not so
control system used to regulate the flow of fuel
critical, such as in fuel lines before the high-
to the fuel controls.
pressure pump filters. The mesh size of this type
of filter varies greatly according to the purpose
Gear-Type Pumps
for which it is used.
Gear-type pumps have straight-line flow
ENGINE-DRIVEN PUMPS
characteristics. However, fuel requirements vary
with flight or ambient air conditions. Hence, a
Engine-driven fuel pumps deliver a continuous
pump of adequate capacity at all engine operating
conditions will have excess capacity over most of
supply of fuel at the proper pressure during
Figure 4-25.-Wafer screen filter.
4-28
