through. The pores or passages vary in size, and
the degree of filtration depends on the flow rate.
Duplex filters are similar to simplex filters
Increases in flow rate tend to dislodge trapped
except in the number of elements and in provision
particles. This filter is limited to low-flow, low
for switching the flow through either element. A
duplex filter may consist of a number of single
An edge-type filter element (fig. 6-29)
element filters arranged in parallel operation, or
separates particles from fluids passing between
it may consist of two or more filters arranged
finely spaced plates. The filter shown features
within a single housing. The full flow can be
stationary cleaner blades that scrape out the
diverted, by operation of valves, through any
to turn the element.
single element. The duplex design is most
commonly used in fuel or hydraulic systems
because the ability to shift to an offline filter when
the elements are cleaned or changed is desirable
TYPES OF FILTERS
without the system being secured.
In this section we will discuss the various filters
(simplex, duplex, full flow, proportional flow,
and indicator) that you will most frequently find
installed in equipment.
The term full-flow applied to a filter means
that all the flow into the filter inlet port passes
through the filtering element. In most full-flow
filters, however, there is a bypass valve preset to
open at a given pressure drop and divert flow past
The simplex filter has one or more cylindrically
the filter element. This prevents a dirty element
shaped fine mesh screens or perforated metal
from restricting flow excessively. Figure 6-30
sheets. The size of the opening in the screens or
shows a full-flow filter. Flow, as shown, is out-
the perforated metal sheets determines the size of
to-in; that is, from around the element through
particles filtered out of the fluid. The design of
it to its center. The bypass opens when total flow
this type of filter is such that total flow must pass
can no longer pass through the contaminated
through a simplex filter.
element without raising the system pressure. The
element is replaceable after removing a single bolt.
Figure 6-29.--Edge-type filter element.
Figure 6-30.--Full-flow filter.