Figure 9-46.Edge-type filter element.
An edge-type filter element (fig. 9-46)
separates particles rom fluids passing between
finely spaced plates. The filter shown features
stationary cleaner blades that scrape out the
collected contaminants when the handle is twisted
to turn the element.
TYPES OF FILTERS
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 simplex filter has one or more cylindrically
shaped fine mesh screens or perforated metal
sheets. The size of the opening in the screens or
the perforated metal sheets determines the size of
particles filtered out of the fluid. The design of
this type of filter is such that total flow must pass
through a simplex filter.
Duplex filters are similar to simplex filters
except in the number of elements and in provision
for switching the flow through either element. A
duplex filter may consist of a number of single
element filters arranged in parallel operation, or
it may consist of two or more filters arranged
within a single housing. The full flow can be
diverted, by operation of valves, through any
single element. The duplex design is most
commonly used in fuel or hydraulic systems
because the ability to shift to an off-line filter
when the elements are cleaned or changed is
desirable without the system being secured.
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 filter element. This prevents a dirty element
from restricting flow excessively. Figure 9-47
shows a full-flow filter. Flow, as shown, is out-
to-in; that is, from around the element, through
it to its center. The bypass opens when total flow
can no longer pass through the contaminated
element without raising the system pressure. The
element is replaceable after removing a single bolt.
A proportional-flow filter (fig. 9-48) may use
the venturi effect to filter a portion of the fluid
flow. The fluid can flow in either direction. As
it passes through the filter body, a venturi throat
causes an increase in velocity and a decrease in
Figure 9-47.Full-flow filter.