construction to the sintered bronze element described
previously. The design is usually a corrugated, sintered,
stainless steel mesh, such as the magnified cross section
shown in view (D) of figure 10-29. One manufacturer
calls the design a Dutch Twill pattern. The curved
passages of the filter element (through which the fluid
passes) limit the length of the particles that pass through
the element. Most filters that use the stainless steel are
equipped with a contamination indicator, described later
in this chapter.
The hydraulic systems of CESE use several
different types of filters. There are a number of factors
to be considered in determining the full classification of
a particular type of filter. When hydraulic filters are
being classified, the following factors are considered:
FLOW CHARACTERISTICS. In the full-flow
filter, all the fluid that enters the unit passes through the
filter element, while in a proportional flow, only a
portion of the fluid passes through the element.
Practically all filters used in the hydraulic systems of
CESE are full flow.
FILTERING MEDIUM. The different filter
elementswire mesh, micronic, and porouswere
discussed earlier. Normally, only one element is used in
each filter; however, some equipment uses two or more
elements in order to obtain the desired degree of
A full-flow, micronic, bypass filter is shown in
figure 10-30. This filter provides a positive filtering
action; however, it offers resistance to flow, particularly
when the element becomes dirty. For this reason, a
full-flow filter usually contains a bypass valve; the valve
automatically opens to allow the fluid to bypass the
element when the flow of fluid is restricted because of
contamination buildup on the element.
Hydraulic fluid enters the filter assembly through
the inlet port in the body and flows around the filter
element inside the filter bowl. Filtering takes place as
the fluid passes through the filter element and into the
hollow core, leaving dirt and impurities deposited on the
outside of the filter medium. The filtered fluid then
flows from the hollow core, through the outlet port, and
continues on through the system.
BYPASS CHARACTERISTICS. TMS bypass
relief valve in the body allows the fluid to bypass the
filter element and pass directly into the outlet port if the
filter element becomes clogged. In many micronic
filters, the relief valve is set to open when the differential
in pressure exceeds 50 psi; for example, if the pressure
at the filter inlet port is 90 psi and the pressure at the
outlet drops below 40 psi, the bypass valve opens and
allows the liquid to bypass the element.
ATTENTION: Oil that bypasses the hydraulic oil
filter is unfiltered oil. his is a clear indication of a
hydraulic system in need of serious maintenance, repair
CONTAMINATION INDICATORS. Contami-
nation indicators are often used on bypass filters. The
full-flow, porous metal, bypass electrical-indicating
Figure 10-30.-Full-flow, bypass type of hydraulic filter.