Maintenance
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(P305):pHseriesMAINTENANCE.fm
41
Operation Manual - SP 305
• The model SP 305 is equipped with a recirculation
type of filtration system, meaning that there is a
pump that sucks oil from the reservoir, pumps it
through the filter and cooler, and back to the tank.
Whenever the engine is running, oil is being
filtered. The filtration is done with a spin-on filter
assembly (Figure 28). It is equipped with an
integral bypass check valve set at 30 PSI. The
bypass valve protects the filter element from
damage, as explained below. The assembly is
equipped with an anti-back-flow check valve,
which prevents oil from draining out of the tank
while you are changing the spin-on element. There
is a dirty filter indicator to tell you when the
element is dirty. You should replace the element
whenever the indicator enters the yellow area and
the oil is heated above 20 degrees Celsius. Under
normal circumstances, the element will need
replacement about every 6 months. The element
has been designed to remove all particles large
enough to cause undue wear and jobsite
breakdowns (beta 10 = 200). You can keep the
hydraulic system running year after year by
replacing the element when replacement is due. Do
not substitute “will fit” elements in this housing.
Bypass Check valve
The filter is equipped with an integral bypass check
valve with a 30 P.S.I. pressure-to-open rating. This is
what it does:
When the filter is clogged with dirt and oil is having a
hard time making it through, the pressure difference
between the filter inlet and the outlet rises. This
pressure difference (commonly referred to as a
pressure differential) is called delta P and is shown as
ΔP. When the ΔP reaches 30 PSI, the check valve opens
and the oil returns to the tank unfiltered. If the filter did
not have the bypass check valve, it would simply break
apart when it was clogged. That could cause the filter
to fail in one of two ways:
1. All of the dirt ever trapped by the filter, plus the
filter itself, could go directly into the system.
2. Worse yet, the filter could split open and leak to
the ground, draining the reservoir, and
contaminating the environment.
Both potential problems are avoided by the bypass
check valve.
To change the element
1. Make sure the engine is shut off. Put the key in
your pocket to prevent someone else from
starting the engine.
2. Position a pan or bucket under the filter housing
to catch drips. The check valve built into the
filter, which prevents back flow, should not allow
much leakage oil, but there will be some. Oil
spills contaminate the environment.
3. Unscrew the filter element. Use an oil filter
wrench, if needed.
4. Remove the spin-on element, and pour the oil out
into the catch pan. Do not reuse this oil.
5. Remove the old element and replace with a new
element. Replace the bowl and tighten according
to the installation instructions that come with the
filter.
6. Start the engine, and check for leaks.
Hydraulic Oils
General information
Hydraulic oils are rated for viscosity, heat dissipation,
foaming characteristics, pour point, anti-wear
additives, anticorrosive additives, lubricating qualities,
compressibility, temperature range, temperature
stability, and other functions. Although many different
brands of oil will meet these specifications, they may
PHfilter.eps
Filter
Element
Dirty Filter
Indicator
Figure 28
The hydraulic oil filter
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