Cub Cadet Domestic Series 5000 Service Manual page 14

Domestic Series 5000 Hydraulics
5.13. When removed, each charge relief valve comes
out as a cartridge. The light compression spring
provides the check valve function. The heavy
compression spring provides system relief. Sys-
tem relief comes into play in the event of a drive
system overload. See Figure 5.13.
Heavy compression
spring (relief function)
Figure 5.13
5.14. The output of the variable displacement pump is
dependent upon the performance of the check
valves.
5.15. The presence of fluid flow from the auxiliary
pump, via the steering unit can be confirmed by
installing a flow meter in place of the tube
between the filter and the top port on the hydro-
static drive. See Figure 5.15.
Figure 5.15
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Light compression spring
(check valve function)
Charge check valve cap
Flow and pressure test
kit in charge pressure line
between filter and hydro-
static drive unit
5.16. With the engine at a minimum speed of 1,200
RPM, fluid flow of roughly 2 GPM (7.60 LPM)
should register on the meter. See Figure 5.16.
Figure 5.16
NOTE: No hydraulically powered systems
should be in motion during this test. The steer-
ing and lift cylinder should be stationary. Con-
firm that the lift control valve is not in the down
position.
5.17. Conclusion: If flow is present, but there is no
pressure, as determined by the 200 PSI gauge,
then the auxiliary pump is producing flow, the
steering unit is passing that flow along to the
return manifold through the T port, but pressure
is being lost in the return circuit. The most likely
culprit is the return circuit check valve.
5.18. Conclusion: If there is neither flow nor pres-
sure, either there is none reaching the return cir-
cuit, or it is being spilled-off through a path that
offers lower resistance.
• The lift control valve is the only other possible
outlet from the return circuit. Lift control valve
failure in this mode would be highly unusual. If
the lift control valve operates normally, this issue
can be eliminated from consideration.
• To discern if the auxiliary pump is functioning,
operate other hydraulic systems. If the steering
and the lift cylinder for the three point hitch fail to
operate, it is safe to assume that the auxiliary
pump is not producing pressure.
• The pressure that operates the lift cylinder
comes from one of two possible return paths
from the steering unit (E port). The charge pres-
sure for the hydrostatic drive comes from the
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