SkyTrak 6036 Service Manual - Manual (Page 171)

Section 9 Hydraulic System
Model 6036/6036T S/N 9B0500 thru 14833 9-21
Warning
Relieve hydraulic pressure before servicing any
hydraulic component. Escaping hydraulic fluid
under pressure can penetrate the skin causing
serious injury.
Right Position
When the grille and frame tilt control lever is
placed in the “right” position, the directional control
valve spool is positioned so that pump applied
pressure is directed through ports E to B, Fig.
9.13, to the rod (retract) end of the frame tilt
cylinder piston. This supply pressure also pilots
open the pilot-operated check valve on the base
(extend) end of the frame tilt cylinder. If supply
pressure reaches 1300 ± 50 psi (89,6 ± 3,4 bar),
the frame tilt “right” relief valve, Fig. 9.13, will
open allowing hydraulic oil to return to the return
filter and reservoir, Fig. 9.13.
Return oil from the base end of the frame tilt
cylinder piston is directed back to the directional
control valve though ports C to F, Fig 9.13, to the
return filter and reservoir. If the return filter
becomes clogged, hydraulic oil will bypass the
filter when the pressure reaches 10 to 15 psi (0,69
to 1,03 bar).
Pilot-operated check valves, Fig. 9.13, in the
frame tilt cylinder permit free flow on both ends of
the cylinder piston when supply pressure is
applied to open either pilot-operated check valve.
When the grille and frame tilt control lever is not
activated, no supply pressure is applied. The two
check valves prevent any back flow of hydraulic oil
and the frame tilt cylinder is locked in position.
9.4.3 Frame Tilt Circuit
a. Description
Hydraulic pressure is applied in the frame tilt
circuit by the 15 gpm section (front half) of the
tandem pump, which draws its fluid through a
suction screen in the reservoir, Fig. 9.13. Pres-
sure is supplied through the sequence valve and
the load sensing steering priority valve to the
secondary control valve. Pressure is then directed
to either side of the frame tilt cylinder piston by the
shifting of a spool in a directional control valve
found in the secondary control valve assembly.
The spool is shifted by the grille and frame tilt
control lever and its associated control cable.
Control lever positions for tilting the frame are as
follows:
Center Position
When the grille and frame tilt control lever is
placed in the center or neutral position, the
directional control valve spool is positioned so that
pump supply pressure is directed through ports D
to A, Fig. 9.13, to the return filter and reservoir.
If the return filter becomes clogged, hydraulic oil
will bypass the filter when the pressure reaches 10
to 15 psi (0,6,9 to 1,03 bar).
Left Position
When the grille and frame tilt control lever is
placed in the “left” position”, the directional control
valve spool is positioned so that pump supply
pressure is directed through ports E to C , Fig.
9.13, to the base (extend) end of the frame tilt
cylinder piston. This supply pressure also pilots
open the pilot-operated check valve on the rod
(retract) end of the frame tilt cylinder. If supply
pressure reaches 1300 ± 50 psi (89,6 ± 3,4 bar),
the frame tilt “left” relief valve, Fig. 9.13, will
open allowing hydraulic oil to return to the return
filter and reservoir, Fig. 9.13.
Return oil from the rod end of the frame tilt cylin-
der piston is directed back to the directional
control valve though ports B to F, Fig. 9.13, to the
return filter and reservoir. If the return filter
becomes clogged, hydraulic oil will bypass the
filter when the pressure reaches 10 to 15 psi
(0,69
to 1,03 bar).
b. Pressure Checks and Adjustments
Frame Tilt Left Relief Valve
1. Engage the park lock, place the travel select
lever in neutral, and stop the engine.
2. Operate the hydraulic controls after the engine
has stopped to relieve any trapped pressure.