SkyTrak 6036 Service Manual User Manual
Page 267
8.51
Model 6036 Legacy
Hydraulic System
Figure 8-22 Cross-Section of Service Brake Valve
4. Pressure in both the front and rear axle brake lines is
equal. A groove in each of the two spools opens to a
cross-hole between the two spool bores, preventing
uneven brake pressure. This feature is called the
“equalizer” function.
5. Power-mode braking begins when the metering
notches (Fig. 8-22, 6) in the spool (7) meter oil from
the inlet port to the spool chamber. Fluid flows from
the spool chamber, through the one-way orifice (8)
and into the brake lines. Brake pressure is controlled
by a force balance between the force applied at the
pedal and the resulting force from pressure in the
spool area.
6. The load sense bleed orifice helps provide stability
and aids in purging air from the system.
Manual Mode
In the event that hydraulic pressure at the inlet port is too
low to provide the braking force required, the service
brake valve automatically transitions to the manual mode
to provide braking power.
Flow paths out of the valve that would rob efficiency are
automatically blocked in the manual mode. The inlet port
check valve seals off the inlet port, and the load sense
shutoff valve closes. The service brake valve then acts as
a two-stage pump.
1. Brake pedal displacement is transmitted to the brake
valve (Fig. 8 -22, 1) at the plunger (2).
2. The series spring (Fig. 8 -22, 3) transmits plunger
displacement to the piston (4).
3. The piston (Fig. 8 -22, 4) and spool (7), functioning
as pumps, send oil to the brake lines. Initially, the
brake lines are vented to the reservoir by an annular
gap between a stepped-down piston diameter and
the piston bore. Flow to the reservoir is restricted
when the piston contacts the piston sealing ring (5).
4. Volume generated by piston displacement causes
the spool make-up check device (Fig. 8 -22, 9) to
unseat. Fluid flows into the spool chamber and out to
the brake lines.
5. Pressure in both the front and rear axle brake lines is
equal. A groove in each of the two spools opens to a
cross-hole between the two spool bores, preventing
uneven brake pressure. This feature is called the
“equalizer” function.
6. At a set piston chamber pressure, a relief valve
(Fig. 8 -22, 10) begins to meter oil and limits the
pressure within the piston chamber. The pressure in
the piston chamber becomes isolated from the
pressure in the spool chamber when the make-up
check device (9) reseats itself.
7. Further displacement of the service brake pedal
causes higher pressure in the spool chamber. The
load sense pin in the make-up check device
(Fig. 8 -22, 9) is sensitive to the increased pressure
and transmits a force to the relief ball. The
increasing force on the relief ball effectively lowers
the relief setting within the piston chamber.
Eventually, the piston chamber pressure reaches
zero, and the valve has moved completely from the
first stage to the second stage. The smaller area of
the second stage permits the brake valve to develop
higher braking pressure.
MS1880
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