SkyTrak 3606 Service Manual - Manual (Page 219)

Hydraulic System
9-25
1. Brake pedal displacement is transmitted to the valve
at the plunger (Fig. 9– 14).
2. The series spring transmits plunger displacement to
the piston.
3. The piston and spool, 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.
4. Volume generated by piston displacement causes the
spool make-up check device to unseat. Oil 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
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 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 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, 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.
8. Controlling the force applied to the service brake
pedal controls the amount of braking power.
9. If the first application of force applied to the service
brake pedal was not enough to deliver the braking
required, the one way orifices at the work ports help
give the brake valve “pump up” ability. The one-way
orifices allow unrestricted flow to the brake lines but
also restrict the rate of decompression.
Model 3606 • Origin 10/99