JLG G6-42P Service Manual - Manual (Page 498)

THREE OPEN CENTER HYDRAULIC POWER BRAKE VALVE DESIGNS
PRIMARY CUP DESIGN
The Primary Cup Design uses a
residual valve. This valve will maintain a
pressure of 12 - 20 PSI in the brake lines
when the pedal is released. When used in
drum brake systems this low pressure aids
in preventing air from entering the brakes
when the vehicle is at rest.
RING SEAL DESIGN
The Ring Seal Design is used mainly
in disc brake systems. The residual valve
is removed from models designed for disc
brake systems because of the pressure
they maintain in the brake lines when the
pedal is released. Even these relatively
low pressures (12 - 20 PSI) would develop
drag in this type of brake.
SLIDING PISTON DESIGN
The Sliding Piston Design was created
with a specific function in mind. A
specially designed piston slides inside the
primary piston when the brake pedal is
actuated. If primary piston strokes too far,
the brake pedal will be pulled down with a
short abrupt stroke. This indicates to the
operator that maintenance is required.
(6)
Residual Valve
Primary Cup
Ring Seal & O-Ring
Check Valve
Sliding Piston
FIGURE 7
FIGURE 8
FIGURE 9