Reference
Only
Manitowoc
Published 05-16-17, Control # 233-03
1-59
999 SERVICE/MAINTENANCE MANUAL
INTRODUCTION
1
Each carbody-jacking cylinder (1) has a counterbalance
valve (2) at the cylinder ports. Counterbalance valves ensure
smooth control when raising or lowering the crane.
Counterbalance valves lock the carbody jacking cylinders in
place if there is a hydraulic line breakage or accidental
operation of control valve when the crane's power is shut
down. Also, counterbalance valves provide relief protection
for the cylinders and shields them from mechanical
overloading.
When a carbody jacking cylinder control valve handle is not
enabled, it assumes a neutral position and hydraulic fluid
passage to carbody jacking cylinder is blocked. In neutral,
both valve section cylinder ports are connected to tank. This
prevents in-line pressure from opening counterbalance
v a l v e , h o l d i n g c a r b o d y l o a d i n p o s i t i o n b y t h e
counterbalance valve.
Carbody Jacking Cylinder Raise
Move desired carbody lever back to
raise
position to raise
carbody-jacking cylinder. This shifts the selected carbody
lower accessory valve to block charge pressure to accessory
pressure switch (6). The accessory pressure switch trips
when the system pressure drops to 120 psi (8,3 bar),
sending an input signal to the PC. The PC sends a negative
output voltage to rear drum pump EDC that tilts rear drum
pump swashplate to stroke pump (3) in the low-pressure side
direction.
Low-pressure side hydraulic fluid flows through high-
pressure carry-over of accessory system valve where
system pressure is 3,000 psi (207 bar). Hydraulic fluid exits
valve section of lower accessory valve into counterbalance
valve. Hydraulic fluid then enters piston end of carbody
jacking cylinder (4), extending cylinder to raise the carbody.
The PC monitors accessory system pressure sender to
control jacking cylinder raising speed rate.
Hydraulic fluid returning to tank from rod end of the carbody
jacking cylinder is blocked by the free flow check valve
section of counterbalance valve and flows through flow
restraining section that has a relief setting of 3,500 psi (240
bar).
The counterbalance valve acts as a deceleration control and
functions with a 3:1 pilot ratio of the relief pressure. This
permits the valve to open when the pressure in rod end of the
cylinder is approximately 1,170 psi (81 bar). Restraining
section of counterbalance valve opens, controlling the fluid
out of the carbody-jacking cylinder.
Hydraulic fluid then flows through free-flow check valve (5)
section of flow control valve before entering lower accessory
valve. Hydraulic fluid leaving the lower accessory valve is
returned to tank.
Carbody Jacking Cylinder Lower
Move desired carbody lever forward to lower
position to
lower carbody jacking cylinder. Selected lower accessory
valve shifts to block charge pressure to accessory pressure
switch (6). The accessory pressure switch trips when the
system pressure drops to 120 psi (8,3 bar), sending an input
signal to the PC. The PC sends a negative output voltage to
rear drum pump EDC that tilts rear drum pump swashplate to
stroke pump (3) in the low-pressure side direction.
Low-pressure side hydraulic fluid flows through high-
pressure carry-over of accessory system valve where the
system pressure is 3,000 psi (207 bar). Hydraulic fluid exits
the valve section of lower accessory valve and flows through
the restraining section of flow control valve.
Restraining section controls the rate of speed for the cylinder
to retract by limiting the velocity of fluid before passing
through free flow check valve (5) section of counterbalance
valve. Hydraulic fluid then proceeds into rod end of carbody
jacking cylinder (4). Hydraulic pressure entrapped by the
cylinder counterbalance valve at piston end of the carbody-
jacking cylinder supports the weight and gravitational force of
the carbody. The PC monitors accessory system pressure
sender to control jacking cylinder lowering speed rate.
Hydraulic fluid exhausting from piston end of the carbody
jacking cylinder is blocked by free flow check valve section of
counterbalance valve and flows through the flow restraining
section that has a relief setting of 3,500 psi (240 bar). The
counterbalance valve serves as a deceleration control and
functions with a 3:1 pilot ratio of the relief pressure,
permitting the valve to open when the pressure in piston end
of the cylinder is approximately 1,170 psi (81 bar). The
restraining section of counterbalance valve opens that
controls fluid out of the carbody-jacking cylinder to lower
accessory valve. Hydraulic fluid leaving the lower accessory
valve is returned to tank.
Summary of Contents for 999
Page 1: ...R e f e r e n c e O n l y Service Maintenance Manual Manitowoc 999 ...
Page 2: ...R e f e r e n c e O n l y ...
Page 4: ...R e f e r e n c e O n l y THE ORIGINAL LANGUAGE OF THIS PUBLICATION IS ENGLISH ...
Page 297: ...R e f e r e n c e O n l y ...
Page 298: ...R e f e r e n c e O n l y ...