National Crane 03-20-2019 Control # 613-06 2-21
NBT30H-2 SERVICE MANUAL HYDRAULIC SYSTEM
equipment should make pressure adjustments when such
adjustments are needed.
Directional Control Valve Manifold
Removal
1. Tag and disconnect the hydraulic and electrical lines
from the valve manifold.
2. Plug the lines and cap ports.
3. Loosen and remove the valve mounting bolts and
remove the valve bank.
Installation
1. Bolt the directional control valve to the enclosure.
2. Reinstall the hydraulic and electrical lines as per
removal tags.
Functional Check
1. Start the engine and run it at normal speed.
2. Operate the control levers. Check for smooth operation
of cylinders and motors.
3. Check the valve bank and lines for leakage. Make
repairs as needed.
Pilot Manifold Valve
Supply oil from the pump is directed to Boom Down,
Telescope Extend, and Hoist Up control levers to keep them
from being operated. When the crane is not locked out or is
in A2B condition, the pilot manifold valve (Figure 2-17) is
allowed to shift and drain oil from these controls to tank. This
will allow these controls to operate these functions again.
Swinging left or right 205 degrees will de-energize the swing
solenoids and block flow for operation of swinging.
Outrigger Manifolds
The outrigger circuits are controlled by two manifolds located
at the front and rear outrigger boxes. The front manifold
contains the extend/retract valve for front and rear
outriggers, front outrigger component valves, and the
optional front jack valve. The rear outrigger manifold
contains the outrigger component valves for the rear
outriggers. The valves are operated by solenoids that are
controlled by switches on the outrigger control box.
Holding Valves
Pilot operated check valves located in the valve block on
each cylinder acts as holding valve to keep the cylinder from
collapse due to hose failure. Do not remove a valve block
unless the cylinder is completely retracted.
Do not try to repair or set the valve pressure. If a holding
valve is suspect, replace it with a new valve.
Swing Gearbox
The swing gearbox is mounted inside the frame and rotates
the turret/boom. The swing gearbox has an integrally
mounted brake that is automatically applied when the swing
control lever is in the neutral position to prevent boom
rotation. The swing brake is spring applied and hydraulically
released. As the controller is moved off center, hydraulic
pressure is automatically applied to release the brake.
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