Published 08-25-09, Control # 077-04 5-1
RT9130E SERVICE MANUAL HOIST AND COUNTERWEIGHT
SECTION 5
HOIST AND COUNTERWEIGHT
DESCRIPTION
One hoist is available, the model HP35-26G. The hoist
incorporates one dual displacement piston motor which
drives a reduction unit within the hoist. The hoist utilizes
planetary reduction with a multi-disc automatic brake that is
spring applied and hydraulically released. An overrunning
clutch allows the hoist to be raised without releasing the
brake while at the same time holding the load until there is
sufficient pressure to release the brake when hoisting down.
The hoist motor controls both speed and torque of the hoist.
There are two modes in which the hoist operates. One mode
is high speed. The pilot solenoid valve shifts the selector
spool on the motor to provide minimum motor displacement.
This gives high line speed and low torque.
The second mode is low speed. The pilot solenoid valve
shifts the selector spool on the motor to provide maximum
motor displacement. This gives low line speeds and high
torque.
THEORY OF OPERATION
Each hoist is controlled by controls in the cab.
When the main hoist control lever in the cab is moved from
neutral, it causes the main hoist section of the directional
control valve to shift the valve spool to route hydraulic flow to
the main hoist motor control valve. The hoist motor control
valve routes the hydraulic flow to the hoist motor. The motor
turns one direction to hoist up, and turns the other direction
to hoist down, depending on whether the hoist controls route
fluid to the hoist up or hoist down port of the hoist motor
control valve.
When the auxiliary hoist control lever in the cab is moved
from neutral, it causes the auxiliary hoist section of the
directional control valve to shift the valve spool to route
hydraulic flow to the auxiliary hoist motor control valve. The
hoist motor control valve routes the hydraulic flow to the hoist
motor. The motor turns one direction to hoist up, and turns
the other direction to hoist down, depending on whether the
hoist controls route fluid to the hoist up or hoist down port of
the hoist motor control valve.
Each hoist motor control valve is used to stop or slow its
hoist when the load is trying to drive the hoist down too
quickly. The motor control valve is piloted open by the hoist
down pressure. If the load lowers faster than the flow of oil in
the hoist down line, the pilot pressure decreases and the
motor control valve partially closes to restrict the oil leaving
the motor until a balance occurs. This results in the load
lowering at a uniform speed based on the position of the
hoist control lever.
During stopping, when the hoist down flow ceases, the pilot
pressure holding the motor control valve open decays to
zero and the motor control valve spool closes, thus blocking
all flow of oil out of the hoist motor. This same pressure
decay allows the spring applied pressure released hoist
brake to apply when the load is fully stopped. This brake acts
as a “parking brake” and holds the load in the stopped
position.
MAINTENANCE
Warm-up Procedure
A warm-up procedure is recommended at each start-up and
is essential at ambient temperatures below +40°F (4°C).
The prime mover should be run at its lowest recommended
RPM with the hydraulic hoist control valve in neutral allowing
sufficient time to warm up the system. The hoist should then
be operated at low speeds, forward and reverse, several
times to prime all lines with warm hydraulic oil, and to
circulate gear lubricant through the planetary gear sets.
DANGER
Failure to properly warm up the hoist, particularly under
low ambient temperature conditions, may result in
temporary brake slippage due to high back pressures
attempting to release the brake, which could result in
property damage, severe personal injury or death.
To Next Page
Loading...
