5
DESCRIPTION OF HOIST
The hoist has four basic component parts:
1. Hoist base
2. Hydraulic motor and brake valve
3. Brake cylinder and motor support
4. Drum assembly
The drum assembly consists of three basic assemblies:
1. Drum with integral ring gear
2. Output planetary gear set
3. Primary planetary gear set
The hydraulic motor is bolted to the motor support which
in turn is bolted to the brake cylinder and the side plate. The
motor end of the drum, running on a ball bearing, is sup-
ported by the brake cylinder. The other end of the drum runs
on a ball bearing on the support bolted to the side plate. The
ring gear for both planetary sets is machined into the drum’s
inside surface.
HOIST OPERATION
The hydraulic motor drives the sun gear of the primary plan-
etary gear set through the splined inner race of the overrun-
ning brake clutch. When driven by the sun gear, the primary
planet gears walk around the ring gear in the drum and drive
the primary planet carrier.
The primary planet carrier drives the output planet sun gear
which, in turn, drives the output planet gears. The output
planet carrier is splined to the bearing support and cannot
rotate. Therefore, as the output planet gears are driven by the
sun gear, they will drive the ring gear/drum.
DUAL BRAKE SYSTEM — DESCRIPTION
The dual brake system consists of a dynamic brake system
and a static brake system.
The dynamic brake system has two operating components:
1. Brake valve assembly
2. Hydraulic motor
The brake valve is basically a counterbalance valve with
good metering characteristics. It contains a check valve to
allow free flow of oil to the motor in the hoisting direction
and a pilot operated, spring-loaded spool valve that blocks
the flow of oil out of the motor when the control valve is
placed in neutral. When the control valve is placed in the
lowering position, the spool valve remains closed until suf-
ficient pilot pressure is applied to the end of the spool to
shift it against spring pressure and open a passage. After the
spool valve cracks open (300-500 PSI cracking pressure)
,the pilot pressure becomes flow-dependent and modulates
the spool valve opening which controls the lowering speed.
Refer to figures 1, 2, and 3.
The static brake system has three operating compo-
nents:
1. Spring applied, multiple friction disc static brake
2. Overrunning brake clutch assembly
3. Hydraulic piston and cylinder
Motor
Control Valve
Pump
To Tank
Brake Valve
Static Brake
Medium
Pressure
Low
Pressure
High
Pressure
Figure 1. Hoisting
Motor
Control Valve
Pump
To Tank
Brake Valve
Static Brake
Medium
Pressure
Low
Pressure
High
Pressure
Figure 2. Lowering (1)
THEORY OF OPERATION
