Theory Of Operation - BRADEN PD12C Series Installation Maintenance And Service Manual

THEORY OF OPERATION

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 assem-
blies:
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 base. The
motor end of the drum, running on a ball bearing, is
supported by the brake cylinder. The other end of the
drum runs on a ball bearing on the support bolted to the
base. 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
planetary gear set through the splined inner race of the
overrunning 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 sup-
port 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 compo-
nents:
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 fl ow of oil to the motor in the hoist-
ing direction and a pilot operated, spring-loaded spool
valve that blocks the fl ow 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 suffi cient pilot pressure is applied
to the end of the spool to shift it against spring pres-
sure and open a passage. After the spool valve cracks
open, the pilot pressure becomes fl ow-dependent and
modulates the spool valve opening which controls the
lowering speed. Refer to fi gures 1, 2, and 3.
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
Figure 1
HOISTING
Static Brake
Brake Valve
Pump
Low Medium
Pressure Pressure
Figure 2
LOWERING 1
Static Brake
Brake Valve
Pump
Low
Medium
Pressure
Pressure
5
Motor
To Tank
Control Valve
High
Pressure
Motor
To Tank
Control Valve
High
Pressure