Theory Of Operation - BRADEN CH400B Installation Maintenance And Service Manual

DESCRIPTION OF HOIST
The hoist is made up of the following sub-assemblies and
parts:
1. Hydraulic motor, brake valve and motor adapter
2. Drum and drum support assembly
3. Motor end support
4. Tie plates
5. Brake clutch assembly
6. Drive assembly with multiple disc parking brake and
internal gearing
DUAL BRAKE SYSTEM
DESCRIPTION
The dual brake system consists of a dynamic brake sys-
tem 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. It
contains a check valve to allow free flow of oil to the motor
in the haul-in direction and a pilot operated, spring load-
ed spool valve that blocks the flow of oil out of the motor
when the control valve is placed in neutral. When the con-
trol valve is placed in the pay-out position, the spool valve
remains closed until sufficient lowering 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,
the lowering pressure becomes flow dependent and mod-
ulates the spool valve opening which controls the lowering
speed. See Figures 1, 2, and 3.
Figure 1
Static Brake
Brake Valve
Pump
Low
Medium
Pressure
Pressure

THEORY OF OPERATION

Motor
To Tank
Control Valve
High
Pressure
Figure 2
Static Brake
Brake Valve
Pump
Low
Medium
Pressure Pressure
Figure 3
Static Brake
Brake Valve
Pump
Low Medium
Pressure Pressure
The static brake system has three operating components:
1. Spring applied, hydraulically released multiple friction
disc brake pack
2. Brake clutch assembly
3. Hydraulic piston and cylinder
The static brake is released by lowering pressure at a
pressure lower than that required to open the brake valve.
This sequence assures that dynamic braking takes place
in the brake valve and little, if any, heat is absorbed by the
friction brake.
The friction brake is a load-holding brake only and has
nothing to do with dynamic braking or rate of descent of a
load. The inner race of the brake clutch is a splined cou-
pling between the motor and the primary sun gear. The
outer race is splined to the friction discs in the brake pack,
while steel separator plates are splined to the stationary
housing. The brake clutch allows this shaft to turn freely
in the haul-in direction, and locks up to force the brake
discs to turn with the shaft in the pay-out direction. See
Figures 4 and 5.
6
Motor
To Tank
Control Valve
High
Pressure
Motor
To Tank
Control Valve
High
Pressure