Basic Planetary Winch Operation

Description of Hoist

  • Hydraulic motor and valve
  • Drum, drum closure, ball bearings and oil seals
  • Base, bearing support and motor adaptor
  • Brake clutch assembly
  • Brake cylinder assembly and multiple-disc brake
  • Planetary gear reducer assemblies
  • Ring Gear

Theory of Operation

The primary sun gear is directly coupled to the hydraulic motor by the inner race of the brake clutch assembly.  As the motor turns in the hoisting directions (normally clockwise), the planetary assemblies reduce the input speed of the motor and rotate the winch drum.  If the output planet carrier is held from turning by the bearing support, the drum rotates in the opposite direction of the motor input shaft.  If the ring is held stationary, the drum rotates in the same direction as the motor shaft.  In the hoisting direction, the static brake remains fully applied and the input shaft rotates freely through the sprag clutch.  When the motor is stopped, the load tries to rotate the winch gear train in the opposite direction.  The sprag clutch on the input shaft immediately locks up, allowing the fully applied static brake to hold the load from dropping.  See Dual Brake System – Operation for a detailed description of the lowering sequence of operation.  


Planetary winch Hoisting Diagram                       Planetary Winch Operation Parking Diagram

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:

  • Brake Valve Assembly
  • 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 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 sufficient pilot pressure is applied to the end of the spool to shift it against spring pressure and open a passage. 
See Figure 1.  After the spool valve cracks open, the pilot pressure becomes flow-dependent and modulates the spool valve opening which controls the lowering speed.  See figures 2, 3 and 4.

The static brake system has three operating components:

  • Spring applied
  • Brake clutch assembly
  • Hydraulic piston and cylinder

The static brake is released by the brake valve pilot pressure at a pressure lower than that required to open the pilot operated spool valve.  This sequence assures that dynamic braking takes place in the brake valve and that little, if any, heat is absorbed by the static, friction brake.

The hydraulic cylinder, when pressurized, will release the spring pressure on the brake discs, allowing the brake discs to turn freely.

The static friction brake is a load holding brake only and has nothing to do with dynamic braking or rate of descent of a load.

Planetary Winch Hydraulic Brake Release figure 1

Planetary Winch Hydraulic Brake Figure 2

Planetary winch Operation Figure 3

Planetary Winch Operation figure 4