Brake Valve -A hydraulic counterbalance valve is usually bolted to the reel-in port of the hydraulic motor. It allows oil to flow freely through the motor in the reel-in direction. When oil pressure tries to rotate the motor in the reel-out direction, the brake valve blocks the flow of oil out of the motor until the internal static brake is released. It then controls reel-out speed based on the load and flow of oil to the motor. All the heat generated by controlling the speed of the load is dissipated by the hydraulic system, not by the internal static brake.
Grooved Drum-A cable drum with grooves on the barrel to ensure the first layer of cable spools properly onto the drum. The grooves can be cast or machined into the drum, or cast or machined into separate pieces that are mechanically fastened to the drum.
NOTE: Only one size cable can be used on a grooved drum.
Sprag or Over-Running Clutch - A mechanical one-way clutch to the input shaft of the winch, between the input shaft and the static mechanical brake. The clutch allows the input shaft to turn freely in the direction required to spool cable onto the drum, then immediately locks the hoist gear train to the mechanical brake when the hoist is stopped, holding the load in place.
Static, Mechanical, or Load-Holding Brake - A multi-disc, spring applied, hydraulically released brake that works together with the sprag clutch to hold a load. This brake is not designed to stop a load being reeled-out, but holds the load in place when the winch is not being operated.
First Layer Line Pull Rating - The maximum rated line pull (in pounds or kilograms) on the first layer of cable. The maximum rating for any particular winch is based on maintaining an acceptable structural design factor and service life. Certain combinations of drum, gear ratio, motor and hydraulic pressure, may reduce this rating.
First Layer Line Speed Rating - The maximum rated line speed (in feet or meters per minute) on the first layer of cable. Certain combinations of drum, gear ratio, motor and hydraulic flow may reduce or increase this rating.
Fleet Angle - The angle between the wire rope's position at the extreme end wrap on a drum, and a line drawn perpendicular to the axis of the drum, through the center of the nearest fixed sheave or load attachment point.
Wrap - A single coil of wire rope wound on a drum.
Layer - All wraps of wire rope on the same level between drum flanges.
Freeboard - The amount of drum flange that is exposed radially past the last layer of wire rope. Minimum freeboard varies with the regulatory organization. ASME B30.5 requires 1/2 in. minimum freeboard.