RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
THEORY OF OPERATION
MAIN WINCH AND SPADE ASSEMBLY
The main winch and spade assembly (Figures 1 and 2) is installed on the nosepiece of the vehicle with the winch located in the
hull beneath the crew compartment, and the spade externally mounted on the front of the vehicle. The major components of
the assembly are a spade; two spade-actuating cylinders; a winch cable; a cable level winder valve; a hydraulic motor; a brake
cylinder; a main winch combination control valve; and the main winch, which is equipped with an internal brake.
The main winch (Figure 1) is installed in the forward part of the vehicle hull beneath the crew compartment. It is used for
heavy-duty winching operations, and has a capacity of 90,000 pounds using a single line.
Figure 1. Main Winch and Spade Assembly--Right-Rear View.
The spade (Figure 2) is hydraulically controlled and is externally mounted on the front of the vehicle. It is primarily used to
stabilize the vehicle when loads above 12,000 pounds are winched or hoisted. The spade is actuated by two, single-end rods,
double-acting hydraulic cylinders. These cylinders retract to raise the spade, and extend to lower it. When the spade control
valve is placed in the RAISE position, hydraulic pressure is introduced in front of the cylinder pistons and bled off behind them.
The piston rods then retract and actuate the crank arms to raise the spade. When the spade control valve is placed in the LOWER
position, hydraulic pressure is introduced behind the pistons and bled off in front of them. The piston rods then extend and
actuate the crank arms to lower the spade. Placing the spade control valve in the HOLD position traps all hydraulic fluid in the
lines, thus preventing the spade from moving either up or down.