head by running the rotor brake disc. The hydraulic disc motor operates only after the gear train engages the teeth of the rotor brake disc. Pressure is cut off to the blade rotation control valve and the motor by the sequence valve.    This action occurs when the gear train has been operated to disengage the rotor brake disc. ROTOR COUPLING.—The rotor coupling is found at the bottom of the rotary-wing shaft. It serves to transfer hydraulic fluid to the rotary-wing head for blade folding. Figure 10-14 shows a cross-sectional view of the coupling. The coupling consists of a spindle that revolves with the rotary-wing shaft. A stationary housing connects to hydraulic lines of blade folding components. Hydraulic fluid is sent through the rotor coupling, and then through the lock valve. Pressure is then sent to the manifold, to the damper-positioner shuttle valve, and to the damper-positioner sequence valves. CONTROL LOCK CYLINDER.—The control lock cylinder is on the No. 2 blade horn assembly rotary-wing head. During the fold cycle, the control lock cylinder locks the flight controls. This occurs only after the blade has been positioned. During the spread cycle, it unlocks the controls. A microswitch within the housing of the cylinder causes the CONT LOCKPIN ADV advisory light in the cockpit to light. In event of hydraulic malfunction, the control lockpin may be operated manually. This is done by turning a sector gear bolt on the aft end of the cylinder. The sector bolt rotates gear teeth on the end of the actuating piston shaft. BLADE FOLD ACCUMULATOR.—A blade fold accumulator is found inside of the rotary-wing sleeve of the No. 1 blade. It has a preload of 1,500-psi nitrogen pressure to maintain hydraulic pressure in the rotary-wing head. The pressure is necessary to keep the damper-positioners extended and the blade locked in the folded position. It serves to compensate for expansion and contraction of the hydraulic fluid because of temperature changes. It also dampens out pressure surges during fold and spread cycles. AUTOMATIC BLADE FOLDING SYSTEM MAINTENANCE Maintenance of the blade fold system consists of periodic inspection, lubrication, operational testing, and troubleshooting.    Allowable maintenance at the organizational level includes alignment, adjustment, and the removal and installation of components. Parts Figure 10-14.—Rotor coupling. replacement and cure date kits are available for intermediate-level repair of defective parts. Before removal of any component, secure the blades to prevent damage. Whenever any part of the system is repaired or replaced, the electrical portion of the system should be tested, as required by the MIM. Operationally check the entire hydraulic portion of the system to ensure proper sequence of operation. The hydraulic testing procedures discussed in the following paragraphs are used as an example. Always consult your MIM for correct procedures. Charge the air accumulator with 1,500 psi of nitrogen, with the blades in the spread position. Connect a source of external hydraulic power to the utility, primary, and auxiliary hydraulic systems. Set pressure to 3,000 psi at approximately 3 gallons per minutes for the utility system. Set pressure to 1,500 psi for the primary and auxiliary servo hydraulic systems. Position the ACCESSORY DRIVE switch to ACCESS DR. The accessory drive light will light. At the start of the testing, make sure that PRI SERVO PRESS, AUX SERVO PRESS, ACCESSORY DRIVE, ROTOR BRAKE ON, and CHECK BLADE FOLD lights will light. The ACCESSORY DRIVE, FLIGHT POS, BLADE SPREAD, EXT PWR ON, PRI SERVO PRESS, and AUX SERVO PRESS lights should be lit. Visually check to see that the lockpins are disengaged. Manually rotate the rotary head until the leading edge of the No. 1 blade is in the aft position. Engage the rotor brake. The rotor brake pressure gauge should read a minimum of 320 psi. Check that the rotor brake light comes on. Place the collective pitch stick in the full low position and the 10-19