CONSTANT RUNOUT VALVE (CROV) WEIGHT SELECTOR

system (fig. 3-3) to rotate the CROV cam. Rotation of this cam forces a plunger down onto a set of levers (fig. 3-4), which in turn forces a valve sleeve and valve stem down to mate with a valve seat to close the valve, shutting off the flow of fluid from the engine cylinder to the engine accumulator, bringing the aircraft to a stop. As stated earlier, the CROV is designed to bring all aircraft, regardless of weight, to a controlled stop while using approximately the same amount of flight deck landing area. This is accomplished by adjusting the allowable opening of the CROV, a smaller, more restrictive opening to arrest a heavy aircraft or a large valve opening to arrest a light aircraft. CONSTANT RUNOUT VALVE (CROV) WEIGHT SELECTOR The aircraft weight selector makes it possible to adjust the CROV for aircraft of different weights by varying the valve opening. See figure 3-4. The size of the initial valve opening is adjusted while the arresting engine is in the BATTERY position. The lead screw receives rotary motion from the motor unit or handwheel and converts it into linear motion. This linear motion positions the upper lever and drives the local and remote indicators. In each of the two levers (upper and lower), the distance between the fulcrum and roller is constant. On the upper lever, the distance between the fulcrum and the point of application of force from the cam is variable, its greatest length being twice that of the lower lever. The lever arm ratio of each lever, therefore, is variable between 1:1 and 2:1. When the upper lever is fully extended, the ratio of each lever is 1:1. In this setting the initial opening of the control valve upon engagement of an aircraft is maximum. The resulting rotation of the cam, caused by the crosshead moving inward, forces the plunger downward. A plunger movement of 1 inch, acting through the upper lever, would move the lower lever 1 inch; the lower lever, in turn, would move the valve sleeve and stem 1 inch downward. The cam is a disc plate type with the desired contour machined on its periphery. As the cam rotates, it forces the plunger down. The plunger is fitted with rollers, top and bottom. The bottom roller on the plunger acts against the top flat bearing surface of the upper lever. The pivot end of the upper lever has a bushed hole that mates with the clevis end of the lead screw yoke. The upper lever is connected to the clevis end of the yoke by a pin. This pin extends beyond the sides of the yoke and acts as a shaft and has a bushed roller mounted on each extended end. The rollers ride inside the guide attached to the housing. The block end of the yoke is connected to the lead screw by two dowel pins. This connection provides the means by which the lead screw adjusts (moves) the upper lever. 3-6 INDICATOR PLATE CONTROL VALVE CAM RAM TRAVEL AND DECK RUNOUT DIAL CONTROL VALVE REF (CROV) DRIVE CHAINS PULLEY PULLEYS CONTROL VALVE DRIVE CABLE MOVEABLE CROSSHEAD PULLEYS ADJUSTABLE ANCHOR ABE3f0303 Figure 3-3.—Constant runout valve drive system.