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Description and functioning of recoil mechanism   ....................................		7

7. DESCRIPTION AND FUNCTIONING OF RECOIL MECHANISM.

a. General. The recoil mechanism is an independent hydropneumatic system. The recuperator cylinder, which is entirely separate from the recoil cylinder, is filled and charged with gas and liquid in direct contact. The recoil cylinder is of the control rod type with a secondary control rod regulating recoil length. Both recuperator and recoil cylinders are supported by the cradle, and the pistons are connected to the top and bottom of the breech ring, respectively.

b. Recuperator Cylinder.

(1) The recuperator cylinder (fig. 15) is secured to the cradle above the piece. A liquid cylinder is fitted eccentrically in the bottom of the outer gas cylinder. The center lines of both cylinders are parallel. The liquid cylinder is completely filled with a glycerine-water solution, and the rest of the mechanism is charged with nitrogen to the proper pressure.

Figure 15 — Recuperator Cylinder

(2) Upon recoil, the recuperator cylinder rod and piston are brought to the rear by the recoiling gun; and the liquid is transferred, by the piston, from the liquid cylinder into the gas cylinder. The gas is compressed by the decreased volume in the cylinder, thus opposing the energy of recoil. While the recuperator cylinder controls a portion of the recoiling energy, the recoil cylinder controls the remainder of the recoiling energy in addition to controlling the length of recoil. In counterrecoil, the motivating force is the expanding gas tending to force the liquid back into the liquid cylinder, thus activating the recuperator cylinder piston. The force of counterrecoil is dampened by the recoil cylinder. After several rounds have been fired, the gas and liquid have emulsified. This condition, however, does not alter the volume pressure relationship, and the liquid is still effective for its original purpose of supplying an adequate pressure seal. The ports in the end of the liquid cylinder are not throttling orifices, and the state of emulsification has no effect on the recoil action.

(3) The piston rod is hollow to eliminate the vacuum which would be caused by the sealed cylinder and plug. This hollow opening also permits exit of the atmospheric air in back of the piston head. The washers are of U-shaped leather and use U-shaped brass spacers. The whole is secured by a large lock nut.

c. Recoil Cylinder.

(1) The recoil cylinder (fig. 16) is located beneath the gun inside the cradle. The cylinder is filled with liquid at atmospheric pressure. The cylinder and the control rod remain stationary. In recoil, the piston rod and counterrecoil control rod move with the breech ring. As the weapon recoils, part of the fluid is forced through the orifices in the piston head and through the control grooves in the recoil control rod. Another portion of the fluid passes through the valve in the control bushing and fills the increasing hollow space behind the head of the recoil control rod. The pressure of the liquid through the constantly narrowing grooves takes up most of the force of recoil and gradually brings the gun to a standstill. Part of the force of recoil is also taken up in the increase of air pressure in the recuperator cylinder.

Figure 16 — Recoil Cylinder

(2) The counterrecoil action is activated by the expanding air in the recuperator cylinder. The braking liquid which is now in front of the recoil piston head runs back through the control bushing of the recoil control rod. The piston rod slides back over the recoil control rod and the counterrecoil control rod penetrates deeper into the recoil control rod, displacing the liquid in the latter. The valve being closed, the fluid is forced through the grooves in the counterrecoil control rod and the holes in the head. The force of counterrecoil is thus reduced, and the gun comes to rest without shock.

(3) To change the length of recoil as required by high angle fire, the recoil control rod is rotated by the length of recoil control linkage (fig. 17). The linkage is operated when the cradle is elevated and serves to rotate the throttling grooves, thus varying the port area over the whole length of recoil.

Figure 17 — Recoil Control Linkage