Page:EB1911 - Volume 20.djvu/261

GARRISON MOUNTINGS] cylinder backwards with it, draws it off its piston rod L and forces it into the air chamber F. The air in the chambers F and G is at a high initial tension and, on recoil, the air in F is further compressed and forced through the valve H into the chamber G. At the conclusion of recoil the air expands and forces the buffer cylinder to the front, which carries with it the gun into its loading position; but the valve H closes and the air has to make its way through a narrow hole before it can act on the end of the buffer, thus preventing violent action, which is further guarded against by the “control ram” M which is bolted into the rear end of the buffer. To prevent leakage of air between the air chamber and the buffer at the gland K the packing employed is a viscous liquid which is in communication by means of the pipe J with the intensifier I. The latter consists of a cylinder containing a piston and rod free to move: the front face of this piston is subject to the pressure of the air in the air chamber, the rear face is in communication with the liquid in the gland. Now, as the piston head is held in position by the pressures on either side of it, and as the effective area of the front face is greater than that of the rear—on account of the rod—the liquid pressure per square inch of the fluid in the gland, &c., must be greater than that of the air in the air chamber, hence the latter cannot escape through the former. The pressure in the chambers F and G is adjusted on preparing for action by an air pump worked by hand. The energy of recoil is further utilized as follows: hydraulic cylinders called compressors are held in the cradle, and in them work rams connected with the cross-head A (sec fig. 85): they are also connected with a hydraulic accumulator (not shown) which can be placed in any convenient position in the work, and the power thus stored up be employed for raising the projectiles, for which purpose two lifts are provided. One of these (W) is in the floor of the emplacement, the other (W) is attached to and moves with the mounting. Underneath and suspended from the circular gun platform RR, which forms a shield, is an overhead railway QQ, on which run trollies, each taking a projectile. The projectiles are stored in the recess shown in section at O. By means of a shell barrow any projectile can be placed on the lift W and raised to a trolley which can be run round over the lift W, which raises the projectile, as shown at S, to a point suitable for loading.

EB1911 - Ordnance Fig 85.png . 85.—Details of Mounting shown in fig. 21.

The British 6″ B.L. Gun.—A typical mounting for guns of type (b) is afforded by the British C.P. (central pivot), Mark II. mounting for the 6″ B.L. Mark VII. gun, a combination which admits of six rounds a minute aimed fire. Fig. 86 shows a side elevation cf the mounting with half the shield removed; fig. 87 a longitudinal section of part of the cradle through the axis of the buffer. The gun, which is trunnionless, recoils in the cradle A; the latter contains a buffer B and two cylindrical boxes containing springs S. Attached to the breech of the gun is a piston rod C with piston D, the latter having an opening or “port” E, through which the oil passes on recoil, the pressure in the buffer, which would otherwise vary with the velocity of the recoil, being kept constant by the variation in the area of aperture afforded by E. This area is governed by the action of the valve key strip F of varying section, which is inserted in the buffer in such a way that as the gun recoils the port E is constrained to pass over it. On recoil the rods J, which are attached to the gun in rear and screwed into the flanged cylinder H in front, force back the front of the springs S, whose rear ends butt up against the rear of the spring boxes. After recoil the springs return the gun to the firing position. To check the violence of this action a control ram G is made use of: the piston rod has a cylindrical hole in front which, as the gun recoils, becomes filled with oil, and before the piston can come up against the front of the buffer this oil has to be displaced by the thrust of the ram G which checks the forward movement of the gun. The cradle A rests on its trunnions in seatings in the lower carriage and is elevated or depressed by the gear K′. The last-named drives the elevating arc L, which is attached to the cradle at M, the axis of the gun moving parallel to the axis of the cradle. In fig. 86 the lower carriage is almost entirely hidden by the gears carried on it, namely, the elevating gear K, the traversing gear N, which works a spur pinion, gearing into the rack O attached to the pedestal P: the elevation indicators Q and R for recording the angle of elevation of the gun and the bracket S′ which support the 6″ armour plate T. The weight of the lower carriage, cradle and gun is taken by a horizontal ring of hard steel balls resting on the top of a massive forged steel “pivot” U, the lower portion of which is shown supported in the cast-iron pedestal. The elevation indicator consists of a sector Q bolted to the cradle trunnions; to its edge is attached a metal tape, the