Field artillery materiel

by Unknown

The cross level is located on the rear edge of the sight shank and serves the gunner in determining the level position of the instrument. The level vial is a glass tube, closed at both ends, and partially filled with a liquid consisting of 4 per cent alcohol and 60 per cent ether, a small bubble remaining in the tube. Graduations are etched on the circumference of the tube to indicate the central position of the bubble. The vial is held in a level-vial tube, the ends being wrapped in paper and set in plaster of paris. The knurled cross-level cover fits over the holder and, together with the level-vial tube, are held in place by the cross-level caps, which close the ends of the holder. When closed, the cover serves as a protection for the vial.

The elevating mechanism consists principally of a sight shank, elevating worm wheel, antibacklash pinion, elevating worm, elevating worm eccentric, elevating scale drum, and scale drum housing.

NOTES ON CARE OF THE 155 HOWITZER.

The executive should be perfectly familiar with the working of the recoil and know when to put a gun out of action due to faulty recoil. The length of the recoil should be such that the end of the gun slides do not recoil over the end of the cradle rails. In counter-recoil, the sleigh should be perceptibly slowed down at a point about 10 centimeters from the front of the cradle, and from there on should ease gently into battery without a sound or shock. Strict watch should be kept to see that no excessive leakage takes place through the stuffing boxes, the valve in the gauge adapter, or the oil hole in the cylinder end nut. Slight leakage can hardly be helped, as one of the stuffing boxes is under more than four hundred pounds of pressure per square inch when the gun is at rest, and three or four times that amount when the gun is in full recoil. However, if a pool of liquid is found after the gun has been standing all night, it is time to report the matter and have the packings replaced. The gun must be dismounted, the stuffing-box repacked, and the dermatine inspected. The dermatine packing is a compound resembling rubber, but it has the quality of resisting any chemical action that the liquid may set up in the recuperator. A worn dermatine packing may be replaced by the simple expedient of turning it wrong side out and then using it again as before. This has actually been tried and found to give good results. Another temporary repair was effected by cutting a ring from a solid truck tire and using it in the place of the dermatine, until a packing of the latter could be obtained.

The French obtain a very tight fit in their stuffing boxes by the peculiar design that allows the liquid pressure to actuate a strong spring which in turn expands the packing against the rod or cylinder wall. Leakage through the recuperator stuffing box will be noticed by the liquid coming out of the oil hole in the right-hand cylinder end nut.

In dismounting French materiel, care must be used to replace the same nuts on the bolts from which they were taken. Threads are not standardized as to diameter; hence, trouble is likely to occur when remounting.

To dismount the tube from the recoil mechanism, or sleigh as it is denoted, a suitably strong overhead beam is selected and the carriage run beneath it. Mount two one-ton duplex blocks on the beam over either end of the tube and thread the bore with a half-inch wire cable sling, in such a manner as to leave a bight at both muzzle and breech ends. Into these loops the hooks of the block catch. Gunny sacks form a suitable packing at the muzzle and breech to prevent the cable damaging these parts of the tube. Provide several blocks of two by four or four by four stuff, to block up the sleigh as it is moved to the rear—as we shall soon see that it does. Remove the locking hoop by knocking out the retaining bolts, and also remove the cradle bolts from their housing on the cradle. This will allow the sleigh to move to the rear of the cradle. Take a strain on the blocks and carefully move the sleigh back over the trail until the recoil-lug key (locking the recoil lug to the sleigh) clears the end of the cradle. Remove the set screw from the bottom of the sleigh which locks the tapered key in place, and proceed to drive the key out with a sledge hammer and a block of wood. During this operation the rear of the sleigh must be blocked up on the trail in order to take the strain off the cradle rails. After the key is cleared, the tube may be raised by means of the two blocks, care being taken to make the lift vertical, otherwise the slots and grooves just in front of the breech will jam and be damaged. Remove the carriage and lower the tube onto blocks. The process of mounting is just the reverse of the above.

The elevating and traversing mechanisms give little trouble, if all gear cases are kept packed in grease. It is extremely important that, in laying for elevation with this piece, the final turns of the handwheel should bring the gun into correct position by raising the breech and not by lowering it. In this way all backlash is taken out of the gearing and the howitzer rests solidly for firing. The gunner may easily be taught to remember this by always having him bring the range bubble to the front of the glass and then slowly elevate the breech, bringing the bubble to him.

The traversing mechanism moves the whole carriage, including gun, along the axle, about the spade as the center of rotation. The traversing screw moves the carriage by being rotated through nut set solidly in the axle. The axle and nut are stationary and the screw moves laterally by means of the traversing handwheel. Hence, the carriage being attached to the screw, must move when the screw moves. Inasmuch as the axle is straight, it must accommodate itself to the arc of the circle described about the spade as the center. It does so by moving tangent to the arc, and consequently one end moves to the front and the other end moves to the rear, carrying the wheels with them. From this it will be seen that before attempting to traverse the piece, the brake must be “off.” The movement of the wheels may be easily seen, if a pencil line be drawn across the tire just above the brake shoe and then the piece traversed. The line will be seen either to raise or lower according to whether the piece be traversed to the right or left.

In filling the “brake” or recoil cylinder, good results have been obtained by merely leveling the gun and filling the brake cylinder until full. Trying to pour out one hundred cubic centimeters of the liquid after the brake is full, as the French drill regulations lay down, is almost impossible; and no bad effects will be noticed provided the gun does not become excessively warm during the firing. If it should become warmed up sufficiently to affect the recoil, level the gun, unscrew filling plug to release the pressure, rescrew, and continue the fire. In using the manometer gauge, to measure the pressure and the height of the liquid in the recuperator, it will be found that the valve in gauge adapter will sometimes stick open to the extent of letting out all the air in the recuperator tanks. The only sure remedy for this is entirely to dismount the gun, remove the adapter, and replace its valve packing, which no doubt will be found to be worn and frayed, or else some foreign substance will be found to be lying between it and its seat. The gauges should be tested about once in three months by means of a standard steam gauge testing apparatus, making the appropriate transformations if the tester be graduated to pounds per square inch as most steam testers are. It will be found that the maximum steam pressures used are rather lower than these gauges read, hence only the lower readings may ordinarily be tested.