The piston is screwed and pinned to the piston rod and is of bronze, slotted to fit lands and grooves in the recoil valve. The piston rod is hollow for almost the entire length. The front end passes through the gland in the cylinder head and piston-rod sleeve. The front of the recoil cylinder is closed by the front cylinder head, which is screwed in place with a gasket. A bronze gland with four rings of 5/16 inch Garlock packing prevents leakage around the piston rod.
The counter-recoil buffer consists of a buffer rod screwed into the buffer nut at the rear end of the recoil cylinder, and extending through the buffer bushing into the interior of the piston rod. The buffer head is screwed and pinned into the front end of the buffer rod. The buffer head is of two diameters and connected by a short cone. The rear end is the smaller diameter and is threaded inside to screw over the buffer rod. The coned surface contains slots leading to a hollow chamber in front. The front end of head is faced and provided with a central bearing for valve stem. The bearing is supported by webs to main body of guide. Valve stem has a stop on rear and a valve screwed to front. Valve is faced to seat on front of the bearing, webs and circular face of main body of guide.
The counter-recoil springs are assembled around spring rods in spring cylinder. Spring rods fit in gun lug and are fixed in place by taper keys driven diagonally through lug and rod. The rod is hollow for entire length, except at the rear, where the outside diameter is decreased to permit entrance in gun lug. Collars are screwed and pinned to front ends of rods. Three coils of inner counter-recoil springs are assembled over the spring rod, surrounded by three coils of outer springs. Inner and outer springs are coiled in opposite direction to prevent nesting, and sets of coils are separated by a bronze separator. Rear ends of cylinder are bushed for spring rods.
The operation of recoil mechanism is as follows:
When the gun is fired it moves back in slides on cradle, carrying with it spring rods, buffer rod, recoil cylinder, and recoil valve. The piston, piston rod, and spring cylinder remain stationary, being fixed to carriage.
75 MM GUN CARRIAGE, MODEL OF 1916.
LONGITUDINAL SECTION, RECOIL AND COUNTER RECOIL MECHANISM
The recoil cylinder being full of oil, this oil is forced by the piston through holes in recoil valve in front of piston up into annular space between valve and cylinder and into space behind and vacated by the piston. The hydraulic resistance caused by forcing the oil through the holes in valve absorbs most of the recoil energy of the gun, and the remaining energy is taken up by compression of the counter-recoil springs and friction.
When the gun reaches the end of recoil all of the recoil energy has been absorbed and the counter-recoil springs acting against spring-rod piston force the gun back to battery position. The purpose of the counter-recoil buffer is to overcome the tendency for gun to return to battery too rapidly, at the same time allowing sufficient speed of counter recoil to permit maximum rapidity of fire. Buffer action is necessary, as the strength of springs required to return the gun to battery at high elevations is greater than is required at lower elevations.
The action of counter-recoil buffer is as follows: