i asked the definitive source for NKP Berkshire information and here is the answer i got...
------------------------------------------------------------------------------
" The S & S1 class NKP Berkshires were built equipped with only four sand lines per side; the front two went down in front of only the front and main drivers for forward operation, and the rear two went down behind the main and rear drivers for backward movement. Along about the summer of 1950 a fifth sand line was added to the front of the sandbox which ran down to the front of the intermediate driver.
The S & S1 engines also had a sanding valve feature which allowed either light or heavy sand application to the front of either the front driver alone or to the front, intermediate, and main drivers. Sand could also be applied to the back of the main and rear drivers in four different levels of intensity for backward movement.
The S2 & S3 engines were equipped with six sand lines; one to the front of each driver and one each to the rear of the main and rear drivers. The engineer’s sanding valve allowed application for forward motion to only the front and main drivers or to all four drivers, one intensity only. Reverse application was to the rear of the main and rear drivers, one intensity only. All sanders utilized air.
It certainly would be my guess that the increased sanding capability of the later engines came about from crew operating experience. I know that when, as a kid, I would watch a 700 lift a freight out of a siding after a meet and there was quite a cloud of sand swirling up around the drivers and the engineer had the throttle quite a ways out where it looked like the lever handle was stuck in his ear. The sound was not soon to be forgotten!"
...Jim Kreider
