Why does 765 have six sanding valves for just four powered axles?

How about, four for forward sanding and two for sanding in reverse?

Edit:

The correct name for those devices is "Sand Traps". The Sanding Valve is what the Engineer operates to activated the sand by supplying compressed air to the various Sand Traps.

Interesting question. I had to do a little photographic research to find out for my self!

If you look in this photo, you can see the number 3 and number 4 drivers have sand tips in both forward and reverse. That would account for the 6 traps, 4 forward, 2 reverse.

Tom

Wouldn't the middle sand traps be used for either forward or reverse?  First and middle going forward. Middle and third going in reverse.

Dan

i'd have to believe the "why" came from feedback on the earlier S1 class.

Dan65train posted:

Wouldn't the middle sand traps be used for either forward or reverse?  First and middle going forward. Middle and third going in reverse.

The sand lines deposit the sand very, very close to the wheel tread/rail juncture. So even if the middle lines did double-duty, there would be some compromise--there would still be several inches of wheel travel before the driver could bite into the sand, depending on the lines' location, thereby negating its purpose.

i asked the definitive source for NKP Berkshire information and here is the answer i got...

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" 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

I had not thought about this in years, but this thread has sparked a memory.  The A-Yard at San Bernardino was on a westward ascending grade, increasing as tracks moved westward.  During the citrus loading season, "turns" would go west on the Second, Third, Fourth, and Redlands Districts with pre-cooled, iced reefers and return with loaded ones, yarding them in the A-Yard.  The top end A-Yard switcher would have to drag out heavy cuts of perishables, and the little Alco S2 switchers did not have the greatest sanders.  So, when I worked those jobs during the produce season, I always scooped up a pile of sand into an empty coffee can, and stepped out onto the back platform to sprinkle extra sand down when the engine was on the hardest part of the pull.  It actually made a difference.

As information, there are usually piles of sand wherever locomotives tie up, from Engineers testing and cleaning out sanders, etc.  Normally, they are a nuisance, but -- sometimes -- handy.