Re: Sanders on steam locomotives

I can't testify to any system that may use pressure to apply sand. It has been my understanding that gravity feed is the only system used. However, that might be different in difficult climates. At SVRy our lokies use gravity. The sand domes keep the sand dry. On #19 a directional air control located on the brake stand within easy reach of the Engineer actuates valves for sand application. Two air valves are located on each side of the dome. One for forward and one for reverse sanding. Sand flows through pipes (1" dia. I believe) to either just forward of the front drivers and a couple inches or so above the rail, or pipes likewise positioned just back of the rear drivers.
I am not a qualified Heisler Engineer yet, but I believe the sand valve is machanically actuated. My understanding is sanding is seldom done on the Heisler.
dan