1. A reversing pneumatic amplifier comprising: A. a first input means through which a pilot pressure is introduced into said amplifier, B. a second input means through which a supply pressure is introduced into said amplifier, C. discharge channel means in communication with the ambient atmosphere, D. an output opening, E. a hollow cylindrical control sleeve having a first open end communicating with said discharge channel means and a second open end communicating with said second input means, F. a slot provided in said sleeve and extending in a radial plane thereof; said slot connecting the inside of said sleeve with said output opening, G. a valve ball movably disposed in said sleeve and adapted to assume first, second and third positions, in said first position said valve ball closes said slot, in said second position communication is established between said second input means and said output opening, in said third position communication is establisheD between said discharge channel means and said output opening, and H. means in engagement with said valve ball and in communication with said first input means for transmitting said pilot pressure indirectly to said valve ball, said pilot pressure being opposed by said supply pressure directly affecting said valve ball through said second input means.