The Collaborative International Dictionary of English v.0.48:

Direct-acting \Di*rect"-act`ing\, a. (Mach.)
   Acting directly, as one part upon another, without the
   intervention of other working parts.
   [1913 Webster]

   Direct-acting steam engine, one in which motion is
      transmitted to the crank without the intervention of a
      beam or lever; -- also called direct-action steam
      engine.

   Direct-acting steam pump, one in which the steam piston rod
      is directly connected with the pump rod; -- also called
      direct-action steam pump.
      [1913 Webster]