148 the only difference in this case is that the fluid connections are provided by mechanical displacement of spool valve 110 of servo valve 71 through handle 200 such action occurring mechanically rather than hydraulically by means of the pilot valve 69 and is effected entirely independently of the pilot valve 69 to obtain opposite movement of the power piston 144 the handle 200 is moved downwardly in the direction of the arrows 204 effecting the same hydraulic connections as described in fig4 except that the pilot valve 69 again remains stationary but the total effect is to communicate hydraulic pressure and fluid flow in the direction of arrows 120 in line 118 such fluid pressure then being transmitted through line 170 to chamber 172 and effecting a lifting action on the piston rod 146 in the direction of arrow 166 the result is the same as achieved by pilot valve 69 fig4 the pilot valve is maintained in a neutral centered position by a spring 75 which is compressed between two spring cages 75a and 75b so that in the center position the spool valve 72 of the pilot valve 69 is maintained in the position shown in fig2 when the spool valve is drawn upwardly an enlarged head 75c acts against cage 75b and the spool valve can be moved until the two cages are brought into engagement one with the other fig3 likewise when the spool valve is moved in the opposite direction as shown.