end seals the spool thus forms two sensing chambers 44 and 45 in the housing bore a central recess 46 on the spool is opposite actuator 27 when the spool is in its normal centered position as shown on fig1 however when the spool shifts towards fig3 position it will move actuator 27 to thereby shift switch ls to its open or lockout mode and disenable the solenoids 18 and 19 this will permit the pilot valves and thus the main valves to move to their closed or exhaust position switch ls will remain in its lockout position until actuator 27 is manually reset even though spool 41 returns to its centered position when the pressures in chambers 44 and 45 are equalized the central portion of shaft 36 is enlarged to provide oppositely facing shoulders 47 and 48 a pair of helical coil compression springs 49 are disposed on shaft 36 on opposite sides of the spool these springs engage collars 51 which in turn engage shoulders 47 and 48 the shouders being spaced apart the same distance as the end surfaces of the spool it will thus be seen that in its normal position spool 41 will be held centered by the two springs however when the spool shifts in one direction and compresses one spring it will not be followed by the other spring which is held captive by its corresponding shaft shoulder sleeves 52 are provided within springs.