{HEAD ~ The switch} opens {TAIL ~ a solenoid valve} which vents the hydraulic pumps which move the tracks of the trencher in the forward direction 
opens
{ HEAD ~ The switch } opens { TAIL ~ a solenoid valve } which vents the hydraulic pumps which move the tracks of the trencher in the forward direction
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH