{HEAD ~ an extension side pressure control valve} provided at {TAIL ~ the extension side bypass flow passage} and adapted to be opened by receiving a pressure in the extension side bypass flow passage, 
{ HEAD ~ an extension side pressure control valve } provided at { TAIL ~ the extension side bypass flow passage } and adapted to be opened by receiving a pressure in the extension side bypass flow passage ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH