a spool provided in the casing and configured to switch {HEAD ~ the output port} between {TAIL ~ the pump port} and the tank port, and 
a spool provided in the casing and configured to switch { HEAD ~ the output port } between { TAIL ~ the pump port } and the tank port , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH