shunt valve

from The Collaborative International Dictionary of English v.0.48

Shunt valve \Shunt valve\ (Mach.)
   A valve permitting a fluid under pressure an easier avenue of
   escape than normally; specif., a valve, actuated by the
   governor, used in one system of marine-engine governing to
   connect both ends of the low-pressure cylinder as a
   supplementary control.
   [Webster 1913 Suppl.]