{HEAD ~ A further broad aspect} relates to {TAIL ~ a valve} having structure for pneumatically or hydraulically closing the valve, and a back up structure for resiliently or mechanically closing the valve 
{ HEAD ~ A further broad aspect } relates to { TAIL ~ a valve } having structure for pneumatically or hydraulically closing the valve , and a back up structure for resiliently or mechanically closing the valve
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH