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