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 {HEAD ~ the valve} 
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 { HEAD ~ the valve }
OTH OTH OTH OTH OTH OTH 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 HEAD HEAD HEAD HEAD HEAD HEAD