{HEAD ~ All the intermediate positions} between these two end positions blocking the orifices 7 allow {TAIL ~ the loss} of head to be adjusted partially as required 
allow
{ HEAD ~ All the intermediate positions } between these two end positions blocking the orifices 7 allow { TAIL ~ the loss } of head to be adjusted partially as required
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH