a stationary cylindrical casing comprising a pair of opposite gables, enclosing said rotatable drum, whereby an annular space is defined between {TAIL ~ said stationary cylindrical casing} and {HEAD ~ said rotatable drum}, 
a stationary cylindrical casing comprising a pair of opposite gables , enclosing said rotatable drum , whereby an annular space is defined between { TAIL ~ said stationary cylindrical casing } and { HEAD ~ said rotatable drum } ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH