10 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
FETURN BEND COIL q 
HEADLEP Coll 
WALL COLL, 
f 
i 
o 
COOOUEAO! 
VERTICAL FETULN BEND HEADER? COL 
FEF URN GENO 1ILAQEL COLL 
Ficgurp 2.—Typical pipe coils for heating dry kilns. All such coils provide for expan- 
sion and contraction of individual pipes and for free flow of condensed steam to the 
drain end. Header coils and return-bend header coils of various types are most 
common ; vertical return-bend coils are used in short kilns that require uniformity 
of temperature. In many cases header coils are made up with two rows of pipe 
instead of only one. The type of wall coil illustrated is ordinarily known as a Z 
coil; in dry-kiln work it is usually placed horizontally 
