24 BULLETIN 8&4, TT. S. DEPARTMENT OP AGRICULTURE. 
STEAM SUPPLY TO COILS. 
The steam supply pipe to the coils should be taken from the top 
of the steam main to avoid drawing dirt and condensation into the 
system. Where the steam main is overhead this will also allow 
provision for expansion. 
Where automatic temperature regulation is used the thermostatic 
valve is placed on the steam supply to each kiln so that it controls 
the supply to all coils. 
After passing the thermostat, the separate supply to each coil 
unit should be taken off through independent valves, in order that 
the different units may be used separately or together. Care should 
be exercised to balance all supplies as to size and resistance to flow 
of steam, in order that no coils may be starved to the advantage of 
other coils. 
Where the coils are over 40 feet long they should be divided in 
two sections lengthwise and supplied from the center of the kiln, as 
shown in figure 8. In this case the supply pipe should be covered 
with waterproof and heat-proof insulator between the operating 
room and the connection to the coils proper, otherwise the exposed 
heating surface at the two ends of the kiln is unbalanced. 
STEAM MAIN SIZES. 
In determining the size of steam mains, first compute the size of 
supply necessary to each kiln and then the size of main required to 
supply all kilns, and reduce in size in proportion to the size of supplies 
taken off. 
Consideration must be given to the following points: 
1. The smaller the main the greater the resistance due to friction 
and to consequent back pressure in the system. 
2. Conversely, the larger the main the less the resistance and the 
greater the efficiency, but also the greater the cost of installation. 
3. The greater the length, the greater the resistance due to friction, 
and the greater the necessity for larger pipe. 
4. Bends, valves, or other equivalent obstructions increase the 
resistance due to friction and must be compensated for. 
For pressures up to 5 pounds gauge, which is the upper limit 
desirable for exhaust systems, the size of mains and supplies may be 
determined from, the table following by A. R. Wolff. 
