CONSTRUCTION AND FIRE PROTECTION OF COTTON WAREHOUSES. 67 
Automatic sprinkler systems for most conditions are one of the two 
general types, known as the " wet " or the " dry " system. In the 
wet system the pipes are filled constantly with water, while in the 
dry system the pipes are filled with air under pressure. In this latter 
case' the fusing of a head from fire allows the air to escape and thereby 
imbalances the water pressure which in turn actuates a valve which 
admits water to the system. This valve is known as the " dry-valve." 
The wet system should be used wherever there is no danger of the 
water in the pipes freezing in winter. Where the climate affords this 
danger of freezing, the dry-pipe system should be used. Some of the 
advantages of the wet system are that water is discharged instantly 
upon the fusing of a head, the possible failure of a dry-valve to 
open is avoided, and the cost of installation is less. 
Sprinkler systems may be arranged so that the pipes are filled with 
water in summer and yet operated as a dry-pipe system in winter. 
This may be accomplished by a supply pipe or " by-pass," extending 
around the dry- valve so that when the " by-pass " is open, water does 
not flow through the dry valve. Such an arrangement is very de- 
sirable. 
One of the first questions to be decided is whether the system shall 
be wet or dry. If in doubt, the best procedure is to get bids on both 
systems and also a definite expression from the insurance rating 
bureau having supervision, as well as to make a careful study of 
local temperature records for a number of winters. In some instances 
the " eaves sprinklers " may be connected to the main system through 
a gate valve and drip so that the exposed piping can be drained dur- 
ing cold nights. However, no chances should be taken toward hav- 
ing a f rozen-up sprinkler system. These statements refer, of course, 
to unheated buildings. 
Sprinkler heads, or nozzles, should be so placed that all ceiling 
area and goods may be reached bj^ the spray. The protection should 
be extended to include all platforms on which cotton is handled. 
The heads should be arranged to give the best protection in con- 
sideration of the construction of the building. The various draw- 
ings previously shown indicate a suitable arrangement in several 
buildings. Usually there should be one line of sprinkler heads down 
the center of each bay (space between timbers) for bays not ex- 
ceeding 12 feet in width. The spacing of the head should not exceed 
12 feet in either direction and preferably should not exceed 10 feet. 
Sprinkler heads nearest walls should not be farther from the wall 
than half the spacing between heads. With these provisions met, 
there may be allowed one sprinkler head to not exceeding 100 square 
