68 BULLETIN 801, U. S. DEPAKTMEXT OE AGRICULTURE. 
feet of floor area. However, a greater number of heads is Yevy 
desirable, one head for every 80 square feet being preferred. 1 
The dry-pipe system demands the use of! an air compressor for 
maintaining air pressure in the pipes. A hand compressor is not at 
all burdensome for warehouses not exceeding 10,000 bales capacity. 
If the pipe joints are tight the leakage of air should be so slight that 
the system will need to be pumped up only once a week. The pressure 
valve, however, should be read every day. 
All valves supplying the sprinkler system should be kept open and 
sealed or tagged conspicuously and inspected frequently in order to 
insure prompt action of the sprinklers. It is well for the manage- 
ment to keep a record of systematic inspections. Several members 
of the force and all foremen should be familiar with these valves. 
1 The position of the head with reference to the ceiling and goods is of the 
utmost importance. Usually the distance of the head below the ceiling should 
be from 3 to 10 inches, 6 or 7 inches being preferred. In the case of fire- 
restrictive construction, protection of the ceiling is of less importance, and the 
drop of the head may be increased. These requirements are appreciated 
when the roof contains monitors or saw-tooth skylights. In any case the 
sprinkler head preferably should be as much as 3 feet above the surface of 
cotton bales, while this distance should not be less than 18 inches, even if 
sprinkler heads are only 8 feet apart. Care should be taken to see that heads 
are not placed so close to the side of beams that the spray is obstructed. 
- The arrangement of piping and the size is of vital importance to effective 
sprinkler operation. If pipes are too small in proportion to their length and 
to the number of heads supplied, the efficiency of the equipment is vitally 
impaired in case of a number of heads opening, as this results in a marked 
reduction in pressure and volume of water delivered. 
This suggests the importance of a suitable location for the sprinkler "riser " 
which supplies water to the system. A comparison of the plans previously 
illustrated will show that for compartments 50 by 100 feet the riser is placed 
in a corner; for compartments which are 100 feet square the riser should be 
at the center of one side, while for compartments less than 100 feet in one 
dimension and greater than 100 feet in the other, the riser should be located 
at the center of the long wall; and if the compartment is greater than 100 
feet in both dimensions, the riser should be at the center of the area, as shown 
by the photograph in Plate XXII, figure 2. It is desirable that the riser 
always be placed at the center of the area, but there are frequently practical 
difficulties involved. For example, in a story of 8* feet the clear height' below 
beams is usually only 7 feet or less ; obviously the lateral supply pipe extending 
from the riser and at right angles to the beams (between which the branch 
lines carrying sprinkler heads are located) would have to be so low as to 
seriously obstruct truckers— hence the advantage of having this supply line 
next to a wall. On the other hand, there are instances where alternate beams 
are carried by a line of girders, in which case it may be best to place the supply 
line under the girders in order that the branch lines may be kept well up 
between the beams. In the case of reinforced concrete girders of very great 
depth it is sometimes desirable to provide pipe thimbles (holes) in the girders 
