CONSTRUCTION AND FIRE PROTECTION OF COTTON WAREHOUSES. 71 
If the warehouse plant is very large and a satisfactory city supply 
is not available, the gravity tank should be used as the primary 
supply and suitable pumps with abundant water available should 
constitute the secondary supply. These supplementary pumps are 
always desirable for a very large plant. With the combination 
of tank and pumps the system is complete in itself, as the pumps 
may be used for filling the tanks, though these may be filled from 
the city supply. 1 * 
The water pressure maintained for hydrant protection should 
be from 50 to 80 pounds, the minimum being that which will give 
two standard hose streams as previously described. The actual 
delivery of water is made the minimum test because the actual pres- 
sure under flow may be very much less than that normally registered 
by the pressure gauge, because of the length, small size, or bad condi- 
tion of the yard piping. The pressure used for the sprinkler system 
may be that used for the hydrant system, the same supply lines 
being used for both. If a low gravity tank constitutes the sprinkler 
supply, the bottom of this tank should be at least 30 feet above 
the highest sprinkler heads. In many instances the gravity tank 
is from 75 to 100 feet high. Frequently an elevation of the ground 
can be used to advantage in affecting a saving in height of the 
tank tower. 
The yard piping system should always be arranged as a "loop 
system " so that water from any source can be delivered to any point 
without undue friction loss. The system should be divided into 
sections by post indicator gate valves in order that changes or re- 
pairs may be made in any part of the line without putting the en- 
tire system out of use. Eepairs and changes, when necessary, should 
be made with as little interruption to the service as possible. The 
loop and section arrangement is of great value in case of a severe 
fire when open hydrants may have to be abandoned as such an 
1 Each source of water supply should be protected against every other supply 
by check valves. The need for this is apparent from the following illustra- 
tions: Suppose a gravity tank primary supply is connected with a city main 
and the city connection is not protected by a check valve, the drainage of this 
part of the city main would drain the tank also and leave no water supply. 
Again, if the tank and pump supplies are used the tank is at an elevation de- 
signed to give the pressure desired for the sprinkler system with dependence 
placed on the pumps for hydrant pressure, the desired increased pressure and 
supply from the pumps when in operation will be dissipated by overflowing of 
the tank unless it is protected by a check valve. Or if the tank is not pro- 
tected against greater city pressure the same overflowing and loss of pressure 
wOuld result. Check valves to protect tanks should always have a by-pass 
around them in order that water may be forced through the by-pass into the 
tank. The by-pass valve should be of the post-indicator gate type. 
