CONSTRUCTION AND FIRE PROTECTION OF COTTON WAREHOUSES. 71 



If the warehouse plant is very V^vga 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 j)umps 

 may be used for filling the tanks, though these may be filled from 

 the city supply.^ 



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 uS:e. Repairs 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 



^ Eacti source of water supply sliOTild be protected against every other supply 

 by check valves. The ueed 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 pressiu-e the same overflowing and loss of pressure 

 would result. Check valves to pi'otect tanks should always have a by-pass 

 around them in order thnt water may be forced through the by-pass into the 

 tank. The by-pass valve should be of the post-indicator gate type. 



