
FOREST SERVICE WATER SPRAY DRY KILN. 33 
above 2 J pounds pressure loss. Interpolate for velocity between tbe 
two nearest diagonal lines marked " velocity in feet per second," 
and multiply by 60 to obtain velocity in feet per minute. 
SIZE OF WATER PIPES. 
Area of pipe in square feet times velocity of flow in feet per minute 
gives the delivery in cubic feet per minute. If the diameter is ex- 
pressed in inches, the formula is as follows: 
The diameter of pipe in inches - 
=4.95 / Gal, per min. =14.29 /lbs, per min. 
A/ Velocity in feet A/ Velocity in feet per 
* per minute. * minute. 
For a velocity of 200 feet per minute, the diameter in inches 
=0.35 Vgallons per minute=20.2 Vpounds per minute. 
The size of supplies and mains can also be determined direct from 
the curves of friction pressure losses, by first determining or assum- 
ing the loss in pressure permissible per 100 feet of straight pipe. 
LOSS OF PRESSURE IN PIPES. 
The pressure loss due to friction may be determined from the 
chart in figure 10. It gives the loss of pressure in pounds per square 
inch per 100 feet length of standard sizes of pipe. In interpreting 
this chart it is convenient to note that for a given diameter gallons 
and cubic feet per minute are one and the same quantity merely 
expressed in different terms, and that for a given velocity of flow the 
quantity of water delivered varies as the square of the diameter. 
A kiln 40 feet long having side spray chambers uses 20 gallons of 
water per minute. To find the size of supply between main and kiln, 
from 20 gallons on left of chart follow horizontally to intersection 
with the diagonal pipe size. One and one-half inch pipe gives a 
velocity of slightly over 3 feet per second or 200 feet per minute with 
pressure loss of 1.2 pounds, while the 2-inch pipe (by interpolation) 
gives a velocity of about 2 feet per second or 120 feet per minute with 
pressure loss of only 0.4 pound. Economy would suggest the use 
of the 1 J-inch pipe. 
The branches from the supply pipe to the spray pipe use 10 gallons 
per minute. It can be seen from the curves that in 1-inch pipe the 
velocity would be nearly 4 feet per second or about 225 feet per min- 
ute, with a pressure loss of 2.5 pounds per 100 feet length; while in \\- 
inch pipe the velocity would be about 2 feet per second, or 120 feet per 
minute, with a pressure loss of only 0.7 pound. In this case the 
larger size would be better. 
The size of all mains and branches should be so proportioned that 
the pressure loss will be equal on both cold and hot water mains 
between the pressure-regulating valves and the mixing valves. 
