32 BULLETIN 894, U. S. DEPARTMENT OE AGRICULTURE. 
humidity is required. It is usually too warm, however, for recir- 
culation for low temperature and for low humidities, and must be 
cooled with cold water or its equivalent. High temperature together 
with high humidity requires an auxiliary hot water supply, which 
is hereinafter described, or else the use of the steam jets in conjunc- 
tion with the sprays during the early stages of the run as described 
on page 30. 
WATER MIXERS. 
Each kiln is supplied with an automatic hot and cold water 
mixing valve, which mixes enough cold water with the recirculating 
water to deliver it to the sprays at the desired temperature. 
During the first part of low-temperature runs the recirculating 
water may not be hot enough to hold the required humidity, and 
in this case it must be heated either by cracking the steam jet valve 
slightly so that the steam will raise the water to the desired tem- 
perature or by mixing in hot water. 
SPRAY HEADS. 
The spray heads consist of small brass nozzles connected by means 
of half bends of ^-inch wrought-iron or brass pipe fitted into reducing 
tees on the supply pipe. The adjustable "vermorel" type of nozzle, 
such as is used in horticultural work, which will deliver 3.5 pounds 
of water per minute at 50 pounds pressure, has been found satis- 
factory. The nozzles have brass disks with .063-inch holes, which 
deliver a coarse spray, not a mist. They should be spaced from 18 
to 20 inches apart in side spray-chambers, and from 12 to 14 inches 
in center spray chambers. The sprays must be lined up centrally 
with respect to the spray chamber, and must point directly downward. 
QUANTITY OF WATER SUPPLY. 
The amount of water delivered per unit of time and unit of kiln 
space is determined by the formula: 
3.5 pounds per spray head multiplied by the number of heads per kiln= 
pounds of water delivered per minute. 
„. Pounds of water ,. 
or. =gallons per minute. 
VELOCITY OF WATER IN PIPES. 
The velocity of water in mains should not exceed 300 feet per 
minute, on account of the loss in pressure due to friction. In the 
smaller supply pipes the velocity should not exceed 180 feet per 
minute. The loss due to friction should not exceed 2 J pounds per 
100 linear feet of pipe. The proper velocity for a given amount of 
water can be determined from the chart on friction pressure losses. 
Find the number of gallons recirculated per minute on the left side 
of the chart and continue across this line until it intersects the line 
