FOREST SERVICE WATER SPRAY DRY KILN. 43 
pressure steam main. The oil separator should drip through a 
grease trap, be valved, and discharge into the sewer. 
Provide a vent pipe for the exhaust main to discharge to the 
atmosphere through a back-pressure valve. 
AIR CHAMBERS. 
The discharge from the pump being intermittent, each successive 
impulse is equivalent to a blow affecting not only the pump but the 
whole system. An air cushion is obtained by installing an air cushion 
chamber, which gives a smooth-flowing and continuous delivery 
to the mains. The air chamber should be on the highest portion of 
the pump and directly over the highest part of the delivery opening. 
The air chamber usually furnished with the pump should be 
removed and an 8-inch wrought-iron pipe long enough to have 
double the capacity of the ordinary air chamber should be sub- 
stituted therefor. 
The supply of air in the air chamber gradually disappears while 
the pump is in motion and requires occasional draining unless some 
method is provided of keeping the air supply constant. One such 
method is to place a pet cock on the pump intake on the intake side 
of the check valve. This pet cock should be on a short nipple an/1 
open to the atmosphere. Cracking the pet cock will provide for 
drawing in enough air at each impulse of the pump to keep the air 
chamber charged. 
PUMP SIZES. 
The amount of recirculated water can be determined according 
to the method used in obtaining the size of mains (see " Water 
Supply"); then 
Gallons of water recirculated per kiln X number of kilns == maximum capacity of 
pump in gallons. 
The pump should be built to withstand a constant working pres- 
sure of not less than 100 pounds. It is advisable that all pumps of an 
installation be of the same size because this permits tke interchange 
of spare parts, facilitates repairs, and makes it possible to use any 
pump on any main in case of a breakdown of the pump regularly 
supplying that main. 
One pump in excess of the actual number required should be 
installed whenever possible as it may prevent shutting down the 
kilns while pumps are being repaired. 
All pumps should be cross connected to all mains through properly 
valved branches. 
The pumps should be capable of supplying the total amount of 
water recirculated per minute at a piston speed of between 30 and 40 
feet per minute. 
