SE Fe me oe 
KILN DRYING HANDBOOK 89 
in the first place and remain so, the arms must be of equal length. 
If the arms are not of equal length, the balance can still be used, 
by always placing the weights on the same pan. The individual 
loose weights may be checked against one another by placing the 
same nominal weight on each pan. 
One common type ot equal-arm balance intended for use with 
loose weights has a scale beam and rider for the final balancing. 
When checking this type of balance for equality of beam length 
by interchanging the weights between the pans, the rider must be 
set at zero. For checking the rider itself, one of the small loose 
weights may be placed upon the left-hand pan, which is the one 
intended for the material to be weighed, and weighed by the rider. 
ADJUSTMENT AT NO LOAD 
Practically all scales and balances have a means for securing accu- 
rate balance at no load, in the beam type usually either loose shot in 
a chamber in the base of the counterpoise or a moveable threaded 
counterweight carried on a reverse extension of the beam. Making 
the adjustment to obtain such balance is the first step in checking. 
PRESSURE GAUGES 
Steam and air pressure gauges, if used simply to give a general 
idea of the amount of pressure available or to check the operation 
of a reducing valve, need not be very accurate. The operator, how- 
ever, should know how to calibrate them so that he may do so when 
necessary. ‘Two general methods of calibration are in common use; 
in one the gauge is compared directly with a standard test gauge 
and in the other the pressure to which the gauge is subjected is 
determined by means of standard weights on a piston of known 
diameter. In both cases the test pressure is produced by means of a 
small, oil-filled hand pump that is provided with connections for 
the gauges and the gauge tester. Testing equipment for light field 
work is carried by all boiler inspectors. If none is available, com- 
parisons can often be made with other gauges, such as those on the 
boilers, and a fair idea of the accuracy of the kiln gauges obtained in 
this manner. 
The gauge under test is subjected to pressures within its range, 
and its errors of indication are noted. Ordinary adjustment of 
minor errors can often be made by pulling the gauge hand from its 
spindle and putting it back again in the proper position. If the fault 
is of a nature such that resetting the hand fails to correct it, the 
gauge should be returned to the manufacturer for repair. 
LOCATION OF INSTRUMENT BULBS 
The drying schedules in this bulletin are based on the assumption 
that the temperature and the humidity in the kiln are both meas- 
ured and controlled at one of the points where the air enters the lum- 
ber pile. The drying conditions at such points are the most severe, 
since the air constantly becomes cooler and more moist as it travels 
through the lumber. | 
Only a thorough examination by means of the smoke test and of 
thermometers hung in different parts of the kiln will determine 
