152 KANSAS UNIVERSITY QUARTERLY. 
steam main, which will cause the condensation of water and moist 
vapors to back up into the buildings before the regulating valve 
opens. This is usually corrected by the use of pumps or traps 
which hold the condensation under control, and it was proposed to 
put in an expensive plant of this kind until the present plan was 
suggested. 
Second—a check valve, Fig. 3, is placed in the 6-inch return 
main at C (Fig. 1) in such a way as to prevent a back pressure of 
10 pounds from passing up into the return pipes which havea 
Fig, '3: 
pressure of 5 pounds. Then when the water and moist steam 
gather on the low pressure side of the check valve, they separate 
and the water rises until the column thus formed increases the 
pressure enough to open the check valve C, the water running 
through until the valve is closed again by the pressure on the 
other side. This valve is entirely self-acting, and the amount of 
water that is allowed to pass out at one time is very small, for 
when the valve is open the area on both sides is equal and when 
the water runs through enough to make the pressures both equal 
the valve will close, but when closed the area of the top is greater 
than that of the bottom and the amount of water in addition which 
is required to equalize the pressure is all that passes through at 
one time. This makes the operation frequent and keeps the water 
in the boilers at about the same level. At night when the steam 
goes down there is no pressure to hold up the water, so the pipes 
empty themselves, and freezing is prevented. The extra water 1s 
needed in the morning, so that in every respect the result is 
satisfactory. 
2, 
