34 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 
vacuum. After all ammonia has been exhausted from the system, 
close the valve in the ammonia discharge pipe and the condenser may 
then be disassembled. 
To pump the air out of condenser. — The main suction and discharge 
valves should remain closed. The by-pass valve on the discharge 
side must be open and the one on the suction side closed. Manufac- 
turers provide some means of opening the by-pass piping, either by a 
pipe tee or some form of cock; this should be opened and the machine 
run until all air is exhausted from the condenser. After all air has 
been exhausted the opening in the discharge by-pass must be closed 
and all valves set as they were originally. Ammonia may now be 
allowed to reenter the condenser, and after turning on the cooling 
water the plant is again ready for operation. 
To pump ammonia out of cold-storage room or cooler coils. — All 
expansion valves must be closed, also the suction stop valves, except 
the suction stop valve on the coil which it is desired to pump out. 
Tins valve must be left open and the machine run until a 10 or 15 
inch vacuum is obtained, when the machine should be stopped for 
two hours in order to allow any remaining liquid in the coils to evapo- 
rate. After the evaporation of the remaining liquid, start the machine 
again and pump down to a 25-inch vacuum. If all liquid has evapo- 
rated and the ammonia valves are tight, the coils should maintain 
the 25-inch vacuum until broken. The suction and discharge valves 
on the machine may now be closed and the part of the system which 
has been pumped out may be opened with safety. 
To pump air out of storage rooms or cooling coils. — See that the main 
discharge stop valve is closed and remove the plug from tee or open 
cock, as the case may" be, in the by-pass just below the discharge 
stop valve. The machine should be started slowly and run until all 
the air is exhausted from the coils, then stop machine and replace 
plug in tee or close cock in the by-pass. 
To pump out compressor. — The same method as above is followed, 
except that the suction stop valve only is closed, as no part of the 
system except the compressor is to be pumped out. 
CARE OF REFRIGERATING MACHINERY. 
In caring for machinery of any kind, one of the most important 
things is cleanliness, and especially is this true of refrigerating appa- 
ratus. If the cooling and condensing surfaces are allowed to become 
coated even slightly their heat-transferring efficiency will be lowered 
materially. 
Where atmospheric condensers are used it is an easy matter when 
the surfaces become coated to clean them with a brush, provided 
the coating is not of the nature of a scale. If the substance is hard, 
it will be necessary to employ files or steel scrapers in removing the 
