LIV. NORMAN SELFE, 
at the same temperature throughout, as was shewn by the diagram 
when referring to compressed air machines. Some compressors 
have water jackets and others dispense with them. At present 
it is enough to remember that the piston of an ordinary compressor 
commences its stroke without offering any resistance to the engine 
apart from friction, because the gas is then of the same pressure 
on both sides of it; the resistance commences with the stroke 
however, and increases until the condenser pressure is reached, 
when the work of the piston continues uniform to the end of the 
stroke ; the greater the ratio of compression the smaller the por- 
tion of the stroke during which gas passes the delivery valve, and 
_ the greater the importance of reducing the waste space or clear- 
ance in the cylinder ends. 
ON THE WAY IN WHICH IDEAL CONDITIONS ARE MET IN TYPICAL 
EXAMPLES OF REFRIGERATING COMPRESSORS. 
1. That the cylinder should fill with gas at a pressure as little 
below that in the expansion coils as possible, The diagrams on 
the wall shew twelve different compressors, single and double 
acting, vertical and horizontal. The horizontal machines with 
horizontal valves must have strong springs to close them and 
the pressure required to move the valve is thus a loss. The 
vertical double acting compressors with horizontal valves have 
the same drawback with the further disadvantage of a greater 
waste space or clearance. In the author’s design, in “Hercules,” 
and “Auldjo,” all single acting and vertical, there is provision for 
absolute equilibrium above and below the piston, quite apart 
from the resistance to the inlet valves ; and in the Antarctic: 
Compound, this provision is found in the low pressure cylinder. 
It will be noticed in the author’s two designs, that the working 
barrels are plain cylindrical castings and the equilibrium ports ¥ 
can be drilled, whereas in other machines there are complicated 
castings with cored passages and cored ports. The Frick 
machine has such a large valve in its piston so beautifully balanced 
_ On springs that it will easily open for the admission of gas. _ . 
