Pressure 
motor exhaust pressure, which is the 
ocean bottom pressure in open system, 
or the line pressure loss in the closed 
system 
area of lost work for 
high exhaust pressure 
less work lost at 
shallow exhaust pressure 
Volume 
Figure 25. Pressure-volume diagram for pneumatic systems. 
Only one of the mechanical transmission systems, the linear-motion 
system, was found to be compact and efficient. This cable system required 
a 1-inch-diameter galvanized bridge rope and produced efficiencies as high 
as 98%. This system is extremely simple and is free from some sources of 
failure that affect electrical and hydraulic systems—shorting or leaking 
along the transmission line. 
Either the three-phase AC system or the linear-motion cable system 
can be developed with commercially available materials. However, the 
mechanical scheme is the more reliable and simpler of the two. 
Summary 
In shallow areas to about 2,500 feet, the one- and two-hose filtered 
seawater systems can operate at good efficiencies with the hose unsupported. 
At greater depths, the one-hose system is more efficient than the two-hose 
system, but the hose will have to be supported by a tension cable or a series 
of buoys. 
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