Although lubrication of the parts of the motor in contact with the 
seawater hydraulic fluid may not be acceptable, lubrication of the power 
transmission (that is, swashplates, connecting rod, timing gears, etc.) should 
prove acceptable if required. Since these units are planned for use in the ocean 
environment at depths to 20,000 feet (9,000 psi), any lubrication system would 
have to be designed to prevent seawater contamination of the lubricant at these 
pressures. |t may be possible to prevent contamination by applying a small over- 
pressure to the lubricant from a spring-pressurized reservoir. This reservoir can 
probably be quite small for portable tools with short periods of use and submer- 
sion. For larger machines, the limitations on size and volume will be less, and 
the reservoir can probably be accommodated if the concept proves feasible. 
The pressures involved at depths up to 20,000 feet create severe sealing 
problems or require pressure compensation, not only for seawater hydraulic 
pumps and motors, but for all mechanisms having spaces from which seawater 
must be excluded. This underscores the desirability of designing a seawater 
pump or motor to require only seawater as a lubricant. 
Another potential problem at ocean depths could be the change of 
material characteristics with pressure. Possible effects would be change of 
hardness in elastomers or change of friction characteristics In plastics in a 
manner analogous to the increase in coefficient of friction or graphite sur- 
faces in a vacuum (Bowden and Tabor, 1950). 
Conclusions 
The development of a seawater hydraulic pump or motor requires 
a material compatible for use with seawater. Alumina ceramic is one material 
having demonstrated a potential for this application. In addition, a trade-off 
study is required of the simplicity and compactness of the vane- and gear-type 
units versus the higher volumetric efficiencies but more complex mechanisms 
of piston-type units. The specific application would also affect this trade-off, 
since volumetric efficiency is of more concern in pumps, while overall mechan- 
ical efficiency, compactness, and light weight are of more concern in the 
development of a motor unit (Henke, 1965). 
Summary 
A systems analysis and preliminary design of a Seafloor Excavator 
have been completed. (See Northrop, 1970, and discussion under ‘’Shallow 
Drilling and Excavating.’”) As part of that study and preliminary design, a 
reliability, weight, and cost comparison was made between an all-electric 
and an electro-hydraulic system for internal power distribution and control 
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