For underwater operations in scuba or shallow water diving gear, 

 the push pump requires only mounting on a suitable base. However, the 

 application of this pump is limited because the maximum pressure that 

 the diver can develop is approximately 1000 psig. The pump is very 

 fatiguing to use because almost all of the developed thrust must be 

 generated by the diver's pumping arm. Most of the test divers were 

 observed to change arms quite often to reduce fatigue. 



The pull stroke pump has the advantage of developing a fourfold 

 larger pressure of 4000 psi with scuba or shallow water gear. The divers 

 are able to more effectively utilize their muscular strength. The pull 

 pump allows the diver to use his leg and back muscles for higher 

 hydraulic pressures or when his arms become fatigued. It is also possible 

 for shorter divers to operate the pump in the standing position in 

 contrast to the usual kneeling position as shown in Figure 7. Here 

 again, the back and leg muscles may be used effectively. The principal 

 disadvantage is that extensive handle modifications are required to 

 convert the pump to a pull stroke, and more weight or attachment force 

 is required to hold the pump base down against the deck (50 pounds vs 

 20 pounds for the push stroke pump) . 



The following features are recommended for future pull pumps : 



1. A pump handle that is readily adjustable in length. (It is 

 faster and results in less total expenditure of energy to use 

 a shorter handle for lighter loads or for use by divers of 

 exceptional strength.) 



2. Padded knee rests with concave upper surfaces designed to fit 

 the contour of the diver's knees. 



3. A metal base plate for the pull pump which permits stud gun or 

 bolting attachment . 



The pump used with the standard Navy deep sea dress (Figures 8 and 

 9) is more difficult to use than the other configurations. The diving 

 helmet and breast plate are heavy and result in much wasted energy when 

 the diver's work results in large body movements. Also, the diver's air 

 hose and valve are in the way when the handle is thrust right and left 

 in the standing position. Some commercially available hard hat gear 

 reduces these disadvantages. The hat and breast plate of this gear are 

 much lighter, and the valve has been moved up on the helmet where it is 

 accessible but not in the diver's way. Hard hat gear does have the 

 distinct advantage of providing the diver with much better buoyancy 

 control than light weight or scuba gear . This permits the diver to 

 safely wear much more weight which is often a distinct advantage in 

 using both manual and power driven tools . 



The diver operated hydraulic pumps all have a sealed hydraulic fluid 

 reservoir. As the hydraulic fluid is removed from the reservoir the 

 internal pressure drops below atmospheric pressure. This is an undesir- 

 able feature for underwater operation. It is preferable to compensate 

 the fluid reservoir to ambient pressure in order to reduce the salt water 

 leakage into the reservoir around the pump piston. The hydraulic pump 

 reservoirs were not pressure compensated for the NCEL tests in order 



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