Where practical, the surface-supplied diving system (SSDS) should be used when working with powered tools (scuba should only be used as a last resort).
2.2.1 Pneumatic Powered Tools
Pneumatic tools can be effectively used underwater but are generally NOT attractive to use for several reasons:
1. The power required (gas volume and pressure) increases with increasing depth of the dive.
2. The exhaust bubbles often obscure vision of the work surface and the escaping gas causes pressure waves, which can nauseate the diver.
3. The exhausts are not sealed which allows seawater to enter the tool mechanism when the tool is not operating.
Because internal components (bearings, seals, and gaskets) are generally not compatible with seawater, pneumatic tools are considered expendable when used in seawater. As a minimum, the tool should be disassembled, cleaned, dried, and oiled immediately after use.
Most pneumatic tools require 90 psig (over bottom pressure) to operate effectively. One advantage of pneumatic tools is that they can be powered from a scuba bottle using a first stage breathing regulator adjusted to reduce tank pressure to 90 psig. A 10-SCFM tool would operate for 7 minutes at the surface and less than 3 minutes at a 60-foot depth using a 72-SCF scuba bottle. Another advantage of pneumatic tools is that they require only one hose and the hose is flexible and relatively small in diameter.
• NAVFAC MO-324, Inspection and Certification of Boilers and Unfired Pressure Vessels.
It is recommended that pneumatic hoses be provided with chafing gear where necessary. Also, tie off hoses to stationary objects to prevent whipping should they become severed.
Oil hydraulic tools are the most common of the powered tools used by commercial and Navy working divers. There is a wide variety of underwater oil hydraulic tools and the user should be sure to specify the underwater application when purchasing the tools. Underwater versions of land oil hydraulic tools usually have additional seals and substitute materials to exclude water from certain areas and minimize corrosion.
Oil hydraulic tools require two hoses: one to supply the fluid to the tool, the other to return the oil to the topside power source. The relatively stiff dual hoses make tool handling more difficult than with pneumatic tools. To provide easier handling at the work site the tools are equipped with smaller diameter, more flexible hoses usually referred to as tool whips (or jumper hoses).
CAUTION Systems that use compressed gas are inherently dangerous. If a hose breaks or is cut, the released energy can cause the loose end to violently whip back and forth. The result can be personnel injury.
All pressure hoses and vessels should be inspected and certified in accordance with:
• NAVSEA S6430-AE-TED-010, Piping Devices, Flexible Hose Assemblies (Volume 1).
• Planned maintenance as applied to specific equipment.
CAUTION Hoses should be in good condition and inspected in accordance with Planned Maintenance System (PMS) and NAVSEA S6430-AE-TED-010.
The connections between the tool whips and supply/return hoses are usually quick disconnect couplings. The couplings should have integral sleeve locking mechanisms to prevent accidental disconnect during transit or while in use.
CAUTION It is NOT good practice to tape the couplings closed to prevent accidental disconnect.
The ability to rapidly disconnect is an important safety feature for underwater tool use.
CAUTION A flow diverter should be installed in the hydraulic hoses approximately 10 feet from the tool.
A common misconception while using hydraulic tools is that increasing system relief or unloader valve pressure will increase tool power. When the tool is in use the supply line pressure is a function of the load on the tool and frictional losses from oil flow in the hoses. Poor performance may be related to hose restrictions, worn tools, improper flow rate, or improper viscosity of the hydraulic fluid.
Take care to be sure that the return hose diameter is large enough to prevent return flow restriction and subsequent retardation of tool operation. The return hose acts like an accumulator which can cause sluggish tool operation. This phenomenon is very noticeable when operating with oil hydraulic rock drills. The result is that tool performance may be severely degraded. Increasing system flow rate will not correct this problem - instead select a larger diameter return hose and check that oil viscosity is not too high.
Another characteristic noticed with long hoses is that energy is stored in the supply hose when the tool is not in operation. This is typical with a closed-centered oil hydraulic system (flow stops when the tool valve is off). As a result, when the tool is first operated it will run faster until the supply hose pressure matches tool demand. The tool may run at a high power level for a few seconds. This is normally not a problem but the operator should be aware that this condition exists.
WARNING Care must be taken when operating any hydraulic tool to be sure the power source flow rate and pressure relief valves have been adjusted to the recommended values for the tool. Hydraulic tools are very powerful and can self destruct if too much flow or pressure is provided.
For example, a tool designed to operate at 4 gpm with 1,500 psi will deliver approximately 3.5 horsepower regardless of the water depth (the tool is basically pressure compensated because the fluid is an incompressible liquid). If the flow is inadvertently set at 8 gpm, the tool will try to deliver up to 7 horsepower and the rotary or impact speed will be doubled. The high speed and extra available horsepower could cause tool damage, personnel injury, bit breakage, or damage to the work in progress.
Operators must ensure that the hydraulic oil used is compatible with the tool and power source. Tool manufacturers provide specific recommendations in the maintenance manuals.
An important factor is hydraulic oil viscosity (thickness). If the fluid viscosity is too low (thin) tool damage can occur, or if it is too high (thick) the tool may become sluggish or inoperable. Fluid viscosity is greatly affected by operating temperature, as shown in Figure 2-1. A fluid used at arctic temperatures will not be suitable for use in the tropics. Also, in cold climates the hydraulic oil may need to be warmed up before the power source is started. At arctic temperatures (-20 to -60°F), viscosity may be so high that internal pump components may break if the fluid is not prewarmed before system operation.
Hydraulic fluids must be kept clean and free of water or seawater. Sometimes it is necessary to change the hydraulic fluid be cause of operational temperature, contamination, or unavailability of the fluid in use to top up the power source reservoir. Mixing different hydraulic fluids is not recommended. The proper procedure is to drain the reservoir and tool umbilicals and refill with the same fluid. Check with the fluid manufacturer if mixing fluids is necessary.
Hydraulic fluid is considered hazardous material and must be handled properly.
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