Hydraulic tools are the most popular kind of tool with working divers because they provide consistent closed-cycle power. These tools are safer to use under water. They do not produce bubbles that obscure the diver's vision and require relatively little maintenance. The tools such as drills impact wrenches, chain saws, disc grinders and cable are modified version of hydraulic tools. They require a power source at the surface or a submersible electro-hydraulic power source that can be located at the work site near the diver. These power sources are compensated to operate at all depths. This requires built in batteries or an electrical umbilical from the surface to run the motor. The tools normally operate at pressures from 1000 psi to 3000 psi.