But first, dozens of holes for explosives must be painstakingly drilled into the rock. One of the biggest drill rigs at work around the world is the 200-ton PV-351 Pit Viper from Atlas Copco, Garland, Tex. Sophisticated hydraulics and an innovative power-splitting system also make it one of the most productive, according to company engineers.
The rig's 1,500-hp diesel engine or 1,400-hp electric motor drive a custom-built gearbox that runs five pumps from Parker Hannifin's Hydraulic Pump Div., Marysville, Ohio. The pumps, in turn, power virtually the entire machine.
According to Ron Sarbach, a Parker technical support manager, the power-splitting setup saves a lot of space. Power-train components do not have to mount on the vehicle's centerline and, thus, can be positioned where they make the most sense. And hydraulics can deliver power efficiently anywhere on the vehicle with a length of hose or tubing, which removes practically all restrictions on placing key components. This let Atlas Copco's engineers optimize every major vehicle operation, says Sarbach.
For example, a pair of Parker Denison P14 variable-displacement, axial-piston pumps a design noted for durability and long service life powers the drill. The units feature 14 in. 3 /rev displacement and a 5,000-psi maximum continuous pressure rating, although they typically operate at 4,500 psi.
"Using a pair of pumps instead of one large unit is more efficient because it eliminates a lot of valving," Sarbach notes. Drilling usually requires two hydraulic circuits one rotates the drill while another feeds it into the hole. They have significantly different flow requirements, so each pump matches a different demand, he explains. A single large pump would require valves to proportion flow into two circuits. "Valves inevitably create operational losses, and when you're dealing with functions consuming 300 to 400 hp, even a 10% loss becomes significant," says Sarbach.
A pair of gearbox-mounted, Parker Denison M14H piston motors turns the drill. Again, two motors instead of one generate major savings. A single motor would require a larger gearbox, gears, and bearings to handle the torque, explains Arnold Law, chief engineer of Atlas Copco's Garland facility. Combining the output from two motors results in a more-compact setup that improves downhole access.
The same P14 pumps also supply bent-axis motors that move the machine from hole to hole. "It's easy to redirect power with hydraulics, which is a big advantage on a rig this size. We don't need a separate transmission and gearbox for the crawler drives, which cuts down on cost, weight, and complexity," Law adds.
The second hydraulic system drives the rig's cooling fans. "Most people don't realize it, but a traditional fan is a power hog, easily consuming up to 10% of an engine's output," says Sarbach. A hydraulic drive lets the fans run independent of engine speed, improving efficiency and saving fuel. "Hydraulic cooling also lets designers position radiators anywhere on the vehicle they don't have to be near the engine," he adds. "That opens up a lot of possibilities, and usually results in a unit that's much easier to service and safer for the crew." The fan drive uses Parker Denison's P7 variable-displacement, axial-piston pump to supply a pair of M7F piston motors. Both pump and motor feature 5,000-psi ratings and 7.25-in. 3 /rev displacements.
The third hydraulic system, powered by a pair of 3,000-psirated Parker Denison T6CC vane pumps, supplies flow to auxiliary systems such as jacks, tower-raising cylinders, and hoist motors. Again, dual pumps reduce valving losses compared with a single large unit.
Parker Hydraulic Pump Div., (800) 551-556, parker.com