When the minds at Cirque du Soleil and McLaren Engineering Group, West Nyack, N. Y., asked Atlantic Industrial Technologies (AIT) to create something that had never been seen in the entertainment or theatrical world, the challenge was set. Cirque wanted to take industrial applications and modify them to suit the needs of their newest, and most ambitious, production. Stretching the boundaries of human physical capabilities is nothing new to Cirque du Soleil, but pushing the laws of physics is altogether different. After many hours of weighing theatric effect with feasibility, the final design emerged.

It was the task of AIT, Shirley, N. Y., to design a hydraulic system that would lift a structure weighing more than a Boeing 757 at a speed of 2 ft/sec. It would have to decelerate in 1.5 sec, position to 0.10-in. repeatability, and withstand the changing center of gravity caused by the stage tilting and rotating. The first priority in all aspects of the project was the safety of the artists.

The MGM Grand Hotel & Casino in Las Vegas is the home of Cirque du Soleil's new epic, KÂ, a saga of separated twins who embark on a perilous journey to fulfill their linked destinies. Danger lies in wait for them at every turn. Archers and spearmen hunt the twins relentlessly, as their quest takes them through a succession of challenging landscapes, from a mysterious seashore to mountains and forests.

The stage, called the Sand Cliff Deck, accompanies the twins all throughout the 90-minute tale. It begins as an ancient ship emerging from the depths of the theatre, transforms into a vertical battleground, and then an ice glacier as projected images bring the stage to life. The Sand Cliff Deck is the largest of several moving performance spaces in the show. It weighs approximately 80,000 lb; combined, the support structure and Sand Cliff Deck weigh 350,000 lb.

Lifting the stage

The 50 by 25 ft rectangular stage is mounted to a gantry that is lifted by four hydraulic cylinders along two columns that are 60 ft apart. The 12-in. bore, 70-ft stroke cylinders were manufactured by Parker Hannifin's Custom Cylinder Div., Eugene, Oreg. The original design called for longer stroke cylinders, but an industrial furnace large enough to harden the rods doesn't exist. Even at 70 ft, the 5-in. diameter rods had to be inserted diagonally to fit into the furnaces. Another challenge was transportation of the cylinders. There are very few tractor-trailer rigs that can transport a 75-ft cylinder. Special trusses were designed for cylinder protection during voyage from Eugene to Las Vegas. These cylinders, when totally extended, are almost as high as the Statue of Liberty and are the largest ever manufactured by Parker Hannifin.

The four vertically mounted cylinders require flow of almost 2200 gpm for the 2-ft/sec lift. This is accomplished by 10 Parker PE series piston pumps sized at 145 cc/rev and driven by five 250-hp motors. Each of the five pump sets produces 130 gpm. Significant dwell time occurs between stage moves, which allows charging accumulators with pressurized fluid. The balance of the flow required is supplied by a farm of 34 50-gal Parker accumulators and 17 350-gal pressurized nitrogen tanks (bottles).

The cylinders are mounted rod down above the stage gantry, and perform the lifting function while retracting. If the cylinders were mounted rod up, they would have to push the stage up. This would cause buckling of the 5-in. diameter, 70-ft. long rods. By mounting cylinders rod down, the rod is always in tension, eliminating the likelihood of buckling. Servo control manifolds are mounted to the rod ports of the cylinders. Each of the four cylinders is controlled independently by its own servovalve manifold. This valve concept utilizes a 3-way, 80mm proportional valves from Atos, York, Pa., and a Parker D3FH series zero-lap servo solenoid valve. The two valves work together to provide both the high flow and fine resolution required.

Oil is fed to the rod side of the cylinder only, the stage is lowered by metering out the oil in a closed-loop circuit from all four cylinders. The reason for not pressurizing the cap end of the cylinders is the fear of bending a cylinder rod, should an anomaly occur in the servo system. It could take only 500 psi on the cap end to bend and damage a 5-in. rod extended 70 ft, if the right conditions exist.

The hydraulic oil chosen for the project was Cosmolubric B220 — from Houghton International Inc., Valley Forge, Pa. — for its fire resistant properties. Between the reservoir (4000 gal) and the piping, provide by GS Hydro, Houston, more than 7000 gal of hydraulic fluid is contained in the theatre and annex building (which houses the hydraulic power unit).

The hydraulic system was designed to run at 3900 psi and produce 6000 hp during peak flow and pressure conditions for 40 sec. After testing, the operating pressures were lowered to 1700 psi.