Application profile: The motors, pumps, and valves that make water dance
To most people, water is for drinking, washing, and keeping their lawns green. To others, such as surfers, skiers, and snowboarders, it is a playground. But to a relatively small group of designers, water is the medium they sculpt and manipulate into fantastic fountains that are dynamic works of art.
Those seemingly simple fountains, however are built on a solid foundation of hydraulic engineering, state-of-the-art pumps, piping, compressors, and, in some cases, patented technologies on par with the most advanced aspects of rocket science.
From the simple . . .
Some fountains use a single type of hydraulic device, one that generates vertical plumes. Designers then rely on repetition, geometry, and creative lighting to bring it to life. Somerset House in London, for example, was recently transformed from government offices into an Arts Centre. As part of the project, architects from Donald Insall Assoc., turned a one-time parking lot into an interactive fountain, a 53x11 grid of water jets set in 45,000 Portuguese granite paving stones. Each of the 11 rows has a dedicated water pump that puts out up to 140 gpm (28 gpm/jet) enough to let each jet climb 16.5 ft into the air.
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Jets are set about 10 ft apart, far enough that on calm days, pedestrians can thread their way through and only get the bottom of their shoes wet. But on windy days, it can be a different and slightly soggy story.
Water is reclaimed and recirculated by a drainage canal surrounding the fountain. It sends water into a 9,500-gallon holding tank where it is filtered, treated with ozone and chlorine, and reused. Typically less than 1% of the water is lost to wind and evaporation on any given day.
Nozzles are set in 6-in.-sq steel plates flush with the pavers. Four fiber-optic lenses surround each jet, and a group of 22 projectors send light to the fountainhead lenses. (Each projector feeds 10 fiber-optic cables.) Two colored gel-wheel filters on each projector combine to illuminate the jets with a choice of 28 possible hues. Using fiber optics and remote-controlled jets means no electrical power is sent to the fountainheads.
During the summer, a programmed show coordinates lighting and the jets' heights, creating rows of waves, and geometric and random shapes that move with music. The fountain is shut down for the winter and protective caps placed over the jets to prevent damage.
. . . to the complex
Of course there are other hydraulic special effects in the fountain designers' toolbox besides the relatively simple vertical jet. Show Fountains in Spring, Tex. (www.showfountains.com), for example, tweaked the vertical jet a bit and turned it into a water lariat. "It's merely a nozzle installed off-axis and mounted on a rotating bearing cup," says Michael Connery, president and CEO of the company. "Rotation comes from water jets on the side of the cup or, if synchronization is critical, we use a motor drive. And mounting several nozzles on one rotating head creates a more elaborate rotating effect." If several lariats are used in a fountain, operators precisely control pump-head pressures to ensure they all spin at the same speed.
Water specialists at WET Design, L.A., designed and patented a variation on the water lariat: the Oarsman. It's a self-contained robotic nozzle that includes a variable-frequency drive, pump, and lights. "Operators or a preprogrammed computer feed it electricity and control data, and it responds by positioning the nozzle in the X-Y axis and adjusting its flow rate for just the right stream height," says Tony Freitas, manager of architecture and facility engineering at WET Design. (WET, by the way, stands for Water Entertainment Technology.) "An Oarsman takes water right out of the fountain and pumps it out at up to 120 gpm. There are no water pipes connected to an Oarsman."
Oarsmen were invented for WET's piece de resistance, the eight-acre fountain in front of the Bellagio Hotel and Casino in Las Vegas. They needed a good-sized jet that could gracefully wave back and forth, smoothly change height, spin, and do it all in time to music. The Bellagio fountain originally had 214 Oarsmen installed, but after some on-site testing and fine-tuning, the WET team removed about a dozen.
Before WET could use the Oarsman, however, it had to develop a ground fault circuit interrupter (GFCI) that could handle Oarman's unusual characteristics. "We were using 208-V, three-phase motors, which are not your typical motors, variable-frequency drives for the pump, and stepper motors for moving the nozzles. All this generates noise and harmonics on the line that conventional GFCI see as current leakage," points out Freitas. "But we didn't try to get a variance or get around the regulations, we just went ahead and designed a GFCI."
WET also has vertical jets called Shooters, and they're used at Bellagio, but they differ from those found in other designers' fountains. There's actually a whole line of Shooters that use the same principles, ranging from NanoShooters to Supershooters.
Shooters consist of a receiver for compressed air, a cylindrical holding tank, and some clever valving. In operation, a valve on the holding tank opens, fills with water from the fountain, and closes. A pipe sends compressed air from an equipment room "onshore" to the receiver where it is stored. When the Shooter is "fired," a valve opens, sending compressed air rushing into the holding tank where it becomes an expanding bubble forcing water out of the tank through a nozzle. "So Shooters can't create jets that last all day," explains Freitas. "They're for instantaneous shots. And the bigger the Shooter, the longer it takes to refill the holding tank, so the longer the lag between consecutive shots." Operators control jet height by adjusting the volume of pressurized air released into the holding tank.
NanoShooters, the smallest in the Shooter family, have holding tanks 2 in. in diameter by 18 in. tall and need only a couple pounds of air pressure, yet propel water 10 to 12 ft high. "They're good for interactive displays," says Freitas, "Especially in large numbers when we create a forest of thin, low-force water jets."
Shooting water like a laser
Axisymmetric laminar flow (ALF) devices generate streams of water with all the water particles having the same flow rate and direction, much like photons in a laser. They look like glass parabolas of water that seem to hang in the air. Observers really can't tell the arcs contain moving water until the flow is switched off. Then they can watch the well-defined tail of the curve chase the hoop of water back into the fountain. Some devices quickly turn on and off, creating 2 or 3 ft of curved water that follows a parabolic path back into the fountain.
Mark Fuller, founder of WET Deign, studied ALF and wrote his undergraduate civil-engineering thesis on the subject at Stanford University. He later went on to feature ALF in Leapfrog, a fountain he designed while working at Disney's Epcot Center.
"We use traditional pumps to pressurize the water, but then send it through a series of chambers, straighteners, and baffles to line up the flow and bring it all to the same speed. Then it leaves the nozzle," says Tony Freitas, a WET Design engineer. "Most streams are about a half-inch wide and travel 15 ft, reaching about 15 ft high. And we can do smaller. But it gets more difficult as you make them larger."
Surface tension helps keep them together in an ALF stream. But when a large stream hits the apex of its arch and accelerates downward, different parts of the stream begin traveling at different speeds. This warps and distorts the once coherent flow, breaking it up. "We've done studies with flows several inches wide and they look good, but not perfect," says Freitas. "It is just difficult to scale up. But we're still working on it."
Another Shooter in the arsenal, the MiniShooter, sends water up to 125 ft into the sky. Bellagio has 798 of them. SuperShooters, the top of the line, use holding tanks that stand 12-ft tall, 1 ft in diameter, and hold about 75 gallons. Their air is stored at 200 psi in 60-gallon receivers. When it is released into the tank, the pressure launches a plume 245 ft high through a 2.5-in. nozzle. Bellagio boasts 192 SuperShooters.
"Not all the water goes to 245 ft," points out Freitas. "When we tested the SuperShooters, all the water did go to the apex. But some of it was already coming down, passing through itself, as the last of the water was still going up. We discovered it looks better if pressure declines during the shot. So the top goes to 245 ft and the bottom only goes to 50 ft, making it look more like a standing column of water."
Another problem with SuperShooters involved the huge pressure drop across the air-control valve. It was forming ice in the valve body. "To cure that, we put a pressure plate a few feet upstream to control the pressure drop. The plate drops the pressure in half, then pressure drops again at the nozzle. Fortunately, it doesn't affect the display much."
Another possible solution, he adds, would be to add an air-drying subsystem to the fountain. "Bellagio has such a big air system, we decided not to. But if we were doing it again, we might include dryers."
Shooters and other devices that rely more on air pressure than water pumps save money, energy, and installation costs according to Freitas. "It would take a 300-hp pump to create one 245-ft-high jet, and there are almost 200 SuperShooters at Bellagio. You would need 60,000-hp worth of pumps and the whole system would have to be sized as if it always worked at maximum load. Compressed air, on the other hand, can be stored, letting you size the system for the average load. We run the compressors continuously and bank air for peak moments. So our compressors, standard rotary screw models, occupy one-tenth the space pumps would. And the pipes sending compressed air out to the various Shooters can be much smaller than the pipes that would be needed to carry incompressible water for equivalent jets."
A more conventional special effect is WET Design's Popjets. Using traditional plumbing and pumps, it creates little marbles of water that can rise about 5 ft, still retaining their spherical shapes. A special nozzle and valve quickly release about a tablespoon of water that forms the liquid spheres. "They're great for close-up displays and interactive fountains since they're friendly even to small children."
For more subtle effects and relaxing fountains, WET often deploys WaterSkins and WaterIrises. Waterskin is a thin membrane of water on polished black granite or stone. The water is about an eighth of an inch deep and thins somewhat as it goes over an edge. "It creates a highly reflective surface, but it requires good flow delivery that doesn't disturb the surface, very flat surfaces, and sharp edges. After that, physics does the rest. And while we didn't invent this, it is on our palette, and like all our efforts, we try to take it to a level as near to perfect as we can get."
A WaterIris, in WET terms, is a circular hydraulic jump, and a hydraulic jump is water transitioning from supercritical to subcritical. "More simply, water comes out of a nozzle very fast into a basin," explains Freitas. "When it slows to a certain point, the water suddenly gets thicker. It's like watching a wave washing in and out from the center of the basin. Slowly varying the flow rate makes the transition point change and generates a very soothing sound."
Fog on demand
Another element used in fountains to set the mood is fog created either by atomizing water or adjusting temperature and humidity. To use the first method, WET Design sends water at 2,000 psi and 0.05 gpm through a 0.006-in. nozzle. The water hits a steel pin positioned precisely over the hole's center and bursts into tiny water particles making mist or fog. "In small close-up displays, we might use 30 nozzles," notes Freitas. "Bellagio has 5,000."
The second method usually involves injecting cool nitrogen into a chamber filled with warm, supersaturated air. The water condenses into airborne water droplets, or fog. The nitrogen expands, pushing the fog out into the display. "It's a drier, finer mist than the brute force method," says Freitas. "It also doesn't make floors slippery or leave a residue. This makes it well suited for indoor use. But it does have a consumable, the nitrogen."
How long the fog lasts and what it does is up to Mother Nature. "Once we create it, it's out of our hands," says Freitas. "When we tested Bellagio's fog system, for example, it created a great bank of fog that started moving toward the road. Before we knew it, fog had engulfed the Strip. Drivers were slamming on the brakes, tires were squealing, and we expected to see a hundred-car pile up. Luckily, there were no collisions and no one got hurt." That's one reason human operators at the Bellagio fountain can intervene in the computer programming that controls the foggers.
Engineers at Show Fountains use fog for something more palpable than setting a mood. They create giant 'water screens" and project movies on them. At first, they relied on the brute-force method, sending 300-psi water into an angled steel plate. The water would smack into the plate and send a sheet of water droplets straight up. "Later developments refined this plate-deflection method and we now use pumps with far less power to create screens 50 ft high and 100 ft wide," says Show Fountain's Connery. "And for some reason, small screens are more fussy about nozzle openings, angles of deflection, and pump pressure than larger screens, Extra time is always needed to fine-tune the smaller nozzles that create screens 15 to 20 ft tall."
Water screens are most effective when images are projected from the rear and in large formats, such as 70-mm film. "Filmmakers record video specifically for water-screen shows, taking full advantage of the magical appearance of images seemingly bursting out of the surrounding water," says Connery.
Mixing fire and water
To add pizzazz to fountains, some designers offer clients devices that showcase fire. A relatively simple one, the Fire Tornado from WET, consists of a tube into which air is sent and made to swirl using a blower. "Add gas and an igniter, and you have a fiery tornado whirling in a tube. You can even touch the tube without getting burned," says Freitas.
A more ambitious and unusual device, WetFire, combines fire and water. It has its genesis in a project WET did for a casino outside San Diego. At night, the fountain was to serve as a stage for a drama involving human actors. At one point a campfire was supposed to emerge from a pool of water. "At first, we envisioned a small jet of natural gas or propane bubbling up through the water. It's been used before, including at the volcano in front of the Mirage Casino," says Freitas. "But we found gas burns 'inside' aerated jets of water. You don't just get fire sitting above water. Instead, you get this mysterious combination of fire and water coexisting."
One challenge with fire devices, and it is common to all fountain technology, is that engineers have to find a way to hide the equipment. When they can, WET uses pyroigniters that can be replaced before every performance. Otherwise, they do their best to hide electrical igniters.
"We design highly technical systems that should appear to not use any technology at all," says Freitas. "We want them to see flowing water and beautiful finishes like stainless steel and polished granite, not pipes and igniters, no valves clicking, no computers flashing."