August 2004

f you’ve built a pool, you can jump right into doing a waterfeature, right? Yes and no. The hydraulic systems are similar, but not identical.

“Builders know 90- to 95 percent of what they need to” regarding waterfeature hydraulics, says George Ayer, vice president of engineering at Crystal Fountains in Concord, Ontario, Canada. “The problem is that last 5 percent can be pretty expensive to learn the hard way.”

Minor mistakes can turn into major disappointments. Imagine the homeowners firing up their aquascape for the first time only to see the rock waterfall trickle rather than flow, or the laminar arcs spurting unevenly with a cavitating pump providing an unpleasant soundtrack.

“The waterfeature is the focal point of the pool,” says Steve Gutai, product manager of pumps, filters, valves and waterfeatures at Jandy in Petaluma, Calif. “Many consumers are keyed into the way it performs.”

Once you get the plumbing in the ground, it’s difficult to redo. To keep your system — and the client — happily humming along, you must prevent problems before they happen. Check out the following scenarios,which outline the most commonly made mistakes in waterfeature hydraulics.

Mistake 1: Inadequate back pressure
Why it happens: Because of their simple hydraulic layouts, free-standing waterfeatures don’t have the built-in back pressure that pool systems do. Pipe runs are fairly short and straight, and there are no heaters, chemical feeders or, too often, filters to create resistance.

The problem: Pumps — particularly the high-head models mostly used in the pool business — need a certain amount of back pressure.

Without it, says Gutai, “The water is traveling faster on the discharge side than is going to the suction side. This creates a state of cavitation. Usually, the pump is loud and you hear sounds like rocks jingling in the back of the motor.” Even if you dodge that bullet, the pump will draw more power than it should, thus shortening the life of the motor.

Best practices: Ideally, there should be enough back pressure so that the pump operates in its 70- to 80 percent efficiency range.

One solution to inadequate back pressure is to use a medium-head pump or a model made specifically for waterfeatures. But be careful when choosing this method. Though medium-head pumps won’t crave as much back pressure as the high-head models, you have to watch how far the pump is placed from the waterfeature.

“If a medium- or low-head pump is located close to the feature, it’s fine,” says Sue Robach, the Redding, Calif.-based national training manager for Sta-Rite Industries. “But if it’s 50- to 70 feet away, it no longer can overcome the amount of resistance put into the system [by] the additional distance away from the feature.”

If you use a high-head pump, you can create the needed back pressure by building resistance into the system. This will create the needed back pressure. One option is to regulate flow by installing a valve, or you can downsize the plumbing as it approaches the nozzle to restrict the water’s movement, says John Ott, Hayward Pool Products’ Western technical service manager, based in Pomona, Calif.

Another way to avoid the problem is to add a bypass line that diverts water to a couple of pool returns, says Ayers of Crystal Fountains. Install valves so you can throttle the flow down. This gives you more flexibility to tailor the flow and head to the needs of the waterfeature, and keep the pump on its curve.

Mistake 2: Building a free-standing waterfeature without a filter and chemical feeder
Why it happens: In theory, a free-standing waterfeature shouldn’t have a bather load, so many builders don’t install filters or sanitation.

The problem: In reality, people will interact with ornamental water fountains in the most surprising ways.

“I’ve seen people at Disneyland change their babies’ diapers and then wash their hands in the water fountain,” adding unexpected bacteria and organics into the water, says Alison Osinski, Ph.D., president of Aquatic Consulting Services in San Diego.

In addition, any vessel can accumulate debris. Solids such as sand and pieces of leaves may clog the nozzle.

Best practices: Install a filter and chemical feeder, especially if the waterfeature has floor drains, which can suck dirt and debris through the system. Filters can add the much-needed back pressure often missing in separate waterfeatures. Some manufacturers offer prefabricated pump and filter systems for waterfeatures.

Mistake 3: Big pump, small pipes
Why it happens: Many builders want to satisfy customers who mistakenly believe more horsepower in a pump is always better than less. In addition, smaller plumbing cuts upfront costs.

The problem: Manufacturers cite oversized pumps and undersized plumbing as a persistent problem in hydraulics. The pump pushes too much water through too small an opening, causing the line velocity to increase dramatically. The water creates friction against the plumbing as it speeds along. It thrashes around corners and squeezes through reducers, which causes turbulence.

In the worst case, the system can’t feed enough water to the pump, which causes it to cavitate. At the least, it will make unnecessary noise. The larger-than-needed pump also wastes energy.

Because the water is in a state of constant flux, you may not end up with the visual effect you want unless the water is “tamed.” Vertical fountains can shoot too far and have a stringy or ragged appearance, says Jon Mitovich, president of Roman Fountains in Albuquerque, N.M. You may see weakened flow, and sheet falls can break up.

When this happens, some builders try to increase flow by using an even larger pump. This just makes things worse.

Best practices: Don’t start by sizing the pump. Instead, figure out your needed flow and pressure first. Next, use a friction/flow chart to determine which pipe size will move the right gallons per minute at an acceptable velocity. ANSI/NSPI standards recommend a maximum of 10 feet per second on discharge-side lines for residential pools with schedule 40 PVC plumbing. However, some fountain manufacturers may recommend lower speeds. Finally, size the pump to match flow, velocity and pressure demands.

Follow manufacturer instructions regarding flow and velocity. Some fountains, such as laminar streams, rely on precise hydraulics. “Laminar is a term that is the opposite of turbulent,” Mitovich says. “You just can’t have any disruption in the stream, whether it’s air entrainment or turbulent flow.”

Mistake 4: Multiple sprays installed without loop plumbing or a manifold
Why it happens: It’s easier to plumb a succession of sprays off a single straight line. Many builders simply run the main line and fit the nozzles to it.

The problem: Without loop plumbing or a manifold, you may not have adequate or consistent pressure going to each nozzle. This can be especially deadly if you have a long, narrow pool with a row of fountains designed to look identical. Without equal distribution to each nozzle, the last fountain or two will be shorter or weaker than the rest.

Best practices: A loop or manifold will deliver water equally. With a manifold, the trunk line splits off symmetrically into smaller ones. The lines are gradually downsized until they feed each nozzle the same amount of water. A loop, the ideal configuration, is formed when the manifold ends are tied together, so the water moves without interruption, resulting in the most consistent flow and pressure.

Keep manifold pipe velocities below 4 feet per second for best distribution, Ayer says. Many manufacturers offer classes and tips on how to loop or manifold the plumbing.

If space won’t allow such a layout, you can valve each spray and make individual adjustments, Mitovich says. He recommends placing the valves outside the pool, below grade, in a valve box that is flush to the ground.

This assures adequate distance from the nozzles and allows easy access. It also means you can just lift the lid of the box and make adjustments without having to climb into the pool.

Mistake 5: Not sizing the pump based on required flow
Why it happens: It can be a challenge to estimate how many gallons per minute are needed for spillover in nonmanufactured waterfeatures.

The problem: The gallons per minute determine how the waterfeature will look and what size equipment you’ll need. Without a flow estimate, you won’t be able to size your equipment — and manufacturers’ technical support won’t be able to help you.

Best practices: With fountains and sheet falls, make sure you read the manufacturer’s instructions.

If you’re creating your own rock waterfall or other multilevel waterfeature, estimate how many gallons per minute per foot you need to move the flow.

If you want to just wet a smooth and monolithic wall, 2 gallons per minute per foot will usually work, experts say. If you’re working with a massive feature and want the water to roar over a rough, irregular surface, such as large boulders, you may need as much as 30 gallons per minute per foot.

Manufacturers also provide engineering tables that indicate how much water flow you’ll need, depending on the weir’s length, size and degree of sharpness.

Take the gallons per minute per foot and multiply it by the weir length to find the total gallons per minute. Then you can size the equipment accordingly.

Mistake 6: Fittings placed too close to the fountain nozzle
Why it happens: Bends and valves are a part of every plumbing scheme. To change the water’s direction or pressure, a builder might install elbow fittings, bushings or valves too close to the nozzle.

The problem: Valves, fittings and other plumbing changes cause turbulence. However, the water should enter the nozzle as smoothly as possible. After going through turns and valves, the water then needs time to calm down. Otherwise, vertical fountains can fall short and laminar streams could lose their tight, glass-tube appearance.

Best practices: Figure out the ideal distance between the nozzle and any interruptions. To do this, take the diameter of the pipe connection to the nozzle and multiply it by 10, says Roman Fountain’s Mitovich. If a 1-inch pipe feeds directly into the nozzle, you’ll need at least 10 inches of straight plumbing into the nozzle. If site conditions won’t allow that much space, install a flow straightener.

Mistake 7: Turbulent source pools
Why it happens: Often when installing rock waterfalls, builders will simply stub up a piece of pipe in the upper pool. The pool fills up and then spills over subsequent drops.

The problem: No major faux pas here, but it doesn’t look as good as it could. The water spurts straight up and stirs the surface, especially if the bowl is too shallow. “The water could start sloshing around up there,” Mitovich says. It looks better and more natural if the pool can slowly and gently well up before spilling over.

Best practices: Make the source pool at least 8- to 12 inches deep. This way, all the action happens at the bottom of the vessel, while the water’s surface stays calm.

Feed the water toward the floor of the source pool rather than having it shoot straight up or sideways. This will help it remain calm. Damping or diverter devices exist to help you do this, but you can just as easily use fittings: Tee off the feed pipe and place an elbow fitting pointing downward on either side. Now the flow will split in two and drop toward the bottom.

You can also manifold the plumbing anytime the source pool is large enough to require multiple feeds.

Mistake 8: Using inappropriate valves on manufactured waterfeatures
Why it happens: It may seem easier to use something you know instead of an unfamiliar part supplied by the fountain manufacturer.

The problem: Manufacturers ship their products with the most appropriate parts. Laminar fountains, for instance, come with globe valves because they work best at smoothing out the stream. With the wrong valve, the fountain might look weak or out of control.

Best practices: Use manufacturer-provided parts. Call for advice if you don’t know how to install them correctly.