Redesigning the pool filter to provide better flow

Scott Webb Headshot

A major reason that cartridge filters have been increasing in popularity in recent years is that they are not backwashed - you just hose them off - and therefore they don't require a backwash valve.

That valve has been a huge energy hog in the system for many years, primarily because it forces the water into extreme turns and changes in direction.

That situation is changing, however. Zodiac has designed a backwash valve that only loses one pound of pressure across the unit (1 psi at 95 gpm), part of its Versa Plumb system, and Pentair is coming out with a version that it promises will cut losses dramatically, as well.

It's all part of a new emphasis on reducing head throughout the pool's entire circulatory arrangement.

Having replaced gluttonous single-speed, high-horsepower pool pumps with modern variable-speed designs, engineers have turned their attention downstream. Reducing flow restriction with larger-diameter pipes and less-convoluted components is the next goal (along with helping builders to understand how to use this new stuff), and this effort includes moving water across the filter without undue head loss.

Just in time, too, for in this new age of expensive energy, high consumption rates have been a drag on growth in the pool industry.

Better Valves, Better Flow

Scott Clay, senior program manager at Pacific Gas & Electric in San Francisco, has been watching the evolution of energy conservation in the pool industry for five years - ever since he began running energy efficiency pool programs for the utility.

After helping to improve the efficiency of pumps, PG&E is promoting more ways to save energy, and making filters operate more efficiently is next on their agenda.

In general, Clay has favored the use of cartridge filters to save energy and for environmental reasons. "Cartridges can work with a very small pressure differential across the filter, one or two pounds, and still provide significant filtration," he says.

For years, that impressively low head loss stood in comparison to 10 pounds or more in the case of sand and DE filters, primarily due to the losses in the backwash valves needed to clean them.

However, improvements in the design of that valve have cut that loss dramatically, according to Steve Gutai, director of product management for hydraulic products, Zodiac Pool Systems, Vista, Calif. "What we developed as part of the Versa Plumb system," he says, "is a backwash valve that has a pressure drop of about one psi.

"The flow goes straight across the valve, so when the water flows from the pump, it goes directly into the filter - there's no multi-chamber flowpath or 90-degree elbow to increase resistance, it just goes in one side and out the other."

Partly due to the hydraulic efficiency and subsequent energy savings of this advance, Gutai says that sand and DE aren't going away anytime soon. "We believe that, even though there currently is a slow-rising trend away from DE and sand filters, they will still be in the market for many years to come."

The energy-efficient valve is part of the overall plan at Zodiac for pool circulation systems - to reduce the operating cost for the consumer by reducing the overall head loss through the components of the system (such as the filter, heater, etc.). This, in turn, allows the consumer to reduce the size and operating cost of the pump. That's the payoff.

Once you reduce head loss in the system," Gutai says, "you can either use a smaller single-speed pump, or a lower horsepower two-speed pump. Or, you can actually use a smaller variable-speed pump instead of the large three-horsepower ones that are conventional to the market."

Break It To Me Gently

Reducing head in the valve is actually a fairly simple matter: Don't make the water change directions. Or if you do, let it turn gently, in a sweeping motion, instead of a sharp 90-degree turn.

That's the direction manufacturers are taking. It's a sharp 90-degree turn, if you will, from building practices of the past.

"When you come out of the ground and go into the pump," says Frank Swindell, senior product manager for filters and valves, Pentair Water Pool and Spa, Sanford, N.C., "most pool builders put in a 90-degree elbow to take water into the pump. What we're looking at is how do we put more of these sweeps in our system and manufacture our product so that the plumbing and components go together like Legos."

Complicating the issue for sand and DE backwashing valves has been the advent of the popular but very-energy-inefficient multiport valve. In these valves, there are numerous, quick, 90-degree turns and very small openings, Swindell says, so the pressure loss is tremendous.

"These multiport valves give you some fancier options, different valve positions let you bypass the filter, rinse, filter mode, closed position and a winterize position," he says. "For that kind of valve, with all the different positions within one valve body, there's not a lot you can do to improve flow, because you've got a lot of places you are trying to redirect water.

"Really and truthfully, though, the most important positions on a valve are filter and backwash."

Pentair's new high-flow valve does just that, Swindell adds. "It's nothing fancy, but it does conserve a tremendous amount of energy. In certain states you can save as much as $200 or $300 a year on your energy bill with this valve."

My Pad Or Yours

Talk of smoothing the flowpath of water in the filter inevitably leads to similar discussions about the system as a whole. Many equipment pads in the United States are a spaghetti pile of pipes and components that make liberal use of 90-degree elbows and small-diameter pipes.

One of the best ways to save energy, Clay says, is to straighten that plumbing out. It's impractical for most residential retrofits, he admits, but in new pools, it's time for new thinking on plumbing layouts.

"Look at a typical backyard pool equipment pad. Either the builder's plans or the homeowner's desires dictate equipment that is out of sight, out of mind. So they use as small a pad as is possible.

"Builders are usually trying to put all the equipment on a pad that is no more than 4-feet square. So that's just asking for a lot of elbows and turns, because you can't line everything up like you should."

Enormous energy savings are possible, he says, if the plumbing is set up more or less in a straight line instead of a scribble. "But you never see that, because that takes at least 8 lineal feet to do it. But really, that doesn't take any more total area than a 4-foot square pad."

The problem, of course, is that a linear plumbing system is harder to hide than a convoluted square one. But Clay adds that homeowners should start taking a hard look at that choice between aesthetic appeal and its financial cost, "because these measures save money and energy."

A Systems Approach

"That would be awesome if they could do that," says Swindell, of long, thin equipment pads that keep water moving in a straight line. He points out that the prevalence of energy-wasting pad designs "comes from the fact that nobody ever took a systems approach from the beginning.

"The pump guy worked on the pump, the valve guy worked on the valve, the filter guy worked on the filter and the installer just tried to get it all hooked up next to the pool. That's how it's been done in the past, and I think that's where the ball has been dropped. That's what has led to the kind of plumbing nightmares that you see on equipment pads today.

"But as you move forward, you will see more and more pads where the plumbing makes a lot more sense and the components are working together. All of the big equipment manufacturers are working on making that happen."

Cut It Off At The Pad

As part of PG&E's commitment to keeping energy demand in check, the utility performs energy audits of commercial pools in California. Recommendations, if followed, can sometimes result in energy savings of up to 80 percent, says Scott Clay, senior program manager at Pacific Gas & Electric in San Francisco.

"For a commercial pool, that equates to something around 80,000 to 100,000 kW hours per year," he says, "which translates to about $30,000 to $40,000 a year. More typically, it's between 30 and 50 percent."

For the most part, this enormous amount of energy can be saved simply by running at lower speeds, and reducing the overall system head. Often it means starting over from scratch with the plumbing.

"We help with a complete retrofit, cut everything off at the pad and start again. We straighten everything out, put on a variable-speed-pump, a large cartridge filter, and you're in business. Then they have to use low speed pumping unless they need more power to raise water up to a solar heater or a cleaner or something else."

Programs like these have been in operation in California for years. The question arises, are they having any impact?

"Well, even though there are 2 million pools in California, it's still minor compared to the overall energy usage of the state. The most telling fact for California is that over the last 20 years, when the state began to become heavily involved in energy efficiency programs, and our population has increased every year and their demands have increased every year, we haven't had to build any power plants to meet that demand."


DE Debris

Another aspect of backwashing that has hampered the growth of DE and sand filters, besides the fact that it necessitates a valve, is the concern about debris entering the water system.

Some municipalities are starting to express a clear preference for the cleaning method of cartridge filters, where the media is simply sprayed off on the ground, rather than backwashing the pool waste down the drain.

"In California," says Scott Clay, senior program manager at Pacific Gas & Electric in San Francisco,"it's getting hard to backwash filters and dump stuff into a drain. Nobody wants that, especially if it's a DE filter, because if the DE gets into a local sewage treatment plant, it causes havoc with their processes."

If a DE filter is cleaned correctly, the DE material stays intact, drops to the bottom of a separation tank, the water is drained off and the DE is put back into the filter.

That only works, Clay says, when the DE particles are not broken down and remain heavy enough to settle out at the bottom of the separation tank. "But what actually happens, especially in these high-pressure systems, is the DE gets crushed right away into a much smaller particle size that not only clogs the spaces between the particles and increases the pressure drop across the filter, but when you go to backwash it, these smaller particles instead of sinking to the bottom, tend to get poured off when you drain the water from your separation tank. And now it's in the municipal water system. That's really hard on the city treatment plant."

Often enough, he adds, the person doing the filter cleaning simply makes a mistake in separating the DE and allows some of it to leak into the wastewater.

For this reason, some cities and counties in California are outlawing DE filters on new pools, he says. "The ones that are there are grandfathered in, but the code calls for them to be replaced by another type."


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