APSP Quarterly - Winter 2008 - (Page 24)

Foundation for Pool & Spa Industry Education 598 Display Way, Sacramento, CA 95838 916-922-8895 suck, the atmosphere pushes.) This difference in pressure, Delta P, will be stronger or weaker depending on the piping system installed with the pump. Strong suction is what can hold a swimmer, with the strongest being found in single-outlet suction systems that can be completely blocked by a body. This is why dual outlets were invented by the industry more than three decades ago, to split the suction between two outlets, reducing the Delta P. This is also an important feature of ANSI/APSP-7. Contrary to what some people believe, suction is not the only, or even the greatest, entrapment threat facing our customers. Water flowing through covers and grates is responsible for the most reported entrapments. Swirling water can entangle hair in or behind the suction outlet cover. The higher the flow rate, the more turbulence there is inside the suction outlet. One possible reason for a greater number of hair entrapment cases is a lack of physical warning or feeling of suction, as hair moves with the water into the outlet. ANSI/APSP-7 addresses this by limiting the flow rate or water velocity. The victim may not notice in time because entanglement happens without a spike or increase in suction. This is an important point to understand because atmospheric vacuum-breaking devices can respond only to an increase in suction, which does not occur when there is hair entanglement. ANSI/APSP-7 provides many compliant safety systems for new construction, but our existing pools and spas are just as important and ANSI/APSP-7 provides answers for these as well. The focus of ANSI/APSP-7 is prevention, and this is why the fi rst option you will fi nd in the standard is for no submerged suction. The idea is simple: You can’t get stuck on a suction outlet if it isn’t there. These circulation systems receive water exclusively from skimmers or gutters. While it is not known how many pumps receive water exclusively from overflow systems, we do know the number is huge when you consider the thousands of vinyl lined and fiberglass pools installed without submerged suction outlets. The idea of building without submerged suction is foreign to many because of the misconception that proper circulation throughout the pool requires floor outlets. The science of fluid dynamics teaches that water can only be pushed, not pulled. Perhaps this is why public health codes require additional return inlets as pool size increases while the number of submerged suction outlets remains the same. The resort pool pictured on page 20 is an example of great circulation without the help of submerged suction outlets. This outstanding water quality is supported by returns every 15 feet and skimmers placed around the perimeter of the pools. This inviting swimming pool receives daily maintenance to keep it clean, but removing debris does not substitute for proper circulation; without it, you won’t get these results. Chances are good you have more experience with overflow circulation than you think because this exact circulation method is installed regularly, only on a small scale. The most common example of suctionfree circulation can be found in pool and spa combinations where spas 24 | AQ A P S P Q UA R T E R LY 350615_Foundation.indd 1 10/25/07 3:04:50 PM http://www.fpsie.org

Table of Contents Feed for the Digital Edition of APSP Quarterly - Winter 2008

APSP Quarterly - Winter 2008 Contents President's Message Guest Editorial APSP Annual Report Hot Tub Council Initiative to Speak with One Voice Suction Safety Challenging the Process Industry Update Keeping Pace: Staying on the Cutting Edge With Lifelong Learning APSP News & Resources Advertisers' Index

APSP Quarterly - Winter 2008

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