Miami Swimming Pool Designer & Aquatic Consultant

Whether your project is in Miami, Los Angeles, Manhattan, Scottsdale, San Francisco, Napa, Aspen, Vail, Dallas or the Hamptons - your pool hydraulic and plumbing system must be in compliance with BOTH the Virginia Graeme Baker Safety Act and the ANSI/APSP-7 2006 Standard.

Component In-Compatibility

Since it’s enactment in 2008, a lot has been written about the Virginia Graeme-Baker Act Safety Act (VGBA).  Yet, in my travels as an expert witness, I continually see indications that the standards and how they are implemented are not understood - by people who design and build pools for a living.

The confusion seems to lie in the complexities of components selection and hydraulic design.

Maximum Line Velocities

ANSI/APSP-7 2006, section 4.4 states “Water velocity in field fabricated piping is based on the maximum system

flow rate.  Maximum water velocity in branch suction piping shall be limited to 6 feet per second (fps) (when one of a pair is blocked). In normal operation then, the branch suction piping velocity is 3 feet per second. All other suction piping velocities shall be 6 fps for public pools or 8 fps for residential pools.”

Basically is says that the plumbing lines that connect to the drain sump should have a line velocity of 3 feet per second when they are in an unblocked condition.  So, at 3 fps a 2 inch pipe is limited to 43 GPM.  And, therein lies the problem.

Prefabricated Drain Channels and Covers

The next hurdle is what is causing all of the confusion to swimming pool builders, designers, state and local health departments, building inspectors and even many drain manufacturers - the compatibility of the drain GPM and line velocities of the connected plumbing.

Though drain sumps, channels and covers that comply with VGBA list a maximum GPM flow rating, it does not mean that the pipe connections below that cover are permitted to flow at that rating. 
 
What the drain cover rating does allow are the grouping of different suction systems.  Multiple branch lines from different pumping systems may be grouped together under a cover, until their cumulative GPM flowrate meets the cover's rating.  This allows multiple system inlets to share a drain cover.

Most of these channel drains only provide 2 inch connection ports, that are limited (by law) to a mere 3 FPS. That equates to ONLY 43 GPM per connection!  

1.   Single inlet unblockable channel drains are available with 196 GPM ratings.  When installed in compliance with the 3 FPS standard, it only has a maximum flow rating of 43 GPM.
2.   Dual inlet unblockable channel drains are available with 227 GPM ratings.  However, when installed in compliance with the 3 FPS standard, it only has a maximum flow rating of 86 GPM.
3.   Triple inlet unblockable channel drains are available with flow ratings of 320 GPM.  Yet, when installed in compliance with the 3 FPS standard they are limited to 129 GPM.

The bottom line is, that just because a pre-fabricated drain cover allows higher flow rates through it’s slots, does not mean that the ANSI/APSP 7 standard can be ignored.

It’s all about component compatibility.

SIDE NOTE

Some jurisdictions and health departments limit the line velocity through the branch suction lines to 1.5 fps. The Texas State Department of Health places such limits on public pools.  Some local jurisdictions adopt the state health department rules for all pools in their domains.  So, it helps to know if this more restrictive standard of 1.5 fps applies to private pools you may be involved with.

Paolo Benedetti - Watershape Consultant, Swimming Pool Designer, Hydraulic Engineering, Expert Witness 

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