Every day, in the midst of the bitter rivalry, politics and
regulatory battles surrounding suction vacuum release systems, pool
builders and service techs live quiet lives installing the
The daily reality of running their businesses is far from the
I-Codes, testing labs,Virginia Graeme Baker Pool and Spa Safety Act,
and Consumer Product Safety Commission. Rather than
participate in the endlessly evolving see-saw of power and
influence, their jobs are to simply understand the technology and
comply with the law.
But how exactly does that technology function?
Getting beyond the controversy to examine the actual workings of
secondary vacuum-releasing devices is no small feat. Nevertheless,
it’s critically important that industry members handling the
products understand what they do, their strengths and limitations,
and the questions that are yet to be answered.
The manufactured option
Safety vacuum release systems and automatic pump shut-offs —
which many collectively refer to as SVRSs — comprise two of
several secondary options listed in the Virginia Graeme Baker Act.
They offer an efficient and straightforward method of retrofitting
existing pools and spas that have single outlets or incorrectly
installed multi-outlet systems (i.e., the drains are less than 3
feet apart, or one has been blocked during plastering). While not
required in most areas, these options also can be used in
residential settings under the same conditions.
In order to conform with VGBA, as well as many state and local
codes, SVRSs must be tested and certified to comply with ASME
A112.19.17. Currently, the law doesn’t require automatic pump
shut-offs to meet the standard; however, in order to gain
third-party certification, virtually all do. The most important
aspect of ASME A112.19.17 lays out time parameters from the initial
blockage of a single outlet until the person is freed. The devices
must be able to function within a specified period of time, which
is calculated based on the plumbing schematic involved — the
longest allowable span is 4.5 seconds through 200 feet of pipe.
Some manufacturers claim their products work in approximately 1
second under certain conditions.
- Safety vacuum release systems
Depending on the model, SVRSs may be installed in a number of
locations throughout the circulation system. When the device senses
a vacuum increase over a particular threshold, it releases a valve,
which allows air into the line, causing the pump to cavitate and
the vacuum to break.
These mechanical systems open the valve in different ways —
some rely on springs, while one model uses magnets. The sensitivity
of a given product depends on its “window,” or the
pressure differential that is allowed before the valve is
Some worry that nuisance tripping of these systems over time,
either sporadic or prolonged, can starve the pump, causing it to
overheat and stop working. In response, many manufacturers limit
the amount of air their units insert into the suction line, thus
maintaining a slight vacuum that will direct a small amount of
water to the pump in the event that the device activates.
- Automatic pump shut-offs
In keeping with its name, this product detects an irregularity and
shuts off the pump.
To sense an entrapment, some automatic pump shut-offs monitor
pressure and vacuum, while others look for a dramatic drop in the
pump’s power usage.
Whereas an SVRS works by adding air into the line, an automatic
pump shut-off disengages the extremely low pressure that causes a
vacuum to occur. Once the pump is off, the pressure equalizes,
thereby dissipating the vacuum. Some manufacturers state that this
happens almost instantly.
Automatic pump shut-offs are electrical devices and, therefore, an
electrician may be required to install them. Some units are
integrated into the pump, which simplifies installation, while
others are freestanding, which may mean they are more suitable for
There are also products combining the function of an SVRS with an
automatic pump shut-off, meaning the device introduces air into the
line as well as shuts off the pump.
Working with secondary systems
SVRSs and automatic pump shut-offs rely on correct installation to
It’s important to remember that no check valves can be
included on the suction side of the pump between the outlets and
the SVRS, and only in limited instances on the return side of the
pump. SVRSs and automatic pump shut-offs are designed to cause air
or pressure to move backward through the suction line; a check
valve would prevent this occurrence and typically should only be
used to divert water through a bypass line to the heater or
chemical feeder. Some SVRSs are not affected by check valves
located between the SVRS and the pump.
“The main thing is when there’s a blockage and the pump
is shut off, that the suction line is open to atmosphere in some
way,” says Steve Barnes, safety and compliance manager for
Pentair Water Pool and Spa, and chairman of the Association of Pool & Spa
Professionals’ Technical Committee.
Builders also should not install hydrostatic relief valves in the
suction outlet sump, because if an entrapment occurs and,
coincidentally, there is a high water level below the pool, the
hydrostatic relief valve could open, allowing enough water into the
suction line that the SVRS would not activate.
“You need to have a secondary sump in the bottom of the pool,
just to put in a hydrostatic relief valve that’s not
connected to any of the other plumbing,” says Michael
Giannamore, vice president of Aqua Pool & Patio Inc. in East
Many manufacturers also specify a certain distance of straight pipe
leading to the pump on the suction side, as this helps smooth out
turbulence at the vacuum-sensing pickup point, allowing for an
enhanced ability to accurately monitor for pressure.
In addition, some manufacturers instruct builders and service techs
to undergo a calibration procedure immediately after installing the
device. This allows certain SVRS models to recognize a pool’s
or spa’s baseline pressure so that it can detect a
differential. In most cases this should take place when the filter
is clean, as a dirty filter will add more pressure to the system,
resulting in the SVRS being calibrated to a higher pressure. Also
note that all units should be tested after installation.
Some SVRSs must be recalibrated occasionally — many say
annually. Additionally, certain models need to be recalibrated, and
all retested, whenever a change is made that could alter the
pressure in the circulation system, such as the installation of a
new pump, filter or solar system, or the addition of a
The problem of nuisance tripping has long been associated with
“Homeowners … blame us because leaves get in the basket
and cause the [device] to go off,” Giannamore says.
“They trip and an alarm goes off, and you hear it all night
long, and then your neighbors hate you.”
SVRSs and automatic pump shut-offs must walk a tightrope between
having the ability to detect when pressure or electrical output has
dropped low enough to indicate entrapment, yet continuing to
function during the pressure and power differentials that occur
Individual models vary in sensitivity —some are designed to
trip at pressure drops of as little as 2 inches of mercury, while
others withstand up to 12 or 13.
Industry professionals also have seen nuisance tripping happen when
the circulation system is initially activated. “There’s
a kick when the pumps are starting up, and that draws the vacuum
down so much just on the initial start — just to get the
momentum of the water going — that it would trip the
unit,” says David Peterson, president/CEO of San Diego-based
Installers can check for potential nuisance trips during
post-installation testing by simulating a partial blockage.
“Close valves gradually versus completely, and just try to
get a sense for what happens to the unit,” says Scott Petty,
product manager, pumps, with Hayward Pool Products in Elizabeth,
N.J. “Get a sense for ‘If I slowly close this, is it
going to make a difference?’”
To minimize nuisance tripping, some manufacturers have added an
automatic reset function that allows the pump to start again,
providing the pressure or power load is back to normal after a
specified number of minutes. At least one system has a function to
differentiate between the sudden pressure change that occurs during
an entrapment, and those that take place gradually, such as when a
filter accumulates dirt.
When do secondary devices make the most sense?
Local code requirements aside, industry professionals agree that
these products are most needed in single-drain pools or vessels
that function that way, meaning the outlets are less than 3 feet
apart or, for some reason, one outlet is not working. Additionally,
even though a pool may have multiple drains, an entrapment hazard
could still exist if the installer undersized the plumbing.
“If you remove the cover and put your hand in the pipe, there
may be quite a bit of hold-down force there,” Peterson
“Because the plumbing is undersized, you may have quite a bit
of vacuum drawing, even though it’s a split pair. In that
case, a backup device would help.”
When it comes to true multi-drain systems, the performance of SVRSs
and automatic pump shut-offs are up for debate, as the standard
does not test for this condition, and not all SVRSs have been known
to activate in this scenario. ASME A112.19.17 outlines the testing
process for single-drain vessels, but recently, the
standard-writing committee began exploring methods to determine
functionality on multi-drain systems and single-drain systems with
Though there is widespread agreement that these secondary devices
can save lives in certain situations, there is still dissension
within the industry regarding which of the five modes of entrapmentthey can
Those against requiring the systems say that, because they cannot
stop or even mitigate all types of entrapment, they should rarely
“The fact that some percentage of [entrapments] could be
helped, some could be mitigated and others there’s nothing
that can be done [isn’t enough],” Barnes says.
“We draw the line at the side of safety that says,
‘We’re not going to pick and choose. We’re going
to prevent all suction entrapments.’”
Both sides concur that these devices are effective against body
entrapment. There is also a consensus that the units are not
successful in preventing two other types: Hair and mechanical
entrapment (See sidebar for more
information). In those cases, introducing air or shutting off
the pump will not alleviate the issue.
The remaining two forms of entrapment — evisceration and limb
— cause more disagreement among the different camps.
The issue of evisceration is especially dicey. Though extremely
rare (there were only two known cases between 1999 and 2009),
evisceration is gruesome to the point of being unthinkable. It also
is the fastest to occur, with time estimates ranging from 0.25 to
1.86 seconds. The speed at which an evisceration can happen depends
on several factors, including the victim’s size, age, gender,
how centered the sphincter is on the drain, and even how recently
he or she ate.
But just as evisceration times vary, so does the response window.
The ASME standard allows backup devices to take as long as 4.5
seconds to stop the vacuum in certain scenarios. But in the case of
evisceration, even a fraction of a second can be crucial.
Additionally, site-specific conditions such as pipe length and
size, and pump horsepower, will affect response time.
For this reason, APSP adamantly stands against claiming that any
technology will mitigate an evisceration once a vacuum is formed.
“It’s just unacceptable, and any public policy
promotion based on that
premise has been rejected by ICC, ANSI, APSP and ASME,”
But the Pool Safety Council, an organization founded and run by the
former president of one of the largest SVRS manufacturers, wants to
explore the possibility further. The group recently collaborated on
a study that resulted in the 1.86-second time estimate.
“A vacuum release or vacuum limiting system, depending
upon pump-to-sump distance, may relieve the dangerous suction force
before full disembowelment occurs,” said PSC founder and
chairman Paul Pennington. “This could be the
difference between life and death for the
A bigger rift seems to be developing over the subject of limb
entrapment (the fifth type) and whether secondary devices can
Both sides agree that some limb entrapments can be alleviated by
these products, but APSP officials take a more cautious approach.
The group contends that it’s possible for swelling to cause
the limb to become stuck so tightly that it remains wedged inside
the pipe even after the suction is interrupted. Even if significant
swelling doesn’t occur, the skin may not respond to efforts
to pull the limb out: Just as it can be more difficult to remove a
ring than to put it on, it can prove impossible to pull a limb out
of the pipe, no matter how readily it slid in, claim APSP
For its part, PSC believes that suction release devices are highly
effective in combating limb entrapment, and officials say most of
the known entrapped limbs were released after the suction was
At the end of the day, there is one thing both sides agree on
— more research is needed.
- Types of SVRSs on the market
- The importance of correct
- The problem of nuisance
- When do secondary devices make the
- Dissension over entrapment
- Five Types of Entrapment
Examining the five recognized types of suction entrapment.
- Entrapment Diagram
A closer look at what happens during an entrapment incident.
- Product Placement
The SVRS devices and automatic pump shut-offs on the market vary in their placement within the circulation system.
- On-site Solution
Suction-limiting vents provide an alternate vacuum-breaking system.