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 devices.

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 opened.
  • 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 retrofits.
  • Hybrids
  • 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 function properly.

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 Windsor, Conn.

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 waterfeature.

Remaining nuisance

The problem of nuisance tripping has long been associated with these products.

“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 every day.

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 Watershape Consulting.

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.

The best application

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 says.

“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 skimmers.

Big questions

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 prevent.

Those against requiring the systems say that, because they cannot stop or even mitigate all types of entrapment, they should rarely be mandated.

“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,” Barnes says.

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 victim.” 

A bigger rift seems to be developing over the subject of limb entrapment (the fifth type) and whether secondary devices can prevent it.

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 officials.

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 eliminated.

At the end of the day, there is one thing both sides agree on — more research is needed.