A safety vacuum release system (SVRS) is a system or a device that disables a pool pump’s suction ability so that a body or object trapped against the suction outlet is freed. It does this by inducting air to the pump and/or powering down the pump motor when it senses a sudden vacuum increase.
An SVRS can be easily installed in any pool, spa or waterfeature.
These devices are built in the pump motor, installed as a
controller, mounted onto the suction pipe, or are as easy as a
replacement of a pump pot drain plug. The SVRS must be installed in
conjunction with an approved VGB drain cover per ASME/ANSI
A112.19.8. Most SVRS’s are designed for use on 0.5 to 10.0
An SVRS can be composed of nine different parts: Cap, base, piston,
piston O-ring, cap O-ring, base O-ring, two screws, a spring and
lube (if needed). All nine parts work together to quickly and
efficiently avoid entrapment in the pool.
Two main methods — electrical and mechanical —
currently are being employed by SVRS’s to temporarily impede
the pump suction. The electrically driven SVRS’s
generally are pump shut-off systems in which the pump motor is
turned off briefly until the entrapment is resolved. The pump will
restart automatically or manually depending on the system
requirements. A mechanical SVRS employs a piston type mechanical
The anti-entrapment functionality of an SVRS works by allowing air
to rapidly fill the suction side of the pump during a high vacuum
occurrence. Upon entrapment, the vacuum level inside the pump is
elevated, creating a differential pressure across the piston.
Atmospheric air pushes the piston, compressing a spring until the
O-ring crosses passages that allow atmospheric air to rapidly fill
the pump pot. This, in turn, makes the pump lose prime and quickly
frees the cause of entrapment from the drain. The entire travel of
the piston occurs within milliseconds.
A mechanical SVRS also will be reset to normal pump operation
either automatically or manually after the entrapment is resolved.
It is recommended that all SVRS’s be calibrated at the pool
site. Some mechanical SVRS’s are equipped with compensation
zones, at which the piston will position itself to accommodate for
the pool and the equipment variations such as the pipe length and
diameter, under the concrete unknowns (elbows and reducers), check
valves, motor horsepower and speed. An SVRS with a compensation
zone requires minimal or no calibration at the pool
The exact method of installation will vary from one manufacturer to
another. To minimize the amount of vacuum generated and to ensure
consistently accurate responses from the unit, some manufacturers
recommend installing the SVRS on the main drain line only —
in other words, without also picking up vacuum from the skimmer.
Proximity to fittings isn’t usually a crucial factor;
however, many manufacturers do recommend installing the unit
somewhere between 5 feet and 18 inches from the pump for best
results. Some units, meanwhile, are designed to attach directly
onto the pump.
A few installation steps are unique to electrical SVRS units. For
one thing, whereas mechanical models are physically plumbed into
the system’s hydraulics, installation of an electrical unit
requires the installer to drill a small hole in the suction-side
plumbing, then connect the pipe to the SVRS with a small tube.
Another important consideration when installing electrical
SVRS’s is to check the local codes, and bond or ground the
unit according to their requirements.
Due to the specific nature of most pool and spa pumps, high vacuum
levels are created at the pump inlet port. Because systems with
larger pumps and more intricate hydraulic setups often generate
higher vacuum, it’s important to choose a unit that’s
appropriately sized for the pool and pump in question. In fact,
sometimes it makes more sense to downsize the pump to generate an
amount of vacuum the SVRS can handle. At any rate, while most units
do have an adjustable vacuum reading, SVRS manufacturers often
recommend a level under 18 inches of mercury.
To ensure proper operation, many manufacturers recommend that all
SVRS’s should be tested three times upon installation. Two
particularly popular methods for simulating an entrapment are
blocking the drain physically and using a ball valve. To test by
blocking the drain, simply maneuver a pole-guided mat over the main
drain. Keep in mind, though, that this method works best for single
main-drain applications. Installing a ball valve just before the
SVRS also can simulate a blockage. Turning the valve on should
instantly change the system’s vacuum and trip the unit. In
fact, leaving the ball valve in place makes it easy for the
homeowner to re-test the system periodically.
A successful test is indicated by the SVRS turning the pump off, by
making the pump lose its priming ability — or both. Observing
the water in the pump pot being replaced with air also indicates a
successful test. Furthermore, it is strongly recommended that the
SVRS be tested periodically, at least once a month during swim
Most SVRS’s include user manuals in which steps for testing
and troubleshooting the device are detailed. Manufacturers also
typically provide live technical support to guide the service
technicians or the end users through the installation and testing
of their systems.