Chapter 5, mechanisms for preventing backflow Flashcards
Air gaps are usually the cheapest form of backflow prevention, true or false?
True
Where Airgas cannot be used, these these assemblies provide a physical barrier to backflow
Mechanical backflow preventers
Two methods of non-mechanical backflow prevention are:
Air Gaps and Barometric Loops
A _____ is a mechanical way to protect against backflow.
Device
This term is referred to as the entire backflow prevention unit, including the mechanism that actually prevent backflow, but also the shut off valves and test cocks
Assembly
What term refers to the backflow prevention mechanism only, it does not include the shut off valves.
Device
Approved assemblies must be shipped from the manufacturer as:
One complete unit
What foundation at the University of Southern California field test backflow assemblies?
The foundation for cross connection, control, and hydraulic research
The backflow preventer must also have shut off valves that have a:
Full flow characteristic
Potential is the essential factor. The purpose is to eliminate unnecessary reduction in pressure since backflow preventer themselves already reduced pressure… true or false
True
This term is defined as capable of withstanding shock without permanent deformation rupture.
Resilient seated
A resilient seated valve usually contains some form of soft rubber or other flexible material that can:
Withstand shock
Shut off valves that are resilient seated are usually designated with what character or characters?
“R” or “RS”
The operating stem on a ball valve type test cock must be:
Blowout proof
To be approved, a backflow preventer must be testable and repairable:
In-line
Being repairable in-line means that the backflow preventer must be
Stay in place
These are the simplest type of mechanical backflow prevention.
Atmospheric vacuum breakers (AVBs)
Atmospheric vacuum breakers can be tested in line. True or false.
False
Atmospheric vacuum breakers can be used to protect against _______ only
Back siphonage
The AVB contains a single disc float, also known as a:
Poppet valve
AVB’s are NOT approved for use where they will be subject to
Continuous pressure in the direction of flow
Shut off valves are not allowed downstream of
AVB’s
After _______ or more hours of continuous pressure, the float can become permanently stuck to the air in the port
12 to 14
What is the image a picture of?
An atmospheric vacuum breaker.
When turning the water off to an atmosphere vacuum breaker, how can it be determined if the float disk is working?
It can be heard as it falls
What is the minimum height that a vacuum breaker must be installed to the underside of its body above the highest outlet?
6 inches
Back for pool runners are required to include an air that indicates the direction of flow in order to be designated what?
Approved
The AVB must never be subject to ________ , since it relies on atmospheric pressure to function
Flooding
True or false AVB provide protection against back pressure
False
This is an atmospheric vacuum breaker that has been adapted to fit on a hose bib or sill cock
Hose bib vacuum breaker
What is the image of picture of?
A pressure vacuum breaker
The pressure vacuum breaker is an ________ instead of a device, it has to shut off valves and two tests.
Assembly
On a pressure vacuum breaker the air inlet and the check valve operate _______ each other
Independently
The AWA specification for a spring loaded, soft seated check valve is that it must be drip tight and hold______ in the direction of flow
1.0 PSI
Generally, the PVB is used for_______. For instance, it is commonly used on lawn irrigation systems
Isolation
Unlike the AVB, the PVB can be used where it will be subjected to:
Continuous pressure
True or false because the PVB can be subjected to continuous pressure, it is acceptable to have a shut off valve downstream of the assembly.
True
The PVB cannot be subjected to
Back pressure
For a PVB, the minimum height Between the bottom of the critical level and the highest point in the system.
12 inches
Lawn irrigation systems are classified as a:
High Hazard
Similar to PVB’s these type of vacuum breakers have two shut off valves, one test cock, and one bleed screw
Spill resistant vacuum breakers.
True or false the SVB does not discharge water when the assembly is pressurized
True
The critical level of a SBV is usually located at the opening of the
Check valve
The springs in a ______ are identical, and sometimes interchangeable
Double check valve assembly
According to AWWA specifications, the springs inside of a double check valve assembly should hold drip tight against
One PSI in the normal direction of flow
According to a WWE specifications, the springs inside of a double check valve assembly should hold drip tight against
One PSI in the normal direction of flow
The maximum pressure drop out across a double check valve assembly is:
10 psi
True or false double check valves do not provide adequate protection against both types of backflow: back siphonage, and back pressure
False
Double check valve assemblies can be subjected to continuous pressure. Under normal flow conditions, the first check valve effectively reduces the supply line pressure by what range?
1.0 to 5.0 psi
The maximum pressure loss allowed across a DC VA cannot exceeded:
10 psi
Double check valve assemblies are only approved for
Low or non-Health hazard situations
DCVAs are traditional used _______ and are installed after the meter or at the point of service
For isolation
Double check valve assemblies should be installed at least ______ and at most _____ above the ground, drainage system, or flood elevation
12 inches to 36 inches
True or false, double check valve assemblies may be installed inside of vaults
True
Vault installations are considered to be:
Confined spaces
These are the only approved backflow preventers that can be installed below ground. This installation is usually discouraged.
Double check valve assemblies
What is this a picture of?
Reduced pressure principle assembly
On an RP, the first check valve is designed to reduce water pressure by a minimum of approximately:
5.0 psi
On an RP the second second check valve is only designed to hold back a minimum of:
1.0 psi
Inside of a RP a _____ is created that will not allow water to backflow
Hydraulic gradient
On an RP the area between the first check valve and the second check valve is referred to as what?
The reduced pressure zone
When the relief valve opens to the atmosphere, it provides what between the two check valves?
An air gap
The spring on an RP relief valve is designed to provide a minimum pressure of
2.0 psi
Under normal operating conditions, the pressure inside the reduce pressure zone is approximately ________ less than the pressure on the supply side of the first check
5.0 to 12.0 PSI
The 5.0 psi deficiency between the high side pressure and the zone pressure allows for some:
Fluctuation in the line pressure
Because the relief foul provides edit protection, the RP is considered adequate for:
High and low hazards
The RP is considered the most ________ backflip as it can be used in all situations except for inside of a vault
Versatile
The RP should be installed so that the vent of the differential relief valve is at least ________ no more than ______ above grade
12 inches, 36 inches
AARP should have a minimum clearance________ on all sides
24”
If a drain line is installed on the relief port a ______ should be provided to avoid creating a cross connection between the assembly and the drain
Manufactured air gap
______ is caused by air in the system or fluctuations in line pressure
Spitting
If there is a loss in supply line pressure to the RP, what happens?
It dumps the zone
A steady drip or continuous flow of water from the vent indicates that the RP is:
Not working properly
There must be a minimum separation of two times the affected area or inside pipe diameter, of the water supply outlet between the outlet and the:
Flood level rim
What is the absolute minimum that must be maintained for an airgap?
1 inch
______ is the attraction of unlike particles.
Adhesion
_______ is the attraction of like particles
Cohesion
_______ is the attraction of like particles
Cohesion
If the water supply outlet is adjacent to a sidewall, within three diameters of the water supply outlet, the minimum air gap must be
Three times the inside diameter of the outlet pipe
A barometric loop of 34 feet high is effective against what form of backflow only?
Back siphonage
A single check valve is not considered a:
Adequate form of backflow prevention
A single check valve cannot be tested:
In line
Dual in-line check valves that cannot be tested. Have a _______ failure rate for both checks within the first five years.
50%
This type of check is designed to detect small weeks or illegal water usage that cannot be detected by the less sensitive meter installed on the large line upstream from this assembly
Detector check
This type of check is designed to detect small weeks or illegal water usage that cannot be detected by the less sensitive meter installed on the large line upstream from this assembly
Detector check
What is the image a picture of?
A double check detector assembly
The maximum pressure loss through a double check detector assembly is:
10psi
For a double detector check assembly the first spring must hold drip tight against
1.0 psi regardless of the size of assembly
What is the maximum size of a reduced pressure detector assembly?
10 inches
What is the maximum size of a reduced pressure detector assembly?
10 inches
Where are reduced pressure detector assemblies frequently used?
Fire sprinkler systems
If a fire sprinkler system does not have any additives and has no chance for auxiliary water supply to be connected then the system is considered
Low hazard
For low hazard fire sprinkler systems what is considered the appropriate assembly?
A double detector check
A detector bypass on a backflow prevention assembly is not necessary if the fire protection system has an
Operating alarm that will indicate if water is flowing
Reduced pressure detector assemblies average about ________ PSI pressure loss
13 or 14
Regular RPZ assemblies about _______ pressure loss
10 psi
Prior to installation, the waterline should be_______ to remove loose materials that could foul the backflow preventer
Thoroughly flushed
True or false sometimes it is recommended that a strainer be located prior to the assembly to trap any loose materials that could otherwise file the assembly
True
True or false, providing a blow off valve after the backflow preventer is not a good idea
False, the blow off valve can be used to remove grease and form materials that are produced when repairing the assembly, or to flush the customers waterline of any contaminants after a backflow incident without contaminating the backflow preventer
True or false, providing a blow off valve after the backflow preventer is not a good idea
False, the blow off valve can be used to remove grease and form materials that are produced when repairing the assembly, or to flush the customers waterline of any contaminants after a backflow incident without contaminating the backflow preventer
This is the increase in pressure in a closed water system due to heating and expanding water
Thermal expansion
This is the increase in pressure in a closed water system due to heating and expanding water
Thermal expansion
For proper function, T and P valves need to be
Exercised regularly
Well, almost backflow preventers may withstand freezing temperatures for short period of time, anytime over what can burst the assembly?
10 hours
To prevent freezing, the customer should either_______ or ________
Enclose the assembly with a heat source, or continuously run water
Backflow preventer should be rebuilt or replaced every?
Five years
Records concerning variance or exemption granted to the system shall be kept for a period and they not less than
Five years following the expiration of the variance and exemption
Any systems subject to the requirements of rule 62–550.800, F. A. C. Shall retain no fewer than how many years original records.
12 years
