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TECHNICAL
common backflow prevention measures are given in table 12 — either an RPZ valve or a double-check valve . Not a single check valve , as this is not considered a backflow preventer .
In many cases , it is not enough to simply install a backflow preventer on the main incoming supply — we need to prevent crosscontamination within the premises as well . That is to say a section or process within an installation that constitutes a hazard must be isolated from the rest of that installation , so the backflow preventer ( s ) must be installed immediately upstream of the process or area . Have a look at Figure 1 .
it states that if there is no such maintenance programme in place ( again , this onus is on us as installers ), that backflow preventer shall not be employed , and the standard air gap requirements shall apply , as this set-up is pretty much maintenance-free .
I wouldn ’ t mention this fact except to illustrate the importance of backflow prevention and its ongoing operation . You do not see this insistence for a maintenance regime in the geyser installation standards , for example . It is recommended , but not enforced to the point where you are prohibited from installing one for lack of a maintenance regime .
Now , let ’ s revisit the various mentions of backflow prevention in SANS 10252-1 .
Remember how the different sections in the standard are organized - 6 for layout , 7 for design , and so on ? It would then stand to reason that each reference to backflow prevention in these sections are done so within a certain context , so for example :
5.4.15 ( materials and the like ) says that check valve shall comply with SANS 1808-10 , and that swing-type metal-to-metal check valves shall not be used in potable systems in buildings .
6.3 ( layout ) gives various minimum and maximum distances between components , configurations , and other positional requirements .
7.4.3 ( design ) appears earlier in this article and speaks to when and where backflow preventers should be used .
Figure 1 : Typical backflow prevention set-up .
8.4.2 ( installation ) lists the following installation requirements , which I |
think are worth listing here : |
a . |
that it can be inspected . |
b . |
that a condition of backflow can be detected . |
c . |
that it is readily accessible without having to alter the |
surrounding structures . |
d . |
that it cannot be flooded by any liquid ; and |
e . |
that vacuum breakers are installed on anti-syphon loops . |
You will notice that all parts of the installation downstream of the backflow preventers are deemed to be non-potable ( NP ). Therefore , multiple backflow preventers are required in these cases .
Backflow prevention devices must be tested and maintained according to manufacturer ’ s details , but these intervals shouldn ’ t be more than 12 months . In Annexure D of SANS 10252-1 ( D . 3.6.3 ),
We can see the importance the creators of the standards place on backflow prevention . Local authorities are usually very strict on this as well , considering the legal ramifications for them when it is shown that they were unable to guarantee the potable water quality provided , as is their mandated duty . It boggles my mind therefore that we as plumbers do not pay more attention to this . I am just as guilty of this , something I aim to change going forward . PA
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www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline January 2022 Volume 27 I Number 11