42 TECHNICAL
Where and how should an RPZ valve be installed ?
By Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
If we refer to the legislation that calls for an RPZ valve it also specifies where and how it should be installed .
Let us start this discussion then by having a look at SANS 10252 / 1 2018 , to see what the legal requirement is : 7.4.3 Prevention of backflow 7.4.3.1 Adequate measures shall be taken to prevent the back-siphonage of water into the following : a . an installation , in all cases where :
1 . the design of terminal fittings installed ( including any hose bibcock , laboratory taps or movable shower units ) is such that a hose or any other flexible pipe can be attached to the fittings , 2 . fire hose reels are installed in a combined installation , 3 . an underground irrigation system can provide contact between polluted water and water within the installation , or 4 . any other fittings can provide contact between polluted water and water within the installation .
Here it clearly states that any installation that has a tap where a hose can be connected , or where the system can in any way make contact between polluted water and the potable supply , a backflow prevention device should be installed . The type of device applicable is also outlined in Table 12 . is any backflow taking place . Therefore , only a Reduced Pressure Zone backflow preventer can be used , as a double check valve type does not make provision for a visual indication of backflow .
This is then the why , but what about the how and where ?
The valve should be installed in such a way that the whole installation is covered , this would mean installing the RPZ Valve just after the Water Meter . If necessary , one may need to protect one ’ s own installation from backflow from toxic zones within the installation . The bottom of the outlet from the valve must be above the level of any possible ponding to prevent any discharged water from being sucked back into the system .
CALAFRICA
One may be concerned by the crime factor in the area where the valve is installed . If this is the case , one may enclose the installation in a brick or concrete surround . Provision must however still be made for a visual indication of any backflow via an outlet in the bottom of the surround .
Here it gives us two different types of equipment that can possibly be used . SANS however continues and states in point 8.4.2 :
8.4.2 Backflow prevention devices 8.4.2.1 Any backflow prevention device shall be installed in such a position that a . it can be readily inspected , b . a condition of backflow in the pipe in which the device is installed can be readily detected , c . it is readily accessible for removal for the purposes of servicing , repair , or replacement , without alteration to the water installation or to the structure within which the device is situated , d . it cannot be flooded by water or any other liquid , and e . in the case of a vacuum breaker , it is installed in an appropriate anti-syphon loop .
8.4.2.2 Any additional installation instructions issued by the manufacturer or supplier of non-return valves shall be complied with . Whatever backflow prevention device is used it must indicate when there
Note that the drawings require that there be an isolating valve ( Ball Cock ) situated before and after the RPZ Valve . One will also need to fit a suitable strainer between the upstream Ball Cock and the RPZ valve .
Backflow prevention can be a very daunting topic , however , if you follow the guidelines set out in SANS10242 / 1 , all installations will be a success story .
For more information feel free to contact the writer . PA
CALAFRICA www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline August 2022 Volume 28 I Number 6