TECHNICAL
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In terms of the National Regulations , SANS10252-1 ( water supply installations for buildings ) refer to 7.4 of SANS 10252-1 ‘ Preservation of Water and Water Quality ’. Reduced Pressure Zone Back Flow Preventers must be installed in any installation where there is a risk of contaminated water or harmful substances being back syphoned or flowing back into a potable water supply line . The regulations state that Back-flow Preventers shall be installed in certain types of installations and buildings , for example :
Medical treatment of people and animals , pharmaceutical or chemical research and manufacturing , dairies , nurseries , stadiums , abattoirs , combined fire systems etc .
Most of the municipal bylaws underpin this by stating that it is the responsibility of the Homeowner ( not the tenant ) to have this maintained once a year . A record must be kept of when this maintenance was done and by whom . The unit must be overhauled or replaced every five years and record of this must also be kept .
A national regulation requires that any Backflow Preventer discharges where it is visible so that any malfunction of the system can be readily detected and attended to . This means that we cannot hide this valve somewhere in a duct or a manhole , it must be above ground level where the discharge is visible . If theft is a factor the valve may be closed with a surround , but the discharge must still be where it is visible . Figure 1 is a drawing of a typical installation .
How does the valve work ? There is a mechanical check valve at the inlet and outlet of the valve . In the middle there is an area ( Zone ) that is open to the atmosphere . As soon as water pressure enters the valve a diaphragm is pushed down , and the relief port is closed . Once this area is now filled with water the second check valve is opened and the downstream plumbing system can be filled with water .
If for any reason the upstream pressure drops below the downstream pressure , the check valves will close , and the Reduced Pressure Zone will open to discharge any water in that area . If any of the check valves are faulty and are causing water to enter the Operating Chamber , a discharge of water will be visible from the Discharge Port to alert any passers-by of the system failure . It would be prudent to have a contact number near the valve so that anybody could contact the responsible person of this .
A full range of spares is available from the manufacturer . Contact your local valve supplier for availability . PA
Figure 2 : Check valves
September 2021 Volume 27 I Number 7 www . plumbingafrica . co . za