Plumbing Africa June 2019 | Page 37

HEALTH AND SANITATION Air gap a. An air gap is required as part of a top-up system for backflow prevention (zone protection). b. Air gaps shall be designed and installed in accordance with applicable national/ provincial/ local codes and regulations. For guidance purposes only, the following guidelines are provided. • The gap must be unobstructed – mechanical supports, fixing the potable water supply pipe to the top-up drainage pipe or other components located at or between the potable water supply pipe and the top-up drainage pipe, are not permitted. • The air gap must be located in an area where it can be observed and inspected. • The air gap must be installed at a height above the flood level rim (overflow) of the rainwater storage tank. If not, there is a risk that rainwater will back up in the top-up drainage pipe and overflow from the air gap. • The air gap height must be at least 25mm [1 in.] or twice the diameter of the water supply pipe. c. Splash and water damage prevention: i. To prevent make-up water from splashing at the air gap, install the following: • flow restrictor, installed upstream of the solenoid valve; and/or • aerator, installed where the potable water supply pipe terminates; and/or • extended length of vertical pipe with the end of the pipe cut at an angle no less than 45° (to produce laminar flow), installed where the potable water supply pipe terminates above the air gap. ii. To prevent water damage to rooms where the air gap is located: • locate air gaps near a floor drain; • install an overflow on the top-up drainage pipe, located downstream of the air gap, to direct excess make-up water to the sanitary sewer (where permitted by local authorities); and • appropriately size and slope the top-up of the drainage piping. www.plumbingafrica.co.za 35 d. Make-up water flow rate i. To ensure RWH system operation during top-up, the following measures are recommended: • the flow rate of make-up water should be equivalent to that of the maximum flow rate of the rainwater supply pump; or • the water level sensor(s) should be configured to provide a sufficient reserve volume in the rainwater storage tank (where said reserve volume shall be equivalent to that of the average daily rainwater demand for the RWH system). MAINTENANCE Following the installation of the RWH system, if the make-up system does not operate, or if it operates when it should not (for example, tops-up the tank when there is a sufficient quantity of rainwater in the tank): a. ensure that the proper control equipment was selected and arranged in accordance with the Design and installation guidelines provided; b. visually examine the RWH system . Backflow preventer testing and maintenance according to manufacturer’s instructions. If the make-up system is operating properly, it is recommended that it still be inspected once every six months to: a. verify that the float switch wires are not tangled with other float switches, the pump or other objects in the tank; b. remove any dirt and/or debris that have accumulated on the float switches, as necessary; and c. observe the make-up system while operating to ensure that water is not overflowing from the top-up drainage pipe at the air gap or discharging from the backflow preventers. If any water is leaking or discharging, refer to the troubleshooting instructions above. While inspecting, cleaning or repairing the make-up system, follow all necessary safety precautions, such as disconnecting the power supply, when necessary. PA In the next article we look at overflow provisions. June 2019 Volume 25 I Number 4