Plumbing Africa PA October 2018 | Page 79

TECHNICAL DYNAMIC (FLOW) PRESSURE VS STATIC PRESSURE Dynamic (flow) pressure is the resultant pressure felt at the end of a pipe installation after the total value of friction loss has been accounted for over the length of the pipe run. Since dynamic pressure is what is experienced at the fixture points, it is strongly linked to the performance of an installation as well as customer satisfaction and user comfort. Flow rate Flow rate is the volume of water passing through a pipe or terminal fitting in a given period and is usually expressed in litres per minute or litres per second. Example One litre per second × (60 seconds) = 60 litres per minute × (60 minutes) = 3 600 litres per hour (3.6 cubic metres per hour), and so on. IMPORTANT TO NOTE Manufacturers of fittings such as taps, mixers, shower heads, and flush valves, usually publish the expected flow rate and performance of their fittings at various www.plumbingafrica.co.za 77 dynamic pressures, or the minimum dynamic pressure at which they will render adequate performance. WHAT DOES SANS SAY? The flow rate required for different terminal fittings to work effectively is specified by the re levant equipment manufacturer. If this information is not available, a general guideline is given within SANS 10252-1: 2004 (table 3 section 4.2.2.) In these tables you will see that there are three different flow rates given; that is likely maximum flow rate, likely minimum flow rate, and design flow rate per fitting. The design flow rate per fitting is usually used for calculations but must be checked against the manufacturer’s specification, if available. The minimum value of dynamic (flow) pressure required for a specific terminal fitting to perform properly is given by the equipment manufacturer. If such information is not available, then a general guideline is also given in SANS 10252:1 2004 section 4.2.2, but care must be taken to ensure that this information concurs with that given by the manufacturer, since many high-performance fittings available today require very specific values to work adequately. See Figure 3. Continued on page 79 >> October 2018 Volume 24 I Number 8