TECHNICAL
79
<< Continued from page 77
From the example information given in Figure 3, it
can be seen that the flush valve needs a minimum of
150kPa dynamic (flow) pressure and a flow rate of 65
litres a minute to perform properly.
It is important then that we understand the interrelationship
between dynamic pressure and flowrate.
The higher the flowrate for a given pipe size the greater
the friction loss, therefore the lower the dynamic pressure
available at the end of the pipe run and vice versa.
PRACTICAL APPLICATION
The understanding of the difference between static and
dynamic (flow) pressure will equip us to:
• Ensure that we take care to measure or evaluate
the available static pressure for an installation
and then take care that there will be sufficient
dynamic pressure at the required flowrate at
terminal fittings so that they work properly and
that we have a satisfied customer.
• To perform diagnostics on installations.
By using a pressure gauge, we are able to
compare the static pressure to the dynamic
pressure. The difference between the two can
tell many stories and can often lead us to a
problematic blockage in a system such as a
clogged line strainer for example.
• Understand why a pressure control valve
serving a SANS 10254 geyser installation
cannot be installed too far away from the
geyser and then scratch our heads as to why
the balanced hot and cold water installation
is not yielding suitable user comfort to the
client’s satisfaction.
www.plumbingafrica.co.za
•
•
•
Understand why we must be careful in our pipe size
and material selections.
To advise our clients with regard to the selection of
terminal fittings so we don’t stand there speechless
while Mrs Jones yells at us that it takes 20 minutes
to fill the bath.
To understand the beginning principles of pipe size
selections.
Figure 3: An example
of manufacturer’s
information.
In the next edition, we will discuss water velocity and the pitfalls
of high water velocities in systems and how to determine the
expected flow rate (flow demand) for an installation, after which
we will be looking at how to size pipes.
The best plumbers never stop learning. PA
October 2018 Volume 24 I Number 8