The hydraulic character of a piping material, determined by the size and smoothness of its bore, enables it to
deliver water at sufficient pressures to overcome static head and operate fixtures, appliances and equipment.
When comparing two smooth-wall materials, such as copper and polypropylene, internal diameter becomes the
critical factor in evaluating hydraulic performance.
Table 1:
Comparison between 460/0 Copper tube (Cu) and Polypropylene tube (PP) showing area of bore,
percentage difference and flow rates.
Table 2:
Comparison of flow rate using the same pressure drop values for the same nominal tube size.
The pressure drop values used are the same as those for copper tube in Table 1.
Today there is a tendency to use pipes made from plastic-type materials. These pipes usually have
thicker walls than conventional copper tubes, so their internal diameters or bores are considerably
smaller. It is after all the bore of the pipe that is important when considering volumes, flow
rates and velocities and not the outside diameter of the pipe.
Just how much the bore does vary is clearly shown in the tables above. it is therefore very
important to note that one type of pipe cannot necessarily be directly substituted for another
even though they have the same outside diameter.
When using plastic pipes, it would be a good rule of thumb to install one nominal size larger
than would normally be specified in steel or copper.
Copper offers substantially greater bore areas than plastic for the same outer diameter of pipe.
Example as per illustration above: 22mm outer diameter copper pipe offers 60% greater bore area
than 22mm outer diameter plastic pipe.
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