Water Distribution

Hydraulic Design

Sizing CPVC Pipe

A FlowGuard Gold® piping system will use the same size pipe that a copper system would for a typical residential installation. For systems using larger sizes, design should be based on fixture demand rates. A FlowGuard Gold system, unlike systems utilizing insert fittings for joining the pipe, offers full-bore flow. This results in significantly reduced head loss.

Design Velocity

The process for establishing a limiting or maximum flow velocity that is applicable to any piping material is not well defined. For some materials, there may be velocities that can create abrasion or erosion, but there is no evidence that this occurs with CPVC piping under any known operating conditions. An investigation of some CPVC systems revealed that velocities of 7 to 17 feet per second could be developed under maximum flow conditions.

A maximum design velocity of 10 feet per second is typically utilized for both hot water and cold water CTS CPVC systems (½” through 2”) and for IPS CPVC hot and cold water distribution systems 4” and smaller. A design velocity of 5 feet per second is typically used for IPS CPVC water distribution systems larger than 4”. This design velocity is based on both field experience and laboratory investigation. The CPVC design velocity is different from copper, which has a recommended maximum design velocity of 5 feet per second for hot water and 8 feet per second for cold water.

The system should be designed and installed utilizing good engineering practices. To avoid water hammer, quick closing valves are not recommended on 2” to 4” IPS water mains when the velocity exceeds 5 ft/sec. It is acceptable to have quick closing valves on the smaller branch lines.

Hazen-William C Factor

Hydraulic calculations for sizing of FlowGuard Gold pipe and fittings should be calculated using a Hazen-William C Factor of 150. While both copper and CPVC use a C Factor of 150 for new systems, as copper ages, the ID of the pipe is subject to pitting and scaling causing pressure loss to increase over time. Since a FlowGuard Gold system is not subject to pitting or scaling, the C Factor will remain constant as the system ages.

Head-Loss Characteristics - Pipe

The flow characteristics of water flowing through piping systems are affected by several factors including system configuration, pipe size and length, friction at the pipe and fitting surfaces, etc. These and other factors cause a reduction in pressure (head-loss, also expressed as pressure drop) over the length of the system. This section deals only with the head-losses that result from frictional forces in the various sizes of CPVC pipe and fittings.
The following formulas were used to calculate water velocities, head-losses and pressure drops as function of flow rates. The results are given in Tables 7 thru 10. Head-loss as a function of water velocity has also been calculated and can be found in Tables 11 thru 14. The Hazen-William formula can be used to adequately describe these losses:

H_L = Frictional head loss (feet of water per 100 feet)
C = Hazen-William factor (150 for CPVC)
F_R = Flow rate (gal/min.)
d_I = Inside diameter of pipe (inches)
V_W = Velocity of water (feet/second)
One foot of water = 0.4335 psi