Closed Flow

• Characteristics of a system of piping and piping components that isolate the internal fluid pressure from the surrounding or external atmosphere principally by means of an air baffle fitted to the connected roof drain(s).

Note:  This refers to pressure flow in pipes. It is commonly known as pipe flow. The opposite of this is open channel flow.

• The flow of water in a conduit may be either open-channel flow or pipe flow. Open-channel flow must have a free surfaces whereas pipe flow has none, since the water must fill the whole conduit. A free surface is subject to atmospheric pressure. Pipe flow, being confined in a closed conduit, exerts no direct atmospheric pressure but hydraulic pressure only.

References

1. ASPE Standard 45 Siphonic Roof Drainage 2007
2. Open-channel Hydraulics, Chow