Siphonic Roof Drains 





ASME A112.6.9


The ASME Standard establishes minimum requirements and provides guidelines for the proper design, installation, examination, and testing of siphonic roof drains. It includes definitions of terms and parameters involved in the proper design of siphonic drainage systems. This Standard applies to roof drains designed, manufactured, and installed in piping systems that are intended to operate under depressurized siphonic conditions created by the connected piping system and create a full-bore flow: the flow of water in a pipe where theoretically 100% of the cross-section of the pipe bore is filled. In practical terms, full-bore flow is regarded as achieved at water content greater than 95% by volume. This Standard includes test procedures to be performed on siphonic roof drain products to document their actual performance and physical limits. These data are to be made available in manufacturer literature for use by designers for selecting the drain product and entering performance characteristics into design calculations.

Manufacturers of siphonic roof drains may utilize existing conventional drain body designs with an air baffle adapter to achieve siphonic capability when connected to a properly engineered siphonic drainage piping system.

The design of any air baffle and drain follows three main principles:



It shall be able to prime the test standpipe quickly. Thus, the height of the baffle above the sump bowl should be minimized. This will help achieve a high Reynolds Number beneath the baffle and the necessary turbulence for proper air to water mixing during priming.



The baffle shall not introduce a limiting effect with respect to maximum flow. In other words, the drain shall be limited in maximum flow capacity by the fixed spigot drain diameter and not by the introduction of a baffle.



The first two goals must be balanced with the desire to have a minimum of water depth on the roof above the baffle, which means that the resistance of the baffle/drain/strainer combination should be minimized.






Jay R Smith Mfg. Co.


Mifab Inc.


Wade Specification Drainage Products


Zurn Industries, Inc.