Hopper Heads
When I have asked architects what a hopper head is for, I get answers such as-:
“They are for ornamental effect.”
“So you can get more than one pipe to run in to one drain pipe.”
The above is true, but completely misses out on their true purpose. A hopper head fitted just below a gutter was the Victorian way of enabling their drain pipes in heavy rain to carry 66% more water. How I hear you cry? Water flowing from a gutter down a drain pipe only runs a third full. However, if you put a hopper head in the system with the outlet pipe from the gutter at least 100mm from the base of the hopper head in heavy rain fall the hopper head fills up with water and hey presto it becomes a syphonic system, causing the drain pipe to run full of water.
Source: Mr Alex Paterson – Accessed 31/03/16 [http://www.gutter.co.uk/index.php/what-we-have-forgotten-about-victorian-gutters-and-drain-pipes/]