sharkeeper
Lifer
- Jan 13, 2001
- 10,886
- 2
- 0
What I meant was if the supply was connected to the drains, the drains would immediately be filled with fresh water, since it is pressurized.
You do understand this, right?
Backflow preventers are to prvent supply side (pressure) water from flowing back from an open spigot, like an irrigation system or a garden hose, back int the system. NOT to keep waste water out.
Your example of the closed loop being tapped into is a better analogy...
Graywater can enter the system if the fixtures inlet pipe is below the basin and there is a sudden drop in pressure that causes the water to siphon back into the supply. This is why modern sinks have the openings higher than the water can ever get.
Backflow preventers aren't normally used in single family dwellings except for the small garden hose varieties that people SHOULD be using when filling a swimming pool, for example.
In multiple unit complexes, they must be used. Make up systems in commercial establishments for boilers and cooling towers, for example must have functioning backflow preventers. I did an inspection once where I noticed the water in the toilet bowls behind a mess hall was pink. Turns out the supply for these heads came from a line that was tapped for the chilled water make up. The chilled water loop runs at 45 psig and is heavily treated with ROCO 4018. The backflow preventer was damaged and anytime the potable water dropped to <45 psig this allowed treated system water to enter the potable system! This is pretty scary since that water is used for a lot of things in the galley!
And yes, if a drain was tied into the supply, fresh water would flow freely down the drains due to the positive (supply) pressure. The example of piss in the shower (which is something people should refrain from IMO) is rather extreme since it's remote that that drainwater would cross over to fresh but it's not impossible.
Cheers!
