Hello,
I'm designing a waste water treatment system, as part of it we'll be gravity draining water from the bottom of a tank, to a pit that's several feet below it. The line that goes from the bottom of the tank to the pit exits subsurface (below water) in the pit, and will have a few 3/8" anti-siphon holes drilled just above the water level in the pit. The line also has a high point / trap that goes above the bottom of the tank to keep a level in the tank at all times.
I've attached a file that shows a rough drawing of the system.
We start out with ΔH1 -- the level of the water in the tank that's above the high point in the drain piping. I would think worst case that level in the tank would drop down until ΔH1=0 and no further. Worst case if there's some type of vacuum in the drian line, there are anti-siphon holes down towards the pit that would take in air and break the vacuum. (ΔH1=5 ft at start on page 1, ΔH1=0 ft final on page 2)
One of my colleagues is telling me that that this high point / trap design, and the anti-siphon holes won't prevent the tank from draining and that we need an air-intake to break vacuum in the line and prevent the tank from being sucked out to the pit. (this design shown on page 2)
I don't believe this is the case, but I don't know how to prove it.
I would prefer not to install this air-intake piping as worst case it would be a leak point if we get excessive pressures in the tank which is a closed vessel and worst case could run liquid full.
Can anyone help me wrap my head around this, or advise whether the existing design of trap piping plus anti-siphon holes will prevent vacuum and complete draining of the tank?
Attached Files
Edited by CH3CH2OH, 08 October 2019 - 11:39 AM.