Re: Basement flooding even after new check valve installed...
Posted by KOCTEP on 2017/5/12 15:51:05
A bit presumptions, but mostly correct.
See we all don't leave on the same elevation level. Some of us have parlor level where others have basement floors.
If you never seen fountains of raw sewage spring up 2' from basins, I invite you tomorrow to Center Street where you will see it for yourself (we will have 2" of cumulative precipitations) Do I need you to explain physics to calculate force needed to create 24" fountain?
It is quite to possible for sewers situated in low laying areas to have back-pressure of 5 or even 10 psi. Our beloved standard 4" PVC fittings are rated to 5.5 psi. If one doesn't have a check-valve expect to see sewage at the nearest maintenance port. If you have more than 153" of water column, you can see your own sh.. regardless your check-valve situation.
And I'll add a bit more: It's all about the weight of water in a column. Let's say your vertical sewer drain pipe (or gutter downspout) is 4" in inside diameter. That means that for every foot of vertical rise there is a weight of 5.45 pounds. Now flush a toilet on the ground floor (above a basement) and you're draining about 10 feet down to the sewer line out to the street. Call it 55 pounds of pressure. Ain't no way, NEVER, the main sewer line is even remotely close to that pressure. Your check valve will happily pass it through-
SCIENCE!! Years ago I had a discussion with another sewer warrior who said the water came in with thousands of pounds of pressure. I gently tried to explain to him water pressure is roughly 0.5 psi per ft of column height. He refused, at length, to believe me. "But there's thousands of gallons out there!!" 10 ft down in the ocean is still only 5 psi.
This also is why it's perfectly ok to pump your basement back into the sewer pipe. It makes no difference to the sewer, the water will end up there either way if you pump it to the street where it runs into the sewer. But your pump will be more efficient only pumping exactly the pressure head needed to get to the flooded sewer water level, rather than to the street.
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