Re: Basement flooding even after new check valve installed...

Posted by jcneighbor on 2017/5/12 17:51:53

iabide wrote:
Science is fun!!!

On that note, as KOCTEP hints, if the back-up in your "house" water (rain + flushes) is higher than whatever the sewer system is seeking, it will find that level somewhere in your house. As a downtown resident, I sometimes get the feeling that level is somewhere halfway between me and the Heights during the intense storms like Friday's.

Also, all this assumes static water pressure; dynamic pressure from movement on the city side may affect check valve functionality at near-neutral pressure, depending on which kind of check valve you may have. Finally, the house water can absolutely accumulate in your pipes (like roof water from Friday's intense dump) faster than it can equalize with where ever the sewer system's "level" may be (1/2 way up to the Heights?) ...thus, again, encouraging it to "level" in your house. To paraphrase Keynes, the pipes can remain out-of-level longer than my floor can remain dry.

Also, jcneighbor: a gentle suggestion to go easy on the snark. Your description of fluid dynamics is incorrect. Static water pressure is not a function of the volume of water, just elevation. A 6" swimming pool of water draining through a straw exerts the same amount of pressure as a 6" test tube at the same elevation draining through a straw of equal diameter. Even if the swimming pool weighs much, much more.

If my science is off, please do let me know. I would appreciate being corrected.

Thanks for the chat everyone and have a safe, dry weekend.

Oh boy, I knew this wouldn't go away easily...

As both Brewster and I already observed, volume has nothing to do with it. You're correcting me for something 2 of us already stated?? I fully understand the different influences of static vs. dynamic pressure, and the fact that "relative" pressure is the issue here. If the pressure in your house pipes is greater that the pressure in the sewer system it will drain. And I also observed that the diameter of any vertical pipe determines what the pressure is at the bottom of that column, measured in pounds per foot of vertical rise. Here's the table:

As far as KOCTEP is concerned, a 2" pipe shooting 2' high means that 1) he/she doesn't have a check valve and lives in a very low lying area and 2) a 2" diameter pipe is 3.14 square inches and that would require a pressure of roughly 6.7 PSI to generate that amount of lift. So if you're crazy-enough to live in a low area without a check valve and the street pipes get under pressure (as they always will in those deluges) which exceeds the pressure of the water in the pipes in the house then yes, you will flood. There's a reason why most people don't put toilets or sinks 5' above the sewer line...

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