KOCTEP wrote:
If you have more than 153" of water column, you can see your own sh.. regardless your check-valve situation.

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.

brewster wrote:
Quote:

jcneighbor wrote:
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.

jcneighbor wrote:
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-

brewster wrote:
Just to clarify with a little physics, water seeks its own level. When your upstairs neighbor flushes, the level in the drainpipe will not rise above the level of the street sewer, it WILL drain, even if you have a check valve. If that sewer level is above your basement toilet or sink, then you have problems already, but they can become shittier.

As for BK, the trendy areas around Park Slope are on relatively high ground.

mfadam wrote:
Do the low lying areas in Brooklyn have similar problems with basement flooding? I'm assuming they have same old sewage infrastructure that NO politician ever upgraded...

It is kinda crazy to think about what DTJC accepts as "part of the deal". I agree that when taxes are 20-40K depending on rowhouse value there will be a lot more pressure on City Hall to get us out of the third world...

HPYC wrote:
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iabide wrote:
One other potential source of flooding: when the sewers are full & your check valve is up, there's nowhere for the storm water from your roof to exit your building. (I'm assuming here you don't route your storm water directly out the alley or the front). I've had this issue from places where a high water table couldn't possibly be the culprit.

Totally agree. Other sources when the check valve is closed include waste water from inside the building (especially if there are multiple units in it), and sump pump discharge. When the city sewer is full and pressurized, there is nowhere for this water to go except backward, where it looks for the path of least resistance - which could be a floor drain, toilet, tub or any other opening in the line between you and the sewer. Tell your upstairs neighbors not to flush when it's raining ;)

iabide wrote:
One other potential source of flooding: when the sewers are full & your check valve is up, there's nowhere for the storm water from your roof to exit your building. (I'm assuming here you don't route your storm water directly out the alley or the front). I've had this issue from places where a high water table couldn't possibly be the culprit.

mfadam wrote:
Ugh. There is a square cut out of the concrete slab to access the main where they put in check valve and you can see dirt/ground all around the pipe. If that were to be filled in with concrete we would have less sewer overflow getting into the basement but would have to cut it open again should the pipe or check valve need work.