Backflow Prevention valve install problem

[Canada Bob]

Recently had a sewer backup in our basement and wanted to install backflow prevention valve (regular Home Depot special....put it in drain, tighten screws to expand rubber gasket and voila!)

However, my floor drain (4" clay pipe) has another small rubber 'hose' which feeds into it from just below the concrete floor. I am told this hose feeds water into the trap to keep sewer gases from getting into the house.

My problem is that I cannot install the backflow preventer because the little hose prevents a uniform seal between the valve and the edge of the drain. Is there an alternative method, device that I can use on this drain opening (without major cost/tearing up the floor)?

[Speedy Jim]

Well, get rid of the little hose and seal the opening with cement/caulk/whatever.

----------------------------- A word of caution: Clay pipe joints leak! Yes.

Normally, this isn't a problem as the flow is confined within the bell/hub joints and under no pressure to speak of.

Now, during a backup in the city sewer, you might have pressure in the clay pipe the order of ~3psi. That is the equivalent of only 6 feet of head.

With the backflow preventer in place, that 3psi may force water out of every joint under the floor. The water pressure then attempts to lift the concrete floor. Huh? Can't happen. Right? Can and does.

Take a floor area of 10 ft X 10 ft as an easy example. With sewer water under the whole area pushing upward.

10 X 10 is 14,400 square inches!

3 pounds per SQUARE INCH pressure results in:

43,000 pounds of force pushing the slab up!!

I've actually seen the results of this many times. Sometimes the *whole* floor doesn't give way, just parts of it heave. Or maybe the clay joints only leak in part of the floor, or maybe the ground can absorb some of the leakage, or maybe it's only

2 feet of head (1psi) and only 14,000 pounds.

But be aware that bad things can happen...

True "backwater" valves are installed before the sewer enters the house so that the above can't happen.

Jim