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Nathan vs. Sump Pump Vapor Lock: How I Could Have Kept My Basement From Flooding With a Drill Bit

Carefully placing a hole in the discharge pipe from a sump pump avoids vapor lock. Doing so 5 years ago would have saved me thousands of dollars, avoided damage to my finished basement, avoided multiple visits from a plumber, and saved me tons of stress. Since drilling the hole there has been no vapor lock and there has been no flooding. But unfortunately I didn’t know what to search for. I didn’t know about vapor lock.

Some background: Just about everyone I know in St. Louis has problems with water coming into their basement. We’re no exception. Shortly after we moved in, we had a heavy rain and our sump pump overflowed, soaking the carpet in the basement. We assumed a power outage was to blame. It happened several more times, the walls and carpets were a moldy wreck, so we finally gave up and ripped everything out. After a long drawn-out battle with our insurance company - proving that they mistakenly gave us “volcano coverage” instead of “basement coverage” - we finally got the 5 grand to refinish the basement. (Aside: how much you wanna bet it was a shitty policy setup interface that caused the agent to make that mistake. Reject flood insurance in Missouri? But take volcano? Gimme a break.)

Then it happened again. We knew it wasn’t due to a power outage because we were in the basement at the time, and we watched as the sump pump made noise while water came flowing out of the pit. Next we assumed it was clogged in the pipes leading to the street. We spent a weekend digging up the pipes. We even put in two backup valves close to the house, so water wouldn’t get pushed back in. But the flooding continued.

You would think I would find something on Google, but the bitch of it was not knowing what to look for. It’s amazing how easy it is to find something once you know the key phrase. In this case, the phrase was vapor lock. In the pipe leading from the sump pump is a check valve that prevents water from coming back down. So when the pump stops, the valve shuts. The problem is a vacuum is created in this process, which prevents the valve from opening again. Water can’t get pumped out, the pump makes noise like it is working just fine, but the water backs up and your basement gets flooded.

The solution to sump pump vapor lock is very simple. All you need to do is drill a hole in the pipe, between the sump pump and the backup valve. When the water is being pumped out, it goes right by the hole. Then when the pump stops, the water left in the pipe shoots out as the pressure is relieved. There probably is a “nicer” solution, but that fact that you can solve the vapor lock problem while your basement is flooding is super-cool.

On our particular setup, the valve is a couple of inches above the top of the pit. So I drilled a small hole between the pump and the valve. The mistake that I made, which you should avoid, is placing the hole too close to the top of the pit. My hole was even angled such that water shoots up over the edge of the pit - as if the pipe was taking a whaz. So I have to make sure the cover is on to deflect the water into the pit. When you do this, make sure the hole is down an inch or two from the top, and angled downward.

In conclusion I am happy to report that our basement has not flooded since.

P.S. Here’s the site that saved the day for me: Sump Pump Installation on pumps-in-stock.com.
P.S.S. I have no idea why the 2 plumbers that visited replaced my sump pump, didn’t check for a hole, and didn’t even mention it. For shame.

© 2009 Nathan Verrill.