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Old 10-07-2009, 03:15 PM   #1
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Huge bang when my sump pump stops

Please help, I am not a plumber but I have some basic knowledge.
moved into a new home this year; my water softener discharges into my sump pump basin, the sump pump works fine but when it stops there is a huge bang in the pipe that leads to the septic tank. I have 2" pipe coming from the pump, it has 2 90's in it (to get it close to the basement wall) then a check valve, it continues up to another 90 and then connects to the septic line - does this need to be vented? See the attachment.
thank you - this is driving my wife crazy- which means it's driving me crazy.
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File Type: pdf sump pump diagram.pdf (28.3 KB, 331 views)


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Old 10-08-2009, 06:19 AM   #2
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Huge bang when my sump pump stops

If all is installed correctly, there is a check valve in the outgoing pipe. If it is the metal(brass) type, it could be noisey when it closes after the pump shuts off. The plastic versions are generally quieter. And the higher the pipe from the check valve , the more force slamming it shut.


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Old 10-08-2009, 09:04 AM   #3
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Huge bang when my sump pump stops

I agree with Bill that it is the check valve "slamming' shut when the pump shuts off. The higher up the line you install the check valve, the more water will run back into the sump (when the pump shuts off) , but sometimes it is worth having this happen to avoid the noise.
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Old 10-08-2009, 02:19 PM   #4
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Huge bang when my sump pump stops

I agree it's likely the check valve but is there a chance that the pump torque is twisting the pipe slightly when it's running and when it shuts off the pipe is snapping back? Can you be down there when it shuts off and see where the noise comes from and if anything is moving?

I'm pretty sure the basin should be vented. I don't know if a vent is needed where it enters your main line.
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Old 10-08-2009, 05:05 PM   #5
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Huge bang when my sump pump stops

If I understand your post correctly, you have your sump pump connected to the septic tank. In my town, this would be a violation, but even if it isn't a violation, this sounds like a bad idea. When your water softener discharges, it is discharging salty water into the sump pit, which is then getting pumped into the septic system. Septic systems are designed to handle potable water and sewage, not salt water, so there is a risk you could kill the bacteria that make your septic system work, which could cost a lot of money to fix.

Generally, a sump pump discharges through a pipe to the low point on your property, or occasionally onto the street or into the street drainage system (only if permitted by your town). I have never seen a sump pump connected to a septic tank.

That said, the bang certainly sounds like water hammer, and the previous two posters probably hit the nail on the head. By the way, a backflow preventer may not be necessary, I used to have one in my sump pump system, however it was such a pain to maintain I removed it, and the system works better without it. In my case, there is not a great deal of water that flows back into the pit when the pump shuts off, so it is not a problem, however if you have a long run of pipe that is going to drain back into your pit, you will reduce the amount of work that the pump has to do by installing the backflow preventer.
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Old 10-09-2009, 09:57 AM   #6
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Huge bang when my sump pump stops

If he keeps his illegal hookup to the septic and removes the check valve he will get gasses from the septic.
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Old 10-10-2009, 12:24 AM   #7
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Huge bang when my sump pump stops

Agreed, it makes absolutely no sense to discharge a sump pump into a septic system. I'd spend the time and money to correct that in short order.

(just to be certain, we're not talking about a sewage ejector pump and not a sump pump are we?)
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Old 10-13-2009, 08:35 AM   #8
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Huge bang when my sump pump stops

The three houses I have had, had sumps, out of those 3, only one was pumped out to the yard. 1 was pumped into the septic tank and the current house has it pumped into the sewer. As for the the last 2, both were setup prior to my taking ownership. My current house has a duplicate discharge that is piped to the yard, yet they had another discharge plumbed into the main waste line. All I can figure is that they had a problem with the line out to the yard (horrible slope).

That being said, even a PVC check can make a ton of noise if the following are true:
-Pedestle pump
-flex tubing discharge
-minimal pump support.

My house had two of the 3 when I moved in (Ped pump, horrible support). I installed a submersible with heavy clear plastic tubing connected to the check and now it is very quiet. The ped pump is still there as backup.


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