Forcemain Surges at Effluent Point

[howertoneng]

I have a 8 inch force main (from a pump station about 1 mile away) that discharges into the effluent channel in a treatment plant. WE have a problem where when it the pumps stations are running, sewereage spew into the air, several feet high, (up to 10 to 12 feet), splatters, if you are anywhere near this discharge point, you will get wet!

This occurrs in a pulsating form, one big surge, a couple of seconds later, another surge, so on..until pumps kick off.

What could be causing the pump station/force main to cause this?

 

[cvg]

sounds like air in the line

 

[bimr]

Sounds like your effluent pipe is draining between pumping events, allowing air to enter the pipe. If this is the case, you might investigate methods to prevent this from happening and keep the pipe full of liquid.

 

[howertoneng]

This is a wet well mounted pump station, pumps are mounted on top of the wet well, there are two stem pipes that extend down into the wet well. After the pumps shut off, should the sewerage in the lift pipes stay in "suction" or should it drain back out? If they drain back out, and the pumps kick back on, could this be where the air is getting into the system?

 

[bimr]

It is possible, although the amount of air that you are describing seem to be much greater than the amount of air in the pump suction.

Is it possible that the suction pipe has a leak allowing air to enter the pump suction?

DO you have an air release valve?

Perhaps a detailed description of your system would make sense.

 

[howertoneng]

thanks, i will check on the suction pipe.
i do not think that the line has a air-release.
will advise, tia

 

[onyeuko]

It is better that the sewerage in the lift pipes stay in "suction" than drain back out into the well as this will create a contineous column of water that will not give room to air column formation(under normal working conditions)The problem is most likely to be an air column problem but check also if you have blockage along the pipe (somewhere close to where the splattering is occuring).
Teddy

 

[Fazmataz]

Also check the profile of your force main. If there are severe dips in it, that may be the cause.

 

[CivEnvEng98]

I'd like to know what the pump pressure gages read during static conditions and when one and/or both of the pumps kick on.

Could you give that info?

 

[howertoneng]

fyi: we have performed some additional investiagations, here is what we have found. 1. this wet well mounted station has a vacuum pump that lifts the column and diplaces the air in the stem pipe. according to manufacturer, it should only run a couple of seconds, because their should only be a minisual amount of air in the stem pipe. It is running for like 30 seconds, whihc tells us the entire stem pipe is draining after pump kick off. We pretty sure the check valve is not holding the stem pipes in suction. We are looking to replace the check valve. Also the forcemain has a 2 to 3 high points, where we may have air pockets in tbe line. We are planning on installing air releases in these locations. For whatever reason the original engineer did not design air releases in the forcemain. We report back later. TIA.

 

[redbridge]

What is the difference in elevation from the high point to the effluent discharge point? If the discharge point is lower than the high point then the velocity of the sewer will increase significantly. In this case you would need air in the line to keep the line from colapsing. The high velocity would cause the surges.