Force Main inspection/cleaning 1

[skier59]

Hello all. Our client has a 10-inch force main that appears to have too much friction for the length of pipe and flows involved. Our calculations show discharge head should be about 5 feet, yet gauge measurements show 22 feet. Flow is about 400 gpm, and the pump is operating on its curve. The pipeline has 45 and 90 degree bends, a gate valve, and a swing check valve before its discharge into another 12-inch diameter force main. I haven't seen the as-built drawings yet, but I'd be surprised if pig launch and recovery are included in the design. Possible suspects we've considered are: (1) faulty air release valve in the pump station (the extra head is suspiciously close to the vertical pipe drop within the pump station), (2) solids accumulation in the pipeline, and (3) construction debris in the pipeline. What options are available for troubleshooting and cleaning this pipeline?

 

[StephenA]

Several things spring to mind.

How long is the pipeline?

The velocity is below the normal self cleaning velocity of 1 metre/second. Can you increase the velocity to achieve self cleaning?

Is there a back pressure from the 12" pressure main causing an increase. i.e. what is the static head?

Can the line be isolated?

Having said that I would check the air valve first, then try increasing flow rate (if the pipe will take the pressure and then look at using a camera (if it will go through the bends).

Other possibilities are A To split the line into 2 lengths and measure pressure in each half to narrow the problem area down and B try a pig if you can load one.

Stephen A

 

[Maury]

I agree with Stephen's suggestions. Make sure that the head calcultions take into account the downstream conditions. Then check the air release valve and the check valve. Debris could be caught on the flap and obstructing flow or preventing it from opening fully. After that, install taps along the line to try to narrow in on the problem.

 

[dicksewerrat]

Once you get to the point of shut down and look, I'd look at the check valve first. You may be able to take out the flap without taking the entire main apart. Put the valve back together without the flap. See what happens. My guess is the valve has NEVER been maintained. And the line has to be cleaned anyway. So bypass pump and take out the bends and either pig the line or send a jet through it.

 

[cvg]

I agree, check valves can easily get plugged. Have you also checked to make sure the gate valve is fully opened?