Back Pressure Issues in Pipeline (pulsing/vibrations)

[buddabeast]

Hi guys, this is my first post in this forum.
I am an operator at a Water Treatment plant and have been offered my first project so want to do a good job.
Poly electrolyte is pumped into a centrifuge to thicken the sludge inside and help dewatering. The poly is plumbed into the sludge input pipeline.
Twice a day we need to flush the centrifuge with water which flow flows through the sludge feed line. When this happens the water also flows back through the pipeline where the poly is pumped from.
The flush water makes it all the way back to the discharge of the poly pump and causes a lot of pulsing of the small <1" plastic pipework. This causes leaks around the discharge valve and isn't good for the pipework in general. There is a rubber section installed to help damped the pulses but it is only held on with hose clips so it leaks there too.
I would like to stop this flow of water going back into the poly dose line. A nsimple non-return may work but may just change the area of pressure buildup.
Maybe a flanged rubber section intead of the rubebr hose may be a good idea also. Or some typoe of pressure relief valve. There is a sustaining valve already on the poly discharge side, but it doesn't work.
Please say if you would like me to draw a diagram to make things clearer.
Anyone got any ideas??

Thanks,
Heath

 

[zdas04]

A diagram or photograph (or both) would help.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[bimr]

I assume that you have a polymer injection/mixing ring which is used to inject polymer into the sludge line. All you have to do is to install a block valve in the polymer line near the injection ring to prevent the water from backflowing through the polymer line. Shut the valve when you plan to backflush.

Do you have a polymer wetting system where you are mixing the liquid polymer and water?

Another option is to install a new water line and inject the water near the centrifuge. In this alternative, you may install a plug valve in the sludge pipe. The valve (when closed) would prevent water from backflowing into the sludge pipe.

A schematic would be helpful.

 

[buddabeast]

Hopefully this helps. We don't carry water for our poly. As it's consistency as it's batched is OK. But it is rigged so carry water can be used this is dosed into the poly line just before it meets the sludge feed line.

 

[buddabeast]

Woops that pdf isn't much good. Here's another

 

[bimr]

It looks like a very crude system.

Polymer is usally mixed with water so that the polymer can be used more economically. The injector/mixing ring is used for the same purpose.

Are you shutting the polymer system pump down when you wash out the sludge pipe? If not, that may be the problem.

You need to add a block valve on the polymer line prior to where the polymer line enters the sludge pipe. Shut the block valve when you want to wash out the sludge pipe.

If you install the block valve, consider adding a relief valve in case someone turns on the polymer pump when the block valve is inadvertently left closed.

 

[buddabeast]

Yeah good idea bimr, as forgetfullness is something I need to take into account. We don't currently turn off the poly pump as operators don't seem to be trusted to turn it on again. The polymer is batched from a hopper into a tank, 25kg bag to 10 000L water to achieve 0.25% solution. That solution is taken from the bulk tank to the dose tank and is what is pumped into the centrifuge. But carrywater can be used to help but I have never seen it in use. I think a valve to stop it back flowing into the poly line and turning the pump off sounds like the most simplistic idea. We don't need poly for flushing of course.
Maybe a non-return valve so we don't need to climb up and close it ourselves.

 

[buddabeast]

I forgot to mention turning the poly pump off trips the centrifuge. Maybe a bypass would work so that the poly pump pumps back to the dose tank.

 

[bimr]

A check valve would work with your setup. Add a relief valve that will relieve back to the polymer suction tank when the backflush is occuring.