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Suction pipe profile

Suction pipe profile

Suction pipe profile

(OP)
I have to design a pump that would transfer settled wastewater from one basin to another. The pump suction pipe is fairly long around 400 ft. Not only that, the ground profile between the basin (Suction side)and the pump station is irregular which means that the pump suction pipe may have several high and low points. The basin on the suction side will always have a steady water depth and the pump NPSH requirements are satisfied. My concern is the air accumulation at the high points. Is there a way to avoid locating air/vac valves on these high points and still get the hydraulics to work?


Thanks in advance.

RE: Suction pipe profile

Plot the profile. Post it.

it's too irregular for you to try to describe the problem, or for another reader to try to advise you while watching you wave your hands. 8<).

RE: Suction pipe profile

I know it's fairly obvious, but locate the pump closer to the first basin our use a submersible pump.

Assuming you can't do that for some reason, you will have difficulties. You don't say whether the pump is higher or lower than the basin liquid level.

Plot the profile to give us a chance of helping you.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Suction pipe profile

Also, if any of the high points are higher than the basin liquid level, how do you plan to fill the pipe? Please include pipe size and flow rate, velocity could be important.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Suction pipe profile

How do we get water up from a well? Fill with a self-priming pump. Put a check valve on the inlet and it might stay primed for awhile too.

If the velocity of the fluid in the pipe is high enough to sweep along the air pockets that form within, then they won't stay there in the suction will they. They will go along and be pulled into the pump. The water velocity in the pipe must be fast enough to sweep along the air bubbles that get pushed almost to the bottom of the next valley and then try to flow against the water current as they try to make their way back up to the top of the same hill they were just forced to cross over.

As a water bubble gets pushed downward, it's diameter decreases because the pressure increases and the buoyancy force driving it up decreases, so it actually gets easier to move forward as the bubble progresses down the hill and loses elevation. Pretty soon, there she goes, across the bottom of the valley and quickly up to the next hill. Repeat until reaching the pump.

Independent events are seldomly independent.

RE: Suction pipe profile

But only if the well is not very deep (say <8m). If the pressure in the suction line goes below the water vapour pressure then it will effectively pull a vacuum which is limited to about 0.1 bara. Hence we need a profile to see how high the high points are.

A great explaination of the issues though (*). 400 ft (120m) is quite a long way so implies quite a large pipe / low velocity so will be interesting to see the details, if they ever arrive. I'll shut up now and see what comes....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Suction pipe profile

Settled waste water basins are probably a bit less than 8 m deep, so there' probably some leeway there.

Independent events are seldomly independent.

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