Rising main
Rising main
(OP)
Im am having an argumentation with a colleague about 2 options for a discharge line.
Option 1 = actual design (discharge line ending up at the hill point, then gravitary).
Option 2 = design modified (discharge line ending up to the downstream point).
He's pretending that the pumping flow rate would be higher with option 2 than it was with option 1 (using the designed pump for option 1).
I think that he's taking in account a vacuum effect that would form after the hill point. How could the flow rate be higher in option 2 than 1 using the same pump?!
Option 1 = actual design (discharge line ending up at the hill point, then gravitary).
Option 2 = design modified (discharge line ending up to the downstream point).
He's pretending that the pumping flow rate would be higher with option 2 than it was with option 1 (using the designed pump for option 1).
I think that he's taking in account a vacuum effect that would form after the hill point. How could the flow rate be higher in option 2 than 1 using the same pump?!





RE: Rising main
The hydraulic gradient from pumping station to outlet at 145.75 m is the key. If this is less than the hydraulic gradient from discharge point to outlet option 2 ( red dashed line) then it may be slightly more flow because the pressure at the high point would be below atmospheric and hence get you a little bit more flow.
However if the opposite is true (blue dashed line)then you will get less flow because there is a higher total resistance.
Of course I could have misinterpreted the arrangement....
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Also: There's usually a good reason why everyone does it that way
RE: Rising main
RE: Rising main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
Pump to option 1 = 468 m of HDPE 150 mm
Pump to option 2 = 626 m of HDPE 150 mm (with an Air/Vacuum Valve).
Pump curve is attached.
RE: Rising main
You are then operating in slack flow conditions which can create problems, but for a 150mm PE pipe with an open end these are not important.
how much more flow is difficult to judge, because as flow increases your pump head decreases and any minor thing can have an important effect, but you could get maybe another 1-15% more flow, but as said, only if you delete the vacuum valve.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
RE: Rising main
many options, but your system is very sensitive to even small variance from predicted flow to real life. One metre extra or less head can make a lot of difference to the flow for your system - most systems are not that sensitive. If you want 16.9l/sec +/- 2% then you need to add some sort of variable control (pump speed or control valve)
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
Without knowing the details of your project, you typically have to pump at a higher velocity going downhill because of the velocity of the air bubbles that are moving backwards. Otherwise you will end up with an air bound pipe or two phase flow.
You don't have to worry about this if the flow is gravity as in Option 1 and you can pump at a lesser rate going uphill.
There is a discussion of this in Sanks' Pump Station Design.
http://www.amazon.com/Pumping-Station-Design-3rd-E...
RE: Rising main
So long as the line is full and assuming an NRV on the pump discharge, the pressure just d/s of the high point at rest should be about 5m absolute. This isn't enough to pull a vacuum, but some dissolved gas might come out. However on re-start this will just move along the line providing you don't have a vacuum relief valve at the top at which point some of the water will just flow away...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
With only 5 meters of elevation, the siphon effect should not make much difference on the pump unless the pipeline is very short.
You typically don't want a vacuum release unless the vacuum release is necessary to protect the pipe from collapsing. At 5 meters elevation, you do not need a vacuum release.
RE: Rising main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
The pump is already in order... I just didn't want to be too far from what we need (16,9 l/s) or we'll have to work with the water levels in the pumping station (start/stop).
RE: Rising main
As said, with such low heads, if you get within 10% of your calculated flow you're going to be doing quite well so if you need to control it more accurately once installed, include some sort of flow control at the pump end.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Rising main
The psi should be gage pressure. 14.7 psig.