TDH - Complex Rising Main
TDH - Complex Rising Main
(OP)
Profile attached.
I want to check the pump total head.
Should I average the
minimum head = 143.4-140.5 + total pipe flow friction losses
and
maximum head = ((154.4-144.4)+(149.0-147.0)+(149.0-148.5) + total pipe flow friction losses)?
Or simply TDH = 154.4 - 143.4 + pipe flow friction losses from this line.
Thanks!
I want to check the pump total head.
Should I average the
minimum head = 143.4-140.5 + total pipe flow friction losses
and
maximum head = ((154.4-144.4)+(149.0-147.0)+(149.0-148.5) + total pipe flow friction losses)?
Or simply TDH = 154.4 - 143.4 + pipe flow friction losses from this line.
Thanks!





RE: TDH - Complex Rising Main
RE: TDH - Complex Rising Main
The pipe friction loss on the other hand should be such that it allows the pressure in the pipe to be above atmospheric pressure at all times. Otherwise the fluid will pull a vacuum on the outlet leg. Also if you have no valve on the outlet and stop pumping, the pipe will self drain to a certian extent.
Draw your results on a graph ( see attached) and if you have or need a back pressure on the end point include that in your calcualtion and just add it to the line friction to obtain your required pump head above the start point.
Remember pump head as shown on apump curve / data sheet is actually differential head so if you have positive pressure or head on the suction of the pump this needs to be subtracted from the required pump discharge head to get the "pump differential head". Sorry if this is obvious.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
With an air valve on the top of the hill (154.4).
Static head calculated with the stop water level.
Adding losses from the aspiration line to the discharge line.
I'm not sure I get things straight.
Geometric Head = 11 meters (154.4-143.4)?
Friction losses = Total length of the pipe
RE: TDH - Complex Rising Main
Providing your friction losses are more than about 12m for the entire line, then forget about the first high point.
However if all you are doing is pumping the water up to the top of the first hill (i.e total friction losses less than 10m), the all your pump needs to do is 10m plus friction losses in the first 193m.
I ask again - what are your calculated friction losses (m/100m) or total and then I can draw the head loss onto your profile and tell you a bit more.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
For a peak flow of 35 L/s, I get 18.8 meters of losses (150 mm CHW = 150 length = 883 m + EK = 3.0 for bends and valve).
Losses = 1.8 m in the aspiration line.
I was thinking that for 35 L/s, the TDH would be 34.4 m (1.8 + 18.8 + 13.9)
You seem to tell me that Geometric head is not 11 meter (water level to the hill) but rather... 3.1 m.
RE: TDH - Complex Rising Main
13.9 m (sum of all the hills)
11 m
3.1 m
or even 1.1 m
RE: TDH - Complex Rising Main
3.1but 2.9)(
1.1but 0.9)RE: TDH - Complex Rising Main
Pressure at each points.
RE: TDH - Complex Rising Main
See attached graph.
Your problem is that because you have an open end, there isn't sufficient back pressure in your pipe to keep the pipe full of liquid past the 149m high point at kp 723m. This point now effectively become the end of your pipe for hydraulic purposes as the flow will be gravity from that point onwards and try anf low faster than the incoming flow (called slack flow). Thus moving back from that high point with your calcualted losses, your pump discharge head to do your flow is 168m-144.4m = 24m assuming that your pump is at the 144.4 m level - the yellow line.
Forget all about the other head losses and concentrate on friction only, plus the high point at the end of the pipeline which actually defines your hydraulic end point, hence static head is actually 149 - 144.4 plus friction of say 18 allowing for the reduced length = 23m - essentially the same as the graphical solution ( I added 1m for graphical purposes).
What you seem to neglect is that for a pipe which is filled with liquid and kept above 0 barg at all times, whilst there is effort to move the liquid up the hill, this is balanced by gravity helping it down the hill on the far side. Think of this as continuous train of trucks for the entire length all joined together. Once you've got trucks from one end to the other then the ones going down the hill will help to pull those going up the hill. The problem you have is that at the 149m mark, the trucks become detached and run down the hill under their own volition, faster than the trucks being pushed along. Thus gaps start to appear between the trucks.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
It'll be able to get over the hillpoint (154.4 m).
(?)
RE: TDH - Complex Rising Main
You will get pressure below 15 psia in the section beyond the last high point, so it might not be smooth flow going into the manhole at the end point.
You will be able to get over all the hills.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
It has a 34 L/s pump with a TDH of .. 17 m.
I was tempted to put a pump with a TDH of 31.4 m to avoid getting pressure below atmospheric in the system.
Could be more $.
Thanks for your time.
RE: TDH - Complex Rising Main
My conclusion is that it doens't pass 34 L/s now with a 17 meter pump.
RE: TDH - Complex Rising Main
There are fine margins so one or two metres either way will make a big difference, e.g. is the high point measurement the pipe or ground level?. The head at the high point could easily be-2 to -3 m and hence drag down the requited head at the inlet. Friction losses are notoriously conservative so you could easily get close to your flow with a 17m pump.
It's just not the best way to do it.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
RE: TDH - Complex Rising Main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
No flow recorded for that small pump station.
It's probably not dramatic though as you say (pumping more often).
RE: TDH - Complex Rising Main
Is it important to maintain pressure above 0 PSI in the system? I wouldn't take the risk to rely on the siphon effect...
I'm thinking about maintaining it above 14.7 PSI.
RE: TDH - Complex Rising Main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
http://www.eng-tips.com/search.cfm?pid=161&act...
RE: TDH - Complex Rising Main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
I wanted to change that design to allow the pressure to be above atmospheric all the way. To do so, I have to increase the TDH (pump) though.
I'm gonna do a drop test next week to see what this pump can discharge (with the air valve closed/on).
RE: TDH - Complex Rising Main
RE: TDH - Complex Rising Main
LI
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
http://www.grundfos.com/content/dam/Global%20Site/...
RE: TDH - Complex Rising Main
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
RE: TDH - Complex Rising Main
See that there's alot of posts about similar issue.
RE: TDH - Complex Rising Main
15.1 L/s.
Putting it in my calculation sheet : TDH = 15 m.
The pump was supposed to be 36 L/s with TDH of 17 m.
RE: TDH - Complex Rising Main
I'm a bit confused about this now...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: TDH - Complex Rising Main
I'm not really surprised as I need at least a 24 m pump to pump 34 L/s.
Simulating it to keep the discharge line above atm. pressure, I need more than 28 m at the pump to pump 34 L/s.
What I don't know is what will happen if I put a 34 L/s - TDH 28 m in that wet well.