Pump Discharging Pipe Length 5

[badr82]

Hi.....
We install a new booster pump (Lawara, 1.5 liter @ 200m head)in mountain area. The length from the booster to the end point is 6km and the discharge pipe is HDPE 63mm outside dia, 16 bar (SDR-11).
The problem was that, the water didn't reach the last point unless we set the discharging pressure @ 20bar.
What is problem??????

 

[badr82]

This is a sketch representing the booster pump

 

[BigInch]

What does the pump curve look like?

1.5 liters per what? Per minute, second, hour?

I think you might have bought a pump with the maximum head of 200 m, but at low or no flow. you need a pump with 200 meters head at 1.5 liters per whatever. Did you buy the right pump?

There may also be problems with air trapped in the line. You need to post a profile showing elevations at high and low points along the pipeline.



From "BigInch's Extremely simple theory of everything."

 

[bimr]

At a flow of 1.5 liters per sec, you have 77 meters of head loss due to fluid flow.

What is the elevation difference? 123 meters is not much elevation difference if you are in the mountains.

 

[Artisi]

The problem is probably friction loss and wrong pump selection.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[badr82]

Thanks for everybody replayed...
I have some questions may help me in this situation:
1-What is the proper way to calculate the friction loss (head loss)?
2-What is the proper pump in this case?
3-Do you advise me to increase the suction and discharging pipes size to avoid friction loss?
We installed air valves every 500 meters.

 

[BigInch]

1.) friction loss can be calculated in many ways. Manning, Churchill, Darcy. Head loss due to friction is only one half of the problem.

2.) A pump with a curve encompassing all your operating points.

3.) The suction line is short and won't make much difference. Increase the size of your 6000 m discharge line.


From "BigInch's Extremely simple theory of everything."

 

[Artisi]

Rather than changing the discharge pipe diam. the economics might just be to increase pump size a little as we are only talking about toy pumps here.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

You can always change the pump, especially toy pumps, but if you get the pipeline size wrong, you're probably going to be paying for that for the life of the system, toy pump or not.

From "BigInch's Extremely simple theory of everything."

 

[badr82]

I don't knew what do you mean by toy pump
It is booster pump
200m head in a mountain area

 

[Artisi]

I was being a little facetious, 1.5 l/s @ 200m head @ 50% pump efficiency is about 6kW, for me this is a toy.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[bimr]

Here is a website that has an online headloss calculator:

http://irrigation.wsu.edu/Content/Calculators/General/Pipeline-Pressure-Loss.php

If you are pumping 1.5 liters/sec, you will have only 0.76 meter/sec velocity in your HDPE 63mm outside dia. pipe. That velocity is on the low side for a water main and there will be no advantage to increasing the pipe size (Unless you want more flow capacity).

Check with the HDPE pipe supplier to determine the maximum pressure rating of the pipe.

Check your pipe elevations.

It seems that your pump (and maybe pipe) was incorrectly specified for the conditions.

 

[BigInch]

Not only the diameter. Not that I use HDPE, but I do believe that it shouldn't be used for much over 15 Barg. 200 m is 20 Barg.

From "BigInch's Extremely simple theory of everything."

 

[bimr]

Correct, Drisco DR11 pipe is rated for a maximum of 13.8 Bar; it may be less because of additional design factors.

 

[JJPellin]

I am interested in a different element of this question. The OP states that they did not get any flow to the end of the pipe until they pinched down on the discharge to get 20 bar discharge pressure. If he had stated that they were only getting 1.0 liter/second but expected to get 1.5 liters/second, then I would suspect that they had higher friction losses than the pump was designed for. But, in order to get no flow to the end of the pipe, I would expect something else.

This sounds like a problem when the pump starts up against an empty line. Without holding back-pressure, the pump runs at very high flow, beyond the end of the curve attempting to flood the line. At that point, the pump may be in severe cavitation. Perhaps the pump is gassing up and loosing flow entirely. But, pinched back to a suitable operating point on the curve, it continues to pump until flow reaches the other end of the long discharge line.

Once flow is established, are you able to open up the pinched valve and get the desired flow rate? Where is the valve that was used to pinch down to 20 bar discharge? Are there any local high spots in the discharge piping that require more than 200 m head to overcome? What sort of air valves are you using at 500 m intervals along the line?


Johnny Pellin

 

[BigInch]

I do think that there are some local high spot issues, which is why I asked for the profile way back up top somewhere. It's nearly impossible to design a pipeline in a "mountanous area" without profile information. A pump with max elevation head capability at the wrong flowrate, or even on the wrong profile can easily fail to deliver anything and might not even start flow. Startup with no water initially in the line could require a pump capable of delivering the sum of elevations of all pipe segments going uphill.

From "BigInch's Extremely simple theory of everything."

 

[bimr]

Another aspect of the problem is that the flow rate is low. At low velocities, air bubbles will not be forced down the pipeline. One would expect that air is probably trapped in pockets if the pipeline is sloped.

This will increase the head that the pump must overcome.

 

[badr82]

Mr. JJPellin
We put a bypass line 20m away from the booster on the discharging pipe to the booster feeding tanks to control the pressure. I just came from the mountain area where the system placed, I set the pressure of the booster to 16bar and after 3 hours the water reached the end point. The pressure at the end point was 1bar.
The air vents used are Hawle make (1 in, female threads).

The booster specifications are:
Brand: Lowara SV816F75T/P
q : 6-14 CUBIC M/H P2: 7.5 KW
H : 199-106M Hmin: 106m
n : 2900 1/min
Motor: 3- PLM132B5/375

 

[badr82]

It is not east to make a profile in that area. I talk some elevations (Sea level as reference) on the pipe rout
Feeding tanks : 900m
Booster : 847m
Lowest point : 810m
End Point : 964m

 

[JJPellin]

I think that BigInch has probably hit upon the key. Until the line is fully flooded and pressurized, you have to overcome the elevation for all of the uphill segments but are not able to recover all of the head coming down the downhill segments.

Based on the wording above, I assumed that you were pinching down on a valve in the line to raise the discharge pressure up to 20 bar. But, your last description indicates that you are spilling back in order to lower the discharge pressure to 16 bar. This also feeds the theory by BigInch that you need more pressure to overcome the profile of your line.

If you were able to get flow from the far end of the line, you need to be able to hold back pressure in the entire line sufficient to vent all of the local high points and flood the line entirely. Once you accomplish this, you might be able to get satisfactory flow, depending on the profile. However, if this system needs to shut down and restart, you are probably going to have to go through the entire process each time.

It is likely that you need a pump with a higher discharge pressure capability.

Star to BigInch. Most of my pumps pump through discharge lines that are pretty much straight and level running through well supported pipe-racks for relatively short distances. The need to understand the implications of running for many miles over varied terrain is better suited to your experience than mine.


Johnny Pellin