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]

BigInch,,,
This is the rout of the pipe in google earth

 

[BigInch]

badr82, Thanks. You're on the right track, but unfortunately the file has nothing to look at inside it. No coordinates. Nothing.

Try highlighting the route then save while it is highlighted.

--------------------------------------------
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="

http://www.opengis.net/kml/2.2"

xmlns:gx="

http://www.google.com/kml/ext/2.2"

xmlns:kml="

http://www.opengis.net/kml/2.2"

xmlns:atom="

http://www.w3.org/2005/Atom">

<Document>
<name>xxx.kmz</name>
<Style id="s_ylw-pushpin">
<IconStyle>
<scale>1.1</scale>
<Icon>
<href>

http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>

</Icon>
<hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
</IconStyle>
</Style>
<StyleMap id="m_ylw-pushpin">
<Pair>
<key>normal</key>
<styleUrl>#s_ylw-pushpin</styleUrl>
</Pair>
<Pair>
<key>highlight</key>
<styleUrl>#s_ylw-pushpin_hl</styleUrl>
</Pair>
</StyleMap>
<Style id="s_ylw-pushpin_hl">
<IconStyle>
<scale>1.3</scale>
<Icon>
<href>

http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>

</Icon>
<hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
</IconStyle>
</Style>
<Placemark>
<name>xxx</name>
<styleUrl>#m_ylw-pushpin</styleUrl>
<LineString>
<tessellate>1</tessellate>
<gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode>
<coordinates>

There should be some Latitude & Longitude coordinates here

</coordinates>
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</kml>


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

 

[badr82]

BigInch...
Please check the attached pics..

 

[badr82]

First point to the right is the feeding tanks
Last point to the left is the end point

 

[BigInch]

Thanks. It is a lot more clear what you have to do now.

I would think that your start up problem is coming from having to "hydraulically" add the slope between 6 Km and 5 Km to the slope at 4.25 Km to 3.25 Km. When you get high discharge pressure during start-up, the flow up to the first peak is low, so when it reaches the peak without enough of a flowrate to fill the downhill segment quickly, the water simply cascades (flows half-full over the peak to a partially filled down-sloped pipe) filling the bottom of the valley. You get no benefit in driving the water up the next hill from that partially filled segment. When pressures at the top of the first peak are low, the volume of air is high. As pressures increase, the volume of air will markedly decrease. Your pumping effort goes into compressing the air in that downhill slope, until it is finally enough to start filling it full of water and begin driving the water and the now lower volume air up the next hill. The same phenomenon may also happen, probably to a lesser extent, across the other local peaks. You won't stop the cascading with an air releas valve at the top of the first peak. Any air will be forced out, but only to be replaced with water vapor in the downslope until the pressure is able to be increased in that segment.

Due to NPSH concerns, I don't think it makes much sense to move the pumps any farther than Km 5.3

Other than that, the profile is not as bad as I thought and I agree that once the air is forced out of the pockets, the constantly increasing average slope should be easier to work with.

The discharge head required at the pump looks to be 125 m or so + whatever flow losses you have from the beginning to the end, so it will be pretty high all the time and may approach as high as 325 m on pump shutdown and during other times of very low flow especially if there is some chance for some quick reverse transient flows during pump shutdown, which I would guess that there is. Take care.

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

 

[bimr]

As previously stated, your problem has to do with air in the pipeline and a low fluid velocity. This is discussed in the book Pumping Station Design by Garr Jones.

On startup, there is not adequate fluid velocity in the downward segments of the force main to force the air bubbles downstream. The term for this condition is "air binding". See the discussion in the attachment. Note the footnote: "Air release valves on small pipelines may be of little or no value".

Your pipeline will be operated at greater than the maximum design pressure of the HDPE pipeline. Consider adding an intermediate booster pump station somewhere near the 3 km mark. ALternatively, you may consider replacing the lower 3 km of pipeline with pipe rated for higher operating pressure. Note that if you continue to overpressurize the pipeline, you incur the risk of pipeline failure and a shortened service life.

You should furnish a quick closing check valve(s) at the booster station to avoid potential water hammer conditions on pump shutdown. It would also be prudent to furnish a pump control valve at the booster station since the pump is starting against a significant water pressure.

There may be some marginal value to relocating the pump station to the 5.3 km mark. You will have to evaluate the relocation cost to determine if it is worth it. Even if you relocated the pump station, it appears you will still be operating the pipeline at higher pressures than the pipeline is rated.

 

[BigInch]

right.
To keep overpressures from occuring you should have a break out tank at an intermediate pump station. The intermediate pump should draw from that tank. Without a tank, you'd need a relief valve in the first pipeline. One of the penalties for underdesigning the pipe. A relief valve is not a bad idea even without the intermediate pump station, given the overpressure, except then the pipeline probably wouldn't work. As it is, it probably won't work for a long time anyway.

you heard it on "Tips".

What would you be doing, if you knew that you could not fail?