×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Pump Discharging Pipe Length
5

Pump Discharging Pipe Length

Pump Discharging Pipe Length

(OP)
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??????

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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.

 

RE: Pump Discharging Pipe Length

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.)  

RE: Pump Discharging Pipe Length

(OP)
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.

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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.)  

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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

RE: Pump Discharging Pipe Length

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.)  

RE: Pump Discharging Pipe Length

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.

 

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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

RE: Pump Discharging Pipe Length

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

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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.

RE: Pump Discharging Pipe Length

(OP)
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

RE: Pump Discharging Pipe Length

(OP)
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

RE: Pump Discharging Pipe Length

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

RE: Pump Discharging Pipe Length

The recommended flow rate for a typical water transmission is 1.8 liters/sec to 3 liters/sec based on economical pumping velocities.

Pumping 1.5 liters/sec for 6 km will give 77 meters of head loss due to fluid flow.

Pumping 1.8 liters/sec for 6 km will give 108 meters of head loss.

Pumping 3.0 liters/sec will give 278 meters of head loss.

Your static pumping head = 964 - 900 = 64 meters. (Note water level at pump feeding tank unknown. You also should provide an additional 20 meters of pressure at the discharge.)

From the pump curve, it looks like the minimum pump flow is 1.5 lps@200 meters.

One would expect that you can pump approximately 1.5 to 1.8 liters per second through your pipe.

The problem on system startup seems to be that the fluid flow rate is too low. At low velocities, air bubbles will not be forced down the pipeline. One would expect that air is probably trapped in pockets where the pipeline is sloped. As the pressure is increased, the air will be forced through the pipeline.

Trapped air increases the head that the pump must overcome since the air bubbles effectively narrow the pipe area available for fluid flow.

You should evaluate the pressure rating of the HDPE in the pipe sections at lower elevations because you may be overpressuring the pipe.

You also may need a pump bypass. At the low pumping rate you will operate at, you may cause the pump to overheat and fail prematurely.

 

RE: Pump Discharging Pipe Length

Can you make a profile from Google Earth?

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

RE: Pump Discharging Pipe Length

(OP)
I don't thing there is an air blocking the flow, due to the number of air vents on the line.We put an air vent every 500m at every high point.
Can we increase the flow rate???
The booster has two pumps of same specifications in parallel arrangement, each has Q= 6-14 cubic meter per hour.
 

RE: Pump Discharging Pipe Length

you now tell us you have 2 pumps in parallel pumping into this line - is this correct?  

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.)  

RE: Pump Discharging Pipe Length

Hwa is thet mei thet hors wettrien the him self nule drinken

When the fluid velocity is low; (1) the air bubbles will not move down the the pipeline and (2) the air bubbles will create additional headloss because the air bubbles are effectively narrowing the pipe diameter. Your fluid velocity is only 2.6 ft/sec which is low (1.5 liters/sec flow in a 48.5 mm ID pipe).

A low flow condition is the same as a zero flow condition. The air will simply not move down the pipeline no matter how many air release valves you install.

You have said the HDPE pipeline is DR11 which means it is typically rated for 13.8 bar working pressure at 80 Degrees F. DR11 HDPE pipe has an ID of 48.5 mm. (You should confirm with the pipe supplier).

http://www.performancepipe.com/en-us/Documents/Tables%201-6.pdf

13.8 Bar - 64 meter static head - 20 meter service static head = 8.2 bar available for pumping head (83.6 meter of head). So you have 83.6 meters of head available for pumping.

If you do not overpressure the pipeline, you are only able to pump 1.45 liters per sec.

If you attempt to pump at a higher flow rate, additional pressure will be necessary from the pump to force the water through and you will overpressurize the lower reaches of the pipeline.

Pumping 1.8 liters/sec for 6 km will result in 125 meters of head loss.

Pumping 3.0 liters/sec for 6 km will result in 322 meters of head loss.

Check the calculations yourself with the online calculator:

http://irrigation.wsu.edu/Content/Calculators/General/Pipe-Velocity.php

You need to determine the water demand, recalculate the water pump requirements, replace the incorrectly sized pumps, and replace the pipeline with one that has the proper pressure rating.
 

RE: Pump Discharging Pipe Length

(OP)
Mr. Artisi
Yes, I have 2 pumps. But they are not working at the same time. We operate one pump and we keep the other for emergency.

RE: Pump Discharging Pipe Length

(OP)
The pressure decreases as the elevation increases.
First point after the pump = 16bar
End = 1bar

RE: Pump Discharging Pipe Length

(OP)
I noticed that, after the pipe was pressurized after starting the pump for 3 hours and the water reached the end point, it does not required more than 16bar and may be less at the pump while it need 20bar when the pipe was empty.
I think we need to install non returning valves to avoid blasting of the pipe due to back pressure when the pump is turned off.

RE: Pump Discharging Pipe Length

(OP)
what type of non returning valves is preferred???

RE: Pump Discharging Pipe Length

You should have check valves on the pumps.

You should also have a pump control valve as well when you are pumping against head. Pump Control Valves are designed to effectively eliminate the surges associated with the starting and stopping of the pump. Electrically interfaced with the pump motor, the valve opens and closes at an adjustable speed, providing a smooth, predictable transition of pump discharge pressure and volume into the system.

http://www.cla-val.com/pdfs/E-60-31.pdf

http://www.controlvalves.com/series/125/125.html

RE: Pump Discharging Pipe Length

Regarding

"I noticed that, after the pipe was pressurized after starting the pump for 3 hours and the water reached the end point, it does not required more than 16 bar and may be less at the pump while it need 20 bar when the pipe was empty."

That is caused by trapped air in the pipe.

RE: Pump Discharging Pipe Length

Exactly it is.  It is also not permitted to overpressure the pipe to 20 bars even if it is only for startup of the system.  The pump will reach that pressure any time the flowrate is low as well.  That just tells you when the pipe will fail.

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

RE: Pump Discharging Pipe Length

(OP)
Thanks for everybody. Really your replays were useful.
I have one last question, is the length of discharge pipe to long (6km)?..If it is, what is the preferred length?

RE: Pump Discharging Pipe Length

I didn't check it, but from the calculations done by others above, it would seem that the length, for it's diameter, is OK for the flow you want to get out of it, asuming that the flow you want to get is 1.5 l/s at the end.

I think you have startup problems, because of the profile which causes higher pressures until all air is out and the line is full of water, but without the profile info, I can't be sure.

Apparently the pump gets water to the end, and if that's the flow you need there, it works.  That said, the only problem I see is the very high pressure during startup, so if the system "works" now, it may not work for long.

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

RE: Pump Discharging Pipe Length

Or, if you can keep the water in it, it will work forever.

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

RE: Pump Discharging Pipe Length

(OP)
I think if the discharge pipe was shorter, the booster will not need to pressurize the system as much as it do with the 6km..
To reduce the length of the pipe we have to put the booster at the nearest possible position to the end point(the water flow due to gravity for 1.5km in the pipe from the booster feeding tanks).

RE: Pump Discharging Pipe Length

That is a good suggestion. Use the available head from the suction side and move the booster pump station downstream.

When pumping 1.45 liters/sec, you have about 14 m of headloss per 1000 meters.

However, you should be aware that you may have the same problems with air bubbles occuring with gravity flow on the suction side. Gravity hydraulic flow problems are more difficult to rectify than pressure flow problems.

RE: Pump Discharging Pipe Length

It will help keep high pressure off of your pipe.  Right now you've probably got a 900-847 + 200 = 253 meter (about 25 Barg) discharge head.  Probably way over pressured.

If you move the pump downstream, say to the low point, you'll have 90m inlet head, when starting up you will still get that discharge head 90 + 200 = 290m, (29 Barg that's why it's easier to get things going) but maybe bust your pipe too, but as flow increases, the inlet pressure will drop, say to 10m, then you'll have 10+200 = 210 m discharge head with no flow.  As flow increases, maybe discharge head will drop to a discharge of 160 m or so.

I have to say I'm getting tired of looking at this still without a profile.

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

RE: Pump Discharging Pipe Length

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>
</LineString>
</Placemark>
</Document>
</kml>
 

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

RE: Pump Discharging Pipe Length

(OP)
First point to the right is the feeding tanks
Last point to the left is the end point

RE: Pump Discharging Pipe Length

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."

RE: Pump Discharging Pipe Length

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.



 

RE: Pump Discharging Pipe Length

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?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources