Head & Friction Loss in PVC Pipe 6

[Antoniog1]

In regards to my earlier posting the ID of the pipe is 104.6 Milimetres AMSL Stands For Above Mean Sea Level, the pipe is 10000 metres long one pipe from reseroir A To Reservoir B with flow measurements taken at intervals with isolation & Scour valves along the pipe to try and determine a point where i have either an obstructed or squashed pipe reducing my flow rate into reservoir B. As can be seen reservoir A Is 47 Metres above reservoir B friction tables from the pipe manufacturer tells me at a head of 47 Metres, a distance of 10000 Metres of pipe should give me a flow rate of 7.5 Litres per second into reservoir B Equates to 450 Litres Per Min with only a measured flow of 310 Litres Per min, an actual drop of 140 Litres per min below calculated flow rate, speaking to the manufacturer in there experince with pipe flow rates have been higher than calculated not below i was just wanting someone else to put the figures into formulas to give me a second oppinion.
Regards Anthony

 

[BigInch]

I ran the 10 km pipe (with pipe roughness 0.0005 inches, or .0125 mm, which I think is about right) and get 350 L/m with 46.5 m of head loss.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[katmar]

Anthony, you should not start a new thread to continue giving more information regarding a previous posting. Keep it all in one thread.

You are not the first person to complain here that you get less flow than the plastic pipe manufacturer's tables suggest. I agree with BigInch's calculated flow. Even if your pipe were prefectly smooth you would get only 365 litre/min. Call the supplier in and make them justify their claims.

But I am not sure about your pipe ID. My tables show Class 9 PVC as having an ID of 87.9 mm for 4" and 108.6 mm for 5". What pipe do you have? To get your required 450 litre/min you need an ID of about 113.5 mm ID.

There are also some inconsistencies in your measured data, or you have made typo's in giving us the data. Your measured flowrates at the 5800 and 7900 metre points are much higher than my calculated numbers. At 5800 m I get 567 l/m and at 7900 m I get 478 l/m. It would seem that you have a large ID pipe for the first 8000 m, and then a smaller ID for the last 2000 m.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Latexman]

L = 10,000 m
ID = 104.6 mm
roughness = 0.0015 mm
s.g. = 1
viscosity = 1 cP
1 inlet loss
1 outlet loss

366 L/min


Good luck,
Latexman

 

[BigInch]

Don't forget he doesn't have 47 m head at the inlet, that's +/- 0 or so. We can only be sure that he has 47 m head when he gets to the 2nd reservoir (47 m outlet pressure), so he's probably not doing too badly, if 47 m is more or less the "average" head. Actually 360 is probably pretty DG.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[BigInch]

I put it to the BigBoy and he says its pretty DG too.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Antoniog1]

Katmar the pipe is 104.6 mm ID PVC Type P Class 9 AS1477-1973 my measured flow rates have been checked numerous times & the pipe is the same diameter for the entire distance, at a distance of 8000 Metres with a head of 61 Metres i have a flow of 630 L/Min Yet At a distance of 8400 metres with a head of 53 Metres i have a flow rate of 410 L/Min a drop of 220 L/min in a distance of 400 Metres with a head loss of 8 metres, then at 8800 metres back to a head of 61 metres my flow rate is still 410 L/Min then at 10000 metres into reservoir B with a head of 46 metres a flow of 310 L/min, my puzzling part is that in the last 1200 Metres of pipe i only lose 100 L/Min in flow with an elevation increase in that 1200 metres of 15 Metres Yet in the previous 800 Metres of pipe I'm loosing 220 L/Min with only an increse in elevation of 8 Metres, Half the distance of pipe, half the head yet over double the flow loss.
I Shall draw a diagram & try Posting it so you can see the layout.
Regards Anthony

 

[BigInch]

See thread378-184348 for how to make a post of a diagram, or see your previous thread for how to make a logical listing of the pipes and describe their configuration using text only.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[25362]

The tables on the Pipe Friction Manual by the American Hydraulic Institute coincide with BigInch estimates.
A long buried sloped pipeline might not always have the same angle with the horizontal with a tangent equal to -0.0047, or -0.47 m/100 m length.
I wonder whether air slugs, original or created by air release, may influence the actual flow rates.

 

[katmar]

Anthony, Thanks for the extra info on the pipe class. My data agrees with yours when I look in the correct table!

From all the info you have now given there are a few things we can conclude for certain. One is that your supplier's claim is nonsense. You will never get 450 litre/min with your current installation. We have several independent calculations now to verify that.

Secondly there are serious inconsistencies in your data. Years of experience have shown me that when some data is wrong, then I should be suspicious of all the data. You need to go back and redo all your length, height and flow measurements. Something is badly wrong.

At the 5800 m point you have measured a flow of 650 l/min while my calculated number is 567 l/min. You are getting 15% more flow than predicted. At a distance of 7900 m (now reported as 8000 m) your measured flow of 630 l/min is 32% higher than the calculated flow of 478 l/min. This does not happen in nature. Either you have an isolation valve leaking and are getting backflow, or you have a head of about 97 m.

Comparing your measured values with my calculations for the 8400, 8800 and 10000 m points shows that your flows are 2%, 9% and 14% lower than mine respectively. We could start asking questions about what valves and fittings are here, or possible blockages, but because the other data is so wrong I would not try to guess what the actual cause of the low flow could be.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Latexman]

Antonio,

When you measure the flow at an intermediate point, please describe exactly what you do, where the measured flow(s) is going, and the equipment/instruments you use. I am unclear about these intermediate flow tests.

Good luck,
Latexman

 

[Antoniog1]

Latexman these flow tests are done at points along the pipe at scour valves where an isolation valve is fitted just downstream of each scour valve to prevent any back flow using an 80 mm calibrated flow metre, distances from reservoirs are all taken in metres from supply reservoir, elevations are taken from surveyors maps when the pipeline was installed in 1983. i am endevouring to draw an outline of the pipe run so you can see the layout, reservoir B Is 47 metres below reservoir A but the 10000 Metres of pipe in between the reservoirs follows the natural contours of the ground with the lowest points being 62 metres below reservoir A I have a scour Outlet where i am getting 630 L/Min & have made sure i have no back flow yet at the next scour outlet only a distance of pipe of 400 Metres And an elevation of 5 metres above first scour outlet my flow rate has fallen to 410 L/Min & i dont feel in that distance even with that elevation you can drop 220 L/Min in flow i feel that in this 400 metre section of pipe i have some form of restriction.
Regards Anthony

 

[Latexman]

I don't know what a scour valve is. Anyone?

Good luck,
Latexman

 

[25362]

Silt removal gate valve ?

 

[katmar]

Anthony, Has the flowrate decreased since 1983? This will tell us whether it is a design problem or a blockage problem.

Have you tried scouring backwards? Towards the end of your line the pipe slopes up towards the second reservoir. It is difficult to scour upwards, especially with the long supply line. Using the second reservoir as the source for scouring will allow you to scour downwards and with a higher flowrate.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Antoniog1]

Suprisingly no flow rates wer recorded when the pipeline was commissioned in 1983 so it leaves us flying blind. On another note my static pressure reading at reservoir B with no water flow is 90 PSI be it 1.4 PSI in a metre this equates to a head of water above reservoir B of 64.28 Metres, is this a more acurate measurement than surveyors measurements or with a pressure reading do you have to make allowances for atmospheric pressure.

My pipe manufacturers friction table states that at a flow of 6.5 L/Sec gives a head loss of .0046Mtrs per metre, now say a length of pipe 450 Metres long has an elevation of 5 metres from start to finish, the pipe head 450 X .0046 = 2.07 Mtrs + 5 for elevation = 7.07 Mtrs total head X 1.4 = 9.898 PSI So if calculations are right i should only need 9.898 PSI to push 6.5 L/Sec along that piece of pipe are these calculations correct or not.

Regards Anthony

 

[BigInch]

0.0047 * 450 = 2.07 meters LOSS, so that's a minus sign.

with 6.5 L/s Flow,
the outlet head = 5 m -2.07 m = 2.93 m head loss.

Pressure Equivalent of 2.93 m water is 4.17 psi @ outlet.




BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[katmar]

Anthony, using a pressure gauge to measure height differences with no flow is a good idea. But you must remember to take into account the height difference between your measuring point and the surface of the water in the reservoir. If the 90 psi you measured is at the surface level in the second reservoir that is fine, but if you are feeding into the bottom of the reservoir then you need to subtract the head from your feeding point to the surface.

In the same way, you need to be sure whether the elevations given by the surveyors for the two reservoirs were to the surface or base level.

If the 90 psi is the true driving force available that makes it very different from the 47 m your surveyors map gave you.

Can you get pressure gauge readings at the scouring points as well?

The atmospheric pressure is irrelevant in this case - one less thing to worry about!

Your calculation is basically OK. I believe 0.0046 m/m loss is a bit low. I would make it 0.0053 m/m, but it is not a big difference. In the flow regime where you are working (Reynolds number +/- 80000) the pipe roughness does not make much difference unless it is VERY rough.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[25362]

27 years of use may have changed the surface roughness.

 

[Antoniog1]

Biginch but if i were to use a pump at the start of that piece of pipe it has to push against the head of the pipe as well as the head of the elevation, pipe head = 2.07 mtrs + elevation of 5 metres the pump would have to increase to a pressure equivalant of 7.07 metres as in your equation the pipe friction is helping the water flow.

Regards Anthony