Head & Friction Loss in PVC Pipe
Head & Friction Loss in PVC Pipe
(OP)
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
Regards Anthony





RE: Head & Friction Loss in PVC Pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Head & Friction Loss in PVC Pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Head & Friction Loss in PVC Pipe
I Shall draw a diagram & try Posting it so you can see the layout.
Regards Anthony
RE: Head & Friction Loss in PVC Pipe
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Head & Friction Loss in PVC Pipe
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.
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
Regards Anthony
RE: Head & Friction Loss in PVC Pipe
Good luck,
Latexman
RE: Head & Friction Loss in PVC Pipe
Silt removal gate valve ?
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
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
RE: Head & Friction Loss in PVC Pipe
27 years of use may have changed the surface roughness.
RE: Head & Friction Loss in PVC Pipe
Regards Anthony
RE: Head & Friction Loss in PVC Pipe
Good luck,
Latexman
RE: Head & Friction Loss in PVC Pipe
Is your pipeline going up or downhill?
You have an elementry problem for which it should be easy to give you some advice, but nobody understands your configuration and confusion still prevails. I think it is better that you figure out how to make a diagram and get it posted, or list your flow elements and reservoirs in a complete and understandable manner, like the example I gave you in your other posting. Try it.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Head & Friction Loss in PVC Pipe
I don't trust the measurements reported. The measurements will have to be valid and believeable before the pipe supplier will believe the data or before you can compare prediction with measurement.
Did I miss something?
Ted
RE: Head & Friction Loss in PVC Pipe
BigInch - if antoniog1 draws a diagram of this system using MS Paint (everyone has access to and knows how to use Paint, right?), can you tell him how to post it here like you did the output of BigBoy? Will he need to store the diagram on webspace somewhere to do this?
Antoniog1:
1 - Left click Start/Programs/Accessories/Paint, or:
S = scour valve
I = Isolation valve
T = tee or branch
~~~\ 60 m
\
\--I-T--\ 50 m
S \ /-----\ 45 m
\--S-T--/ 40 m \
I \-----\ 35 m
\
\
\~~~ 20 m
A picture is worth a thousand words!
2 - At these test points, is the scour valve mounted in the 104.6 mm ID PVC Type P Class 9 pipe that runs from Reservoir A to B?
3 - - At these test points, is the scour valve mounted in a pipe that tees (branches) into the 104.6 mm ID PVC Type P Class 9 pipe that runs from Reservoir A to B?
4 - At these test points, is the isolation valve mounted in the 104.6 mm ID PVC Type P Class 9 pipe that runs from Reservoir A to B?
5 - - At these test points, is the isolation valve mounted in a pipe that tees (branches) into the 104.6 mm ID PVC Type P Class 9 pipe that runs from Reservoir A to B?
Good luck,
Latexman
RE: Head & Friction Loss in PVC Pipe
again,
See thread378-184348: "Parallel" Pump Head Calculation: "Parallel" Pump Head Calculation for how to post diagrams
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com