Flow in a pipe for water supply 1

[PalomaP]

By knowing pipe pressure (6 bar gauge) and pipe diameter (60 mm). How can I know the flow? I guess I dont have enough data, however could anyone tell me the typical flow speeds for a pipe of water supply?
Thanks a lot

 

[BigInch]

If you know 2 of any of these three prime variables, you can find the unknown value using one of several flow equations (Churchill is my favorite).

1.) Flow
2.) Pressure drop from inlet to outlet
3.) Diameter

Generally you should keep velocities to a max of around 2 m/s to avoid both excessive surge pressures ("water hammer") and particulate matter from eroding the inside of the pipe. If you have clean water where particulates are not a big problem and can do a detailed surge analysis, higher velocities are attainable. Over 3 m/s you might have to make special provisions for surges, such as relief valves going to a tank or reservoir, but exactly what is needed will depend on system configuration, pump speeds, valve closing times. Its best to get a good transient analysis program to see if and where you might develop such problems and determine the best solutions.

You might have a look at my web pages, where I have a couple of little docs about both "Designing a Pipeline" and "Surge Analysis". I think I might have mentioned some of these kinda' things. Hope its usefull to you.

http://virtualpipeline.spaces.msn.com

 

[quark]

You have to do a reverse calculation. If the receiving end is maintained at atmospheric pressure, you have a pressure drop of 6 bar in the line. This is total of static and dynamic pressures. Say, if you have 2m static then you have 4m dynamic pressure. Then 4m goes to the LHS of D-W equation and calculate velocity from the RHS. You need to do some trial and errors.

You can use this dP Calculator for simulation.

 

[BigInch]

I FORGOT THE pipeline LENGTH!!!

How could I??? For sure I'M not firing all cylinders this morning.

http://virtualpipeline.spaces.msn.com

 

[PalomaP]

I am not very sure how to do it...It is a new project for a fire protection system and I require to know the flow of the general supply water pipe to be able to calculate the time I need to fill a tank. The available pressure of the water supply from the street is 6 bar. The pipe diameter 60 mm... how can i get the flow??
Thanks a lot in advance

 

[BigInch]

Paloma, I am (as most all of us here are) very happy to help and give as many tips as we can, but I think you might need more assistance than what some guys on the internet can give you spouting a few lines on Eng-tips. Do you have anyone at your company that has done this before that could help you? Its time to get some engineer with experience involved with your project.

Any fluids textbook will have an example problem or two showing exactly how to determine the flow of water through a pipe segment.

http://virtualpipeline.spaces.msn.com

 

[PEDARRIN2]

It sounds like you might want to do a hydrant test where they will ascertain the system pressure at no flow (static) and then flow another hydrant which will determine the flow at they hydrant while reading the flow pressure at the second hydrant. Then you just graph the two points and you have a system flow curve which will tell you the flow at any pressure on that system.

Unless I misunderstand, that should tell you what you want to know. But as was said before, find somebody who has some experience and get them on board.

 

[gerhardl]

.. BigInch (as seen before) is giving sound advice!

You should in addition note that firewater solutions very often require 3-10 times (say) of the 'normal' max capacity of a flow system.

Or, put in another way: given an (old) exisiting water main supply system on the one side and a (new) requirement for firefighting supply of water on the other side, the two very often do not match.

Suggestion:

1. In stead of starting on the filling time/capacity, obtain the minimum/maximum requirements for supply to the firefighting system, from the firefighting requirements.
(Note: see point 5a!)

2. Then presume a set of 'normally obtainable' velocities in the your branch from the main pipeline (some samples from (say) 0,5m/s to (say) max 3m/s and check the resulting amount against requirements for your tank supply.
(If your branching pipeline diameter is not decided, presume also this)

3. This will at once give an indication if the system is at all par with requirements or not.

4 If not: something must probably be redesigned or reevaluated. (Short-time operation for firefighting may for some valves and systems be allowed higher than 3m/s, but is not to be generally recommended)

5 If yes, then you of course have to go through the engineering task of

a) Check if the amount required actually is available from the main, and will not particullary reduce the pressure in the main during operation. (Available inflow - pressurizing pumps/devices capacity and other users maximum outtake at the same time).

Note: If not available data for the main supply you have to check that 6 bar (measured?) is accurate and fairly constant, and at the same time check input capacity, consumer outtake and total losses on the main. Do not forget to check for consumers lower down on the main. You do not want to cut out their supply and firefighting abilities while you are putting out your own fire!

Also here presumptions may be necessary to check against possible/probable limits!

b) given the (positive?) answer from a, check detailed that the branch can give the necessary amount (checking losses in pipeline and systems against necessary total pressure difference)