Pipe Flow Calculation

If you are disregarding factors like friction, etc. then the total flow will be evenly divided into the six 1 1/4" branches, as long as the elevation of the piping does not exceed 50m. In the real world where factors like friction and the relationship between pressure and flow must be accounted for it becomes more complex.

Hello Ace,

Thx for your reply.

Can you tell me approximately how to calculate will be the flow through 1 1/4" or it will be just say here 800lit/min divided by number of branches?

Thx

If the resistance to flow were equal in all branches, then the flow would be equal in all branches.

I hope that you have asked the question to which a solution will benefit you.

from your drawing , all pipes are connected in parallel ,so flow will be equal in all ,that if all the individual pipes 1 1/4 inch under the same head. if different heads it will be different accordingly.Also pump discharge 800 l/min, if it work under 5o m head . for different head you have to return for pump curve .

Pumps are usually rated for max rate - in this case 800l/min - and max head (50m for this one) BUT these are either/or, so the pump will move 800l/min where no head is present, and stop flowing by the time 50m is exceeded. The curve will show approximate rates for anywhere in between.

If the objective is equal flow in each line, then a few 1¹/₄in valves need to be added to the sketch, together with some way of measuring the flow in each line.

Slack,

Not necessary in a hypothetical system without losses or imbalalces.

Practicalities are just sooooo inconvenient.

What is at the open end of the laterals?

For example a sprinkler with a 10mm nozzle will deliver about 133 l/m at a working pressure of 5 bar. a 12mm nozzle would do it at about 2.5 bar.

The following practical procedure to calculate the friction and total head at the pump.

Start at the furthest emitter and calculate loss of 133 l/m up to the first T

then add losses for 266 to the next T

the 400 l/m branch need not to be calculated because it will be less than the longer branch. assuming all is level.

eventually 800 l/m up to the pump and water source.

fittings should be equated to length of pipe.

add static and working pressure of the emitter.

the same procedure should be followed for different flows and different emitters to obtain a system curve at the pump.

The pump duty point is where the pump and system curves cross.

What is the purpose of the setup ?

Why not go here:

Pipe Flow Calculation

Iyn,

Many thx for this.

RR

Ralish..

You seem to have identified your need for a network based piping system analysis.

Is this the first hydraulic network you have ever worked on ?

Where will this piping system be installed ?

Hydraulic engineering software exists that will assist you in performing a more exact calculation. (www.aft.com).

Tell us about your final resolution to this problem

Rallish,

From the diagram it seems water is NOT BEING LIFTED.

If you disregard the friction factor, the Head Loss in the Pipe will be NIL.

Pump Flow is a function of Diff. Pressure.

At Nil Pressure, Pump will deliver much more than 800 l/min.,(refer the characterisrtic curves)

The Correct way - Estimate the Pressure Losses in the longest branch at 800 l /min. Use Iteration to arrive at correct theoritical Pressure loss and Pump Flow and then divide in the 2 streams based on the location.

If the Water Lift is quite substantial, you can disregard the Friction losses in the pipe. But NOT Otherwise.

Hope it helps in better understanding.

Thanks

I'd like to try to help by saying that the six 1-1/4" lines do appear to be parallel to each other, and the two 3" intermediate lines also appear to be parallel to each other, but the intermediate line farthest away from the pump has (half as much ?) more main-line friction to be overcome than the intermediate line nearest the pump. Therefore the amount of frictional head to be overcome for each 3" intermediate line is different.

Also, four of the 1-1/4" lines appear to be connected with the equivalent of a 3" x 1-1/4" taps, while the other two 1-1/4" lines may be fed by taps with closed-off ends. It needs to be clear what the actual configuration is. The same goes for whether the end of the furthest end of the 3" main line is a closed-off tee, or a closed-off wye, or some kind of elbow.

Also, it would also make a difference if all the piping were to have the frictional resistance of, say, cast iron versus stainless steel, or some other (combination of) materials.

And, do all six 1-1/4" lines have the same sort of knozzles, say, on their ends, submerged, or do they discharge unconstrained thru other kinds of outlets into the open air?

The point is that the question can not be more meaningfully answered without more meaningful details...

The OP is ignoring all friction losses. Go figure.

Your suggested site is very good, but I think I am glad, in the case of this OP, that said site does not have the worked-out examples of analysed systems which he seems to really want...

Not that you need it, but here's a "GA" from me, anyway.

In this network there will be slight differences in pipe friction to the six various outlets. But basically each branch will receive 1/6 of the total flow. Do you need absolute precision?

As I am not a piping engineer I start from the assumption that 3in and 1.25in are the actual i.d. of the pipes. My calculation puts the 3in pipe flow of 800l/min at 2.92m/sec.

The flow speed through the 1.25in pipes (assuming equal flows) would be slightly lower (in proportion to the areas of (1 x Area3")/(6 x Area1.25")).

The most problematic loss I would expect from direction change, so this could be minimised by use of sweep T's (which depending on outlet resistance, would also help to balance the flow between the 6 smaller pipes).

Sorry no help on actual calculation - I let the experts comment.

PLEASE, I NEED YOU, COMPLETE ALL FIGURE AND MORE CLARIFICATION

GALINDO, ALBERTO