My Third Tutorial in WaterCad Pipe Netwo

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Water Water Pipe NetworksPipe Networks

Third Tutorial in Third Tutorial in WaterCadWaterCad

Diagnosing of Pipe Diagnosing of Pipe NetworkNetwork By: Dr. Mohamed By: Dr. Mohamed ElgamalElgamal

Network via Network via WaterCadWaterCad

Objectives

The lecture in hand is divided into two parts:

-Part 1: We will work in Tutorial No. 3 in Watercad;

-Part 2: We will discuss important issues related to the

pipe network.

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Tutorial in Tutorial in WaterCadWaterCad

In the First Part of This Lecture

-In the first part we will carry out the forth tutorial in

watercad.

-The purpose of this tutorial is to train the students

how to:

-Carry out network diagnosis;

-How to identify the major problems in the network,

-How to propose solutions for the diagnosed problems;

Tutorial in Tutorial in WaterCadWaterCad

In the Second Part of This Lecture

-We will discuss the following important topics:

how to:

-Estimate water leakage from a network;

-How to identify network reliability;

-Others…

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First Part First Part (Tutorial (Tutorial 44)) Problem Statement

You have been given the shown network, and have been asked to

carry out a network diagnosis to identify its efficiency, reliability

and hydraulic performance.

To carry out this tutorial, you

need to have this file:

Tutorial3(Original)

First Part First Part (Tutorial (Tutorial 44)) Steps

Step #1:Open the project file [Tutorial3(Original)].

Step #2:Run the file using the steady state solver.

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First Part First Part (Tutorial (Tutorial 33)) Steps

Step #3: Start diagnosing the network

Step #3a: Scroll the messages listed in the User Notifications

It is clear that we have a lot of negative pressures at different

locations in the network.

What are the causes of having negative pressure?

Network Diagnosis

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Before we answer that question we need to emphasize that: -Negative pressure means that the HGL is below the invert level of the pipe network. -Watercad can still solve the network and produces the velocity and the flow in all the pipes regardless of having a negative pressure (even if it exceeds the vapor pressure limit)

Network Diagnosis

Negative pressure might be due to one of the following: -reflect the actual real case; -might be due to poor network design; -Might be due to errors in the network data entry.

Network Diagnosis

Examples Please?

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Negative pressure might be due to actual situation like:

Network Diagnosis

Negative pressure might be due to actual situation like:

Network Diagnosis

If suction tank is sufficiently far

from the pump

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Possible case of high flow

Possible case of low flow

Negative pressure might exist in the low flow case even if the system was designed

properly for the high flow case

Network Diagnosis Negative pressure might be due to actual situation like pumping over a hill:

Negative pressure might be due to actual situation like pumping from a well to a downward tank

Network Diagnosis

TOC

Ris

er

Negative pressure zone

H.G.L.

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Negative pressure might be due to Poor Network Design like: 1. Node served is at too high of an elevation

with regard to source/tanks (Error in Junction

Elevation or proposed tower tank is too low);

2. Excessive head loss (pipes too small for

flow);

3. Pump has run too far out on its curve (wrong

pump for demand).

Network Diagnosis

Negative pressure might be due to Poor Network Design like: -Node served is at too high of an elevation with

regard to source/tanks (Error in Junction Elevation or

proposed tower tank is too low);

Examples of Network Diagnosis

Negative pressure

zone

Too low water tower tank

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Negative pressure might be due to Poor Network Design like: -Node served is at too high of an elevation with

regard to source/tanks (Error in Junction Elevation or

proposed tower tank is too low);


No Negative pressure

exists

Elevation of water tower

tank is sufficient.

Negative pressure might be due to Poor Network Design like: - Excessive head loss (pipes too small for flow);



exists

High m/km head lost

Dead end

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Negative pressure might be due to Poor Network Design like: - Excessive head loss (pipes too small for flow);



exists

Increase pipe diameter of

the first part

Dead end

New HGL.

First Part First Part (Tutorial (Tutorial 44)) Let’s Continue Network Diagnosis

Step #3b: Look at the junction flex tables

It is clear that the negative pressure exceeds the cavitations. i.e. it

is physically not realistic;

This indicates that Watercad does not consider water to air

conversion (it is not a multi-phase model).

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Step #3c: Look at the pipe flex tables

Huge head loss rates and

pipe velocities


Step #3d: Look at the pump operating points

Operating point located far to

the right (runaway flow with

minimum pump head)

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It is clear that the used pump curve is not suitable

Step #3e: Compare the total demand with the operating point


No apparent errors in I.L. at junctions or reservoirs. Therefore,

the excessive negative pressure that exceeds cavitations due

to:

- Many pipe diameters are undersized;

- Pump curve is not suitable.

Step #4: Summarize problems in network

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Can I just revise the pump curve and this will solve all

the problems?

The answer is no because the negative

pressure head values are huge. This means

that pipe diameters should be adjusted first.


Step #5: Carry out suggested network adjustments based on

your assessment into a number of trials

Trial one: adjust pipe diameters.

To do so, we need to identify first the pipes that has head lost

> Say 10 m/km (as an initial trial)

You could use the color coding to do so…

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Pipes that exceeds 10 m/km of head losses can be easily

identified now.


We have different schools of pipe network design

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Pipes that exceeds 10 m/km of head losses can be easily

identified now.

Increase pipe

diameters to 400mm

Increase pipe

diameters to 500mm


Save the file under new name : Tutorial3(step1 revised diameters).

Note: all headloss < 10m/km

But pressure is still negative

Re-Run the file and check headloss

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Save the file under new name : Tutorial4(step1 revised diameters).

However the negative values have

been significantly reduced

Max. negative value is 3.3 bars.

This means, we need pump head to

increase by at least say 45m

First Part First Part (Tutorial (Tutorial 44)) Carry out 2nd step of corrections

Revise the pump as follow then run again

Pump Curve & Definition After Revision

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Explore the new operating point

New Operating Point


Explore the new pressure at each junction

Pressures at all junctions are

reasonably positive

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Draw Contour Lines for the pressure head


Draw Contour Lines for the pressure head

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Second PartSecond Part Estimation of Water Leakage

UFW: Unaccounted For Water: is the portion of total

consumption that is “lost” due to system leakage, theft, unmetered

services, or other causes

Second PartSecond Part UFW Worldwide

http://www.sgi-spa.it/images/1308155238.jpg

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Second PartSecond Part Estimation of Water Leakage

Water Leakage is the largest component of UFW and it can be

estimated using Lambert formula:

Water Leakage (L/day)

= Fncx(18 x Lm + 0.8 x Nc + 25 x Lp) x P

Total Length

of Main Lines

(Km)

Total Length of

Distribution

(Km)

Total Number

of Connections

Average Pressure

head throughout

the network

(m)

Factor

Reflecting

Network

Condition

Fnc = 1 for new or well maintained network;

Fnc > 1 for old networks (1 to 10)

Documents

My Third Tutorial in WaterCad Pipe Netwo