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Troubleshooting in Water reticulation

Table of Contents

You may encounter some warnings/errors while running for your water reticulation project. 

Residue Pressure Problem #

The following warning appears;

“Some of the residue pressure is either lower than 7.5 for Peak Flow or 7.5 for Fire Flow, or higher than 30 for either“

Where to check #

Output > Excel Report > Nodes for Peak Calculation/Fire Calculation 

Steps to troubleshoot #

Equation to get Residual Pressure is as below:

Hydraulic Grade Line (HGL) – Highest Supply Level (HSL)

Check Fix Head value (as it will affect Hydraulic Grade Line) #

“Input > Node > Spread Input > Node Head value”

How is Fix head related to Hydraulic Grade Line? The equation is as below, or you may also refer to this blog (Water Reticulation Benchmark)

Equation:

Hydraulic Grade Line (HGL)     

= Fix Head – Head Loss

Example:

If the residual pressure is less than 7.5 m (the minimum residual pressure), you may need to check on the fixed head value whether it is too low in comparison with HSL, or have the value of water elevated tank height added with Ground Level (this is applied to elevated water tank design)?   

Given: 

Fix head = 40 m,
*if you are using Elevated Water Tank, the value of Fix Head is height of the building + Ground Level

Highest Supply Level = 33.47 m 

Head Loss = ~ 0 m

Residual Pressure = 6.53 m (less than the minimum 7.5 m)

Above calculation shows that the residual pressure is less than the minimum, therefore you might need to recheck the value of the Fixed Head. Same goes to the situation if the residual pressure is above the maximum, the fixed head value might be too high. If the Fixed Head is correct, see No. 2. 

Check Ground Level value (as it will affect the Highest Supply Level) #

“Input > Node > Ground Level”

How is Ground Level related to Highest Supply Level? The equation is as below, or you may also refer to this blog (Water Reticulation Benchmark)

Equation:

Highest Supply Level (HSL)

= Ground Level + Tank Water Level 

Example:

Referring to the image below, one of the residual pressures is more than the maximum (30 m maximum). 

The calculation of the residual pressure for the Node 2 above is

= HGL – Ground Level + Tank Water Level 

= 40 – 0 + 5

= 35 m 

0 m ground level at Node 2 seems to be odd in comparison with the surrounding levels. So you might need to recheck on the ground level for that particular node, since it will affect the HSL and residual pressure. 

But what if all of the above troubleshootings are done and the values of GL, Fix head are all correct, that the residual pressure is impossible to satisfy the pressure range specified by the authority. Therefore, you might need to opt for an additional pump or valve. 

Change the Diameter of the Pipe #

Residual pressure can also be affected by head loss. One of the components included in the calculation of head loss is Diameter. As diameter changes, the head loss also will be changed. By lowering the value of head loss, the residual pressure can be increased. In order to decrease the head loss, diameter can be adjusted by increasing the size of the diameter, and vice versa. 

The calculation of the head loss can be referred to in this “Manual Head Loss Calculation Benchmark with MES Software” blog, or you can refer to this Online Calculator.  

Where to check the head loss value #

Output > Excel Report > Pipes for Peak/Fire Calculation > Head Loss

Where to change the pipe diameter #

Input > Pipe > Spread Input > Diameter

Check on Water Demand #

Residual pressure is also affected by the flow discharge, Q which came from the water demand input. As Q is affected, the head loss also will be affected. The calculation of the head loss can be referred in the blog post as attached in the section 1.2.3. Although wrong input of water demand rarely happens, you may also need to recheck on the value in case there is any misinput. 

Benchmarks of water reticulation can also be referred to in this “Water Reticulation Benchmark” blog. 

Where to check the Q #

Output > Excel Report > Pipes for Peak/Fire Calculation > Flow 

Where to check on Water Demand #

Input > Node > Spread Input > Water Demand

Add Pump #

Given a situation that the pressure is not sufficient to satisfy the minimum residual pressure, therefore you might need a pump in order to boost the pressure. 

Where to add #

Pipe > Spread Input > Pumps/Valve

Other related posts: #

Add Valve #

Say the maximum residual pressure is 30 m and the analysis shows you 40 m residual pressure, which fails the analysis. Therefore, you might need to add a valve in order to control the pressure to be within range. 

Where to add #

Pipe > Spread Input > Pumps/Valve

Authority Discussion #

What if the values are all correct and the pump/valves are not possible for your layout, you might need to discuss with authority and present them with the calculation, showing that the requirement is indeed not possible given the constraint. 

Low or High Head Loss  #

Where to check #

Output > Excel Report > Pipes for Peak Calculation/Fire Calculation > Head Loss column 

Steps to troubleshoot: #

Firstly, you have to know the basic equation of calculating the head loss, only then you are able to identify the variables.

Hazen-Williams Equation:  V = k C (D/4)0.63 S0.54   where   S = hf / L  and   Q = V π D2 / 4

V = velocity (m/s)

k = conversion factor (1.85 for SI unit)

C = Hazen-Williams Coefficient

D = diameter (m)

S = energy Slope (m/km)

hf = head loss (m)

L = length (m)

Q = discharge (m3/s)

You may also refer to this blog post for further details; Manual Head Loss Calculation benchmark with MES Software. You may also refer to this online calculator for trial and error calculation. 

Usually, water demand and the length are fixed, so there is not much to be changed on those variables. Therefore, what’s left is to change the Diameter of the pipe. (please refer to the equation, or refer to the blog post to understand better). 

However, changes to the diameter might lead to the failure of the Residual Pressure as they are closely related to each other. Further discussion with the authority is required if further changes will fail the design, given the constraint of the project.   

Network does not contain any node with fix head #

Where to check #

“Input > Node > Fix Head”

Steps to troubleshoot #

  1. Insert at least one fix head in Node Spread Input,         OR
  2. In rare cases, if the error still happens although a fixed head was assigned,  it is most probably due to a disconnected node. So basically a new network is created and no fixed head. Therefore, adjust the nodes to be connected to resolve it. 

Network does not contain any node with water demand #

Where to check #

“Input > Node > Spread Input > Water Demand Column”

Step to troubleshoot #

Define at least a node with water demand . Click the water demand calculator and add in water demand

Water demand of the node must be <= 0 #

Where to check #

“Input > Node > Spread Input > Water Demand”

Steps to troubleshoot #

Water demand is drawing out the water, hence it must be -ve sign

  1. Add negative sign of the keyed in water demand, OR
  2. Use Water Demand Calculator as it will automatically calculate it for you 

Some fix head node(s) has/have water flowing in #

Where to check #

“Input > Node > Spread Input > Fix Head > Node Head”

Steps to troubleshoot #

  1. Recheck on the number of Fix Head in a network (usually only one fix head for a network), OR
  2. If there are multiple fix heads, recheck on the Node Head value and make sure that the values are not more than one another

Power provided by constant power pump must be greater than 0 #

Where to check #

“Input > Pipe > Spread Input > Pumps/Valve column > Pump > Power Value”

Step to troubleshoot #

  • Insert a value which is more than 0 for the Power

Valve x can not be connected to a tank #

Where to check #

“Input > Pipe > Spread Input > Pumps/Valve column > Valve”

Step to troubleshoot #

  • Valves cannot be placed at the first pipe. If you insist on placing it at the first pipe, create a dummy pipe, as long as the valve is not located at the first pipe. 

Fire flow calculation is not generated  #

Where to check #

  • Fire flow calculation is not included in Excel Report Output 
  • Fire flow calculation is not included in Textual Report Output 
  • Fire flow is not shown in Schematic Plan Output

Steps to troubleshoot #

  1. Assign hydrants 

 “Input > Node > Spread Input > Hydrant (assign Yes)”

  1. Fire flow calculation is not generated although Hydrant Accessory is assigned. Accessories are only symbolic of the item, hence it does not have any effect on the calculation. Therefore, refer to step number 1 to solve it. 

Blank Loop Verification Output #

Where to check #

Your network design type (looped/branch)

Explanation #

Loop Verification Output is only for looped networks. If the network is branched, this output will not be generated. 

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