Water Distribution Level 1

Front 1

What is a Distribution System?

Back 1

Distribution system is a network of pipelines that distribute water to the consumers.They are designed to adequately satisfy the water requirement for a combination of
• Domestic
• Commercial
• Industrial
• Fire fighting purposes

Front 2

What are the principle components of a distribution system?

Back 2

• Pipes
• Valves
• Storage Reservoirs (Equalization)
• Fire Hydrants
• Service lines
• Meters
• Pumping stations
• Pressure tanks

Front 3

What is the most common forms of chlorine used for disinfection?
a) Chlorine Dioxide, Hydrogen Chloride
b) Calcium Hypochlorite, Sodium Hypochlorite
c) H.T.H, Sodium Chlorite
d) Chloramine, Chlorate

Back 3

b) Calcium Hypochlorite, Sodium Hypochlorite

Front 4

What are typical duties of a water distribution operator?

Back 4

• Excavate trenches, install shoring
• Maintain pipes, valves, pumps and equipment
• Tap and install connections into main lines
• Read water meters
• Operate and maintain well pumps
• Detect and correct hazardous atmospheres
• Be part of a cross connection control program
• Read and update maps and records
• Communicate with the public
• Troubleshoot complaints
• Develop and follow safety rules

Front 5

How does a Tree Distribution system work?

Back 5

Tree distribution system:(Similar to the branching of a tree)
• Main (trunk) line
is the main source of water supply. There is no water distribution to consumers from trunk line
• Sub-mains
are connected to the main line and they are along the main roads
• Branches
are connected to the sub-mains and they are along the streets.
*Lastly service connections are given to the consumers from branches.

Front 6

What are the advantages and disavantages to a Tree Distribution system?

Back 6

Advantages:
It is a very simple method of water distribution.
- This method requires comparatively less number of cut-off valves.

Disadvantages:
- The area receiving water from a pipe under repair is without water until the work is completed.
- In this system, there are large number of dead ends where water does not circulate Sediments accumulate due to stagnation of the dead end and bacterial growth may occur at these points. (To overcome this problem drain valves are provided at dead ends and stagnant water is drained out by periodically opening these valves but a large amount of water is wasted.)
- It is difficult to maintain chlorine residual at the dead ends of the pipe.
- Water available for fire-fighting will be limited since it is being supplied by only one water main.
- The pressure at the end of the line may become undesirably low

Front 7

How does a Grid Distribution system work?

Back 7

In grid pattern, all the pipes are interconnected with no dead-ends. In such a system, water can reach any point from more than one direction.

Front 8

What are the advantages and disavantages to a Grid Distribution system?

Back 8

Advantages:
- Since water in the supply system is free to flow in more than one direction, stagnation does not occur as readily as in the branching pattern.
- In case of repair or break down in a pipe, the area connected to that pipe will continue to receive water, as water will flow to that area from the other side.
- Water reaches all points with minimum head loss.
- At the time of fires, by manipulating the cut-off valves, plenty of water supply may be diverted and concentrated for fire-fighting.

Disadvantages:
- Cost of pipe laying is more because relatively more length of pipes is required.
- More number of valves are required.
- The calculation of pipe sizes are more complicated.

Front 9

How does a Loop Distribution system work?

Back 9

Loops are provided in a grid pattern to improve water pressure in portions of a city (industrial, business and commercial areas).
Loops should be strategically located so that as the city develops the water pressure should be sustained.
The advantages and disadvantages of this pattern are the same as those of the grid pattern.

Front 10

What are the two most common types of valves used in a distribution system?

Back 10

Isolation valve (stop or shutoff valves) typically gate valve or butterfly valve are used to isolate sections of pipe for maintenance/repair and isolate fire hydrants

Control valves (pressure reducing, pressure sustaining, pressure-relief, flow control, throttling and check valves) are used to control the flow or pressure.

F.Y.I.
Other valves found in the distribution system include
• Blow-off valves: located at low points &/ or dead ends
• Air release/vacuum valves: located at high points

Front 11

The requirement of special butt-welding equipment and training to fuse joints is a disavantage associated with __ pipe.
a) Polyvinyl Chloride
b) Steel
c) Asbestos Cement
d) Cast Iron

Back 11

a) Polyvinyl Chloride (PVC)
F.Y.I.
Widly used in construction due to the ease of construction, lower cost, resistance to corrosion, favorable C factor that lessens the resistance to flow and therefor has better hydraulic performance characteristics than other types of pipe materials. usually used in AWWA C900 with various pressure ratings ( Class 150 (psi)) in sizes from 4 to 12 inch.

Steel Pipe - is usually used for mains where internal pressures are higher than would normally be expected due to its very high tensile strength and can withstand enormous internal pressures before failing. It is lighter than ductile iron and concrete pipe. Due to its metal composition it is subject to corrosion so an internal coal tar eposy lining/ cement linings are used and for exterior pipe protection, polyethylene linings are used. Cathodic protection is another form of corrosion pervention.

Asbestos Cement (AC) - is made from asbestos fiber (majority of the strength), silica sand, and cement. It is relatively east to handle and join althought it is ridged and cannot be bent or twisted it has a carrying capacity slightly less than PVC. AWWA C400 availabe in 3 pressure classes from 4 to 36 inches.

Iron - Ductile iron will take some bending and twisting without breakage but to protect the internal pipe cement mortar lining and bituminous or polyethylene coatings are used to protect the outside of the pipe. AWWA C151 come in sizes from 3 to 18 inches with pressure ratings from 350 psi to 500 psi

Front 12

What is the Average Demand?

Back 12

The total demand for water during a period of time divided by the number of days in that period

Front 13

What is the Peak Demand?

Back 13

The highest instantaneous flow rate during a given time period

Front 14

What is the main purpose of a water storage facility?

Back 14

• Provide a sufficient amount of water to equalize the demand fluctuations
• Help stabilize adequate pressure throughout the entire system
• Provide water for average and peak demands
• Provide reserve supply for fire/emergency

Front 15

What are the main types of storage reservoirs?

Back 15

• Elevated
• In-ground
• Ground level storage tanks
• Clearwells
• Standpipes
• Hydro-pneumatic or pressure tanks

Front 16

What is the purpose of a surge tank?

Back 16

To absorb sudden rises of pressure, as well as to quickly provide extra water during a brief drop in pressure.

Front 17

What is the main purpose of an elevated reservoir?

Back 17

To pressurize a water supply system, provide emergency storage for fire protection/power outages and to help reduce the required size and capacity of mains and booster stations.

Front 18

What is the purpose of booster pumps?

Back 18

Pumps are used to impart energy to the water in order to boost it to a higher elevation or to increase pressure.

Front 19

What are the 4 piping classifications between the treatment plant and the consumers?

Back 19

• Transmission (Trunk Main)
Carry large amounts of water
• Distribution Main (Sub-Main)
Smaller in diameter and usually follow city streets
• Service Line (Branch)
Carry water from distribution main to consumer and vary in pipe size depending on flow/pressure requirements
• Service Connection and
Premise Plumbing (Not utility operated, maintained, funded)

Front 20

What is the normal range of distribution pressure that should be maintained?
a) 20 - 40 psi (140 - 275 kPa)
b) 14.5 - 29 psi (100 - 200 kPa)
c) 29 - 58 psi ( 200 - 400 kPa)
d) 40 - 80 psi (280 - 550 kPa)

Back 20

d) 40 - 80 psi (280 - 550 kPa)

Front 21

Why is positive pressure needed in the distribution system?

Back 21

• To prevent the creation of a vacuum effect on the water an may damage plumbing(vacuums can cause contamination due to infiltration, backflow or cross connection)
• To provide consumers with desired pressure
• Higher pressure required during low demand periods -ABOVE 100 psi CAN CAUSE DAMAGE
• Lower pressure required during high demand periods - NEVER BELOW 20 psi -

Front 22

Which of the following identifies factors which must be considered when selecting pipe for use in a distribution system?
a) low friction loss, availability and submergence
b) compatibility with existing piping material, cost and lifestyle
c) durability, corrosion resistance and compatibility with potable water
d) strength, ease of handling, O.H. & S. certification

Back 22

c) durability, corrosion resistance and compatibility with potable water

F.Y.I.
Also consider ability to deliver the quantity of water required, durability of both internal/external forces to have a long life
Most pipe is ductile iron, concrete mix, PVC, reinforced plastic, and steel

Front 23

What is the most common type of valve in the distribution system?
a) Ball valve
b) Diaphragm valve
c) Gate valve
d) Globe valve

Back 23

c) Gate valve
Gate valves are primarily used to permit or prevent the flow of liquids, but typical gate valves shouldn't be used for regulating flow

F.Y.I.
Ball valve = is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The ball valve, along with the butterfly valve and plug valve, are part of the family of quarter turn valves.

Globe valve = is a type of valve used for regulating flow

Front 24

A dead-end water main can cause what kind of problems in the system?

Back 24

• Stagnant water (low/no chlorine)
• Low pressure

Front 25

What are the most common joints used when installing ductile iron pipe?

Back 25

•
•

Front 26

Water mains installed parallel to sanitary sewer lines should be at least_________feet apart.

Back 26

-

Front 27

All trenches at or deeper than feet must be properly shored or cut to angle of repose

Back 27

-

Front 28

List a function that an air relief valve serves

Back 28

• To release pressurized air from the system

Front 29

Fire hydrants should not be more than feet apart. Why?

Back 29

--

Front 30

List the two types of fire hydrants that are used in a distribution system.

Back 30

-

Front 31

A device installed on the service connection directly downstream from the meter to prevent backflow is called ____________________ ____________________ ____________________.

Back 31

-

Front 32

What is the head in feet if the water distribution system reads 40 psi?

Back 32

-

Front 33

A water storage tank contains 40 feet of water. What is the pressure at the bottom of the tank in psi?

Back 33

-

Front 34

If you have 75 feet of pressure head, what is the pressure in psi?

Back 34

-

Front 35

What are the two types of backflow that can occur through cross-connections?

Back 35

-

Front 36

When flushing or flow testing a fire hydrant, what might the consumer experience?

Back 36

-

Front 37

What is the minimum flushing velocity required when cleaning water mains?

Back 37

-

Front 38

What is the factor or value used to indicate the smoothness of the interior of a pipe known as?

Back 38

-

Front 39

Hydraulic gradient tests are used for what purpose?

Back 39

-

Front 40

How often should fire hydrants be inspected?

Back 40

-

Front 41

Which is an indicator of a possible leak in the system?
a) vibration felt on hydrants, valves, ect.
b) Large bodies of water during a dry day
c) Decrease in distribution pressure at peak usage periods
d) all of the above

Back 41

d) all of the above

Front 42

Which type of backflow prevention device is best used when dangerous materials are present at the water usage location?
a) air gap separation
b) reduced pressure device
c) double check device
d) Vacuum breaker

Back 42

b) reduced pressure device