Week 9 and 10 - Wet Utilities
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49 Terms
What are the two components used to calculate total site water demand?
Domestic demand and fire demand
Which demand usually controls pipe sizing in design?
Fire demand (not domestic)
Why does fire demand control design rather than domestic demand?
Because fire flows require extremely high short-term flow rates compared to normal daily use
What two factors influence average daily domestic demand?
Population and land use
Why does land use affect demand?
Different facilities use water differently (e.g., houses vs theaters)
What is the formula for domestic demand?
Demand=(people)×(gpd per person)
What is the demand for 400 people at 10 gpd/person? (unadjusted)
4000
Do you include employees in demand calculations?
yes, all occupants
When do residential peak demands occur?
Morning (7–11 AM) and evening (4–8 PM)
Why do peaks occur?
daily routines
What two factors determine fire flow requirements?
Building size and construction material
What is the acceptable pressure range?
20–80 psi
What happens if pressure is too high?
Pipe/system damage
What happens if pressure is too low?
Poor service + weak fire protection
What is the minimum acceptable velocity?
2 ft/s
What is the maximum acceptable velocity?
10 ft/s
Why is low velocity bad?
Water quality issues
Why is high velocity bad?
Pipe damage and friction loss
Why is storage required?
sustain fire flow
2000 gpm for 4 hours = ? (in gallons)
480,000
hat is a sanitary sewer?
Pipe conveying wastewater
What is a lateral?
Pipe connecting building to main
What is a trunk sewer?
Large pipe receiving flow from large areas
What percent of sewage is water?
99%
Why can sewage be treated like water in calculations?
mostly water
What two parameters define sewage strength?
BOD and SS
What is BOD?
Oxygen needed to break down organic matter
What determines wastewater design flow?
Population and land use
Why are peak factors used?
To account for simultaneous high usage
Peak factor for laterals?
400%
Peak factor for mains?
250%
Peak factor for interceptors?
200%
Preferred sewer system type?
gravity flow
Why is gravity preferred?
cheaper and less maintenance
When is a pump station needed?
When gravity flow is not possible
What are drawbacks?
Expensive and maintenance heavy
What is cleansing velocity?
2 ft/s
Why is cleansing velocity important?
preventing solids from settling
Minimum sewer main diameter?
8 in
Minimum service pipe?
6 in
Most common sewer pipe material?
PVC
What does SDR represent? (equation)
Diameter ÷ wall thickness
Purpose of manholes?
Access for inspection/maintenance
When are manholes required?
alignment changes, diameter changes, junctions, end of lines
Purpose of cleanouts?
Maintenance access (private systems)
Typical spacing?
75 ft max
When are drop manholes used?
>2 ft elevation difference
Purpose of a dropped manhole?
Reduce turbulence and allow maintenance
When are septic systems NOT allowed?
when municipal sewer is available