Chp 5 Flashcards
Water properties
Incompressible
Weight varies at different temperatures
Weigihs 62.4 lb/ft^3 or 8.3 lb/gal
Waters ability to fight fire
Absorb heat
Smother
Smother liquid fires with density >1
Smother with steam
Advantages of water
Expands 1700x upon steam (higher at greater temps)
Cheap and readily available
Disadvantages of water
High surface tension Doesn't stop radiant heat Can react with metals Freezes Conducts electricity Heavy
Pressure
Force per unit area exerted by a liquid or gas
Force
Measure of impact of weight within a specific area
Moves direction of an object
1 sq” of water weighs 0.434 lbs
Column 2.304 ft high exerts 1 psi
Principles of pressure
1: pressure is perpendicular to any surface
2: fluid pressure is the same in all directions
3: Applied pressure is transmitted equally in all directions
4: Pressure in an open vessel is proportional to its depth
5: also to its density
6: Pressure at the bottom is independent of shape
Types of pressure
Atmospheric Head Static Normal operating Residual Flow pressure (velocity pressure)
Atmospheric pressure
14.7 psi at sea level (standard)
Most gauges are psi plus atmospheric or psig
psig is psi gauge
psia absolute is psi above a perfect vacuum absolute zero
Vacuum
Pressure that is less than atmospheric
Head
Height of a water supply above discharge
Head pressure is pressure due to elevation
0.434 psi per ft
Divide feet of head by 2.304 to get head pressure
Static pressure
Pressure in a system before it flows from a hydrant
Normal operating pressure
Pressure found in a distribution system during normal consumption demands. Since water is always flowing, basically residual pressure of a system.
Diff of static and normal operating pressure is FL
Residual pressure
Pressure at the test hydrant while water is flowing
Portion of total available pressure not used to overcome friction loss or gravity
Flow pressure
aka velocity pressure
forward velocity pressure while water is flowing from an opening
Only exerted forward not the sides because its not encased
Altitude
Geographic position in relation to sea level. Drops approx 0.5 psi for every 1,000ft change
Elevation
Gain or loss in pressure due to change in elevation from center line of the pump
Friction loss
Loss of pressure created by turbulence of water moving against interior walls of the pipe
Friction loss causes
Movement of water molecules against each other Lining of the hose Couplings Kinks or bends Change in hose size or orifice Improper gasket size Old hose (up to 50%) Same in piping but add valves
Measuring friction loss
Coefficient of friction measured by inserting in line gauges in hose or pipe and testing difference in residual pressure
1st principle of friction loss
FL varies directly with the length of hose
2nd principle of friction loss
FL varies approx to the square of the increase in velocity
3rd principle of friction loss
FL varies inversely as the fifth power of the diameter of the hose
4th principle of friction loss
For a given velocity FL is the same regardless of pressure. Overcome by larger hose or dual lines
Critical velocity
Practical limit of velocity. When agitation is he enough to cancel PDP
Reducing FL
Hose length
Hose diameter
Sharp bends
Water hammer
Force created by the rapid deceleration of water causing an increase in pressure
Sources of water supply
Ground water: well, spring
Surface water: Lake river
Combination (rare)
Also desalination
Means of moving water
Direct pump
Gravity fed
Combination
Water treatment
Coagulation, sedimentation, filtration or addition of chemicals, bacteria or organisms, add fluoride or ozone
Dead end hydrant
Receives water from only one direction
Circulating feed hydrant
Aka looped line receives water from two directions.
Much less friction loss
Grid distribution system
Primary Feeders: large pipes, widespread spacing
Secondary feeders: intermediate pipes that reinforce the grid
Distributors: grid arrangement of smaller mains serving hydrants.
Water main valves
Good for isolating problems
Rarely used, test often
Indicating or non indicating
PIV
Valve on underground water mains on supply main of installed fire protections systems
OS&Y
Control valve for a sprinkler system
Center screw shows if open or closedCo
Non indicating valves
Most common in public water distribution systems
Normally in valve boxes or manholes
Control valves
Generally gate valves
OS&Y or non rising stem (should show number of turns to fully open/close)
Water pipe
Usually cast iron, ductile iron, asbestos cement, steel, plastic, or concrete
Water supply capacity
Average daily consumption; average daily for 1 yr
Maximum daily consumption: max 24 hr within 3 day period
Peak hourly consumption: max 1 hr amount
Private water systems
Just for fire
For sanitary and fire
Or for fire and mfg
Usually separate pipes for fire protection and industrial use to save money
Hydrant Colors
Light Blue: >1500 gpm
Green: 1000 - 1499 gpm
Orange: 500 - 99 gpm
Red: <500 gpm
