Ch 5 Principles of Water Flashcards
Characteristics of Water
-Water (H20) two hydrogen one oxygen
-Freeze 32F 0C
-Liquid 32F-212F
-Boils 212F 100C
-1-gallon weighs 8.3lb
-Cools or absorbs heat from a fire as well smother (remove oxygen)
-Smoothers fires in combustible liquids whose specific gravity greater then 1
Advantages:
-Greater heat absorbing capacity
-Large amount of heat required to change to steam
-Converted to steam occupies 1700 times its original volume
Disadvantages:
-Higher surface tension makes difficult to soak
-Reacts with certain fuels or metals
-Wetting agents may be mixed to reduce its surface tension and increase penetration
Pressure vs Force
Pressure: force per unit area
Force: measure of weight in pounds or newtons
Principals of Pressure
- First- Fluid pressure is perpendicular to any surface on which it acts
- Second- Fluid pressure at rest is same intensity in all directions
- Third- Pressure applied to a confined fluid is transmitted equally in all directions on same grade line
-Example 100 feet tall 100psi top gauge is 100psi bottom is 143.4 psi because of weight of water in standpipe - Fourth- Pressure of a liquid in an open vessel is proportional to its depth
-Example depth of first container 1 foot second is 2 feet third is 3 feet. Pressure in second is double the first and pressure in third is triple the first - Fifth- Pressure of liquid in open container is proportional to density of liquid
Mercury 1 inch, water 13.55 inch
Mercury is 13.55 times denser then water - Sixth- Pressure of a liquid at the bottom of a vessel is independent of the shape of the vessel
What is atmospheric pressure at sea level?
14.7psi
- greater at lower altitudes
what is a PSIG and what does it measure?
- pounds per square inch guage
- it measures PSIA( pounds per square inch absolute) which is actual atmospheric pressure
Vacuum
- any pressure less than atmospheric
Perfect Vacuum
- pressure of absolute zero
Head Pressure
- Refers to the height of a water supply above the discharge
-Example water supply 100 feet above discharge (100 ft of head)
-Every 1-foot increase .434 psi gained
-100 ft divided by 2.304 is 43.4 psi
Static Pressure
- stored potential energy available to force water through pipes, fittings, hoses, and adapters
- static means at rest, or without motion
Normal Operating Pressure
- Pressure found in system during normal consumption
- Friction caused by water flowing through pipes, valves is the difference between static pressure
Residual Pressure
Portion of the total available pressure not used to overcome friction loss
Flow (Velocity) Pressure
- While water is flowing through discharge the forward velocity pressure is flow pressure
-Use pitot tube a gauge to read
Pressure Loss and Gain
Elevation- Center line of pump or bottom of static source above or below ground
-Gain or loss in hose line due to elevation
-When nozzle above the pump pressure loss
-When nozzle below pump pressure gain
Altitude- Geographic position of object in relation to sea level
-Atmospheric pressure decreases .5 every 1,000 feet
Causes of Friction Loss
Friction Loss:
-movement of water molecules
-Inside surface of piping
-Couplings
-Bends/kinks
-Change in hose size or orifice
-Improper gasket size
Friction Loss in Piping:
-FL in older hose can be 50% greater
-Movement of molecule
-Linings of the fire hose
-Pipe fittings
-Valves
-Flush hydrants periodically
Principles of Friction Loss
- First- If conditions are the same friction loss varies directly with length of hose
-Example: 100ft has 10psi friction loss 200ft has 20 psi friction loss - Second- Hoses same size, friction loss varies approximately with the square of increase in velocity of flow
-Example: length of 3 in hose flowing 200gpm has loss of 3.2. as flow doubles from 200gpm to 400gpm friction loss increases four times (2²=4). When tripled 200gpm to 600gpm friction loss increase nine times (3²=9). - Third- For same discharge, friction loss varies as the fifth power of diameter of hose
-Friction loss will decrease when diameter of hose increases
-4-inch supply instead of 3-inch equates to 76% reduction ( (2.5)⁵/3⁵ = 97.66/243 = .4) - Fourth- For a given velocity, friction loss is approximately the same regardless of the pressure on the water
-Example 100gpm passed through 3 inch in certain time water must travel at a specified velocity. Four 1 ½ inch hoses are needed to flow 100gpm at same velocity as a single 3 inch - *Diameter of hose determines velocity to get the same gpms (smaller hose, greater Velocity needed to get same volume)
Reducing Friction Loss
- Hose length- Reduce the length of lay and increase the diameter
- Hose diameter- Using larger diameter hose for a long water supply
-May be reduced to appropriate diameter
-Should not be increased so much becomes difficult to handle - Critical Velocity- Friction becomes so great that resistance agitates the entire stream
- Sharp bends (Kinks)- Avoided by proper hose handling
Water Hammer
- Sudden stopping of water moving through hose or pipe resulting in energy surge in opposite direction
- Force create by the rapid deceleration of water
- With large volumes of water, can damage the pump, appliances, hose, or water system itself
- Closing a valve or nozzle to quickly
- Prevent by slowly closing nozzles and valves
Principles of Municipal Water Supply
- principal function is to provide potable water
- When a large volume of water is needed, request water department to increase water pressure
- Primary water can be obtained from:
-surface water- rivers and lakes
-ground water- water wells or springs
Means of Moving Water
- Direct Pumping- Take water from primary source and discharge it through filtration and treatments
- Gravity System- Water source at higher elevation
-sufficient when source is located several hundred feet higher
-least common - Combination System- Most communities use this
-elevated storage tanks supply the gravity flow
Water Distribution System
- Receives water from pumping station and delivers it throughout the area
- Dead end Hydrant- receives water from one direction
- Circulating Hydrant- receives water from two or more directions
- Grid system- Utilizes lateral feeders for improved distribution
- Primary Feeders- Large pipes with relatively large spacing
- Secondary Feeders- Intermediate sized piped that reinforce the grid
-Aid the required fire flow at any point - Distributors- Smaller mains serving individual fire hydrants
Water Main Valves
- Provide a means for controlling flow of water through the distribution piping
- Operate once a year
- Two types of indicating valves (Show whether gate or valve seat is open, closed, or partially closed) (usually in private systems):
-NOT common in municipal water systems
-Most commonly found in private systems
-Post Indicating Valve- Hollow metal post attached to valve housing- Indicates if open or shut with words
-Outside screw and yoke- Control valve for sprinkler system - Center screw indicates if valve is open or close
- Threads out valve is open
- Indicates if open or shut with words
- Non-indicating Valves- most common in public (municiple) water distribution
-Usually gate or butterfly valves (butterfly better for long periods of inactivity)
-can be rising or non-rising stems
-Non-rising- stem gate valves should be marked with a number for how many turns necessary to completely close valve
Underground water pipes are usually made of:
cast iron, ductile, iron, steel, plastic, or concrete
Water System Capacity (Consumption)
- Average daily consumption ADC- Is average amount of water used per day based on total water used in distribution system over one year
- Maximum daily consumption MDC- Total amount of water used in 24-hour interval within a three-year period
- Peak hourly consumption PHC- Maximum amount of water used in 1-hour interval over 1 day
Private Water Supply
- Get water from municipal water supply systems
- Used for one of the following purposes:
-Provide water strictly for fire protection
-Provide water for sanitary and fire protection
-Provide water for fire protection and manufacturing process - Prevent cross contamination
-may have non-potable water - If there is question about the reliability, departments should make arrangements to augment private water supply for large scale operations
-relaying from municipal source
-drafting
