Chapter # 8 Theoretical Pressure Calculations Flashcards
What are two advantages of drivers knowing how to perform theoretical calculations?
Allows them to predetermine approximate PDP for preconnected hoselines on their assigned apparatus.
Serves as a tool in pre-incident planning for uncommon hose lays.
Name factors that cause friction loss.
Hose condition. Coupling condition. Kinks. volume of water flowing per minute (primary factor).
A pressure loss or gain due to elevation changes.
Elevation Pressure
What is total pressure loss (TPL)?
FL + Elevation pressure.
What are they two methods to determine friction loss?
Actual test. Calculations.
What is the most accurate way of determining friction loss?
Hands on field test.
What is the old friction loss equation?
2Q^2 + Q
What made the old friction loss equation obsolete?
Improvements in firehose technology and construction in the latter half of the 20th century. (old way provided way to high numbers)
What determines the actual coefficient of a fire hose?
The condition of the hose and the manufacturer.
Coefficients provided in the manual are a worst case scenario and therefore. probable result in what?
Higher numbers than what the actually friction loss is.
Friction loss coefficients-single hoselines.
3/4 = 1,100. 1 = 150. 1 1/4 = 80. 1 1/2 = 24. 1 3/4 w/1 1/2 couplings = 15.5. 2 = 8. 2 1/2 = 2. 3 w/2 1/2 = 0.8. 3 w/3 = 0.677. 3 1/2 = 0.34. 4 = 0.2. 4 1/2 = 0.1. 5 = 0.08. 6 = 0.05.
Stand pipes - 4 = 0.374. 5 = 0.126. 6 = 0.052.
When conducting coefficients test on hose test only what at a time?
The same type of hose.
List what tools are required to conduct a coefficient test on fire hose.
Pitot tube or flowmeter. Two inline meters calibrated in increments of 5 psi. Hose to be tested. Smoothbore nozzle (if using a pitot tube). Any nozzle (flowmeter).
How much hose should be layed out when doing coefficient testing, if the hose is in 50’ length? 100’ lengths?
50’ = 300’ / 100’ = 400’
When doing coefficient testing on hose where should the gauges be placed?
Gauge 1 = At the connection between the first and second length of hose. Gauge 2 = 200’ from gauge one (no matter the length of hose sections being used).
If using a flowmeter while doing coefficient hose testing, where should it be placed?
Anywhere NOT between the meters.
When conducting coefficient hose testing, how many test should be done?
3-4 test, each test having a different PDP.
What should be recorded when conducting a coefficient hose test?
PDP. Gauge 1 and 2 readings. Flowmeter or pitot gauge readings.
List hoseline appliances.
Reducers. Increasers. Gates. Wyes. Manifolds. Aerial apparatus. Standpipe Systems.
Appliance friction loss is insignificant in what cases?
When the flow is less than 350 gpm.
In the text a master stream is considered to have a 25 psi friction loss not matter what?
The GPM flowing.
Water exerts a pressure of ……….psi per foot of elevation.
0.434
Elevation pressure equation.
EP=0.5H or EP = 5 psi x (#of stories - 1).
What are the two basic categories of hose layouts?
Simple and Complex
What type of hose layouts are considered simple?
Single hoselines. Multiple but equal length. Equal wyed lines. Equal Siamese lines.
The most common used hose layout.
Single Hose line
What can be done to keep friction loss in check when large amounts of water are needed?
Lay two or more parallel hoselines and Siamese them close to the fire.
When two hose lines of equal length are siamesed, friction loss is approximately ………. of that of a single hoseline at the same nozzle pressure.
25%
When three hoselines of equal length are siamesed, friction loss is approximately …… of that of a single line if equal nozzle pressure is maintained.
10%
Friction loss coefficients. Siamesed lines of equal length.
Two 2 1/2" = 0.5. Three 2 1/2" = 0.22. Two 3" w/2 1/2 coupl = 0.2. One 3" w/2 1/2" coupl, one 2 1/2" = 0.3 One 3" w/3" coupl, one 2 1/2" = 0.27 Two 2 1/2", one 3" w/2 1/2" coupl = 0.16 Two 3" w/2 1/2" coupl, one 2 1/2" = 0.12
Name examples of complex hose lay outs.
Stand pipe operations. Unequal length multiple and wyed hoselines. Manifold hoselines. Master Streams.
Most FD’s have predetermines pressures for what?
FDC’s
It is not usually necessary to calculate the friction loss in hard piping because why?
It has little effect on the end result.
With multiple lines of unequal size, the total pressure loss in the system is based on what?
The highest loss of the lines.
If a hose line calculation includes a master stream with multiple lines of unequal length supplying it, what should be used?
A average of the hose line length. Add the length of all hose lines and then divide by the number of hoses supplying the master stream. Use the Siamese lines coefficients.
If a master stream devices is being supplied by a combination of hoses that is not listed on the Siamese coefficient chart, what should you do?
Assume each line is flowing an equal amount of water.
What psi loss is in a aerial water way in the manual? Is elevation included in that?
25 psi. No, elevation still has to be factored in.`
Remember to use Siamese coefficients when what?
There are multiple lines feeding a Siamese or master stream!!!
What is a standard fog nozzle pressure? Low pressure fog nozzle?
Standard = 100. Low pressure = 50 or 75 psi.
Centrifugal fire pumps are able to take advantage of what?
Incoming pressure
The difference between the pump discharge pressure and the incoming pressure from the hydrant.
Net Pump Discharge Pressure (NPDP)
Take into account all factors that contribute to the amount of work the pump must do to produce a fire stream.
Net pump discharge pressure (NPDP)
Net pump discharge pressure equation.
NPDP = PDP - Intake Reading. (not true when operating from a draft)
