Ch. 8 Fireground Hydraulics Calculations

Question 1

When relaying to another pumper when do you know you’re at the correct PSI?

Answer 1

increase PSI until flowmeter no longer increases

Question 2

Flowmeters

Answer 2

-Reduce the number of pressure calculations required by driver
-Measures and display water flow in gallons per minute (GPM)
-NFPA 1901 for every discharge outlet equipped with flowmeter, a pressure gauge shall also be provided
-Must display flow in increments of 10 GPM
-Each discharge equipped w/ one must have a digital readout within 6 inches of the control valve. If PSI guage is also located there, they must be within 2 inches
-Flowmeter should be accurate to tolerance of +/- 3%
-Meaning should not be more then 3 gallons high or low for every 100 GPM

Question 3

Types of Flowmeters

Answer 3

• Paddlewheel- Mounted at the top of a straight section of discharge pipe so only a small portion of device extends into waterway
  -Reduces the impediment to waterflow and lessons the chance of damage from and debris in the pipe
• Spring probe- Stainless steel spring to detect water movement greater the flow more the springs bend
  -Maintenance free with only one moving part

Question 4

Relay Pumping

Answer 4

• May feed a supply line without knowing the volume of water flowing from receiving pumper
• As you increase throttle, the discharge reading on flowmeter will rise
  -increase until the flowmeter reading no longer increases
• Intake pressure cannot be allowed to drop 20 psi

Question 5

Hydraulic Calculators

Answer 5

• will determine the pump discharge pressure required for virtually any hose layout
• may be either manual or electronic

Question 6

Condensed Q Formula

Answer 6

3 inches. FL=Q²
FL per 100 feet= Q²
Q= number of hundreds of gallons the square it
Amount will be 20 percent greater than FL formula
Example 200gpm discharged from nozzle 100 feet of 3-inch hose
Q= 200gpm divided by 100 =2
FL = 2² = 4 psi per 100 feet 3-inch hose

4 inches FL=Q²/5
FL per 100 feet = Q square divided by 5
Q= number of hundreds of gallons per minute
Example pressure loss in 500 feet 4-inch flowing 1,000 gallons
Q= 1,000 gpm divided by 100 = 10
Fl= 10²= 100 dived by 5 = 20 psi per 100 feet 4 inch
TPL= 20 x 5 (500 hose length) = 100 psi

5 inches FL=Q²/15
FL per 100 feet= Q squared divided by 15
Example 800-foot layout of 5-inch hose flowing 1,000 gallons
Q= 1,000 gpm divided by 100= 10
FL= 10² = 100 divided by 15= 6.67 psi per 100 feet 5-inch
TPL= 6.67 x 8 (800 hose length) = 53.36 psi

used for 3, 4, and 5-inch hose

Question 7

GPM Flowing method

Answer 7

-Used for solid and fog streams
-Does not apply with 2 ½ inch hose flowing less then 160 gpm
-Subtract 10 from the first two numbers of gpm flow
-Accurate loss per 100 feet 2 ½ -inch hose is obtained

Example:
Total pressure loss due to friction in a 400-foot layout of 2 ½ using 250 gpm fog nozzle 100 psi
Flow= 250gpm
FL= 15 psi per 100 feet 2 ½ inch hose
TPL= 15x4= 60 psi in 400 feet of 2 ½ -inch hose

1 ½ -inch hose divided into three sections:
- Upper section Represents flows from 50-75 gpm
-Shows friction loss is the same as it is in 2 ½ -inch hose with four times as much water flowing
Example flowing 50 gpm first multiply the flow times four which is 200 gpm. Then subtract 10 from 20 (200gpm). The result is 10 psi per 100 feet
- Middle Section Represents flows from 80-100 gpm
-Friction loss simply increases by 3 psi for every 20 gpm increase in flow through a 2 ½ -inch hose
- Lower Section Represents flows from 105-125 gpm
-Friction loss increases 4 psi for every 20 gpm increase in flow through a 2 ½ -inch hose