LET’S DO SOME MATH!
Fire Service Hydraulics
During this presentation, we are going to explore
the how and why of fire service hydraulics.
We are going to start out fairly basic, and with
each detail we cover, we will discover why it is
important to know this material, and how it
affects our performance on the fire ground.
Fire Service Hydraulics
Some of this information may not be directly
related to ‘hydraulics,’ but you will see how it ties
together.
Whatever happens, don’t be intimidated by the
math. We’ll take it one step at time so that it is
completely understandable.
For some, this is fairly new territory, and for others,
it will be a good refresher.
Let’s get started.
Fire Service Hydraulics
Why are hydraulics critical?
We want the fire fighter to fight the fire, not the hose line. That is why
knowing fire service hydraulics is so critical.
Knowing hydraulics gives the fire engineer important safety information
He needs to know:
• what the apparatus discharge
pressures need to be,
• how much friction loss will
he have to deal with,
• how much water is left
in a hydrant.
Fire Service Hydraulics
It is critical to understand where the numbers come from
when operating an apparatus pump.
Odds are, your fire department has a “rule of thumb”
regarding pump pressures for pre-connected hose lines
or lines that are used more often. Therefore, you don’t
have to remember or try to use these formulas at a fire.
Unless the hose lay is different from what you are used
to, a “rule of thumb” should work fine.
BE AWARE …
If you don’t know these formulas, you will one day need
them because of a different hose lay, and it will happen
at the worst possible time.
Fire Service Hydraulics
Let’s go over some definitions
Order of Operations
Co-efficient
Square & Square Root
More to come …
Fire Service Hydraulics
Order of Operations
This is one of those math rules we have to live
with. It basically states that certain math
operations (add, subtract, multiply, divide) will be
completed prior to others.
Rule 1: First perform any calculations
inside parentheses.
Rule 2: Next perform all multiplications and
divisions, working from left to right.
Rule 3: Lastly, perform all additions and
subtractions, working from left to right.
Please Excuse My Dear Aunt Sally
#1 Parenthesis
#2 Exponents ( sq and cubes)
#3 Multiply
#4 Divide
#5 Add
#6 Subtract
Please Excuse My Dear Aunt Sally
Here’s an example
4+5x6–7
1st is to multiply 5 x 6 = 30
4 + 30 - 7
2nd is to add 4 + 30 = 34
34 - 7
Lastly, subtract 34 – 7 = 27
27 is the answer.
Fire Service Hydraulics
Why is this important?
When calculating friction loss formulas, the
order of operation is critical otherwise you
will not get the correct answer.
Remember the 6 steps and you can’t go
wrong.
Co-efficient
Co-efficient is the resistance of one material
passing next to another material.
For example, water passing next to the
material inside of a fire hose.
For our purposes, we will define Co-efficient
as the resistance to flow of water inside of
a hose.
Fire Service Hydraulics
Why is this important for me to know?
With every different size, length and type
of fire hose, the amount of resistance to
water flow will change. When the
resistance of flow changes, the pressure
needed at the pump discharge will also
change.
Co-efficient
The Coefficient of a fire service hose is
expressed with a numerical value.
The higher the numerical value, the higher
the coefficient. This means that more
energy is required to push the water
through the fire hose.
Square(²) and Square Root (√)
To find the square of a number, simply
multiply that number times itself.
Example -- 4² = 16 is the same as 4 x 4 = 16
Or
7.07 ² which is 7.07 x 7.07 which equals 50.
FYI- 50 happens to be the nozzle pressure for
hand lines with smooth bore nozzles.
Square(²) and Square Root (√)
For square root (√) operations, we must
determine the two exact numbers, that
when multiplied by each other, equal the
number that we already have. (clear as
mud?)
The square root of 64 is 8.
8 x 8 = 64. Easy enough.
It is written to look like this
√64 = 8
Square(²) and Square Root (√)
Fortunately for us in the fire service, there are only
two main square roots we need to know.
They are 50 and 80:
• 50 is the amount of pressure for a hand line with
a smooth bore nozzle
• 80 is the amount of pressure for a master stream
device with a smooth bore nozzle
Fire Service Hydraulics
With this information, let’s find the square root ‘√’
of these two nozzle pressures.
1st – smooth bore pressure of a hand line is 50 psi
√50 = 7.07
2nd – smooth bore pressure of a master stream
device is 80 psi
√80 = 8.94
Fire Service Hydraulics
Let’s try a couple more square root
problems with a calculator.
√81 = ?
√36 = ?
√88 = ?
*NOTE* Go to the next slide for some tips on using the Windows calculator.
Fire Service Hydraulics
A couple of tips for using Windows® calculator:
With Windows calculator using square roots, enter the number that you
want to find the square root of and then click “sqrt”.
To find a number’s “square” with this calculator:
Select ‘View’
‘Scientific’
Enter the number you would like to square, and then press the “x^2”
key
Note: You will need the decimal equivalent of the fraction part of the tip
size to enter into the calculator. The next slide has a table with
fraction and decimal equivalents.
Fire Service Hydraulics
To find the decimal equivalent of any
fraction, divide the top number by
the bottom number.
Fraction
Decimal
1/16”
.0625
1/8”
.125
1/4”
.25
3/8”
.375
1/2”
.5
5/8”
.625
3/4”
.75
7/8”
.875
Fire Service Hydraulics
Did you get …
√81 = 9
√36 = 6
√88 = 9.380831519646859109131260227
To shorten this a bit we’ll say 9.4
Please Excuse My Dear Aunt Sally
O-K
Now, let’s put a couple of the things we’ve learned
together.
4 * √49 = ?
Did you get…
4 * √49 = 28?
Please Excuse My Dear Aunt Sally
Let us try another one …
5.5 * 2.5²
Did you get …
5.5 * 2.5² = 34.375
Excellent!
Fire Service Hydraulics
The following formula is the one that
will be used the most.
This little math formula will work with fog nozzles
and smooth bore nozzles.
We are going to find Friction Loss using only
hoses, no appliances. (example: a gated wye)
Fire Service Hydraulics
Finding Friction Loss
FL = C*Q²*L
FL = Friction Loss
C = Friction Loss Coefficient
Q² = Flow rate in hundreds of gallons
(flow/100 and then squared)
L = Hose length in hundreds of feet
(length/100)
Fire Service Hydraulics
We’ll start off with “C” which is
the hose coefficient.
“C” = the resistance to flow of water
inside of a hose.
The table on the next slide lists several sizes of fire
hoses and their coefficients.
Fire Service Hydraulics
You can print this for future reference
this is slide #27
Hose Size
¾” redline
1 ½” line
Coefficient
1,100
24
1 ¾” line with
15.5
1 ½” couplings
2 ½”
2
3”
.8
4”
0.2
5”
0.08
Fire Service Hydraulics
Next is “Q²” which is the flow
rate of the water.
Note: Unless you know the flow rate of the nozzle
that you are using, you will have to use another
formula (which we will discuss later) to find your gallons
per minute. Once this value is known, we have
to divide it by 100 and then square the result
Q= (nozzle flow/100) ²
Fire Service Hydraulics
Now, let’s try one. Using an adjustable
gallonage fog nozzle with the flow rate set
at 125 gallons per minute.
Divide 125 by 100= 1.25
Then square it, 1.25² = 1.56
Fire Service Hydraulics
“L” = Total feet of hose divided by 100.
Example: 150 feet of any size hose is
150 / 100 = 1.5
Note: Hose diameter is not important for this
part of the equation.
Also note: Some fire service hydraulic calculations use hose length
as 100’ minimums, even if it requires two sections to make a 100’.
We will look at these in more detail later on.
Fire Service Hydraulics
Now let’s put this together.
150 feet of 1-1/2” hose flowing 125 gallons
per minute. We know that we need 100
pounds of pressure at the fog nozzle.
Fire Service Hydraulics
FL = C*Q²*L
C=24
(from the hose coefficient table)
Q²=1.56
(125 gallons per minute divided by 100 and then squared)
L=1.5
(150 feet of hose divided by 100)
Our formula is:
FL=24*1.56*1.5
Fire Service Hydraulics
FL=24*1.56*1.5
Did you get …
FL = 56 ?
Let’s try another one.
Fire Service Hydraulics
FL = C*Q²*L
You are flowing 250 gallons per minute through
2-1/2” line that is 200 feet long.
Fire Service Hydraulics
Did you get
FL = 25 ?
Very Good.
We know now that we have 25 psi of friction
loss in our hose lay.
Remember, we have to have 100 psi at the
nozzle for adequate water flow. With that
said, what does our pump discharge
pressure have to be?
Fire Service Hydraulics
Let’s have another formula for that.
EP = NP + FL
EP = Engine Pressure (pump discharge pressure)
NP = Nozzle Pressure (which is 100 psi)
FL = Friction Loss (which we now know is 10 psi)
EP = 100 + 25
Engine Pressure (pump discharge pressure) = 125 psi
Fire Service Hydraulics
Remember, we want the fire fighter to fight the fire,
not the hose line. That is why knowing fire
service hydraulics is so critical.
Fire Service Hydraulics
We mentioned about finding flow rates or
gallons per minute (GPM).
Before we go any further, the following formula is
used for smooth bore nozzles. Depending on the
region and department you are on, you might
not use smooth bore nozzles often, but it is
important to know how this formula works.
GPM for smoothbore nozzles
The formula used to determine GPM
for smoothbore nozzles.
GPM = 29.7 * d² * √NP
Fire Service Hydraulics
GPM = 29.7 d² √NP
• 29.7 is a constant
• d² = the diameter of the nozzle squared
• √NP = square root of the nozzle pressure
– Master stream devices operate at 80 psi
therefore the square root will be 8.9
– Handline devices operate at 50 psi therefore
the square root will be 7.07
Fire Service Hydraulics
What is d² when using a 1-1/4 inch
smooth bore tip?
1-1/4²
Or
1.25 * 1.25
(Refer to slides 20 & 21 if you need assistance)
Did you get
1.56?
Great!
Fire Service Hydraulics
Finally, the square root (√) of the
Nozzle Pressure (NP)
We discussed earlier that the nozzle pressure for a
smooth bore master stream device is 80 psi.
So, the square root of 80 is 8.9
√80 = 8.9
Fire Service Hydraulics
O-K, let’s put it together.
GPM = 29.7 * d² * √NP
Our example:
We are flowing a hand line with a 7/8”
smooth bore nozzle.
Fire Service Hydraulics
O-K, Did you get 160 GPM?
GPM = 29.7 * d² * √NP
gpm = 29.7 * .765 * 7.07
gpm 22.7 * 7.07
160 gpm
The next slide is very important.
Fire Service Hydraulics
CHEAT! Every Chance You Get!
Not on a test, but at a fire.
Use EVERYTHING to your advantage at a
fire. The fire does not care!
With that being said,
Remember two things:*
Fire Service Hydraulics
*The square root of a smooth bore nozzle on a
hand line is 7.07
*The square root of a smooth bore on a
master stream device is 8.9
Use the chart with decimal conversions on slide #20.
Develop your own conversion charts that you have easy
access to at a fire.
If you do this, you will not be known as a ‘cheater’ but as being
clever. Your chief will say, “That engineer knows his stuff”.
Use everything to your advantage.
Fire Service Hydraulics
Let’s try one more GPM formula.
You are flowing water through a master
stream device with a 1-3/8” tip.
GPM=29.7 *d² * √NP
Fire Service Hydraulics
O-K, Did you get 499 GPM?
EXCELLENT !
If you have any questions about this stuff don’t hesitate to let me know.
I can be reached via e-mail at
dale@lonestarfirespecialties.com
Please include your phone number on the e-mail
thanks
Fire Service Hydraulics
Next Step:
We have discussed finding friction loss, engine pressure,
and gallons per minute.
Let’s put it together.
You are pumping at a commercial structure fire.
You have a hand line on the ground with 200 feet of 1-3/4”
hose with a 3/4” smooth bore tip.
What is your:
1: GPM
2: Friction Loss
3: Engine Pressure
Fire Service Hydraulics
Let’s start with GPM.
We have a hand line (7.07) with a 3/4” (.75)
tip.
GPM = 29.7 * d² * √NP
GPM = 29.7 * .56 * 7.07
Fire Service Hydraulics
Did you get 118 gallons per minute?
Good.
Now we have to find friction loss.
FL = C * Q² * L
Fire Service Hydraulics
Friction loss
FL = C * Q² * L
We know from the chart on slide 27 that C = 15.5 and the flow is 118
gpm. Don’t forget we divide the flow by 100 and then square it.
118 / 100 = 1.18
1.18² = 1.39
Q² = 1.39
So far we have FL = 15.5 * 1.39 * L
L is the total length of the hose divided by 100
200 / 100 = 2
THUSLY,
FL = 15.5 * 1.39 * 2
Fire Service Hydraulics
Did you get 43 pounds of friction loss?
Great!
Now all we need is (EP) Engine Pressure
Fire Service Hydraulics
(EP) Engine Pressure
EP = NP + FL
EP = 50 + 43
EP = 93 psi
Fire Service Hydraulics
Wonderful.
So, our answers are:
1: GPM is 118 gpm
2: Friction Loss is 43 psi
3: Engine Pressure is 93 psi
Fire Service Hydraulics
One more …
(This part’s almost over)
You are operating your apparatus at a commercial
structure fire with 250 feet of 2-1/2 inch hose on
the ground and a 1-1/4” inch nozzle.
Find…
1: GPM
2: Friction Loss
3: Engine Pressure
Fire Service Hydraulics
Here are the formulas you will need:
GPM = 29.7 *d² * √NP
FL = C * Q² * L
EP = NP + FL
Remember…
(any flow over 350 gpm is considered a master stream)
Good Luck & Don’t Cheat.
Cheat on the Fire Ground!
Fire Service Hydraulics
Did you get:
GPM = 413 gpm
FL = 69 psi
EP = 149
Moving right along …
Fire Service Hydraulics
The next section of fire service
hydraulics we are going to cover
deals with everything else.
We will discuss:
• nozzle reaction,
• friction loss due to appliances
• pressure loss or gain due to
elevation.
Nozzle Reaction
Let’s start with Nozzle Reaction.
The main purpose for knowing about nozzle
reaction is to illustrate the force that pushes
back on the nozzle as water is flowing. If the
nozzle is closed there is no nozzle reaction.
Sir Isaac Newton’s laws of physics play a major
role in understanding what we, as engineers,
need to know and have to deal with on the fire
ground.
Nozzle Reaction
Newton said:
For every action, there is an opposite and equal
reaction.
Have you ever operated an attack line and the
engineer had the pressure too high?
You were fighting the nozzle and hose instead of
the fire.
This will explain why.
Nozzle Reaction
There are two formulas for calculating
nozzle reaction; one for smooth bore and
one for fog nozzles.
We’ll talk about smooth bore first.
NR = 1.57 * d² * NP
NR = Nozzle Reaction
1.57 is a constant
d² is the diameter of the nozzle, squared
NP = nozzle pressure
Nozzle Reaction
If we have a hand line with a 7/8” tip, what will the nozzle
reaction be?
NR = 1.57 * d² * NP
Let’s start with diameter.
d² = .765
We know that because this is a hand line the NP will be 50.
Therefore….
NR = 1.57 * .765 * 50
NR = 60 psi
(click here refer to slide #20 for fraction to decimal conversion)
Nozzle Reaction
60 psi is how much pressure your firefighter is
having to overcome to fight the fire.
Let’s try one more
You have a 1-1/8” tip operating as a master stream
device. What is the nozzle reaction?
NR = 1.57 * d² * NP
Nozzle Reaction
Did you get 158 psi?
Great!
This illustrates how much counterforce your
firefighters are having to deal with while
fighting the fire. THIS is why it is important
to pump the correct pressures.
One more, and that’s fog nozzles
Nozzle Reaction
The formula for finding nozzle reaction for a
fog nozzle is:
NR = 0.0505 * Q * √NP
A couple of differences:
In this equation, Q is total flow.
It is not flow divided by 100 and squared.
Nozzle Reaction
• The second difference is with fog nozzles
we take the square root of the nozzle
pressure, NOT square the nozzle pressure
as with the smooth bore.
Nozzle Reaction
Let’s try this one.
NR = 0.0505 * Q * √NP
Actually, this one is a bit easier because we already know
that most fog nozzles operate at 100 psi, therefore the
square root is 10.
If we have a fog nozzle flowing 150 gpm, our formula looks
like this.
NR = 0.0505 * 150 * 10
(0.0505 is this formula’s constant)
What is the Nozzle Reaction?
Nozzle Reaction
Did you get 75 psi?
Great Job!!
Try one more.
You have a fog nozzle flowing 200 gpm.
Nozzle Reaction
Did you get 101 psi?
The point to this is:
If you pump your apparatus correctly, life
will be easier on your firefighter.
You will be a hero, not a zero.
Moving right along.
Friction Loss due to Appliances
What is an appliance?
An appliance is any fire related device through which water
will flow.
• Friction Loss due to appliances in hand lines is typically
not factored into the equation.
• As a general rule of thumb, calculate the friction loss of
EACH appliance at 10 psi when flow is >350gpm.
• Aerials and Master Streams are 25 psi.
Now, let’s look at a formula we have already worked, and
modify it a little bit.
Friction Loss due to Appliances
EP = FL + NP
Look familiar?
We are going to add in friction loss from one appliance into
this equation.
EP = FL + AFL + NP
*note* for our illustration we are using “AFL” for appliance friction loss. There
are many ways to express this equation. We are doing this for clarity only.
IFSTA® pumping apparatus handbook chapter 8 has more information on
this topic.
SO …
Friction Loss due to Appliances
EP = FL + AFL + NP
If we have two appliances, example a Siamese
and a reducer, AFL will equal 20 psi.
So, all we need to do when creating this equation
is add 20 to the friction loss of the hose and to
the nozzle pressure.
Pressure Loss or Gain due to
Elevation
• How high is the nozzle above you?
• How low is the nozzle below you?
These two questions will need to be answered so
that you, the engineer, can supply your
firefighters with the correct pressure.
Fire Service Hydraulics
Water column is the amount of pressure exerted
by a one foot tall column of water.
A one foot tall column of water exerts .434 psi of
pressure.
(not to be confused with weight)
Real close to ½ pound.
For ease of calculations, we’ll say for every 1 foot
of elevation, we’ll add 1/2 pound of pressure to
our pump.
O-K, have you ever tried adding 1/2 pound of
pressure to your pump?
Pressure Loss or Gain due to
Elevation
We will call these pressure differences either
+EL or –EL
for elevation gain or loss.
In other words, if your firefighter is operating above
your pump on a hill that is approximately 40 feet
high, then you will need to do WHAT?
Add 20 psi to your pump pressure.
This is based on water column pressure.
Elevation Loss
How about this, for every 10 feet of elevation, let’s
add 5 psi to our pump pressure.
Each floor of a building =10 ft or 5 psi
Simple Enough …
Elevation Loss
If we have 40 feet of elevation, let’s add that to our
equation:
EP = FL + EL + NP
So, we have
• Friction Loss of the hose line
• Friction Loss due to elevation
&
• Nozzle Pressure.
Elevation Loss
If you have any high rise buildings in your
response area, friction loss due to elevation
will definitely need to be Added to your EP.
Fire floor -1 * 5 = EL
EL is the same
if you are pumping to a
•
•
hose line that is running up the stairs
standpipe that is installed in the building,.
Fire Service Hydraulics
What happens if our fire operation is below grade?
The same 1/2 pound per foot rule still applies, but
the difference is we subtract that pressure from
our pump discharge pressure.
IF your fire ground is below the pump, in a small
valley, where your apparatus cannot gain
access, and it is 40 feet below the pump,
then …
Fire Service Hydraulics
Subtract 20 pounds of pressure from your pump
discharge pressure.
EP = FL + NP – EL
Friction Loss of the hose
(plus)
Nozzle Pressure that is required
(minus)
Elevation
Fire Service Hydraulics
We’ve done all of this math.
WHY?
The reason:
These formulas are the foundation of what we do
as Engineers on a fire truck. While we might not
use these formulas at all fires, we need to know
where the numbers for the pressures and flows
come from.
Fire Service Hydraulics
As mentioned earlier, nozzles are purchased
for a variety of reasons. It can be because
of brand loyalty, pattern characteristics, or
price.
Fire Service Hydraulics
All fog nozzles, whether they are adjustable,
constant or automatic, will have a flow
rating attached to them. Typically, a
certain flow rate at a certain pressure, AT
the nozzle. Now to get this flow rate
correct, you have to have the correct
pressure at the nozzle which means you
have to compensate for Friction Loss.
Fire Service Hydraulics
We have spent some time going over the
mathematical formulas for finding friction
loss. Please know that this is
IMPORTANT information.
With that being said, let’s cheat.
How is the best way to determine the flow
rate of a fog nozzle?
Fire Service Hydraulics
We have pre-fire plans for our buildings. The strategies
and tactics are outlined, and we have a good idea of
what we’ll do when we get there. Let’s do the same
thing for operating our apparatus pump when we get
there. Just like pre-fire plans, it will take a little effort.
What we want to do is determine the flow and pressure
from a variety of hose line and appliance configurations.
We’ll start by connecting different hose lines and nozzles.
Fire Service Hydraulics
Connect your hose lines in a configuration that you might
use someday on a fire.
Somewhere, between the pump and nozzle, install a flow
meter. Begin flowing water until the flows are correct
and then write down the Engine Pressure.
Simple Enough.
(No Flow meter? Check with your local water company. Many have flow
meters with standard 2-1/2” fire service threads that they will let the fire
department use at no cost.)
Fire Service Hydraulics
Example Chart For Calculating Engine Pressure
(You are welcome to use this chart for any of your equipment, or develop your own chart for the
specific needs of your department. You’re only limited by your imagination!)
Hose
Length
Hose
Diameter
Nozzle
Flow
Rate
Engine
Pressure
Test 1
150’
1-3/4”
adjustable
95
120 psi
Test 2
150’
1-3/4”
adjustable
125
136 psi
Test 3
150’
1-3/4”
automatic
150
152 psi
Test 4
150’
2-1/2”
automatic
275
121 psi
Test 5
250’
2-1/2”
automatic
275
138 psi
Test 6
250’
1-3/4”
SB 7/8”
160
129 psi
Fire Service Hydraulics
So far, we have discussed calculations that are based on
hose coefficients and appliance friction losses that are,
well, kind of old. With new technology, the friction loss of
fire hoses and appliances has decreased through the
last 20 years.
LoneStar Fire Specialties recommends that you conduct
your own tests, with the equipment that you actually
carry on your apparatus and develop charts that can and
will assist you, as an engineer, on the fire ground. They
are easy to create, although it does take a little bit of
effort. We believe that you will find it to be well worth
your time.
Fire Service Hydraulics
Now, let’s look, briefly, at a comparison between
hose sizes and what we are capable of flowing
through them.
For our example, we will assume that we are
flowing 200 gallons per minute through
a 150 feet of hose with a fog nozzle.
What size hose will we need to flow that
amount of water?
( Remember our Friction Loss Formula.)
Fire Service Hydraulics
FL = C * Q² * L
If we use 1-1/2” hose, this is the equation:
FL = 24 * 4 * 1.5
Our friction loss is 144 psi !
For a total discharge pressure of 244 psi.
If we use 2-1/2” hose, this is the equation:
FL = 2 * 4 * 1.5
Our friction loss is 12 psi
For discharge pressure of 112 psi.
See the difference.
Fire Service Hydraulics
Quick Note:
NFPA 1911, pump testing, only requires an
apparatus to pump
70% of rated flow at 200 psi.
Flowing too much water through too small of a
hose will needlessly overwork the engine.
Fire Service Hydraulics
Now, let’s talk about some math that you really do
need on the fire ground.
We have gone through and developed our charts
for all of the hoses, nozzles, and appliances that
we carry on the fire truck. That stuff will remain
constant.
Question: What do we have on the fire ground that
is NOT constant, is dynamic, is always different,
and can change in the middle of a fire?
The Fire Hydrant
Illustration courtesy IFSTA®
Fire Service Hydraulics
In this part of the presentation we’re going to talk
about fire hydrants, our source of water.
We don’t want the word ‘critical’ to become
overused, however, knowing how much water
you have in your fire hydrant is critical.
We are going to look at some more math formulas
to determine how much water is left in a hydrant.
It is always good to understand how to get to the
correct answer by using formulas but, during the
hands on training day we will show you a very
practical and effective way to determine if your
hydrant will support additional flow.
Fire Service Hydraulics
These are the formulas available for the
engineer to use to find the amount of
water available in a hydrant
#1 Percentage Method
#2 First Digit Method
#3 Squaring The Lines Method
Fire Service Hydraulics
With all available math formulas for calculating how much
water is left in a fire hydrant, all of them require that the
engineer know the static pressure.
If you will remember from the Water Supplies presentation,
the difference between static pressure and residual
pressure is that static pressure is water at rest, that is, it
is not moving (flowing) into the fire pump.
Fire Service Hydraulics
If water is flowing into the fire pump, then the
residual pressure is what’s left over.
Again, in order to use these formulas, you have to
know what the static pressure is. In order to do
that, you have to know how to read gauges and
understand what they are telling you.
In many cases, you will use water from the booster
tank to begin fire fighting operations, and then
as more companies arrive, the engineer will be
able to get a constant water supply.
Fire Service Hydraulics
Since that is the case, how can the engineer know what the
static pressure is?
You have to be quick and paying very close attention
to your pump panel.
With that, let’s look at the percentage method.
We covered the percentage method in Water Supplies.
We may have mentioned that it is critical to know how
much water you have left in a hydrant.
No matter which formula or method you choose to use.
Fire Service Hydraulics
A quick note about the order of operations
If any numbers are in parenthesis (), they are to be calculated first.
For example:
(6+4) * (2+3) =
10 * 5
or
(6 + 2²) * (3 + √16)=
(6 + 4) * (3 + 4)=
10 * 7
<<<< Onward >>>>
Fire Service Hydraulics
Percentage Method
Percentage drop = (Static – Residual)(100) / Static
Example – One line flowing 200 gpm
Static pressure 70 psi
Residual pressure 63
Percentage drop = (70-63)(100)/70
Percentage drop = (7)(100) / 70
Percentage drop = 700 / 70
Percentage drop = 10%
Now what?
Fire Service Hydraulics
Our answer is 10%. By using the
chart on the right, we can get very
close and estimate how much
water is left in the fire hydrant.
According to the chart, with 10% left,
we have at least 3 times the
amount of water that is currently
being used. If we are already
flowing 200 gpm, this chart
indicates we have at least another
600 gpm available.
% decrease of
pumper intake
pressure
Additional water
available
0-10%
3 times amount of
water being
delivered
11-15%
2 times amount of
water being
delivered
16-25%
same amount of
water being
delivered
Over 25%
More water
MIGHT be
available
Fire Service Hydraulics
Summary
Fire Service hydraulics are the basis for what we as engineers do. Not only are
we responsible for getting our crews to the scene and back safely, but we have
to operate the truck correctly when we get there. Use what you have learned.
Give your firefighters a break, don’t make them fight the hose.
When LoneStar Fire Specialties comes to your department, you will see first hand
how all of this information can affect your job performance on the fire ground.
Fire Service hydraulics isn’t the most fun you can have, but this we guarantee,
during the hands on training,
You will have a blast!
We’ll see ya soon!
And again, if you have any questions about this topic or any others, please let me
know.
e-mail to dale@lonestarfirespecialties.com
Please don’t forget to include your phone number.
Thanks and have a GREAT Day !