# Thread: 5" vs 3" supply hose

1. ## 5" vs 3" supply hose

Help me out! I'm trying to gather some info to help with a 'discussion' at my station. We have extra 5" hose and we want to put 500' on our one engine that currently only has 3" since our hydrants are spaced on 500' intervals(where we have them that is).

I have a member who says that its a waste of time there's nothing that 5" can do that dual 3's can't do and besides 3" is easier to pick up. Unfortunately some people take this man's word as gospel.

Admittedly I am not one of those number crunching water flow guys so I am looking to you guys for some help to justify(or not) the addition of the 5"

Bottom line is for comparison sake how many 3" lines does it take to equal or exceed a single 5" lay? Oh yeah and this is like high school math class... show your work please!

2. This has been talked about a lot. Check out:

Synopsis: 5" is way better because of the decrease in friction loss.

3. There is always less friction loss in the large hose, regardless of water flow. Go with the 5". 2 - 3" lines has friction loss closer to 1 - 4" line.

4. Originally Posted by FFTrainer
Help me out! I'm trying to gather some info to help with a 'discussion' at my station. We have extra 5" hose and we want to put 500' on our one engine that currently only has 3" since our hydrants are spaced on 500' intervals(where we have them that is).

I have a member who says that its a waste of time there's nothing that 5" can do that dual 3's can't do and besides 3" is easier to pick up. Unfortunately some people take this man's word as gospel.

Admittedly I am not one of those number crunching water flow guys so I am looking to you guys for some help to justify(or not) the addition of the 5"

Bottom line is for comparison sake how many 3" lines does it take to equal or exceed a single 5" lay? Oh yeah and this is like high school math class... show your work please!

It takes 3 3" lines to equal 1 5 " line

ie. 1000 gpm

1000gpm/3= 333gpm (Q)

.8x(3.33x3.33)=8.87112 psi/100ft

now for 5"

.08x(10X10)=8 psi/100ft

Now that you are wondering what the h***

The formula is

FL= CQ2L

FL- Friction loss
C- hose diameter coefficient
Q2- gallonage(Flow divided by 100) then squared
L-length of hose divided by 100

the " C" for 3" is 0.8

the "C" for 5" is 0.08

the "C" for 4" is 0.2

1.5"-24.0

1.75"-15.5

2.0"-8

2.5"-2

Don't forget these calculations are theoretical...

actual flows can differ with brand and age of hose.

Not all hose of same diameter will flow the same.

Hope this helps a bit.

Don

5. FFTrainer-
My calcs show that it takes closer to 4 - 3" lines to equal that of a single 5". I use Hazen-Williams, which the std. empirical friction loss formula for water at normal range of temps.
That formula is FL = [(4.52 * Q^1.87)/(C^1.87 *d^4.87)]*L
where
Q is flow in gpm
C is the friction factor
d is diamter in inches
L length in feet

With a C-factor in the range of 180-190 which is typical for modern hose, for a 500 ft. lay, friction loss is equal at about 20 psi for 1000 gpm thru the 5" and 260 gpm for each 3". So that's almost 4 - 3" to equal the 5"

Another way to look at it - if you dept primarily uses a forward lay without a pumper on the hydrant, the 5" will move 1000 gpm with 20 psi of FL. So if you have 40 psi hydrants at 1000 gpm or better you can flow the entire 1000 gpm (leave 20 psi residual at the hydrant, 20 psi for FL, and take your pump suction just to about 0). If you want to try to move 1000 gpm through your dual 3's, that's almost 70 psi of FL in a 500 ft lay and now you need a 90 psi at 1000 hydrant.

If you are making forward lays with no engine on the hydrant, dual 3's is not even in the ballpark of 5" unless you are satisfied with 300-500 gpm max.

If you reverse lay typically or always put an engine on the hydrant, then I would probably say the other member is at least got an argument because you make up for the higher FL with pump pressure, particulary if you are only talking 500 ft.

One option you might consider as middle of the road is go 4". 4" will slightly out perform the dual 3's and now you have just a single line to pick up vs. the dual 3's and I've never heard anyone complain about the size of 4".

6. And anybody who thinks that it is easier to pick up two lengths of 3" vs one length of 5" needs to have his head examined...that is twice the number of feet to pick up not to mention if you are actually laying comparable hose lines as stated you will need 3 or 4 of these 3" hoses to equal that one 5". That's going to take a lot more time and energy to pick up no matter how you slice it

Birken

7. Originally Posted by kfactor

One option you might consider as middle of the road is go 4". 4" will slightly out perform the dual 3's and now you have just a single line to pick up vs. the dual 3's and I've never heard anyone complain about the size of 4".

No malice intended, but "settling" with 4" is doing nothing short of saying that you find it acceptable to lose out on the ability of higher end flows when really needed. The real issue here is we're so lacking in expierencing big fires that we get away with small supply hose, poor supply line configurations, no relay valves or no engines on hydrants etc. Sure, it works for the typical bedroom fire, but wen you've got a house well off thats moving into the exposures and you can only get a measly 800 gpm from your dual 3's or single 4" line then you are F'ed. Why buy the big pump and carry small hose??? Dont be lazy or make uninformed decisions. Plan to deal with what we exist for, fires.

8. Finally found my book...

From IFSTA Driver/Operator 1st Ed. (c) 1999

Maximum relay distance in feet (with 20 PSI residual pressure)

250 GPM
Single 3": 3600 ft
Dual 3": 14,400 ft
Single 4": 13,200 ft
Single 5": 33,000 ft

500 GPM
Single 3": 900 ft
Dual 3": 3600 ft
Single 4": 3300 ft
Single 5": 8250 ft

1000 GPM
Single 3": 225 ft
Dual 3": 900 ft
Single 4": 825 ft
Single 5": 2050 ft

This data reflects the lines as pumped from engine to engine with the typical 20 PSi residual factor added. It is easy to figure if you run your own numbers.

The math is simple...
-Figure the friction loss per 100'
-determine total friction loss

You can also flow test a few hydrants to determine your typical flows/pressures to use with the above valculation.

Remember, without an engine boosting the plug, your hydrant discharge pressures would need to add the total friction loss per given flow. I doubt the hydrants you have can perform at the pressures we're talking about. So the listed flows aren;t possible until your second due engine arrives.

An easy way to think about the pressure required to move water through supply hose is think of the residual pressure of a hydrant as the pressure you would pump from your engine if you were in relay (or on the plug). The hydrant cant increase its pressure when it is flowing, so as you demand more water from it, its pressure will drop, thereby reducing the distance it can move that water due to friction loss. Using smaller hose will seriously impact this distance and efficiency.

So at the end of todays lesson we learned that if you went out and replaced all of your dual beds of 3" line with single beds of 4" you actually went backwards in efficiency!!

9. So at the end of todays lesson we learned that if you went out and replaced all of your dual beds of 3" line with single beds of 4" you actually went backwards in efficiency!! [/QUOTE]

So prof...show us all the simple math to back up what you said....

My calculations says they flow equal using the formula

FL=CxQ2xL

C=.8 for 3"
C=.2 for 4"

That being said it takes 2000 ft of 3" hose to the work of 1000 ft of 4" hose
thats alot of hose to roll up after a fire.

The above formula comes from IFSTA and the results of the math
say they both have 20lbs.FL /100ft.

Don

10. Yep, youre right. After I spent time with my book its about the same. I posted the first time in a rush without time to double check my numbers. I used to be pretty skeptical of double 3" lines, now I can see that they certainly still have a place if thats what you've been using and you have decent hydrants/spacing etc. I'll take a spoonful of crow now, thanks

My quote should more resemble that if you are happy with the flow performance of dual 3's than switching to single 4 makes sense. If youre looking to increase total flow or efficiency at any given distance, switch to 5". If you're going to buy new hose, all of the above information should be taken into account.

Heres what I did on my scratch pad tonite. I'll preface this by saying I used simple formulas and charts and my IFSTA Book. My crude formula is basically the FL formula you use to calculate discharge lines. EP=NP+FL

Where

EP equals the required hydrant pressure or pump discharge pressure to move the given GPM's

NP=the residual pressure of 20 PSI

FL=the given friction loss of the hose

I took 250 (operating pressure of 3" hose) minus 20 for 230 PSI maximum allowable friction loss in this hose. 230/5 equals 46 (max FL per 100'). On a pocket chart I took the closest FL (45 PSI for 750 GPM).

I took 180 (operating pressure of typical 4/5" hose) minus 20 for 165 PSI maximum allowable friction loss in this hose. 165/5 equals 33 (max FL per 100'). On a pocket chart I took the closest FL (43.2 PSI for 4" and 26.4 PSI for 5").

The result doesn't show the exact max flow, but comes close enough to show comparisons. Someone here can probably refine it a bit.

Somehow I know there's an easier way to do it, but after cross checking my findings they confirm. So, from a non-math wiz. There ya have it.

Over 500', you can expect the following "APPROXIMATE" flows/pressures
Single 3": 750 GPM delivered @ 245 PSI
Dual 3": 1500 GPM delivered @ 245 PSI (ea)
Single 4": 1300 GPM delivered @ 182 PSI
Single 5": 2000 GPM delivered @ 152 PSI (prob. closer to 2200 GPM)

The above figures acount for 20 PSI residual and assume 250 PSI max operating pressure for 3" and 185 Max for 4"/5". I know that there are different hose pressure ratings with new vs. old hose and brands etc. I had to use something as a baseline.

11. Sorry for the slightly skewed info, here's my thought process...

I felt it appropriate to explain my position when making the reply to this particular topic. When first reading this, it was a question I've asked others, heard asked and read about in the past. I didn't have a definitive answer in my head, other than I know enough about hose to know that 5" outperforms all its junior competitors. This question presented me a challenge. I dug out my IFSTA book and FL chart, got a note pad and calculator, sat down after dinner and punched numbers like a fool. As an educated educator, I recognize not all of us in this field are math gurus, I can attest to that. I HATE math. I love pumps, engine work and the like, but suck at math. It's been my goal in educating others to find ways to teach the concepts without the use of complicated formulas and equations. Decide for yourself if thats right, wrong or indifferent.

With the aforementioned points being considered, I felt that the original poster needed some numbers to take back that were simple and proof enough to close the case. Not a Q=A+xyz-3(2)+82 etc equation. To me, this argument ends when you prove two things. What is the maximum GPM you can flow through each diameter line and what is the maximum distance you can flow several predetermined flows. Thats what I did. Hope it helps. I'll keep watching and hopefully learn a thing or two. Thanks for keeping me straight.

12. Originally Posted by MG3610
Yep, youre right. After I spent time with my book its about the same. I posted the first time in a rush without time to double check my numbers. I used to be pretty skeptical of double 3" lines, now I can see that they certainly still have a place if thats what you've been using and you have decent hydrants/spacing etc. I'll take a spoonful of crow now, thanks

My quote should more resemble that if you are happy with the flow performance of dual 3's than switching to single 4 makes sense. If youre looking to increase total flow or efficiency at any given distance, switch to 5". If you're going to buy new hose, all of the above information should be taken into account.

Heres what I did on my scratch pad tonite. I'll preface this by saying I used simple formulas and charts and my IFSTA Book. My crude formula is basically the FL formula you use to calculate discharge lines. EP=NP+FL

Where

EP equals the required hydrant pressure or pump discharge pressure to move the given GPM's

NP=the residual pressure of 20 PSI

FL=the given friction loss of the hose

I took 250 (operating pressure of 3" hose) minus 20 for 230 PSI maximum allowable friction loss in this hose. 230/5 equals 46 (max FL per 100'). On a pocket chart I took the closest FL (45 PSI for 750 GPM).

I took 180 (operating pressure of typical 4/5" hose) minus 20 for 165 PSI maximum allowable friction loss in this hose. 165/5 equals 33 (max FL per 100'). On a pocket chart I took the closest FL (43.2 PSI for 4" and 26.4 PSI for 5").

The result doesn't show the exact max flow, but comes close enough to show comparisons. Someone here can probably refine it a bit.

Somehow I know there's an easier way to do it, but after cross checking my findings they confirm. So, from a non-math wiz. There ya have it.

Over 500', you can expect the following "APPROXIMATE" flows/pressures
Single 3": 750 GPM delivered @ 245 PSI
Dual 3": 1500 GPM delivered @ 245 PSI (ea)
Single 4": 1300 GPM delivered @ 182 PSI
Single 5": 2000 GPM delivered @ 152 PSI (prob. closer to 2200 GPM)

The above figures acount for 20 PSI residual and assume 250 PSI max operating pressure for 3" and 185 Max for 4"/5". I know that there are different hose pressure ratings with new vs. old hose and brands etc. I had to use something as a baseline.

Don't forget a class A fire pump gives:\

100% of rated capacity at 150psi
70% " " at 200psi
50% " " at 250psi

So to pump 1500gpm through 2x3" at 245psi with one pumper ???

I haven't seen too many 3000 gpm pumpers around.

And yes, higher than rated capacities of a given pumper can be achieved
but it requires large case pumps,(ie.Hale Q-Max) horsepower and if at draft,
suction hose on both sides of the pump.
I have seen a 1500gpm pump do 2400gpm from draft this way.

13. Originally Posted by don120
Don't forget a class A fire pump gives:\

100% of rated capacity at 150psi
70% " " at 200psi
50% " " at 250psi

So to pump 1500gpm through 2x3" at 245psi with one pumper ???

I haven't seen too many 3000 gpm pumpers around.

And yes, higher than rated capacities of a given pumper can be achieved
but it requires large case pumps,(ie.Hale Q-Max) horsepower and if at draft,
suction hose on both sides of the pump.
I have seen a 1500gpm pump do 2400gpm from draft this way.
All what you have said is true but remember that the pressures the pump is rated at are additive, therefore if you need 245 EP to pump the dual 3s, but have 80 psi coming in from the hydrant to the suction of the pump (that's what it is around here) your pump only needs to add 165 psi, which, if it is a fresh pump, is exactly the overload rating it is tested to at full capacity, therefore you could get 1500 through those dual 3s but that is assuming a hot hydrant and you are using every ounce of the pump's rated capability and then some.

Birken

14. Originally Posted by don120
I haven't seen too many 3000 gpm pumpers around.
We have one. Its actually only rated at 2500 but with 4 6" intakes and 4 12' lengths of suction hose, it can pump 3500 GPM.

Its also easier and more efficient at higher pressures if you have a 2 stage pump, which is becoming a thing of the past.

We also have quite a few hydrants on 16" mains with 80-110 PSI static pressures that flow test at 3000+ GPM

15. Originally Posted by don120
Don't forget a class A fire pump gives:\

100% of rated capacity at 150psi
70% " " at 200psi
50% " " at 250psi

So to pump 1500gpm through 2x3" at 245psi with one pumper ???
I never identified the hydrant/pumper setup required for the flows, that wasn't my point. My point was to identify the hose flow capabilities. I simply posted the approximate maximum expected flows from the given hose lays.

I have a hard time reading the intent of your posts. If you are just trying to play the I'm right/you're wrong game...whatever. I'm not an idiot. I also fessed up to my errors and moved on. I'f you're just razzin me, thats fine.

Any half interested operator should understand that you need a pumper on the plug or a good hydrant to acheive some of the flows I Identified.

If all a company uses is dual 3's, then I would imagine that at some point in time they might need to pump 1500 GPM. If thats something that they can't do because the pumps on their rigs arent big enough or they have bad hydrants, then they arent providing good service/proper equipment to their district.

The concept of net engine pressure (the pump adds energy to the incoming water), as Birken described is something you didn't mention when you were trying to discredit my numbers. When we pump our handlines, it's usually on almost engine idle speed because we work off hydrants and only have to make up an additional 20-50 PSI or so.

16. I don't mean to razz you, I've been an instructor at a Vermont fire school
for over ten years.Many firefighters read these forums.When we start talking
pumping capacities and friction loss,the ability of centrifical pumps to
"profit" from hydrant pressure...I often hear "I read somewhere...that...."
they end up quoting only part of the theory behind pumpng water and fail to
get the whole story....and end not understading the principals behind "why".

To me this is part of the reason some FD's aren't moving foward when it comes
to improving their capacities in moving water to the fireground.

They stick with "We've been doing it with 2.5 " hose for years,never had
a problem...The problems started when our closest mutual aid FD went and
bought 4" supply hose."

Sorry if I gave a smartass tone in my posts.

I just want the less experienced F/F to be better informed.

Again my appoligies.

Don Urquhart
Captain
Montreal Fire Department

Jan.21,2006
LODD - Capt.Marcel Marleau
Montreal Fire Dept.

17. So what about our standard hose bed configuration on our 3 Engine Co.'s:

1000' of 5" Stortz
1000' of 6" Stortz
250' of 2-1/2" lightweight hose

Hydrant spacing of 300' in our entire response area.

Just throwing it out there for thought. Tell your friend that you want to buy 6" for the rigs and he will jump at the chance to use 5". LOL.

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