# Thread: 4" hose vs. 3" hose question

1. ## 4" hose vs. 3" hose question

We were thinking about changing our 3" supply hose to 4" supply hose. Can anyone tell me how a single 1500'lay of 4", compares to the double lay of 3" hose that we use now. (1500' is the longest hydrant to house run in our village) Can anyone tell me where to find a chart?

2. im going to try and attatch a excel program that I believe came from someone here. It allows you to plug in your own numbers and see exact flows, fl's etc.
Here goes:

3. nuts. didn't work. Email me and I'll send it to you.

4. Gee, multiple challenges

Ok, first assumption I'm making is a 1500gpm pump. And it's assigned to the hydrant to pump to the fireground pumper.

One factor is 3" hose can take a higher operating pressure than supply LDH. Assuming, again, you have old fashion double jacketed rubber lined hose.

Also, did the calculations using 20psi incoming pressure on the fireground.

220psi Pump Discharge Pressure.
400gpm will go just over 1,500' in a single 3".
2 1,500' lines will move 800gpm.
A 1500gpm pump should be able to do 800gpm @ 220psi. Might be pushing it on an old pump from draft, but shouldn't be a problem from a hydrant.
Now, if you only have a 1000gpm pump it only puts out 70psi @ 200psi, so assuming you have 20psi coming from the hydrant to the source pumper, it's the limiting factor since you're only pumping out 700gpm @ 220psi.

When we move to LDH, there's two classes, most commonly Supply LDH with a working pressure of 180psi.

180psi Pump Discharge Pressure
1,000gpm will go over 1,500' in a single 4" (using a good quality, modern LDH like Angus Hi-Vol.)
1,000gpm @ 180psi is easily doable by a 1500gpm pumper.
1,000gpm @ 180psi from a 1,000gpm pumper will need a pretty good hydrant (30psi residual pressure while flowing the 1,000gpm) but depending on your system is within reason.

Now, if you do have a 1500gpm source pumper, 1500gpm will go 2,000' in a modern LDH like Angus Hi-Vol 5". I don't have the figures for competitors like Snap-Tite, but there probably in the 1,500'+/- range.

Matt

5. Dalmation90-

Your assumptions were very close. We position an engine at the hydrant with a double lay of 3" hose to a quint which is at the scene. Our current pumper is a 1000gpm, but we are looking at a new pumper with a 1250 or 1500gpm. We need to figure out if one 4" lay will supply more water than two 3" lays over the same distance. As I said before, our longest stretch is under 1500'. It sure would be nice to re-pack one hose vs. two. Our hydrant pressures average about 45psi.

Quint1Driver-

I emailed you about that excel program.

6. Your 1000 gpm pump is rated to deliver 1000gpm @ 150 psi.
Using Two 3" lines this pumper can deliver 1000gpm 550'
Using a single 4" line 1000gpm can be delivered 650'
Using a single 5" line 1000gpm can be delivered 1950'
I got these figures from The Rural Firefighting Handbook By Larry Davis and Dominic Colletti. I would recomend going to the 5" hose.

7. ## Agree with Bendone

If you are able to go with 5", do it. You will loose some total length in your lay, but will more than make up for it in flow and reduced friction loss. It is a bitch to work with but a huge improvement over 4".

Our new KME pumper was speced out to carry 2200' of 5" with a 1000 gallons of water without doing anything unusual with the design of the truck. We also have 400' of 3" and a 250' 2 1/2" preconnect in the hosebed. You should not have a problem getting 1500' of 5" on an average size new pumper. You just need to be careful how you pack the hose.

8. ## LDH

Have to agree with PATF. If your going to goto LDH go to 5". Friction loss is next to zero. If your specing a new engine there is know reason why it will not handle 1500'. YES it is heavy , but there is no cleanup , no washing hose no drying no changing hose to get the kinks out and the best part. while it does cost more, with ldh you save money by not having to have a complete hose change sitting around which also means less hose to clean and test. when pumping it better for the engine to because of less friction loss you dont have to pump as hard. We even switched to 5" for feeding standpipes and sprinklers. There having all connections changed to the 5" storz.

9. I too say GO 5".

10. I agree to go for the 5" if you can afford it and your engine will push that much.

But as Dalmations calc's show, the four inch will still move slightly more than two single 3" lines, and with a fraction of the friction loss. I have been through the budget justification for LDH, and 1500" of 5" will probably cost you up to \$3000 more than the same amount of 4".

The benefits are clear, but that can be a lot of money for a small volley dept. The difference alone would be 5% of my entire annual budget.

Don't scrap the idea if you can't get the 5". You will still benefit from the 4".

11. Don't forget, your 1000gpm pump is rated at a draft, from a hydrant you'll get more, a considerable bit more if the hydrants are good.

Also, do a forum search, this subject has come up numerous times and there are a lot of good arguments with the math to back it up hidden in the archives of the firehouse forums.

Here's just one example...
http://cms.firehouse.com/forums2/sho...=dual+friction

12. ## 4 vs 3

it is the same friction loss at 750 gpm and the charts only show both flowing 750 gpm

13. it is the same friction loss at 750 gpm and the charts only show both flowing 750 gpm

Take that chart, cut it into little pieces so no one's tempted to recover it from the trash, and then throw it out.

First, the physics of the situation dictate it's impossible for 3" and 4" hose with the same liner material to have the same friction loss. Unless you have physical damage or obstruction to the hose's liner, and design & construction of the hose being equal, 4" will have 1/4 the friction loss at a given flow.

Second, if your chart stops at 750gpm, it's hopelessly out of date.

Modern design of fire hose can bring about even more dramatic differences.

Most charts you see in the fire service use double jacketed, rubber lined hose as there reference point.

3" db/rl has a coefficient of friction of 0.8
4" db/rl has a coefficient of friction of 0.2 (and almost no one uses this for LDH)
4" Angus Hi-Vol, with different construction & liners, achieves 0.1

14. write down another vote for the 5"

we switched from 4 to 5 and noticed a big diference i say if its in your budget go 5

Here is our load on our current second out pumper (once you click the link go down to the bottom to view) Click here for hoseloads

15. ## Re: 4" hose vs. 3" hose question

Originally posted by LFDAC21
1500' is the longest hydrant to house run in our village
Just a little food for thought, if you had to tap a 2nd hydrant, might you have another lay longer than 1500? I have found that at major incidents we have to skip hydrants to insure good water flow. Had one here two years ago where we skipped 3 hydrants to get water off a different main. Having the 5" allowed us to have a very long run w/o a relay.

Put my vote down for 5"

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