I have a pretty specific question about friction loss.
When you have multiple lines of different diameter from a hydrant to an engine, (Say: two 2 1/2" lines and and one 4" line each into the engine using separate intakes for each line), how do you know the GPM flowing through each of the lines?
Presumably all of the lines are under the same hydrant pressure, and for arguments sake they are all the same length and the total flow from the engine is 1000 GPM. How could I compare the friction loss in my supply hoses?
Essentially, how could I determine what would be gained by going from a set up where I only have one 4" line from the hydrant supplying my engine to a set up where I have two 2 1/2" lines and one 4" line from the hydrant?
Related (but not exactly what I am looking for) info I have found suggests that:
When two or more hoselines are used to supply water to a desired point or appliance, calculations are simplified by calculating the friction loss in the average length of the siamesed hoselines. Each hoseline will deliver its equal share of water because the pressure applied by the fire pump will equalize in the hoselines. Discharge rate will be divided by the number of siamesed hoselines when determining gpm for each hoseline."
The problem with this info is that all of the lines are the same diameter and they are feeding a siamese appliance.
I have also found charts with coefficients like:
Two 2 1/2" lines and One 3" line friction loss coefficient = 0.16
How do they come up with these numbers?
I have a good understanding of calculating friction loss in general. I am just missing some explanation in this area so don't hesitate giving a complex response.
Thanks for your time,
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Results 1 to 9 of 9
07-09-2010, 05:05 PM #1
- Join Date
- Jul 2010
Friction Loss multiple lines to from hydrant to pump. Different diameters.
07-09-2010, 09:13 PM #2
Get out and flow the apparatus with the set up. This will tell you what exactly you are getting. Don't forget that you can run a 4" off of the hydrant steamer tap into your truck while running a 2 1/2" to 4" adapter off the hydrant to your 2 1/2" intake. This will reduce the friction loss from the hydrant to the 2 1/2" intake and allow you to maximize the flow into the pump.
You can either figure out what pressure you are able to supply to different lines or if you have access to a pitot gauge it will tell you what you are actually flowing. Task Force Tips also has inline flow meters that tell you what pressure and GPM you are flowing for a 2 1/2" line.
Hope this helped.
WaltTrain like you want to fight.
07-10-2010, 01:10 AM #3
- Join Date
- Mar 2006
- Southern California
Originally posted by ...123...:
How could I compare the friction loss in my supply hoses?
The theoretical flow rate for 4" is 750-1,000 g.p.m. so I'm kinda curious why you would use (2) 2 1/2" hoses? Based on this, I could see using a 4" hose and a 2 1/2" hose. Your total available output is going to be based on your number of discharges, size of discharges and water supply; all tied together. I hope what I'm trying to say is typing correctly and makes sense.
If you used a single 2 1/2" you could presume that you're flowing between the rate flow that I listed above and presume that the rest is being supplied by the 4" hose. You could also open-up a similar g.p.m. 2 1/2" and calculate your static pressure loss which would again give you an approximation of what your bringing-in from that line.
Flow-meters are also awesome, but I've only seen them on discharges..... Takes the guess work out of what you have flowing from that discharge and makes the math really easy.
It's been a few years since I was an Engineer and I hope that I'm steering you in the correct direction. Feel free to correct my information Guys, so that ...123... gets the correct info."Be LOUD, Be PROUD..... It just might save your can someday when goin' through an intersection!!!!!"
Life on the Truck (Quint) is good.....
Eat til you're sleepy..... Sleep til you're hungry..... And repeat.....
07-10-2010, 03:23 AM #4
- Join Date
- Jan 2007
- Pa Wilds
123... : FFWALT is right on the mark with doing some tests with your apparatus. The biggest problems that you will encounter will be the friction losses in the plumbing of your intakes. If you use the "Pony Suction" gated inlets for the 2 1/2" lines, there is a good probability that you will have large losses due to the number of elbows and also from the 2 1/2" inlet valves. There is a way to estimate the flow ratios of various hose combinations if they are all the same length. Look at some published friction loss tables for various size hoses. Lets say that a 5" line shows 25 psi loss per hundred at 2,000 gpm. Then look at the 4" for the same 25 psi loss. My table for 4" shows 1,000 gpm at 25 psi per hundred. So if we paralleled a 4" and a 5" We could say that 2/3 of the water (2,000 gpm) would pass through the 5" and 1/3 of the volume (1,000 gpm) would go through the 4" line. For any other total flow the ratio of 2/3 to 1/3 would hold for the combination. Lets say we needed 900 gpm. Then 600 gpm would pass through the 5" and 300 gpm would go through the 4" line. Remenber this is an estimate, but check the friction loss of 5" at 600 gpm, you should find a loss of around 2.2 psi per hundred ft. A very similar loss (2 1/4 psi) should appear for 300 gpm through 4" hose. My numbers say that 3" (with 2 1/2" couplings) at 500 gpm is about 25 psi and 2 1/2" hose should be 333 gpm at about 25 psi per hundred feet. Your problem with a 4" and a 2 1/2" paralleled 1/4 of the total should pass through the 2 1/2" and 3/4 through the 4" line. Adding a second 2 1/2 should result in 1/5 the flow through each 2 1/2 and 3/5 through the 4" line. For this arrangement at 1,000 gpm total the pressure loss should be about 10 psi per hundred with 200 gpm going through each 2 1/2 and 600 gpm through the 4" line. While this concept works for the theoretical number cruncher, it is only an educated guess when using real pumping conditions because the hose manufacturer, lining, type of cord, style of weave, number of jackets, hydrant nipples, truck plumbing and about a hundred other things all cause differences in the flow of water achieved for a particular set-up. Try a set-up with a gauge on one of the hydrant nipples. Then establish a known flow using only the 4" line, later cut in the 2 1/2" line and measure the hydrant pressure at the same flow. For the exact same flow the hydrant pressure should be exactly the same, but the intake pressure on the engine should be higher.
07-10-2010, 04:23 AM #5
- Join Date
- Jul 2010
Supply line gpm estimates when using multiple lines
Thanks for the replies guys.
I like the detail you provided when calculating the approximate flows through each of the different sized lines. I will run the numbers using that info and see what I come up with, and then do some flowing!
07-11-2010, 06:49 PM #6
- Join Date
- May 2001
- Greensboro, NC USA
I started a thread comparing the increases in flow rates of various intake setups using 4" and 2½” hose. I didn't measure friction loss, I measured the increase in flow that each connection allowed.
Maximizing Hydrant Connections - Water Flow Test ResultsI’m sure most of you have heard the term “maximizing a hydrant” which involves attaching lines to every port of a hydrant to get every ounce of available water into your pump. But exactly how much more does that give us than a 4½" port alone? I’d always wondered how much more, so I decided to perform a test using a flow test kit. Keep in mind that these results will not reflect the performance of all hydrants, but it is good info just the same.
The hydrant used was a private hydrant in the parking lot of vacant commercial property; its static pressure was 65 psi and it's on an 8" water main.
The pump used was a Hale QMax rated at 1,000 GPM with a 2.1 ratio, and it was driven by a Detroit 60 series.
First, we stretched 100’ of 4” hose off our 4” discharge and connected it to a ground monitor. Then we attached a 2½” smooth bore pitot tip used for service testing. We then made the following hydrant connections:
A. 4½” steamer to Piston Intake using 50’ of 4” hose
B. 2½” port to auxiliary intake using to 50’ of 2½” hose
C. 2½” port to 4” Storz adapter to front intake using to 50’ of 4” hose
Then we tested how many GPM we could get from each combination of intake arrangements, opening each as needed, and drawing the residual intake pressure to 10 psi each time.
A - 1,306 GPM
A & B - 1,481 GPM - 13% more than 4½" port alone
A & C - 1,751 GPM - 34% more than 4½" port alone
A, B, & C - 1,784 GPM - 37% more than 4½" port alone
The big point here is that using LDH hose on the 2½” port, feeding a large intake yielded more than twice the amount of additional water than using a 2½” hose to a small intake. I think this is evidence that we need two large valved intakes on every Engine/Quint to receive large volumes of water, and two LDH discharges to move this water to another location. And I do mean true LDH discharges, not 2½'s with LDH adapters screwed on.
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07-12-2010, 03:26 AM #7
- Join Date
- Jul 2010
What I got from this
Thanks, this info was really helpful. I was able to extract your idea of comparing friction loss charts for different sized hoses and then matching the friction loss numbers to see how much GPM is flowing to create that friction loss. Knowing that the pressure in the lines will equalize in the system of hoses because they are supplied by the same hydrant allows me to reverse calculate to create a friction loss coefficient for say two 2 1/2" lines and one 4" line.
I looked at the chart to see where a 4" line had 31 PSI friction loss in 100 feet. This happens at 1250 GPM. I then looked at the 2 1/2" chart to see where 32 PSI loss occurred (closest number on the chart). This is at 400 GPM. Now using this information I can say that I would be able to flow 2050 GPM with 31.5 psi loss using 2 2 1/2" lines and one 4" line. To compare this to using just one 4" line I had to calculate the friction loss of flow of 2050 (400 GPM + 400 GPM + 1250 GPM) through the 4" line. I know the friction loss coefficient for this is c= 0.2.
FL = 0.2* (20.5)*(20.5)*1 (100 foot length) and FL = 84, so now I need to figure out what new value of c would give me the original number of 31.5. This will be the coefficient for a hose set up with two 2 1/2" and one 4" line. So 20.5*20.5 = 420.25. I played around with my calculator changing the coefficient from .2 to smaller numbers until I reached a number close to the 31.5. As a result I came up with a coefficient for this set up where c = 0.075.
Try it 420.5 * .075 = 31.54 (close enough for my purposes!)
420.5 * .06 = 25.23 (too low)
420.5 * .09 =37.845 (too high)
Last edited by ...123...; 07-12-2010 at 10:31 AM.
09-04-2010, 03:08 AM #8
- Join Date
- Jul 2010
The big point here is that using LDH hose on the 2½” port, feeding a large intake yielded more than twice the amount of additional water than using a 2½” hose to a small intake.
That is good to know.
Last edited by ...123...; 09-04-2010 at 02:50 PM.
09-04-2010, 03:11 AM #9
- Join Date
- Jul 2010
Hey I found an iPhone app that allows me to set up all of these different arrangements. Shows friction loss for me I just build the lines.
only helps if you have iPod or iPhone though.
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