Fire hose flow rate 1

[dicksewerrat]

Here isa simple problem I cannot get my head around. I hav100 ft. of 2 inch fire hose. Pressure at the hydrant is 60 psi static. What will I get for a flow rate for this hose? Hose is open to atmosphere. Ia sure I have done this in the past but I feel am missng something

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[RWF7437]

Usually, this problem is stated somewhat differently:

"If the residual pressure at the hydrant is allowed to fall to 20 psi what flow will be available ? "

If stated this way it is fairly simple to use both the Darcy -Weisbach equation and the Bernoulli equation to calculate the available flow at 20 psi residual pressure.

You will need to look up the friction factor (f) for the 2" hose. It is probably about 0.020. Total available head is 60 psi-20 psi or about 40psi which is equivalent to 93.6 feet of water.

The flow can be calculated by trial and error or by using a program such as EPANet2.

good luck

 

[RWF7437]

http://www.dcfp.navy.mil/library/tables/frictionloss.htm

 

[Artisi]

Check with your local fire department, they should have tables for flowrates based on hydrant pressure / hose length.

 

[RWF7437]

Correction !

I should have said, "If the residual pressure at the NOZZLE is allowed to fall to 20 psi what flow will be available ? "

Using the Table provided in my previously posted link, I get a flow of about 248 gpm and a friction factor "f" of about 0.018.

 

[CarlB]

I don't believe the 20 psi comes in to play, at the hydrant or the nozzle. 20 psi is used for establishing maximum available hydrant flow, when pumped and drawn down to 20 psi.

You really need to know the supply system characteristics to do it accurately. If it has "unlimited" supply, then you can assume pressure remains at 60 psi when the hose is flowing. Run the bernoulli eguation between the hydrant and the nozzle, account for hose friction loss, nozzle loss, and dynamic head at exit. pressure at the outlet is zero.

If you have hydrant flow test data, then you include this data in the equation, as the pressure will drop some at the hydrant.

 

[bimr]

I agree with CarlB that you have to know the supply system characteristics to do it accurately. You also must take into consideration the elevation of the hose nozzle relative to the hydrant. That elevation may account for +/- 100 feet of head.

If these factors are not taken into consideration, then you are just asking how much flow goes through a fire hose.

 

[Artisi]

Go to your favourite search engine (google) and type in "calculate the flow rate for fire hose" - or something similar - I came up with the following link - I haven't run it or even looked at it - up to you to investigate

http://www.tucows.com/preview/279857

As I noted before - go to your local fire dept. they should have all the info you need.

 

[riskengr]

You can get a rough estimate by assuming that the hose will flow its maximum flowrate with no pressure left at the end of the hose. Assuming the hydrant stays at 60-psi and you are using 100 ft of open ended 2" hose (pressure drop across the line of 60 psi) you will max out in the area of 300 - 320 GPM. The actual flow will probably be less.

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[dicksewerrat]

Thank you, all for your help.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com