Some simple questions...
Sorta new here, i creep alot but dont post much, but i will try my best to explain my situation.
I work for a small Township Volunteer/Part Time fire department in Northeast, Ohio. We run Fire and EMS calls, about 250 a year (I know, slllooowwwww).
Anyways, i have a few questions about hose, nozzle pressure.
We recently did a training where out first out pumper (E-One 1250 gpm pump, 1000 gallons onboard) tried to drain its tank as fast as possible with two 1 3/4 handlines pulled, in a "Blitz attack" type situation. Basically we were seeing how long we could flow water before having to establish a supply.
Anyways, if we had 250 feet of 1 3/4 hose, flat ground, one with a combination nozzle, the other with a smoothbore nozzle, what would the pressure have to be on each on order to get maximum effective GPM? I know there are breakdowns on tip sizes and what-not, so all information would be appreciated. I have gone through some water pressure classes and stuff of that nature, but honestly, the numbers are sketchy in my head and i would like to see a little discussion on the matter. I have my answer that i "Believe it should be", and that answer is different then my pump operators.
Akron Brass smoothbore is what i had, not sure the make of the combo nozzle the other Firefighter had. Most Liklely Akron.
Negative on Iphone.
We flow 160-170gpm from our 1 3/4 lines. Calculations and formulas are great...to get you started. But they may not tell you what is flowing in YOUR situation. Differences in hose brand has a lot to do with flow rates/friction loss. You won't know until you borrow a flow meter and test with your pump/hose/nozzles. Otherwise, you will just be working with "theories".
For us, 2 1 3/4 lines would be 320gpm. We have a 750gal tank. Full flow gives us almost 2 1/2 minutes before the tank runs dry.
Of course, 2 lines flowing fully for 2 minutes straight....not always best attack. Especially if only working off tank water.
Combo nozzle 100psi at nozzle unless low pressure. Any smooth bore 50psi at nozzle. Didn't say what you want each line to flow so i used 150 gpm. So 150 gpm on 250' 1-3/4 using 100 psi fog nozzle got me PDP of 187 psi. using 7/8" tip and 161 gpm for smoothbore got PDP of 150 psi. For true flow try getting hold flowmeter kit and test flow your lines.
Thats the basic rule we try to follow, 100 and 50...
Originally Posted by Eng3ineer
Just remember you are limited by the size of your tank to pump plumbing. And a single 2-1/2 is way more effective on a "blitz" attack than 2 1-3/4"
They should never reach the capacity of the T2P piping with two 1 3/4" lines, regardless of GPM. You are looking at around 500 GPM on a modern engine with a 1250 pump.
Originally Posted by slackjawedyokel
OP- you did not provide enough information to answer your questions. Just saying you have one smooth bore and one fog leaves out alot; what size smooth bore? What flow/pressure fog nozzle?
As others have mentioned, all the calculations and theories out there will get you in the ballpark, but the only way to know for sure is to throw a flow meter and some pressure gauges in the line and do your own tests.
Is this a riddle?
If so, what is the prize?
Basic nozzle flow equation, where Q = flow(GPM), d = diameter of smooth bore nozzle(inches), Np = nozzle pressure(PSI)
Q = 29.87 x d x d x Sq. Rt. of Np
For a 1” tip operating at 50 psi nozzle pressure the flow will be:
Q = 29.87 x 1 x 1 x Sq. Rt. of 50 = 29.87 x 7.07 = 211 gpm.
Cross check your knowledge with a calculator using ¾”, 7/8” and 15/16” smooth bores and you should find the following: 130, 162, and 186 gpm.
Applying these flows to the 250 ft. layout of 1 ¾” hose you described…..
The “K” formula looks like this: Fl = K x Q x Q x L
Where: Fl is the pressure drop through the hose, K is a factor for the diameter of the hose(12 for 1 ¾”), Q is the flow in 100’s of GPM’s or flow / 100, and L is the number of 100 ft. joints of hose.
For the 1” smooth bore with a flow of 211 gpm, the loss in the hose will be:
Fl = 12 x 2.11 x 2.11 x 2.5 = 133 psi
Then the Engine pressure for a 1” smooth bore nozzle on a 250 ft. length of 1 ¾” hose should be:
Ep = Fl + Np or 133 + 50 = 183psi
Do the calculations for each of the other sizes and you should find engine pressures of: 100, 128 and 154 psi for the above sizes of smooth bore nozzles. There are some other things going on inside most pump panels. I suggest you open the inspection door to your pump compartment, get a hand light and begin to trace some piping on your preconnect lines. Each time you see a 90 degree elbow, imagine that you see an additional 15 feet of piping. I have seen some plumber’s nightmares over the years, and it is not unusual to need engine pressures that are from 15 to 40 psi higher than the calculations for hose alone. As others have suggested, try to borrow a flow meter and measure the actual flow at the calculated pressure. If it is not adequate, raise the engine pressure until you flow the proper amount from each line. Then prepare a sheet with the correct discharge pressures, and tape it to the pump panel as a reminder to the pump operator.
Combination nozzles (unless low pressure) require 100 psi at the base of the nozzle. If they are selectable gallonage, then use the set gallonage to figure the friction loss in the hose line. Add this to the standard nozzle operating pressure to get the correct engine pressure needed.
Automatic nozzles present a unique set of problems for firefighters and pump operators. Because of the automatic adjustment of the nozzle baffle, the stream will always have a good looking arc and reach, but might not open enough to allow the proper flow to reach the fire. Automatic nozzles need to be periodically tested for performance, cleaned and lubricated. In the last annual test conducted on 39 nozzles there were eight (8) that were not properly functioning. If using TFT nozzles, I would urge you to go the their web site and read the information on how to maintain and lubricate their automatic nozzles.
It is amazing how fast all of that goes out the window when you actually throw on a pressure and flow gauge to see what you REALLY need to be pumping your trucks at. The theories are good in the classroom and for practicing, but in the field, they are often times way off.
Originally Posted by KuhShise