Hydraulic equations

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Permalink Reply by Bob Franklin on April 6, 2009 at 11:35pm

Hi Colin,

We developed a simple "rule of thumb" friction loss for our engineers. 1-1/2 hose is 30 psi per 100
1-3/4 hose is 20 psi per 100
2-1/2 hose is 10 psi per 100
3 hose is 5 psi per 100
All you have to add is your nozzle pressure and lenght of line and you are all set!
We use 50 psi nozzles for our 1-3/4. we carry 200 ft with nozzle, FL=40+ Np 50 = 90/100 Pump discharge pressure.
Some engineers have marked the gauges for normal pump ops, knowing if at the add a line they know how much to adjust the pump throttle.

Come visit me a "Let's Talk Pumps", FDIC, Thursday 1030-1215, Room 206-207
Hope this helps,
Bob Franklin

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Permalink Reply by Jason Gennaro on April 7, 2009 at 4:38pm

+1 on what this guy said.

If you really want to know what you're flowing you're going to have to get the flow meter and pitot gauge. Every fire apparatus has different bends, valves, and whatnot even if they're sister vehicles. The point here is even if you have the same exact trucks they'll flow different. The pitot and flow meter are you're best bet to get the correct pressures.

If you don't want to go that route due to financials or whatever get in touch with the hose, nozzle, and appliance vendors and get their data. It won't be the most accurate but it's better than the hand method or generic formulas. My opinion. Good luck bro.

Adam Miceli said:

I'd second running your own tests and developing your own cards. We've found that different hose and discharges have a significant difference in FL. We use the C Formulas as a baseline, but nothing beats a calibrated flow meter and pitot gauge to determine actual friction loss and preset gauges.

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Permalink Reply by Antiquefirelt on April 8, 2009 at 7:34am

Bob Franklin said:

Hi Colin,
We developed a simple "rule of thumb" friction loss for our engineers. 1-1/2 hose is 30 psi per 100 1-3/4 hose is 20 psi per 100
2-1/2 hose is 10 psi per 100
3 hose is 5 psi per 100
All you have to add is your nozzle pressure and lenght of line and you are all set!
We use 50 psi nozzles for our 1-3/4. we carry 200 ft with nozzle, FL=40+ Np 50 = 90/100 Pump discharge pressure.
Some engineers have marked the gauges for normal pump ops, knowing if at the add a line they know how much to adjust the pump throttle.

Come visit me a "Let's Talk Pumps", FDIC, Thursday 1030-1215, Room 206-207
Hope this helps,
Bob Franklin

Bob, did you guys test your hose and pumps to validate your numbers? In particular the 1.75" FL you show as 20 psi by formula would be accurate at less than 125 gpm and the 3" FL at 5 psi is theoretically/mathematically correct for under 335 gpm both far less GPM than normally flowed through the respective hoses. Again, these number could very well be true given newer hose tends to be "oversize" in dia. and liners tend to create much less drag than older types. We've found a huge difference in our three types of 1.75" hose all between 35-72 psi FL @ 185 gpm per 100 ft.

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Permalink Reply by Keenan Mulvaney on April 9, 2009 at 12:01pm

Pump operators at the University Fire Department are trained to memorize a given set of GPM's, Frictions losses and operations and use a standard equation for hydraulic calculations. We train so that operators have a thorough understanding of field hydraulics and when they become certified on the apparatus they can choose to use cheat sheets. Most members will carry a dry erase marker, that helps with doing the equations.

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