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Old 03-27-2012, 06:15 PM
Sawtooth Sawtooth is offline
 
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Default Question about friction loss

Hi guys
I'm a Helitack leader and have been packing my hose bag with 1" hose and a load of 5/8 for a few years now for initial attack. The advantage of this is that I can pack more hose to cover more distance to a potential water source. However, I've been considering the significant friction loss with 1" hose vs. 1.5" hose, and I'm starting to wonder whether sacrificing 100 feet of hose for the 1.5" would be advantageous.

Sorry for the imperial units. I've got it calculated that with a pump discharge of 100 gpm, and 100 feet of hose, you will have 150 PSI of friction loss on 1", whereas all things equal, you will only have 24 PSI loss on 1.5 inch hose. This could have a significant effect on nozzle pressure over several hundred feet.

My question is, with a wildland pump (a mini striker, specifically), which is almost always running at full bore regardless of hose diameter, will the heightened volume of water in the 1.5" hose have more of an effect on nozzle pressure than the friction loss of the 1" hose? It seems a lot of guys I talk to think that with the larger diameter hose, the small pump will be pushing more water and you will therefore experience less nozzle pressure. I'm just not sure if this is the case given the significant difference in friction loss. Any help from you experienced pump operators would help me decide whether or not to rethink my initial attack bag.

Thanks
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Old 04-27-2012, 06:50 PM
rmpmike rmpmike is offline
 
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Quote:
Originally Posted by Sawtooth View Post
My question is, with a wildland pump (a mini striker, specifically), which is almost always running at full bore regardless of hose diameter, will the heightened volume of water in the 1.5" hose have more of an effect on nozzle pressure than the friction loss of the 1" hose? It seems a lot of guys I talk to think that with the larger diameter hose, the small pump will be pushing more water and you will therefore experience less nozzle pressure. I'm just not sure if this is the case given the significant difference in friction loss.
I think the opposite would be true, all things equal. The pump isn't necessarily pushing more water (water mass isn't going to make a huge difference). The flow is going to be restricted by the 5/8" hose and the nozzle you have at the end of it. My guess is that you're actually pushing about 10 GPM through the tip? If you were pushing 100 GPM, you'd be dribbling out the tip at best regardless of the hose size with that pump. (see attached photo for pump max specs)

Based on my assumption of 10 GPM, your 100' of 1" line will lose 1.5 psi, the 1.5" line will lose approx 0.24 psi. Pretty minimal difference...

My opinion - if the mini striker is your source pump, I think you've got the best balance with the 1" hose.

Mike
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Old 05-12-2012, 11:24 AM
bloggins bloggins is offline
 
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You can have a 100gpm pump but you need to calculate your figures based on what is coming out of the nozzle to determine what your actual FLOW is. Your figures need to be calculated based on what amount of water is coming out the nozzle, not what CAN come out of the pump.

Your friction loss calculations appear to be based on 100gpm which would be an awful lot to expect out of a 1" hose. To give some idea let's look at the friction loss calculation based on FL = C(475/100) squared x number of lengths. This is a metric formulation so I'll calculate it that way and then convert it to PSI.

C = the coefficient / constant for the hose diameter / couplings in question. Constant for 1.5" is 11 while the 1" Constant is 70.

(475/100) is basically just flow in liters divided by 100. Yes 475 is actually 125 gallons but it's a familiar number (to me) so I'll use it in this example.

So basically calculation on the 1inch / 25mm line is 70 x (4.75 x 4.75)x 1 100 foot (30 meter) length of hose. That ends up being 1540kpa which in PSI is 220 friction loss.

That's how much you're losing- so this calculation tells me something isn't right in your evaluation. I think you need to take a look at what your nozzle is rated for.

With equal flow on a 1.5" / 38mm line the calculation is generally the same but multiplied by 11 instead of 70 so for simplicity let's just divide our end result by 7... which ends up being 30psi or so. The textbook says you lose 250kpa / length (30m) of 38mm to friction loss when flowing 475lpm.

So to wrap this up- your nozzle pressure (which I'm assuming you mean nozzle reaction) will likely have more to do with your nozzle's rated flow AND the pressure at which the water is leaving the nozzle. With our fog nozzles (structural) for example the text book (per se) "requires" 100psi. A person can assume that nozzle reaction for a 1" line flowing 10gpm out of a fog nozzle at 100psi is going to be substantially less than a 1.5" line flowing 100gpm at 100psi.

And if you're going to be dragging 1.5" line around the bushes while maintaining the same 10gpm flow rates... well... the pump is ALWAYS running full bore by the sounds of it... then you'd be getting the 10gpm at much higher pressure (less lost in the hose) which will be harder to work with and your line will be substantially heavier when filled with water.

Hope I haven't gone off track but I think if you recalculate based on nozzle flow instead of the pump rating you may be able to more accurately assess the better option.
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Old 01-23-2013, 06:48 PM
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b3harris b3harris is offline
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Default I asked a brain

The guy that gave me this info is a full on brainiac with this stuff. I don't know it but I was sure interested until I got his response. now I feel I have to learn more.. but here it is.

Best of luck
billy

gpm = A X Ve X C X K

Ve = 12.16 √p

A is the area of the hose in sq ft (./. 144)
Ve is the velocity of the water
where p is the discharge pressure of the hose (the end after the friction losses)
C is to convert seconds to minutes (60)
K is to convert to imperial or US gpm I use US so 7.68 gal per sq ft

It really depends of the pump and the final length of hose. I am not sure of the pumps specs. The pump has to fill the hose.

You can see by the formula 1" hose gpm is 30.56 X √p were 1 1/2" hose gpm is 68.76 X √p. Were the gpm is in US gpm and p is in psi.
So it really depends on what you need and how big the pump is. If the displacement is big enough to give the gpm the 1 1/2 hose will deliver twice the flow at less loss, but if the pump is not big enough you will loose pressure just filling the hose.

REMEMBER the hose has a nozzle on it!! The final flow is calulated using the office diameter and a dispersion factor using the pressure at the backside of the orfice. The nozzle orfice is the final restriction, not the pipe diameter. The formual above will work.
I hope this helps.
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  #5  
Old 01-25-2013, 10:24 AM
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Roree403 Roree403 is offline
 
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Proper pump discharge pressures and nozzle pressure are aimed at interior structural firefighting. Friction loss does apply to this scenario however you indicated that the smaller diameter hose seems to work fine for you. Based on your environment and your desire to keep weight down while increasing the amount of hose you can carry, coupled with the fact that you don't need large volumes of water to put out most wildland fires, stick with what works.

Cause some days, vise grips work better than a wrench.
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