Volunteer question only

[everybodygoes 331]

Because I know the answer already from anyone who was trained heavily and frequently I would like if only our volunteer members answer the following question.

You have 4 lengths of 1.75 line with a combination (fog) nozzle on it. How many PSI would you provide at the pump panel. Please if you could provide an example of your math.

Thanks

[FirNaTine 370]

Because I know the answer already from anyone who was trained heavily and frequently I would like if only our volunteer members answer the following question.

You have 4 lengths of 1.75 line with a combination (fog) nozzle on it. How many PSI would you provide at the pump panel. Please if you could provide an example of your math.

Thanks

Open it up to Career guys too. Id love to see some of the answers! LOL!

[pfd430 5]

The answer to your question is dependent upon 3 factors

1. Length of hose - which in the formula is L and usually expressed in 100' lengths - so in your example it is 2

2. The diameter of the hose and the associated coefficient 1-3/4" hose has a coefficient of 15.5

3. The GPM Flow desired - The more water, the higher the friction loss. For your question, let's assume 175 GPM - which is expressed in the formula as Q² (squared)

The formula for friction loss is FL = C x (Q)² x L

Friction loss for your question is expressed below:

FL= 15.5 * 2* (1.75)²

FL=15.5 x 2 x 3.06

FL= 94.86

Therefore given that you are using a standard fog nozzle which requires 100 PSI at the tip (some work at 75) the Engine Pressure required to obtain the required 175 GPM Flow would be 195PSI.

If you are operating from a hydrant this is not a problem. However if you are working from a tank or draft, remember that the efficiency of a centrifugal pump decreases as pressure goes up. Look at the test plate on your pup panel, at 200 PSI the pumps capacity is reduced 70% so if you have a 1500 GPM pump, at 200 PSI capacity is reduced to 1050 GPM. Similarly if you have a 1000 GPM rated pump, at 200 PSI the capacity is reduced to 700 GPM.

Finally - good planning will help reduce the required pressure and increase the Engine Pressure required. Some ideas include:

Changing to a Solid Bore Nozzle. These nozzles require only 50 PSI at the tip to deliver the required flow so swapping out nozzles would reduce the Engine pressure required to 150PSI increasing the capacity of the pump to 100%.

Changing out the first two lengths of hose to 2-1/2" Diameter hose which has a lower coefficient (2) would also reduce the required engine pressure, and provide the interior companies with the comfort of the 1-3/4" hose and Fog Nozzle.

FL = C x (Q)² x L / 100

For 2-1/2" Hose the Friction Loss would be:

2 x 1.75²x 1 or 6 PSI per 100 Feet

As we determined above the Friction Loss for 1-3/4" hose is about 48 PSI so by changing out 100' of 1-3/4" for 2-1/2" at the truck would reduce the engine pressure required for the desired flow of 175 GPM to 100 PSI at the nozzle, + 54 PSI friction Loss which would result in an Engine pressure requirement of 154 PSI. Change to solid bore and you can bring it down to 100 PSI.

Knowing these options is the difference between a knob turner and puller and a good MPO.

I hope that answered your questions. I will come back to this forum if you have any more.

One last thing. After 40 years as a volunteer, in a very busy department, I would never expect that for the 1 or 2% of the time knowing these formulas is required the MPO would go through these calculations. But they must be aware that if you needed to add an extra 100' of hose to your example, the engine pressure would be 300 and that becomes very dangerous as you are approaching hose test burst strength and exceeding it with the resulting water hammer resulting from opening and closing the nozzle any other way but VERY slowly which never happens on the fire ground.

Edited June 5, 2014 by pfd430

[CHIEFPHIL 90]

First, what is the GPM ? .... I'll go with 150 GPM = 160 PSI

I use the 1.75 rule of thumb method:

Thumb =1 for 100 gpm

Pointer = 2 for 125 gpm

Middle = 3 for 150 gpm

Ring = 4 for 175 gpm

Pinkey =5 for 200 gpm

Multiply the number of the finger by 10 that is the friction loss for 100'

Hence , 150 gpm = Middle finger 3 x 10 = 30 per 100' x 2 (200/100) = 60 + 100 for nozzle pressure. = 160 psi

[FirNaTine 370]

First, what is the GPM ? .... I'll go with 150 GPM = 160 PSI

I use the 1.75 rule of thumb method:

Thumb =1 for 100 gpm

Pointer = 2 for 125 gpm

Middle = 3 for 150 gpm

Ring = 4 for 175 gpm

Pinkey =5 for 200 gpm

Multiply the number of the finger by 10 that is the friction loss for 100'

Hence , 150 gpm = Middle finger 3 x 10 = 30 per 100' x 2 (200/100) = 60 + 100 for nozzle pressure. = 160 psi

And a lot simpler to figure out at 3am when the place is wripping. Take the NASA formula above and toss it! WTF!

[everybodygoes 331]

I know how I would do it, especially if you have pre connected cross lay lines. Keep the simple tricks coming. You have no idea how many times I have had to call for more pressure, not once have I ever had to ask for a decrease, that is what the shut off is for.

[firecapt32 282]

Two times they will yell

1- not enough

2-too much

as long as no one is yelling your doing pretty good.

preset at 150 and adjust from there

[TimesUp 148]

When I got on everybody said"just pump 150" 10 years later and nobody can add up FL and NP. Then we went to smoothbore's and added 2.5" after the first 6 lengths of 1.75. It was some show! long stretch short stretches. A good short cut is worth its weight in gold. But if that's all that's taught then get the Benny Hill music ready.

[dwcfireman 656]

First, what is the GPM ? .... I'll go with 150 GPM = 160 PSI

I use the 1.75 rule of thumb method:

Thumb =1 for 100 gpm

Pointer = 2 for 125 gpm

Middle = 3 for 150 gpm

Ring = 4 for 175 gpm

Pinkey =5 for 200 gpm

Multiply the number of the finger by 10 that is the friction loss for 100'

Hence , 150 gpm = Middle finger 3 x 10 = 30 per 100' x 2 (200/100) = 60 + 100 for nozzle pressure. = 160 psi

I also use this method (for when I have to do the math). I generally rely on memory because I can memorize almost everything that I see or read. However, NEVER RELY ON MEMORIZATION, especially when you're working with something technical, like an engine pump. Always remember to practice your math skills while you practice your pumping skills! I practice my math by talking through it aloud so I can reassure myself mind that I'm getting the correct flow and pressure.

Also, keeping flow/pressure charts in the MPO compartment helps a lot, especially when the fire is ripping and you don't have much time to think.

[FireMedic049 597]

I know how I would do it, especially if you have pre connected cross lay lines. Keep the simple tricks coming. You have no idea how many times I have had to call for more pressure, not once have I ever had to ask for a decrease, that is what the shut off is for.

Although, I can't officially comment on the OP's question , I'd imagine that it'd be ok to add a couple of "simple tricks".

I guess it depends on how you look at the first one as to whether or not it's "simple", but for pre-connected lines, I've heard of departments flow testing their lines/nozzle combination(s) to find the psi for the intended GPM and then marking that psi on the discharge guage. Some have even marked more than one target point for a line.

It takes some upfront work, but on the scene you just need to throttle up to the predetermined mark.

The second is a "rule of thumb" type thing. For small handlines, nozzle pressure plus 15 psi per 50 foot section of hose. For large handlines, nozzle pressure plus 5 psi per 50 foot section of hose. It's not exact, but it'll put you in the ballpark and can adjust as necessary. Using this at my department puts our small handlines at roughly 185gpm and 95psi for 150 feet and 110psi for 200 feet using 50psi nozzles. I forget the gpm for the larger line offhand, but it's in the ballpark of what is commonly flowed from those lines.

[CHIEFPHIL 90]

I also use this method (for when I have to do the math). I generally rely on memory because I can memorize almost everything that I see or read. However, NEVER RELY ON MEMORIZATION, especially when you're working with something technical, like an engine pump. Always remember to practice your math skills while you practice your pumping skills! I practice my math by talking through it aloud so I can reassure myself mind that I'm getting the correct flow and pressure.

Also, keeping flow/pressure charts in the MPO compartment helps a lot, especially when the fire is ripping and you don't have much time to think.

To help with the right pressures ( good ball-park), on all the pre-connects and deck gun, we labeled each discharge with minimum and a maximum pressure.

Also... training, raining and training...

I like the talking out the math... good idea.

[pfd430 5]

One more addition to my earlier post. Technology has certainly changed since we were required to calculate friction loss as more and more engines are now being supplied with Flow Meters. These devices, when calibrated (annually) provide a pretty accurate indication of the flow through the plumbing and out the nozzle. Pumping to the desired GPM flow is easier, provided the nozzle man on the line gives the MPO some time to adjust the flow by opening up the nozzle fully PRIOR to entering the building. It only takes an extra 5 seconds after bleeding out the line, to set the engine pressure which corresponds to the appropriate desired flow.

However you determine the Engine pressure, remember to set the governor or pressure relief valve if you are flowing water from more than one line from the engine.

[dwcfireman 656]

One thing I want to throw in here is the point where as we replace older engines with new, state-of-the-art rigs we're losing our ability to do the math and retain the knowledge that and engineer needs to know. We're starting to over-automate our rigs, albeit some cases warrant the automation (such as ARFF). It's over-simplified to train a new engineer to hit the green preset button and tell them "don't let pressure get too high" and "don't let the vaccuum drop below 0." I'm sure everyone loves the idea of a "set and forget" pump operaion, but we need to stay on top of our training and know the science behind it and why it works "that" way. After all, that preset button is linked through a computer to the pump and apparatus engine to do all the math for you, and you have to remember that computers (both the hardware and the software) have impecable timing when they're ready to crash.

Also... training, training and training...

BAM! That's all we have to do!

[dwcfireman 656]

Two times they will yell

1- not enough

2-too much

I know of some departmentsw upstate that rely on this method. They will more or less wait for the nozzleman to bleed the line, and then adjust the pressure to just before the point where the nozzleman becomes airborne. To fix an issue like that I will refer to CHIEFPHIL's statement that I requoted above.

[TimesUp 148]

Flow meters are great if you have the time to stand there and stare at the flow meter, and wait for the nozzelman to open up and the guys to get the kinks out

[everybodygoes 331]

The rule of thumb for me is always 15-20 per length of 1.75 plus 50 for smooth and 90 for combination. 15 if its level, add 5 for a change in elevation. For 2.5 its only 5 per length and 50 and 90. I to this day can never figure out why anyone would say 100psi is enough when using 1.75 line, but I hear it all the time and its damn annoying!

[robert benz 344]

The rule of thumb for me is always 15-20 per length of 1.75 plus 50 for smooth and 90 for combination. 15 if its level, add 5 for a change in elevation. For 2.5 its only 5 per length and 50 and 90. I to this day can never figure out why anyone would say 100psi is enough when using 1.75 line, but I hear it all the time and its damn annoying!

because it is easier to operate! My 2cents I hate the give me more give me less pressure sh*t. The pump operator should know what he is pumping so that when the inside team asks for more pressure, the pump operator should know right away there is a problem somewhere between the pump and the nozzle, kink, burst length, clog, etc. jacking up the pressure till the wheels are bouncing off the ground is not gonna solve that problem. Driving is more that waving to the crowd. I am going back to my cave now.

[antiquefirelt 994]

Flow meters are great if you have the time to stand there and stare at the flow meter, and wait for the nozzelman to open up and the guys to get the kinks out

How is that different from having to adjust the pressure when the nozzle is open vs. closed? Unless you preset the line to a known psi with the nozzle closed, that will drop to the correct pis with the nozzle open and kinks out, it would seem that you need to dial in the correct number while the line is flowing properly. This is why not only the MPO but the nozzleman too, must properly flow the line before committing. Giving the nozzle a quick 1 second squirt will not ensure you have an adequate fire stream and doesn't allow the MPO to set the pump (old school pump anyway).

[Dinosaur 844]

How is this a "volunteer only" question?