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Hydraulics
I just felt the need to post a new forum on Hydraulics. I have noticed alot of driver/operators do not know how to calculate friction loss and all that fun stuff. I am a loser and like hydraulics :P. It just bothers me how they expect to pump the truck but yet cant figure out all the friction loss and all that. If anyone wants to learn let me know, I love to teach this stuff.
Replies to This Discussion
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Permalink Reply by Chris on
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I too am a friction loss guy, (tho I have been on a truck for 3 years with no hose) I know most of the coeficients, but dont generally use them. We pito all our preconnects, from the pito or using rule of thumb for our dead loads. We have found significant differences depending on year and manufact, with friction loss.
Anyway, I mean not offend anyone but have to ask, are you guys really running 125gpm give or take on your handlines still!? And if so, why?
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Permalink Reply by David Earl Gregory on
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Don't know if this is what you're asking or not but here goes. Back when I was doing it the formula we were taught was 2XQ2+Q or, 2 times Quantity squared plus Quantity. That was for 2 1/2" hose. Right before I got out of the fire service the 3" w/2 1/2" couplings was coming into vogue in my area and the FL rule of thumb there was Q2 or, Quantity squared. We used 1 1/2" preconnects then at 150' lengths and rule of thumb calculations then was 15 lbs. per 50' section.
Hope that helps.
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Permalink Reply by Paul Montpetit on
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I have been through the classes and well to be honest I found an easier way than trying figure out what flow rate we will run for each particular application....We experimented in training with a flow meter on the end of the line...ran 100 feet of hose, then 150, then 200 and then 250...we played with the numbers until we were sure that we were flowing 125gpm.....I have another item for you...were you aware that if you are using CAFS with class A foam that you can decrease your Fire flow rate by ay least 25%
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Permalink Reply by FETC on
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I am with you Chris, 125 gpm??? The new target flow for a handline with modern plastic and synthetics burning is 175 gpm. What I have seen with old school 125 gpm nozzles with 1.5" line is your (NF) is so great that kids today can't hold on to them so the pump operator is reducing the pressure to afford control... guess what if your not pumping it at the required PSI your 125 is more like 95 gpm.
Our 1.75" with low pressure nozzle is 50% easier to manuever and flow 175 gpm with two guys.
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Permalink Reply by Jeff Cole on
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Thankfully you guys addressed that "125 psi pdp for a 200' preconnect"! There is SO many factors to consider, thatwhen you just go by some "rules of thumb' you are probabaly falling wayyyy short of any real gpm flows. First, you must consider what your target flows are, then you must flow test each discharge on your apparatus. Yes, they ARE different. One well-known department found 5 - 90 degree elbows in their number 1 preconnect on pumper manufacturer! What they THOUGHT they were getting was actually far less than what they were getting.
The brand of hose used is also a factor. And then there are those always-popular to debate tools...nozzles! Years ago when many departments switched from 1.5" to 1.75" hose, they bought some nozzles that SAID "200 gpm" on them, and perhaps evaluated stream reach, but that was it. Without the proper nozzle pressures actually pumped, and sometimes those pressures required were excessive...there was actually little, if any change in water delivery rate from the old 1.5".
Of course this will be argued for along time. But the ONLY way to really know what your flowing is to use a calibrated digital flow meter off each discharge (because the plumbing may be different for any given discharge and or manufacturer), and use one standardized manufacturer of hose, or if you have several brands, your gonna have to take some time and do the work.
Even 150gpm is questionable to me. We have had hundreds of new, lightweight constructed twonhouses, MFD's, and Condo's built over the last few years. A target flow with 1.75" hose is more towards the 180 gpm mark. Standpipe loads are in the 220-250 gpm range. I am exploring the use of certain nozzles and 2" hose for certain applications. A 100psi, or even 75psi nozzle with 1.75' hose is just not appropriate for standpipe use. The other big issue I see is far too many departments are still pulling the preconnected 1.75' line for heavy fire, and even exterior attack. And then they wonder why they are failing to contain, and control the fire. Anything more than a few rooms requires a much larger flow, regardless of quick you can deploy the line...makes no difference if your "out gunned".
I have heard the numbers of "35 psi per 100' of 1.75" hose" used for calculating friction loss. Agaian, it all depends on your actual FLOW. If the nozzles you are using require excessive pdp to achieve the targeted flow advertised on the nozzle, you have been suckered by salesmen! Most likely the excessive pressures force you to throttle down the pressure, which lessens your gpm right back down to an ineffective flow rate. So what's the point?
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Permalink Reply by Ben Waller on
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The coefficients are simply a way to standardize friction loss formulas for different hose diameters.
If you use coefficients, you're still "a friction loss guy".
Apparatus-mounted flowmeters can end all that for you.
Note the digital flowmeter at the pump operator's helmet level, about a foot to the left of his head.
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Flowmeters make things so easy that I sometimes see operators making things more complicated than they really are.
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We use Akron Assault nozzles on our 1.75 inch and our 2.5 inch.
The nozzles are break-aparts with a 50 PSI fog tip on a 50 PSI smoothbore.
The 1.75 inch smoothbores are milled to 15/16" and the 2.5 smoothbores are 1 and 1/8.
We target 150 GPM with the 1.75 inch fog tip and 185 GPM with the smoothbore.
We target 250 GPM with the 2.5 inch fog tip and 250 GPM with the smoothbore.
We start pumping at 100 PSI for a 200 foot preconnect and add pressure as needed to obtain the needed flow depending on elevation, bends, etc.
We know that we can get 300 GPM with our two 1.75 inch crosslays - we've tested it over and over with the apparatus-mounted flowmeters, portable flowmeters, and with hydraulics calculations.
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Permalink Reply by Jay Nicholson on
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Whatever happened to the good old days. Throttle up until the nozzleman came off the ground and back off 5.
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Permalink Reply by Alex Sharp on
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That's one thing that I never got. Memorizing friction loss for lengths of specific hose. When you flow different GPM's through it that changes unless you only flow certain GPM's. That has never done me any good because if we are fighting a fire with 200' of 1 3/4" hose at 175 GPM. Using the calculation of CQ^2L (Coefficient times the quantity [GPM] squared times the length)(using a standard coefficient of 10 here in CA without actually figuring out the actual friction loss for specific brands of hose) Then it is 10 x 1.75^2 x 2 = 61.25. Dividing that by 4 you get 15 p.s.i. per 50'. Now you do the same length of hose but now it is mop up and you are flowing 100gpm. you get 20. Divide 20 by 4 and you get 5 p.s.i. friction loss per 50' section.
That's why I never got when people say that this hose only has X friction loss per 50'. It changes with the GPM flow. Unless you only ever flow a certain GPM then there is no merit to that method in my opinion. If you see where I have gone wrong and can explain this one to me, please do.
We have a pump chart on the engine but all the engineers know what to pump the preconnects at for flat ground. The pump chart we use for when we add hose or change the GPM etc...
I still like using the equations and the such and after I have everything done to our standard I go back with a dry erase marker and do the calculations on the side of the engine. I have done this at every fire I have pumped and figured everything out to a tee.
At least once a month I go over for a couple of hours friction loss calculations, GPM calculations and different scenarios. It helps keep me fresh.
It kind of pissed me off when people want to drive and pump but don't want to learn those "stupid calculations" to pump. I mean you pump everything at 150 right.
Now don't get me wrong I have pumped long hose lay's on a wildland fire. (some up to 3000' of hose on a single hose lay) it is almost impossible to figure that out. Then you are in constant contact with the nozzleman and he is telling you to boost the pressure or knock it down a bit. (for 3000' at 90 GPM the answer is 583 psi friction loss. Add this to 100 for your nozzle and you have a whopping PDP of 683psi. You're hose can't handle this so you just go by the seat of your pants. (This was not on level ground it was up and down hill).
On one fire we were relaying from a Mark 3 pump in a creek 400' of hose below us and around 100' elevation drop. For us to know that we were supplying enough water and keeping enough for our mop up we draped it over a branch and made a arch to the intake just above the ground and laid sticks on the ground. If it was over on this side then we were taking to much and if it was over on the other side we were supplying to much but right in the middle and everyone was happy.
Here is one last extreme. My captain and an engineer who was really good at math, I mean really good. They were drafting out of a stream supplied hole that they blocked off. They measured the stream flow by measuring the capacity of their Bullard wildland helmets and then collecting it in their helmets. (very small stream). They then measured the depth and diameter of the almost spherical pit and then did a little math. They had sticks with different colored flagging on it. When it reached X color it had X gallons in it. and the stream filled it up at X gpm. so we only could use X amount of GPM otherwise we would dry up. (We were there for 2 days at the same spot so we had time to do this)
anyways enough from me for now.
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Permalink Reply by Patti Walz on
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I would love to learn. Right now I am trying to wrap my brain around the book.
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Permalink Reply by Mike Schlags (Captain Busy) Retd on
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Why on earth is a "white hat" standing next to a pump panel? Can this be a photograph illustrating micromanagement at it's finest... Can you imagine being the kid at the panel and having both a captain and chief looking over your shoulder...
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