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  1. #1
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    Question Efficient Flow Of Hose

    I am looking for the efficient flow of 1", 1 1/2", 1 3/4", 2", 2 1/2", 3", 5" and finally 6" Hose.

    I have seen the chart somewheres, but cant find it anymore. (My Luck)

    Thanks
    This is My Opinion and not of anyone elses!!


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    I have never heard of such a chart. It sounds like a good idea though. I assume it refers to the maximum GPM before friction loss becomes excessive. I wonder if it takes into account the longer lengths of supply hose, and lower initial pressure (hydrant pressure) that are likely to be encountered?

    Birken

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    "maximum effficient flow" is a hard number to pin down and is dependant on the type of hose you use, the size of your pump, and length of the lay. Acording to my handy Jaffrey friction loss card (see graph below) you can flow up to 750gpm in 2 1/2 hose, but it will cost you 121.6psi per 100 feet of hose. Is this practical? If its 50' of hose going to a tanker maybe, if its 200' supplying a sprinkler, well unless you've got 400psi rated hose and a 3000gpm pump the answer is no.

    For the most part I've been taught that 20-25psi/100feet is the max acceptable loss, and if that's the case here are your numbers:

    Hose.....Flow........Loss/100
    1 1/2in..100gpm....25psi
    1 3/4in..175gpm....23.5psi
    2in........200gpm...26.3psi
    2 1/2in..,350gpm...26.5psi
    3 in.......500gpm....21.4
    4in........1000gpm..19.8psi
    5in........2000gpm..24psi
    6in........3000gpm..21.2psi (this data from http://www.tamparubber.com/mainpres.htm)

    It should be noted that these are "stock" numbers which can vary based on hose type (some flow better than others), hose lay (curves and kinks obviously increase friction) and water charateristics such as temp and any additived which decrease friction (wet water or foam). In my FD we routinely plan and get 200gpm in our 1 3/4 handlines because we run 0.3% class A foam. The website at Tamparubber has a very usefull friction chart for hose from 1/2" to 12", although it looks to be a little conservative (vs. fire hose tables) at smaller hose sizes.
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    We were talking to a Pierce tech seven days ago who said he has seen 750 GPM through 50' of 2.5'' and 1,400 GPM from a 2.5'' discharge with a 4.5'' adapter and 5'' hose.

    Want to know for sure? Buy a gauge and go out and play with it.
    FTM - PTB

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    I have some of those pocket cards (not right here though) that show FL and I was working out how much you could get through a single 50' 3" hose. It depends entirely on the hydrant pressure and available flow obviously but around here it could be as high as 1100 GPM, that's right, 1100 GPM through a 3" off the hydrant because the static pressure is very high and the available flow is also very high and so the residual won't be much less than the static. We are talking, I think, about 80 psi of FL through the hose, some of the hydrants here doing 110+ psi.

    Even though you could get this to work, it would not be a very good idea. The problem is when you restrict your intake to a soda straw like that, every little change in the outgoing flow is going to change the intake pressure a lot, and so the pressure the guys on the hose lines are seeing will be going up and down like crazy, and the engineer will be going nuts trying to adjust the throttle. One of the best reasons to use large diameter hose is that it stabilizes intake pressure, at least if you are on a strong hydrant.

    Birken

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    MembersZone Subscriber BVFD1983's Avatar
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    I was out playing around one day with the old reserve engine down below the hill where the pressure is up to 140 PSI.

    Try a 20 foot 6'' hose connected straight to the steemer at 130 hydrant pressure.
    FTM - PTB

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    Yeah that is about what we have most lower elevations around here. It makes it more of a PITA these days with modern fire engines because they have higher idle speed, and the pump gear box has a higher overdrive ratio too because the engine adds another 50-60 psi to the inlet pressure at idle. with 130 in plus another 50 that leaves you with 180 out. A relief valve doesn't do much good at these pressures....I suppose it is better than having the opposite problem though

    Birken
    Last edited by BirkenVogt; 10-17-2005 at 03:32 PM.

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    Quote Originally Posted by BirkenVogt
    A relief valve doesn't do much good at these pressures.
    Town where I used to work had a simular water main pressure, along the docks at the water front you couldn't leave a garden hose turned on over night because the pressure would blow it apart.

    The department had an SOP that engineers would set the PRV to 200psi at the begining of the shift. Of course this was done with tank water. When we'd have a fire down on the waterfront the hose crews would get one hell of a ride since with a static of 110+psi and the PRV "set" to 200psi you'd get no relief until you hit 310+psi.

    It was not until some time later when I took a decent pumps course that I learned that PRV's worked on differential not total pressure.

    Ah the good old days, when men were men, and hoses were as rigid as iron pipe!
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    Well the PRV senses actual discharge pressure, it is just that they relieve to pump suction, and have to have like a 50-70 psi differential to work. So if you set it to 150 like we do it starts to open at 150 but relieving 150 psi water into 120 psi water does not get a whole lot done....

    Birken

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    I think "maximum efficient flow" is kind of a useless figure. Who came up with them, anyway? Were they based on today's low-friction loss hose, or the junk of 30 years ago? Is it really something worth considering, or is it just another one of those "rules" that we still teach in hydraulics classes?

    Fire304 - I would also point out that the ~25psi/100 feet is probably based on a few things:

    - Most common pre-connect length in the US is usually 200'
    - Most fog nozzles (used by the majority of the departments in the world - for better or for worse) operate at 100psi NP
    - Most pump operators have some strange reservation about routinely pumping pressures above 150psi - pumping at 150 is like cooking at 350.

    -------

    Rather than wasting time with some arbitrary number, I would rather see department's base their hose size choices on the actual measured friction loss of the hose that they will be using, the NPs of the nozzles they will actually be using, the length of the preconnect that they really need (does 150' or 200' really reach every time?), and the PDPs that they can actually afford to use, based on pump type and capacity and expected discharge scenarios.

    Remember that our hose is rated to 400psi, our plumbing to 600psi, and our mamouth modern pumps will still put out 50%r capacity at 250 or 300 psi (single and two-stage, respectively) - will we ever use 2,000gpm from handlines? Or would the 2,000gpm pump putting out 1,000gpm at 250psi still be more than adequate? Our large pumps are really for master stream and high-flow handlines - interior attack lines rarely have a place at our 2,000+gpm fires.

    More often than not, avoidance of higher engine pressures tends to be due to some irrational psychological reservation, rather than actual equipment limitations. Just a few thoughts.

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    While I agree that the limit is rather arbatrary, I believe the 25psi/100 is based on the steepness of the loss curve, at that point you have to significantly increase your pressure for a measurable increase in flow.

    I don't know what kind of hose you're using, but my preconnects are rated 250psi and my LDH is 180psi, and besides that, I don't want to have to try and drag a line charged to 400psi, 200 is as stiff as a 2X4 and a bear to handle.

    Also, the problem with the huge pumps we are seeing is that running a 2000gpm pump at 250psi while flowing 175gpm is murder on the pump. These big pumps cavitate at idle until you are flowing 25% or more of capacity. Increase the pressure and you need to increase the flow even more to avoid beating the pump. Talking with some very senior EVT's they believe we'll see a trend back to 2-stage pumps as the first generation of super pumps start needing serious work due to discharge cavitation.

    I totally agree with you that old friction tables are just that, old. Every engine company should come up with their own friction tables based on the type and length of hose they run. When we did it I was very surprised at how much better our Nieder hose was vs. the tables.
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  12. #12
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    Quote Originally Posted by Fire304
    Also, the problem with the huge pumps we are seeing is that running a 2000gpm pump at 250psi while flowing 175gpm is murder on the pump. These big pumps cavitate at idle until you are flowing 25% or more of capacity. Increase the pressure and you need to increase the flow even more to avoid beating the pump. Talking with some very senior EVT's they believe we'll see a trend back to 2-stage pumps as the first generation of super pumps start needing serious work due to discharge cavitation.
    I don't know who you have been talking to but cavitation is not the result of running a large pump with low flow, quite the opposite. It is a result of turning the pump up too high where it "outruns" the supply, as in, trying to pump too much at a draft or when the intake pressure is low. Cavitation is an intake phenomenon, not a discharge one.

    What happens to any pump that is not flowing much is it simply overheats the water in the pump. This can be prevented by opening discharges or bleeders to ground and/or overflowing the tank to assure a supply of cool water is constantly running through the pump.

    Birken

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    Rich,

    I understand that the limit is based on the loss curve, but I still believe that it is all relative - that is, what point you pick on the curve. Clearly those of us pumping higher pressures than normal are getting significantly higher flows, so we're certainly not talking about huge pressure increases for every gallon. I don't think that that point would come until much further along the loss curve.

    As for hose - your DJ interior attack lines should all be NFPA service test rated at 400psi. Now of course you take the 90% recommendation and you're looking at a maximum of 360psi, but I still wouldn't recommend anything close to that. I'm talking about flows in the 200-250psi range, with the very occasional increase closer to 300psi.

    Your supply line is probably 200psi service test, giving you the 180psi mark (many push it to 185), but I'm speaking of attack lines anyway.

    As for stiffness, many of the newer hoses, even at higher pressures, still maintain significant flexibility/tight loop diameters. I am usually concerned with the opposite phenomenon: kinking due to low EPs.

    -----

    If you have any data regarding your statements about large pumps at high pressures/low volumes, I would be interested in reading it. We've never noticed any problems with our 1,500gpm in the 200-300psi range.


    Glad to see that you've been out testing your hose to see your real-world FL. I agree with you 100% on having custom, measured FL/pump charts for every engine, every line.

  14. #14
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    Cavitation is independent of flow rate. Cavitation occurs when the Net Positive Suction Head Required (NPSHR) equals or exceeds Net Positive Suction Head Available NPSHA. This can occur at 1 gpm or 10,000 gpm. When the pressure in the pump is equal to or less than the vapor pressure of the liquid being pumped (i.e., water), the liquid boils creating vapor bubbles (not air bubbles) and the phenomenon known as cavitation occurs.

    Hopefully, the pump curve provided with the engine has a NPSHR curve. It should be below the Flow Rate vs Pressure pump curve. It is typically express pressure in “feet”. You have to convert it to “psi”. This is psia, not psig (unless stated otherwise). You will probably find that at 0 psig (14.7 psia) on the compound gauge, the NPSHR is less in most situations. This allows one to pump at negative suction pressures.

    When elevation loss and friction loss on the suction side of the pump (water distribution system piping, hydrants, hose, pump piping, etc.) gets excessive, the pressure inside of the pump decreases. When this pressure diminishes to that of the vapor pressure of water, cavitation occurs.

    Temperature of the water does have an effect on the vapor pressure and adjustments may be necessary.

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    OK, luckily for you I decided 3 pages was a little too much of a response for this issue so I’ll boil it down to this:

    Tip cavitation occurs at the trailing edge of the impeller and should not be confused with pump cavitaton. A vacuum is formed where the blade ends and the two masses of water on each side of the blade try to catch up to each other. You can see this in the water on a boat’s propeller:

    In this picture the tip vortex is made up of tiny vacuum bubbles which are carried away from the blade, but when there is no water flow the bubbles are hit by the next blade of the propeller or, in our case, the impeller. Tip cavitation always occurs, the faster the blade is moving through the water the worse it gets. To make the huge pumps manufacturers increase the diameter of the pump. Larger diameter = even faster tip speed = more cavitation. To avoid tip cavitation damage you must flow enough water to push the bubbles far enough away from the blades to protect them. One way designers try to minimize tip cavitation is to sharpen the trailing edge of the blade (you see this in all foils). Unfortunately cavitation damage to the tip of the blade dulls and pits the impeller which leads to more cavitation.

    There is nothing we as operators can do to prevent tip separation, it’s a design issue. All we can do is flow enough water to move the stream away from the edges of the impeller. How much water? I’ve been told that number is somewhere around 25% the volume of the pump.

    Now when I first heard about this I was very skeptical, then I saw the photos. I learned about it when I took EVT F-3, Fire Pumps and Accessories. My instructor is a mechanic for a major metropolitan department. He had photos of a number of relatively young pumps which needed new impellers because they were beginning to fail pump testing. Anywhere from 1/4 ot 3/4 of an inch of the tip of the vanes were chewed right off the impeller and pitting extended down 2-3 inches along the vanes. This is damage we don’t see in 1250 or 1500gpm pumps after 30 years of service. In speaking with other master EVT's I've heard this is becoming more common, larger pumps are failing faster than smaller and two stage pumps. Many techs see this damage and think it was caused by sand or other debris, even on trucks that run exclusively in hydranted areas. The opinion that I heard at this class was that right now Hale and Waterous are paying for the problem when its brought to their attention, but often is it not. When it becomes too much of a problem they will begin to push two-stage pumps again.
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    304, Thanks for the very informative post.

    In the impellers you speak of, has there been a very clear correlation between the pumps that routinely pump at high pressures (say, over 200psi) and the worn out impellers? Are the ones with the highest extent of the damage the ones that typically pump at the highest pressures?

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    Yeah thanks, straighten me right up. I too have the Ca. equivalent of the 40 hour pump class but it was not part of the curriculum. Fortunately I do not have any super pumps here yet either.

    Seems to me like something that could be solved with a simple modification to a relief valve, except rather than opening due to discharge pressure, it would be controlled so that it opens enough to keep the water moving adequately. Of course this would be inefficient but it goes with the territory I guess. I think trying to get modern engineers to understand 2-stage again will be a problem, and keep us fire mechanics busy with things like busted clappers.

    Of course we still have to deal with the other things that are referred to as cavitation but are not, such as air leaks on the suction side and pump overheating. Everyone knows any time anything goes wrong with a pump it is "cavitation"

    Birken

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    Blitz, I can't say any more than, acording to what I've been told, the problem is in the "big" pumps like the Hale QMax (1750-2500gpm)etc. As pump pressure increases you should reduce the life span of the vacuum bubbles by squeezing them shut. Balance that with the fact that the pump will be spinning faster to make pressure. So my best guess is the problem is directly related to impellor size.

    You do bring up an interesting point that high pressure pumps typically have much smaller impellors. My understanding of european high pressure pumpers is that they have three impellors, one pair of which could be parrallel or series, the last always in series. I don't know how FDNY high rise rigs are plumbed, be curious if anyone out there knows.

    What we need is a Tesla pump, the impellor has no vanes. Of course even with modern technology we can't build one that would last, but I'm sure we'll work it out.

    Birken this information was not part of the class, it was the intructor's personal experience, he was just sharing it with us. I hear what you're saying brother, tank's out of water and "the pump cavitates", showing 20 inches of vacuum on the 2 1/2 inch intake while trying to fill the tank and the engine's running at 1700rpm and the truck is "making funny sounds."

    You know there is another problem with these big pumps which is "real" cavitation, my 2000gpm pumper will flow 800gpm at idle, but the tank to pump is only good for 500gpm (per NFPA 1901). It's our SOG to always idle up while sitting on scene, so now I'm running 1000rpm, my pump wants to flow much more water than the tank can supply if I leave the tank fill wide open. If I gate back I'll errode the valve (which is the same type of cavitation, "flow cavitation" as tip cavitation).

    To make matters even worse I just saw the specs on E-One's new mid-mount tower ladder, they use a commercial 3000gpm pump which has been plumbed down to 2000gpm (the pump had 10" intakes which are necked down to 6" just before the steamer intakes), so the impellor is even larger than the Q-Max and you don't have the ability to use the huge volme of the pump!

    Nutz! Got an EMS call, more later...
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    Quote Originally Posted by Fire304
    If I gate back I'll errode the valve (which is the same type of cavitation, "flow cavitation" as tip cavitation).
    I'll take that any day A valve is a whole lot easier to rebuild than a pump

    I haven't taken the time to look yet but what is the purpose of these super duper pumps? Is it something that is actually needed on a fireground or is it ISO rating or something else? Around here we have 1250s and 1000s and even a 750 and they are plenty adequate especially with a hot hydrant behind them which is the norm. In the commercial areas of town which are older we can outstrip the water supply with only one pumper, in the resedential areas which have better water supply, we don't need that much water anyway.

    Birken

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    Carefull what you wish for, the "too big" argument has been run around here several times but that won't stop me. Consider this:

    You've got a 95' tower truck with a 1500gpm rated pipe on it. What do you need to pump it? Friction loss on an aerial of this type is 60-100psi (the sister quint to my pumper, Tower 1, gets about 80psi loss at full extention). The tip is up at 95' so you've got 45psi elevation loss. Running the big smooth bore tip you need 80 psi tip pressure.

    80+45+80=205psi pump pressure.

    What size pump do you need to pump 1500gpm at 200psi? 2000gpm!

    Now this is from draft, but you've got to built it for the "worse case" situation. And let me tell you, I've been in the bucket of T-1 when flowing 1500gpm that's one impressive stream of water.

    Since T-1 is a quint, with 5"LDH I can supply it from draft with from 1200feet away using my 2000gpm pumper. Sweet
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