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  1. #1
    MembersZone Subscriber FFPotenziano's Avatar
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    Default Single Stage vs. Two Stage

    Can anyone break the single stage pump vs. the two stage pump for a paramedic?


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    MembersZone Subscriber npfd801's Avatar
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    Quote Originally Posted by FFPotenziano View Post
    Can anyone break the single stage pump vs. the two stage pump for a paramedic?
    I know someone will come on here explain it better than I can, but here's my take, in a nutshell:

    Single stage pump: Water goes in the intake, through the impeller, and goes out through the discharge manifold. Not usually an issue for the high torque diesel engines we run these days, as they manage to get enough pressure for most departments needs and have the simpler operation of the single stage pump.

    Two stage pump: Can operate in volume or pressure mode. In volume mode, operates similar to a single stage pump. All water from the intake goes through the impeller once, hits the discharge manifold and goes on it's merry way. This is basically pumping two parallel streams of water through the impeller. In pressure mode, a transfer valve diverts the flow of the water after it has gone through the impeller once, and sends this pressurized water back through the impeller a second time, increasing the pressure even more. You won't get the same volume while running through series or pressure mode, but you'll get much higher discharge pressures.

    In low volume situations, you can run your engine at much lower rpms and achieve pump pressures needed to operate hand lines. However, once/if you need big water, you would need to switch back to volume or parallel mode. Cities with very tall high rise building with standpipes and sprinkler systems will often have two or three stage pumps to have the capability to pump these systems with a pressure adequate to overcome the loss created by the higher elevation.

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    MembersZone Subscriber FFPotenziano's Avatar
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    Thank you

    We switched from a single stage Quantum (20 of them) to a two-stage Enforcer (5 of them) and back to the two-stage Quantum (1 of them).
    Last edited by FFPotenziano; 03-07-2008 at 09:47 PM.

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    Forum Member Fire304's Avatar
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    I've only broken a two stage, but will be happy to try on a single if you provide it
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    Default in my humble opinion

    With todays modern and efficient pumps and high powered diesel engines there isnt much need for two stage pumps. They do have their benifits if you do a lot of low gpm high pressure pumping. An old timer once explained that two stage pumps were primarily designed because of the limited torgue curve and high rev of gasoline engines in older trucks. Todays truck dont have that issue thus my statement that in most uses a single stage will serve you better. Also, keep in mind a single stage pump usually cost less and has less moving parts to fail or wear. Good luck with your decision. JR

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    Forum Member edge1317's Avatar
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    I think I've heard somewhere that FDNY has a number of two-stages to supply standpipes in highrises. This is just an "I heard" so I could be (and probably am) wrong. I'm sure that any place with a large highrise probably has a number of two-stage. Perhaps someone with larger highrises could chime in. If there isn't any need for them anymore they wouldn't be made.

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    The biggest difference, you can acheive higher pressures in the 600 PSI range (at lower total output capability) with a 2 stage and with a single stage you are limited to about 300 PSI. These numbers are also dependent on the incoming pressures and subject to some slight adjustments.

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    Quote Originally Posted by FFPotenziano View Post
    Can anyone break the single stage pump vs. the two stage pump for a paramedic?
    I've got a few medics who could break either type! OK, maybe some firemen too. But more likely is that most would rather break the ambulances.

    Joking aside, we just switched to speccing a single stage after running two stages for years. Basically we have nothing over six stories so the hi-pressure need was not there. The simplicity and nww diesel motors lent credibility ot this decision as well.
    Last edited by RFDACM02; 04-16-2008 at 03:20 PM.

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    Forum Member canuck1's Avatar
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    Default two

    Quote Originally Posted by npfd801 View Post
    Two stage pump: Can operate in volume or pressure mode. In volume mode, operates similar to a single stage pump. All water from the intake goes through the impeller once, hits the discharge manifold and goes on it's merry way. This is basically pumping two parallel streams of water through the impeller. In pressure mode, a transfer valve diverts the flow of the water after it has gone through the impeller once, and sends this pressurized water back through the impeller a second time, increasing the pressure even more. You won't get the same volume while running through series or pressure mode, but you'll get much higher discharge pressures.

    .
    Two stage pumps have 2 impellers in a single pump housing. The main drive shaft is connected to both impellers. The impellers are generally identical in size and capacity. They can be run in SERIES for max pressure, or in PARALLEL for max volume.

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    Forum Member FWDbuff's Avatar
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    Quote Originally Posted by edge1317 View Post
    I think I've heard somewhere that FDNY has a number of two-stages to supply standpipes in highrises. This is just an "I heard" so I could be (and probably am) wrong. I'm sure that any place with a large highrise probably has a number of two-stage. Perhaps someone with larger highrises could chime in. If there isn't any need for them anymore they wouldn't be made.
    FDNY has a number of companies in Manhattan and some parts of Bklyn that have three-stage pumpers for high rise work.
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    Forum Member edge1317's Avatar
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    Perhaps that was what I was think of, three-stage.

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    Forum Member Fire304's Avatar
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    Quote Originally Posted by firefuss View Post
    The friction inside the pump was so much that the water coming in the intake couldn't cool it down enough. ..
    Ah, dude, there is no way you can overheat a properly working pump while flowing water. Its way too late and I'm too tired to do the calcuations, but the heat absorbtion capabilities of water, even at only 150gpm you'd need 125,000BTU's per minute to heat that water up just 100F, no where near enough to cause damage. The oil fired boiler which heats my home is only rated 60,000 btu per hour! If you had a 500HP engine and converted every single pony to heat you'd only make 21,200BTU's.

    If you overheated your pump you were not flowing enough water and/or were cavitating, period. Single or dual stage pump, it would not matter, no flow = eventual pump damage. When you stop the flow suddenly you are converting all your HP into BTU's (no flow, power has to go somewhere) and you will very rapidly burn out your pump.


    Definitions if you want to do your own math:
    1 BTU = 1 gallon H2O rise 1 degree F
    1 HP = 42.4 BTU
    1 gal = 8.34 lbs but you already knew that
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    Red face

    Quote Originally Posted by firefuss View Post
    Although you're thinking along the lines of simplicity, thats not always right. Most pumpers out there use a centrifugal pump. As water enters the pump, the impeller spins it through a gradually reducing casing called a volute, due to the shape of he pump, centripetal force causes the water to move faster and increase in pressure. While todays diesel motors are more than capable of supplying adequate pressure by themselves, a two stage pump offers much needed engine relief for said motors. For instance: a single stage pump can deliver 150 gpm at 100 psi at around 1100 rpm, while a 2 stage pumper operating in series can deliver 150 gpm at 100 psi at about 750 rpm. Those numbers aren't exact but you get the point. I've actually been on a job where we pumped a deluge type sprinkler system at a lumber yard with a single stage pumper, 2 3inch lines to a standpipe at 150 psi. The friction inside the pump was so much that the water coming in the intake couldn't cool it down enough. The emergency cooler kept activating, and even the emergency pump dump. And that was only around 1000 rpms for a few hours. The same fire with a 2 stage pumper could have avoided damaging (yes it was damaged) one of our trucks...

    but i guess its all relative...
    Like fire 304 said ,you can't over heat a pump that is flowing water .
    I noticed in your post that you were connected to the standpipe but were supplying a deluge type sprinkler system. Those are completely different FD connections.
    so maybe you weren't flowing any water.maybe a big oops on your part?

    Don

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    Lightbulb Wow its like lighting a fuse on a rocket!

    I believe the point which you came around to again is that 150 psi is no indication of flow and the BTU's which are required to raise the temperture of the pump to the point that the thermal relief valve would dump if moving water would be unlikely. But not completely impossible. I have know doubt that your feet were warm with pump water. The reason is whats interesting.

    Let me assume if you will that you were not the only truck pumping into that system. And the possibility that you may not have been moving the water you are assuming due to plumbing restriction in the building or other. Of course that is unless your truck is equipped with flow meters on the discharging line(s). Speculation I know and not to pass judgement but truly there are gaps in the info you provided which led to the questions you seem to be disregarding as "they dont know sh?*" I think most of us read these post to expand our knowledge on subjects or situations to which we may not have been exposed. To simply disregard others point of view and there source is limiting to ones own growth.

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    How about this....

    I am not arguing the fact that either incident occurred, and I don't think anyone else is. Based on what information you have given, there has to be another variable that is being overlooked. I'm not interesting in pointing fingers, I'm interested in making sure this doesn't happen to my rig or anyone else's.

    I presume that the truck was taken out of service after this happened. What was broken? Were the only repairs necessary directly related to the pump overheating, or was there other stuff that needed repair?

    Fire pumps are designed to be cooled by the water they are flowing. Generally speaking, pumps tend to overheat if there is no flow, or an inadequate flow. If your flow was less than needed to keep the pump cool, or there was no flow at all, your pump will begin to overheat. If your dumps are activating to cool the pump, "cracking" the tank fill is not enough to cool the pump in a timely manner. It is nearly impossible to figure out how much water you are diverting to the booster tank when a valve is partially open unless you have a flow meter on your tank fill line (not likely). Those dump lines and pump cooler lines are rather small and cannot fend off the inevitable alone. How much water was dumping out of your tank after you cracked the fill valve?

    You were supplying an FDC, I would venture to say that these lines were not constantly flowing. Especially since you stated that this incident went on for 9 hours. If you were still supplying lines supplied to a standpipe system after that long, I'd say there was a lot of overhaul which means low or no flow. Just a bunch of "hook and squirt" ops. PSI does not indicate water flow. You do not "flow" 150psi, you maintain it. As a matter of fact, your SOG should state that you should maintain a pressure of 150, not flow it. Usually as additional lines are added your discharge pressure drops and you have to increase RPMs to maintain that pressure since GPMs have risen. I'm quoting both experience and books. You flow GPMs.

    What was your motor RPM while doing this? What is your water system's normal operating pressure? Did you have a residual pressure that was different than you NOP? Some of this information can indicate where your flow was.
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    Just when you think you have it figured out take a look at a Rosenbauer NH Pump. Pumps Normal Pressure and High Pressure at the same time allowing you to perform different operations with one pump setting.

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    It just occured to me there is one other possible explanation for the pump overheat, a pressure relief valve set to say, 140-145psi, if it were forgotten at this setting (and either the indicator light was inop, not visible due to conditions, or ignored) you could still get 150psi out of the truck but you'd have to crank the rpm way up to the point where you were able to outflow the dump plumbing. The result would be lots of rpm (and HP) but the water would be circulating in a short loop through the pressure relief resulting in no cooling effect from the water once is was heat loaded (very quickly). Even if you were flowing some water (it would have to be fairly small, like less than 50gpm) it would be possible to over heat the pump this way.
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    Don't you hate it when the other shift (it's always the other shift) presets your relief valve? That's a good point Fire, but it still comes down to a low total pump GPM. If you're moving significant water that won't make your pump overheat, it'll just make your relief valve useless.
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    Default correction

    Quote Originally Posted by Fire304 View Post
    Ah, dude, there is no way you can overheat a properly working pump while flowing water. Its way too late and I'm too tired to do the calcuations, but the heat absorbtion capabilities of water, even at only 150gpm you'd need 125,000BTU's per minute to heat that water up just 100F, no where near enough to cause damage. The oil fired boiler which heats my home is only rated 60,000 btu per hour! If you had a 500HP engine and converted every single pony to heat you'd only make 21,200BTU's.

    If you overheated your pump you were not flowing enough water and/or were cavitating, period. Single or dual stage pump, it would not matter, no flow = eventual pump damage. When you stop the flow suddenly you are converting all your HP into BTU's (no flow, power has to go somewhere) and you will very rapidly burn out your pump.


    Definitions if you want to do your own math:
    1 BTU = 1 gallon H2O rise 1 degree F
    1 HP = 42.4 BTU
    1 gal = 8.34 lbs but you already knew that

    By the way Fire304 a BTU is the amount of energy required to raise one pound of water one degree.

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    You started out by saying.....


    Quote Originally Posted by firefuss View Post
    I've actually been on a job where we pumped a deluge type sprinkler system at a lumber yard with a single stage pumper, 2 3inch lines to a standpipe at 150 psi. The friction inside the pump was so much that the water coming in the intake couldn't cool it down enough. The emergency cooler kept activating, and even the emergency pump dump. And that was only around 1000 rpms for a few hours. The same fire with a 2 stage pumper could have avoided damaging (yes it was damaged) one of our trucks...
    When you were questioned about it you got defensive and said.....


    wow, another person that says somethings impossible... were you there? No? I was, so I said standpipe instead of outside FDC, I type fast. Whoops on typing, not on the pump overheating, WHILE connected to a hydrant, WHILE flowing 150 psi to th FIRE DEPARTMENT CONNECTION.

    When a truck runs for 9 hours straight pumping things can go wrong. I NEVER SAID it wasn't a malfunction. I just said it happened. Get off the "that could never happen" bus. Or go ..... nevermind, it wouldn't matter anyways



    So was it too much friction or a malfunction? I've never pumped for nine hours straight. Did the apparatus need to be refueled during that time?

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