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  1. #1
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    Default Pump Capacity Question

    First of all, hope everyone is having a good holiday, and best wishes for the new year.

    I have a question relating to net discharge pressure and pump capacity.
    The truck has a 1500 gpm darley single stage pump and the pump rating plate reads as follows. 150psi=1501 gpm. 200psi=1050 gpm. 250psi=750 gpm. The discharges on the truck are set up as follows:
    Front bumper: TFT 70-200gpm nozzle, 100' 1 1/2, 185 discharge pressure
    Front Crosslay: TFT 70-200gpm nozzle, 200' 1 3/4, 230 discharge pressure
    Rear Crosslay: TFT 70-200gpm nozzle, 200' 1 3/4 230 discharge pressure
    Left rear: 400' 5"LDH
    Middle Rear: TFT 50-350gpm Nozzle, 200' 2 1/2, 170 discharge pressure
    Right Rear: TFT 50-350gpm Nozzle, 200' 2 1/2, 170 discharge pressure

    If I run the master discharge at 240, and have both crosslays and rear lays going, is the pump going to be able to discharge the 1100gpms for running all lines at the max gallonage, or would it be better to run the crosslays at 200psi with the 4 lines out? The nozzle discharge pressures were obtained by using friction loss calculations and the flowmeter.


  2. #2
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    If you weren't aware, your pump rating is at draft most likely with a 10ft lift through 20 feet of suction hose. Your pump is likely rated with a single suction line, but may require two. You would have to verify that on the acceptance test sheet.

    The simple answer is probably not, but with some hitches.

    Using the master gauge is only going to tell you the main pump body pressure, not any loss in the individual discharges.

    If you are operating in any other more favorable conditions than the acceptance testing plaque ratings, such as from a hydrant, less lift etc you will most likely have no issues.

    Other issues you need to contend with are any friction loss in the piping. If you did actual flow tests on the rig, then this is something you pobably accounted for. If not, you might find some interesting results.

    To reach 1100GPM, you need a sufficent hydrant capable of giving you that flow with NO less than 10 to 20 PSI residual reading on your intake (coumpound) gauge or drafting conditions equal to or better than when the rig was tested. If you want to test hydrants to verify this, use the 2" tip on your wagon pipe at 80 PSI and assure you have not dropped below 20 PSI (10 absolute minimum) on your intake gauge.

    I did some crude math and I came up with each PSI equals 15 GPM in your pump's rating. That said, at 240 PSI, your flow is about 900 GPM. At 200 PSI output pressure, you are at 1050 GPM. Remember, these numbers are all at draft, not using the benefit of incoming pressure.

    If you are on a hydrant thats capable of the 1100 GPM you are looking for, and it delivers that 1100 GPM at, lets say 40 PSI (read on your compound gauge) then your pump must only produce 200 PSI to make 240 PSI, and that will work because you know the water supply is capable of delivering that flow. The same hydrant, if delivering 1100 GPM at 60 PSI, will only require your pump to produce 180 PSI.

    A good suggestion would be to dump the automatic nozzles. The extra 50 PSI they require will, in fact, limit your total flow capability when you are operating at draft or off a marginal water supply. If your TFT's have the low pressure setting, run them in low pressure mode as a matter of habit, it will do nothing but benefit you from a hydraulic standpoint.

    If you intend to keep your current nozzles, realize that the waek link when drafting are high nozzle tip pressures, small hose and long hose lays. SO, shortening hose lays, using larger hose diameters and cutting nozzle pressure (read use of fixed gallonage or smooth bores) will be your way to solve issues. You may also see relief at draft from use of additional suction lines from other intakes and shorter lengths of suction hose whenever/wherever possible as well as use of low resistance strainers. I should also note that drafting through the main pump intake as a primary means of water supply is an absolute must for these types of flows.
    Last edited by MG3610; 12-26-2009 at 10:12 PM.

  3. #3
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    Quote Originally Posted by fordrules View Post
    First of all, hope everyone is having a good holiday, and best wishes for the new year.

    I have a question relating to net discharge pressure and pump capacity.
    The truck has a 1500 gpm darley single stage pump and the pump rating plate reads as follows. 150psi=1501 gpm. 200psi=1050 gpm. 250psi=750 gpm. The discharges on the truck are set up as follows:
    Front bumper: TFT 70-200gpm nozzle, 100' 1 1/2, 185 discharge pressure
    Front Crosslay: TFT 70-200gpm nozzle, 200' 1 3/4, 230 discharge pressure
    Rear Crosslay: TFT 70-200gpm nozzle, 200' 1 3/4 230 discharge pressure
    Left rear: 400' 5"LDH
    Middle Rear: TFT 50-350gpm Nozzle, 200' 2 1/2, 170 discharge pressure
    Right Rear: TFT 50-350gpm Nozzle, 200' 2 1/2, 170 discharge pressure

    If I run the master discharge at 240, and have both crosslays and rear lays going, is the pump going to be able to discharge the 1100gpms for running all lines at the max gallonage, or would it be better to run the crosslays at 200psi with the 4 lines out? The nozzle discharge pressures were obtained by using friction loss calculations and the flowmeter.
    The short answer is, if you have it coming in, you can get it out. Obviously, there are qualifications.

    What that says is that a centrifugal pump takes advantage of the incoming pressure and adds to it. Example: If you have adequate gpm with 50 psi incoming pressure, and want to discharge at 240, your net pump pressure would be 190 psi. Your 200 psi rating is 1050 gpm, you want to discharge 1100. A little head math intepolation says you're right there.

    If you're have an incoming pressure of 75 psi, your net discharge pressure would be 165 and you're well within range.

    If KuhShise picks up on this he will surely give us a much more learned explanation. I, for one, always look forward to his contributions to the literature of the subject.

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    Thanks Chief Engineer 11 anD MG ,

    I should mention that we don't have hydrants in our area and use tanker shuttles and drop tanks. Mostly we use the 6" front suctions and low level strainers. I know the front suction goes down to 5" under the truck which probably results in lower capacity to begin with. Looking at your replies it may be wise to cut the pressure on the crosslays when flowing the rear lays at the same time.

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    Quote Originally Posted by fordrules View Post
    Thanks Chief Engineer 11 anD MG ,

    I should mention that we don't have hydrants in our area and use tanker shuttles and drop tanks. Mostly we use the 6" front suctions and low level strainers. I know the front suction goes down to 5" under the truck which probably results in lower capacity to begin with. Looking at your replies it may be wise to cut the pressure on the crosslays when flowing the rear lays at the same time.
    Using only your front suction, your 1500 GPM pump is probably about a 1000 GPM pump on a good day.

    http://www.gotbigwater.com/content/a...les_05.pdfRead the above article and others on the www.gotbigwater.com website. Its good info.

    To verify flow from your front suction, drop a line in the water and fire up your wagon pipe until your discharge gauge starts to flutter (when the pump begins to cavitate) and read the gauge on the gun. The 2" tip will be flowing the following GPM at the goven PSI..approximate. If you have a pitot tube, its even a better way to record the results.
    -50 PSI=840 GPM
    -55 PSI=880 GPM
    -60 PSI=920 GPM
    -65 PSI=965 GPM
    -70 PSI=995 GPM
    -75 PSI=1025 GPM
    -80 PSI=1065 GPM
    -85 PSI=1095 GPM
    -90 PSI=1125 GPM

    You can cut the pressures, and still have usable handlines. Figure the 1 3/4" lines at 150 GPM and the 2 1/2" lines at 250 GPM and you end up with the following pump pressure requirements:
    -Crosslay-170 PSI
    -Crosslay-170 PSI
    -Rear-120 PSI
    -Rear-120 PSI
    My numbers are paper numbers, not includuing your rigs piping losses or variations for your hose. They could amount to as much as 20-30 PSI for a crosslay.
    Last edited by MG3610; 12-26-2009 at 10:42 PM.

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    Another question, using a 10' section of 6" hard suction off of one of the side intakes into the pump, how much would that increase my capacity?

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    Quote Originally Posted by fordrules View Post
    Another question, using a 10' section of 6" hard suction off of one of the side intakes into the pump, how much would that increase my capacity?
    Most likely you will be able to get more than 1500 GPM. A single section of 6" at 10 feet long with 2-3 feet of lift (using a portable tank) is much more favorable than the pump test conditions in most cases. Use caution though, the low level strainer may be the weak link. Some of them offer high restrictions. If you have access to your pumps initial delivery pump testing data, it will tell you what conditions it met its rating at (specifically if your pump requires a single suction or dual suctions. If it was done by UL, you can call them and get a copy.

    Ultimately, your best measure is to do some real world testing. Using the methods I described above, you can fairly easily determine what your pump is capable of flowing. You should acquire a pitot tube if you havent yet.

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    Thanks to MG and Chief Engineer 11 for all your replies. Will have to do some flow tests.

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    Quote Originally Posted by MG3610 View Post
    If you intend to keep your current nozzles, realize that the waek link when drafting are high nozzle tip pressures, small hose and long hose lays. SO, shortening hose lays, using larger hose diameters and cutting nozzle pressure (read use of fixed gallonage or smooth bores) will be your way to solve issues. You may also see relief at draft from use of additional suction lines from other intakes and shorter lengths of suction hose whenever/wherever possible as well as use of low resistance strainers. I should also note that drafting through the main pump intake as a primary means of water supply is an absolute must for these types of flows.
    Some of our other engines use Akron selectable and constant gallonage nozzles which run signifigantly lower discharge pressures. I just don't think the chief would spend the money to outfit the truck with new nozzles so I'm trying to make the best with whats there. I have noticed the TFT's run a lot higher pressure than other nozzles we use.

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    Default Sleepless night? Its your fault!!

    Fordrules, I have been turning this over in my mind all night. There are a number of answers and questions that need to be considered. Since your firefighters are the most important parts of the system, let’s consider what they are encountering. An automatic nozzle delivering at 100 psi has a reaction force equal to half the gpm’s. The cross lays with fully opened bales at 200 gpm have a kickback of 100 lbs. The 1 ¾” hose with water weighs about 1 lb per foot plus a 5 lb nozzle, so we are now at 155 lbs of work. Add to this two SCBA’s and gear at 35 lbs each and the work load on the attack crew is 225 lbs. I try to keep the workload under 100 lbs per man, and 80 or less is much better. I know that you are instructing the nozzleman to open the bail just far enough to kill fire, so he is probably using about 150 gpm or 75 lbs of reaction. This gets the crew’s load back under 100 lbs per man. The question is now about the “Safety Factor” of 50 gpm or some other lesser value that you decide upon. Second question and answer concerns the effective reach of the line. Let’s assume the reach is 40 feet, so a 40 by 40 room 10 ft. high by the IOWA formula needs 160 gpm for 30 seconds. Almost an exact match for the 150 gpm delivery rate. If you and they are comfortable with an extra 30 gpm for safety, then 200 psi EP will be adequate for the crosslays.

    Applying the same logic to the 2 ½” rear P.C.’s, a discharge pressure of 200 psi will be close to your specified 170 psi. This allows the pump operator to set a single pressure, and both interior and exterior lines the ability to adjust application rates to what they are comfortable handling. The nozzleman is supposed to be the one who controls application rate with an automatic nozzle. Let’s say the rear 2 ½” preconnect is being operated at 180 gpm (3rd bale click) and the P.O. gates the line to 175 psi. If the nozzleman needs more water and opens the bale fully, he will only get what can pass through the gated back valve. Thus a difference of opinion between the P.O. and the nozzleman.

    Next thing that comes to mind is the engine RPM when delivering 240 psi. Since a single stage pump must turn at ever higher speed to achieve higher discharge pressure, just how close to the governed speed must the engine turn to achieve 240 psi.? A good rule of thumb is to keep it below 80% of the goverened “No Load” speed. A 2150 rpm Detroit should be kept below 1710 rpm if possible. 90% would be the absolute maximum at 1935 rpm.

    In your last post, you mention working from a drop tank using front suction. Rarely, when teaching Rural Fireground Watermovement classes, have we been able to achieve more than 800 gpm. from a tanker shuttle on a continuous basis. The front suction should be capable of flows approaching 1200 gpm based upon your description, but you really should try supplying a master stream using the flow meter and increase the flow until you reach cavitation through the front suction. There are so many ways of plumbing that it is almost impossible to calculate the losses.
    My personal opinion would be to operate at 180 to 200 psi engine pressure, leave the gates on both the cross lays and the 2 ½” lines nearly fully opened. Perhaps 10 psi drop, just to keep track of which lines are flowing water. Remember K.I.S.S. At 180 psi your pump is capable of about 1250 gpm and with all lines operating, including the bumperline, your delivery would be very close to that. The last piece of the puzzle is your ability to get 1250 gpm through the front suction. I don’t think you will get the 1100 gpm at 240 psi without pushing the engine pretty hard.

    Kuh Shise

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    Kuh Shise,

    Sorry for any lack of sleep! And thank you for your informative post. That's why I love this site, there is so much knowledge and experience here I know I can get my questions answereed.

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    Use the Akron Turbojets to your advantage.

    If you have the low range models, 125 GPM is the highest you can set them to. If you have the mid range you have 95-125-150-200 and high range is 125-150-200-250. You can set the nozzles to the highest setting and "underpump them" to reduce nozzle tip pressure (requiring less pump pressure. For example: the mid range tip set to 200 GPM will flow about 150 GPM at about 60 PSI nozzle pressure, offering a very usable stream (albeit at less than the "designed" flow, but still very effective). In this example, you are using a 200 GPM nozzle as a low pressure 150 GPM nozzle. See what I mean? The pump pressure for the 150 GPM setting would be 170 on 200ft of 1 3/4". On 200 GPM at 60 PSI tip pressure its 130 pump pressure. Your reach drops maybe 10-15 feet, but is still in the 100+ foot range.

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    Quote Originally Posted by fordrules View Post
    Some of our other engines use Akron selectable and constant gallonage nozzles which run signifigantly lower discharge pressures. I just don't think the chief would spend the money to outfit the truck with new nozzles so I'm trying to make the best with whats there. I have noticed the TFT's run a lot higher pressure than other nozzles we use.
    Its good that you recognize that the TFT require more pressure due to their flow range. Your numbers indicate you grasp friction loss and pump pressures. You are well ahead of the game compared to many "operators".

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    Thanks MG.

    I flow tested and calculated discharge pressures for all of the nozzles we use. The difference between the flowmeter and calculated data I came up with was within 10-15 psi.
    We have the turbojets that run 95-125-150-200 on the crosslays on a few of our trucks. We also have a couple of playpipes set up with the 125-150-200-250 on the rear hosebeds. I do like the pressures these run much more than TFT. It also seems the nozzle reaction is better.

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    Default From Larry Davis' "Rural Fireground Ops #2

    Tried reducing the file size, but I'm not sure it is small enough. Maybe too small to read at 87K

    Yes! darn program just makes it unreadable...Guess I'll try Photobucket and go from there.


    Try this location: http://s679.photobucket.com/albums/v...uctionhose.jpg

    Kuh Shise
    Attached Images Attached Images  
    Last edited by KuhShise; 12-27-2009 at 12:25 PM. Reason: Add Photobucket Address

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    Thanks for the info

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    Quote Originally Posted by KuhShise View Post
    The cross lays with fully opened bales at 200 gpm have a kickback of 100 lbs. The 1 ¾” hose with water weighs about 1 lb per foot plus a 5 lb nozzle, so we are now at 155 lbs of work.
    Kuh Shise
    Kuh Shise, just out of curiosity, what is the reaction force for a 2 1/2 nozzle?

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    Default Nozzle Reaction Force

    Reaction for a solid stream nozzle is 1.5 * d * d * Np so a 1" nozzle at 50 psi Np has a reaction force of 75 lbs. A 2" tip on a master stream at 80 psi has a reaction force of 480 lbs.
    If you convert a fog nozzle back to a solid stream equivalent and then calculate the reaction force it turns out to be 0.505 times the nozzle pressure. So any 100 psi fog nozzle is going to give you a reaction force in pounds equal to half the volume discharged in gpm. A 250 gpm fog nozzle has 125 lbs of kick back. A 350 gpm automatic at 100 psi nozzle pressure will beat the crap out of a couple of firefighters with a reaction force of 175 lbs. 3 good FF's with a couple of Rodgers rope tools can successfully maintain control of the sort of lines you have coming off the rear of your rig. A master stream device must be secured because with a reaction force reaching 500 lbs will whip a couple of 3 inch lines and an 80 pound deck gun around like a Lab with a duck.

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    Kushise is the wizard..I'm a knuckle dragger....so here are some links to flow and reaction charts...

    Smooth bore discharge charts:
    http://www.elkhartbrass.com/files/aa...0Discharge.pdf

    Nozzle reaction:
    http://www.elkhartbrass.com/files/aa...e%20Compar.pdf

    http://www.akronbrass.com/uploadedFi...d-Reaction.pdf

    http://www.tft.com/literature/librar...ture&LibCat=14

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    Since you guys are discussing nozzles and reaction force I need to speak up about the Akron Zero Torque nozzles. Some of the guys saw them at the state fire school and thought they were the best things ever. I was a skeptic. Got some to demo and they make one huge difference, I'm a believer. We have them on every preconnect, 2 1/2"'s and some skids. Found out that we could do the conversion ourselves for a little over a $100 a nozzle if we had the correct ones. Makes flowing water a lot easier. Worth looking into if it interest you guys.
    Train like you want to fight.
    www.kvfd.net

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