Thread: GPM vs. PSI

  1. #1
    Fyrball105 Guest

    Question GPM vs. PSI

    I'm having alittle trouble wil the GMP, PSI thing. I want our dept. to turn up the pumps to push for more GPM. At this time with a 1 3/4 we're pumping at 145 PSI, to get the 100 PSI tip presure tp nozzle is rated for>> I want to take automatic nozzles rated higher and turn up pumps to 200 PSI to increase the GPM on fire to cause faster knock down. Was wondering if any one has tryed or is doing something like this and how is it going? And any advice from the engineers on PSI settings in welcome.. thanks all, be safe out there

  2. #2
    mtnfireguy Guest


    Depending on the type of nozzles youre using you can get 125pgm at 150psi

    Yes, you can go to 200psi and get more flow with some auto nozzles, but the hose becomes hard and more difficult to handle.

  3. #3
    D. Anderson Guest


    We pump 175PSI and get 150 GPM out of the 1-3/4 preconnect tanklines we use. The lines don't seem too hard to use to me, and you're putting a lot of water on the fire. Twelve of our twenty engine companies are three person companies and seem to get the hose where it needs to go, sometimes with some timely help from the truckies. Four person engines are sweet though, no help needed!

  4. #4
    KEA Guest


    Amen Fyrball105! More GPM is what its all about.

    In order to best answer your questions could you please give us some more info.

    How many feet of hose are you using? Do you know the brand?
    What is the desired flow your looking for?
    Is your nozzle going to be a 100-psi nozzle or 75-psi nozzle?
    Is this hose coming off of your pre-connect?

    Do you have an inline pressure gauge and access to flow meters?

    I'll await your response before attempting to give you some basic figures.

    Stay Safe
    Kirk Allen
    First Strike Technologies, Inc.

    [This message has been edited by KEA (edited January 24, 2000).]

  5. #5
    Fyrball105 Guest


    I'm sorry I left at some info. that needed to be figured in> I'm talking about the croos lay pre-connects, which both have 150' of 1 3/4 hose on them, not sure type of hose( knowing our money spender, not the best hose)> we use TFT nozzles the autos I want to use is rated up to 250 GPM. I know is is harder to move to hose, we have tryed it, not the training stance, where we stand up, but we ran though fire ground attack stance> full PPE with airpack. I'm 5'8" 110 lbs very small, I took nozzle, my back up is 5'9"-6'> about 250. we found harder to move but it could be done long enough to made knock down possable.If any more info needed just ask. thanks y'all..

  6. #6
    KEA Guest



    I will assume your Nozzle pressure for your automatics is 100-psi. If your goal is 250-gpm with your current equipment you would need to pump approximatly 245-psi pump discharge pressure. 220-psi for the low pressure 75-psi automatic. This is based on nozzle pressure and friction loss. PLEASE NOTE THAT THIS DOES NOT REFLECT THE FRICTION LOSS YOU MIGHT HAVE IN YOUR PRE-CONNECT PLUMBING.

    Your goal of 250-gpm would have a friction loss of 145-psi "IF" the formula is correct. FL=CQ2L Using 15.5 as C we know that 15.5 X 6.25 (250gpm/100gpm squared)X 1.5 (150' of hose) =145.31-psi Friction Loss

    In Illinois the state standard for 1 3/4" hose is FL=10Q2L. Using this formula you will find that the friction loss is 93.75 for your 150 foot hose lay.

    Now that you have two very distinct numbers to work with, I would tell you that you need to use pressure gauges and flow meters to get you in the ball park.

    Hope this helps
    Kirk Allen
    First Strike Technologies, Inc.

  7. #7
    Capt. Zada Guest


    I like Kirk's ideas on determining flow and friction loss with pressure guages and flow meters. I wish that we had a flow meter. The friction loss through the trucks plumbing could be a big factor. Have you ever looked at how some pumps are plumbed? It's a wonder that we get any flow from some of them. Would connecting the inlet tubing of the pressure guages of preconnects to the discharge outlets instead of at or near the valves eliminate the need to measure the plumbing friction loss?

    Disclaimer: Don't stir it up, it you don't want to smell it.

    [This message has been edited by Capt. Zada (edited January 26, 2000).]

  8. #8
    S. Cook Guest



    We're sort of doing what you describe, but we're not running at 200psi pump.

    All 1-3/4" and 2" attack lines now have 325gpm SM-30's on them for more flow, before we used 200gpm SM-20's. We've got some more eval to do, but we've increased our typical operating pressures to 175psi, puts us at about 200gpm on the 150' 1-3/4". One person can handle it no problem.

    [This message has been edited by S. Cook (edited January 27, 2000).]

  9. #9
    smitheps Guest


    If you are really looking for more gpm the way to go is larger hose. Have you considered using 2in can pump at lower psi and get more gpm than the 1 3/4 line will offer. If the fire that you are attacking is so large that you are not knocking it down with the 1 3/4, the proper thing to do is call for a 2 1/2 line, not to tell your MPO to beat the hell out of the engine.

  10. #10
    STBURNE Guest


    If more GPM is what you desire, (which I hope is what we all want), go with low pressure nozzles. The limiting factor on GPM is not so much hose size (to a point of course) but nozzle reaction. You can always hold the most GPM's with the least NR.

    NR=1.57*d2*NP (smooth bore tip)
    NR=0.0505*GPM*square root of NP (fog tip on 90 degree pattern)

    Plug in your different nozzle pressures to easily see how much NP reduces NR.

    Better yet, pull the engine out with a flow meter and inline pressure gauges and see for yourself in training. No flow meter? Use a smoothbore, pitot guage, and good 'ole math.

  11. #11
    STBURNE Guest


    Capt. Zada,

    Right on! This is where the gauges should be attached. I have wondered myself why they are not.

  12. #12
    KEA Guest


    One of the things we have encouraged departments to do is when purchasing a new rig, spec the pressure pick up as close to the hose connection as possible. Just as Capt. Zada suggested. The other thing you can do with your current rigs is plug the current pressure pickup and re-tap the pickup as close to the hose as possible. I'ts really simply to do and doesnt cost more than 10-15 bucks for the hardware.

    If any one is interested in some of the pre-connect friction loss tests we have done let me know and I will forward them to you.

    Good luck & pump right!
    Kirk Allen
    First Strike Technologies, Inc.

  13. #13
    KEA Guest


    STBURNE: Point well said! How many departments went from 1 1/2" hose to 1 3/4" and insisted they were getting more water yet they never changed the nozzle.

    I think Rod Carringer with TFT said it best! "The day of the 100psi nozzle pressure is OVER."

    Low pressure is the way to go, as long as the volume is their!

    Stay Safe
    Kirk Allen
    First Strike Technologies, Inc.

  14. #14
    NUMBY Guest


    With the idea being the most GPM with the least amount of effort we use the following setup. 150'of 1 3/4" with a 15/16 smoothbore nozzle. Talk about easy with very little nozzle reaction. This will flow 182 GPM with the gauge at the pump panel being at 130. Smoothbore nozzles are great because they only require 50 lbs. psi at the nozzle. this can be held very easily by one firefighter. Just an idea, it has worked out great for us. There are also other advantages with the smoothbore, but that is a whole different argument, let me know if you want to discuss it.

  15. #15
    Spirk Guest


    Fyrball 105, I think it's fantastic hearing you ask the question of how to get more"GPMS" and more "PUNCH" in the same basket!! Volume = knockdown!!
    What we do is very simple:
    Our crosslays are 200 feet of 1 3/4" hose
    Our nozzles are TFT automatics, to 350GPM
    Our crosslays are plumbed in a "LOOP"
    (I'll explain in a minute)
    Our firefighting formula for how much volume we want to use at a fire is 1GPM for every 1PSI. In other words, we run 125PSI on an initial attack which gives us 125 GPM. If the fire requires a lessor or larger flow the pump operator is notified as to what we want and the PSI is adjusted to the correct amount equal to the GPM's we need. Of course you do realize that this only gives us about 90PSI at the nozzle. Summary: It has worked FATASTIC!! I personally have used 1 3/4" hose at low and high pressures and it is not that hard to move around. Try the same thing with a 2 1/2" hose and then tell me the smaller hose is hard to move. The best thing for you to do is to do some testing with a pitot guage at certain pump pressures and set up what will work for your dept. and your community.
    O.K. the "LOOP" plumbing for the crosslays is simply by plumbing them from two discharge ports on the top of your pump therefore forming a loop. We use no less than 2" diameter piping to the mattys and 3" piping off of the pump. 500 GPM from the plumbing is no problem and it does not increase your friction loss much at all.
    Hope my info is useful and whatever you decide I'm sure will work for you. Good Luck!

    Bill Spirka, Capt.

  16. #16
    KEA Guest


    >Just an idea, it has worked out great for us. >


    Truth Seeker
    Kirk Allen
    First Strike Technologis, Inc.

  17. #17
    STBURNE Guest


    Spirk-I am having difficulty understanding what you mean with the loop? Can you elaborate? Thanks.

  18. #18
    Spirk Guest


    STBURNE, Sorry I couldn"t get back to you sooner. I will be happy to explain our "LOOP" system for plumbing mattydales.
    Every fire pump has a certain number of discharge ports that are manufactured into it. Departments dictate what they want for outlets and the manufacturer plumbs them to an appropriate discharge port off the pump.
    Most pumps when they are completed have "extra" discharge ports that were not used during the plumbing set-up.
    We suggested to our manufacturers that instead of using "one" pump discharge port to supply a special manufactured manifold for our mattydales, that they use "two".
    What this does is supply the mattydale manifold from both sides instead of one.
    The GPM's are increased dramaticlly and friction loss is very minimal.
    Like I mentioned earlier , we specified 3" piping off of the pump to the manifold on both ends and 2" piping to supply our 1 3/4" lines. (We have 4 lines that will flow 250 GPM each.)
    I hope that this helps you. If you have any more questions just ask. I'd be glad to give them a shot!

    Bill Spirka, Capt,

  19. #19
    Ray34 Guest


    Question is max water flow what you really want? I believe that how the water is applied is more important then how much water is applied. You can figure out what the range of your nozzles are by figuring friction losses, but I prefer the KISS method. Seeing this is your pre-connect attack line, I would recommend that at your next drill you perform a test. Put your typical nozzle crew (one, two or three persons/ big or small personnel)on the hose line and run the pressure up until they are at comfortable working pressure, then make that SOP. If you need more water, run a second line, but keep you hand lines manageable to your personnel.

  20. #20
    CFD-E3 Guest


    Try taking a look at the pump capacity label on the pump panel of your rig. Most engines pump their rated capacity at 150psi. Which means at 150 psi you are getting the most amount of water out of your truck as you can. At 200 psi you get 70% of its capacity. Say you have a 1250GPM engine, 150psi= 1250gpm. 200psi=875gpm. The higher you run the pressure the less water the rig is actually putting out.

  21. #21
    DD Guest


    CFD-E3; Are you talking about drafting operations or supplied lines?

    The capacity of the pump is rated at a 10 foot draft. A lot of pumps will exceed their rated capacity at draft.

    Supply a 1,000 gpm pump with 1,500 gpm through a 5 inch line and see how many gpm it will discharge. It will be a lot more than 1,000 gpm and at higher than rated pressure.
    Try it with a 750 gpm or even 500 gpm pump.

    Most engines will not flow up to their rated capacity when the pump is supplied from the booster tank. This is because the plumbing from the tank to the pump is too small and/or has too many bends in it.

  22. #22
    LHS Guest


    However, many pto drive pumps today will not and cannot exceed their rated pump capacities hooked to a hydrant or drafting. That would include almost all rear mounts and pump and roll pumps. They are rpm limited electronically. If you push too hard you break something.

  23. #23
    DD Guest


    I haven't ever dealt with a pto driven pump except a Waterous CPK-2, 300 g.p.m., on a mini pumper. I almost forgot the 53 Chevy with a pto driven gear pump with no relief system. The nozzle couldn't be shut off without blowing something apart.

  24. #24
    KEA Guest


    Check out the post on High Pump Pressures/ Low Capacity in the Fireground Tactics forum.

    Your on track!
    Stay Safe Kirk

  25. #25
    G Koons Guest


    Remember the basis. More pressure less GPM. For a good initial knock down consider a
    1 3/4" line with a straight tip. Works for us.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Log in

Click here to log in or register