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Rated Pump Capacity

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  • Rated Pump Capacity

    Can a pump produce more than it's "rated" capacity?

    I've read many a post where precents of capacity are used, which only apply to static water supply. Was wondering what kind of numbers others have come up with, especially 2000+ pumps. I know what our 1250gpm pumps have achieved in field tests.

  • #2
    Yes. If you hydrant has a good flow and an adequet static pressure, you can more than flow your rated pump capacity. Can't say how much more but I'd bet the formula to figure out how much more could be found in NFPA Fire Protection Handbook.
    Before Everything, Stop And First Evaluate


    • #3
      A pump's "rated" capacity is achieved by being able to perform 3 things (4 at initial acceptance):

      1. Must be able to pump full capacity at 150 PSI NET PUMP PRESSURE
      (Net Pump Pressure is the difference between inlet pressure and discharge pressure, no matter whether inlet is positive or negative)

      2. Must be able to pump 70% capacity at 200 PSI N.P.P.

      3. Must be able to pump 50% capacity at 250 PSI N.P.P.

      4. At initial acceptance only, must be able to pump full capacity at 165 PSI N.P.P.

      These are the performance points for the rating, but the pump will perform throughout, as well as outside, this range. They will pump more than rated capacity at less than 150 PSI. The lower the pressure, the higher the flow they will maintain. The higher the pressure, the lower the flow they will maintain.

      And pumps don't "produce" anything, they put energy into water. They can't pump out more than they take in, and "Pumps don't pump pressure, they pump water." A nickel for every time my college hydraulics professor pounded that one into our heads! (Sorry, I got carried away....)
      Last edited by TWEJFD; 09-05-2003, 02:02 PM.
      Essex Junction Fire Dept.


      • #4

        You bring up some good points. I know how pumps are rated per NFPA 1901, which are done at a 10' draft from a static source.
        The pressure's you mentioned (150,200,250,165-overload test) only apply when the pump is at draft. When hooked to a hydrant the pump simply adds "energy" to move the available water through hose. You are right that pumps don't pump psi they pump water, but pressure is the medium we use to move water.

        What I am looking for is gpm's above the "rated" capacity when connected to a positive source.

        Example: Our 1250gpm pumps (Waterour single stage) have produced 2200gpm.

        Hydrant - +3000gpm

        Set up: 1-6" line 15', 1-5" line 20', 1-3" line 50' to hydrant.

        Discharging to: 2x50'-3" to 2" tip 75psi NP, truck mounted 2" tip 75 psi NP, 50'-21/2" to 1" tip 45psi NP. A pitot gauge was used on all tips. Although the pump didn't appear to cavitate and there was still a good residual psi it seemed to max out at 2200gpm.

        If any of you have numbers like that please share them, especailly if they are pumps over 1500gpm.

        jsd You should go out and pump and let us know, at least you won't be sweating when you do it!



        • #5
          It all depends on who makes the pump. As an example we have 1250 single stage pumps from Hale. The impeller is the same as a 1500 and at a drill on a very good hydrant we got close to 1800 gpm out of it.

          I wouldn't count on anything but capacity out of your pump as a rule


          • #6
            Okay, now I get it. I apologize for misunderstanding your original post.

            I believe I've seen a table with that type of info in a book by Larry Davis. I have it at home, so I'll try to remember to look for it tonight, then get back to you.
            Essex Junction Fire Dept.


            • #7
              The answer to can a pump pump more than its rated capacity is yes or no. If you have an electronic transmission it can be programed to produce a maximum torque and even rpm. In that case, the answer will be No. A pto pump the answer is almost always no.

              We have 2250 pumps and yesterday went out and pumper our terminator monitor at 3429 gpm at 125 psi tip pressure using a pair of 5 inch lines to the gun. We also supplied our deck gun with a 1 3/8 inch tip at 150 psi, for another 694 gpm and then ran out of hydrant supply. It takes four of our rigs at draft to supply our 14,000 gpm monitor, each with three five inch discharge lines into the 28 5 inch connections on the gun.

              It all depends on the pump, the transmission gear ratio and any electronic limiters. Macks especially are quite capable at twice the pump capacity, not likely at draft but from a positive pressure source.

              You can also cheat, we have a 500 gpm pump that using turbo drafts will fill tankers at 1600 gpm.

              Last night we did a 3250 foot relay with our 300 psi 5 inch hose at the end of the line we pitot's a 2 1/2" smooth bore tip at 140 psi. Big pumps allow high discharge pressures and high flows long distances.
              Last edited by magnolia; 09-10-2003, 11:20 AM.


              • #8
                I looked for that table last night, but could not find it. The only one I found has maximum theoretical pumping distances for different size pumpers pumping different GPM flows. I suppose its possible to use that info and interpolate what you're after, but I've got to believe there's a better way.

                BTW, I also checked the Fire Protection Handbook, but couldn't find it there either.

                Essex Junction Fire Dept.


                • #9
                  Here's a shot of our 1,500gpm pumper flowing nearly 2,000gpm at draft through dual 30' 6" suctions - no problem. We're going to take it out again and see if we can push the envelope a little bit.

                  The best part of the drill was that a couple of 18-year olds were the brains behind the operation. The senior member of the crew just stood back and let them roll with the punches.

                  After setting up the two 6" suctions and dual master streams (2" tip fixed, 1.75" tip portable), they found that the primer on the truck was dead. While most departments would have called it quits and told command that they couldn't secure a water supply, the rookies had another idea.

                  They put a check valve on the strainer on one suction and back-filled the line with tank water. Then they let tank water flow freely through the open suction and simultaneously opened the deck gun. The water flowing through the check valve'd suction self-primed the second line and within a minute they were flowing both master streams at nearly 2,000gpm.

                  In a situation where most crews would have failed the secure a water supply and lost the fire building, a little bit of quick thinking by this crew allowed them to prime not just one, but two suction lines and greatly exceed the pump's capacity at draft.


                  • #10
                    Water flow in has to equal water flow out.

                    If you hook a 1000 gpm pumper to a hydrant that flows 3000 gpm at 20 psi residual on its own you are going to get 3000 gpm when the intake pressure reads about 20 psi (I'm neglecting some intake friction loss here for the sake of clarity).

                    a ship in a harbor is safe. . . but that's not what ships are for


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