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Will two pumps increase output?

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  • Will two pumps increase output?

    Here is the situation. A late 50s' Air Force dormitory with 3 floors with water circulating for heat/ac. The problem is not enough water is circulating. We figure this is either blockage in the line or the pump wasn't sized for the building. The theory goes that when they plumbed the first building they sized the pump for just radiant heat off the pipes, no radiators with fans. When they moved to the problem building they assumed (one of many hugely wrong design flaws)it was the same and put in the same size pump. They were wrong, this building, like two others on campus have radiators in each room (30 15x15 rooms per floor). The other buildings on campus that have radiators have huge pumps in the basement that handle the job, but not the problem building. Just the pump as described above. The answer as prescribed by Blackmore and Glunt is to add a pump in the line.
    My question is will that do the job? Does adding 25gpm to 25gpm make 50gpm or whatever the numbers are?
    Hope this is clearer than mud! Thanks.
    God Bless You Super Good!!!

  • #2
    Re: Will two pumps increase output?

    Before you get too carried away, you need to look at the pipe size you have and take a hard look at velocity. Changing to a larger pump will increase the flow if the system can handle it.

    Two pumps in parallel (the return line will "tee" off and feed each pump and the reverse on the supply side) will increase the flow. but this can be a dangerous situation if the piping system is not sized to accomodiate that flow rate. Too high of a velocity will quickly erode the pipe.

    Two 25 gpm pumps inline with each other will not increase your flow. You would have a 25 gpm pump feeding a 25 gpm pump. Nothing gained.

    IF the system worked fine before, I would say you have a problem with the new pump (not enough flow/head).

    It sounds to me like you need to verify a few things before you go and add another pump

    Comment


    • #3
      Re: Will two pumps increase output?

      Add to that the question of how the loops are set up.
      Monoflo? split? How many linear feet? Sq feet vs BTU output on the boiler?
      Another point is height, the higher the loops go, the less air it takes to bind or slow the flow.
      Is there a noticeable difference from one floor to another?
      Are there bleeders on the zones?

      Comment


      • #4
        Re: Will two pumps increase output?

        Originally posted by biscuit View Post

        Two 25 gpm pumps inline with each other will not increase your flow. You would have a 25 gpm pump feeding a 25 gpm pump. Nothing gained.
        biscuit, i agree with everything you said

        they need to check all the tables and flows. if not they will create a serious second problem

        except that i had a job in a hotel that they used a grundfos pump for an indoor water fall. the pump was not a submersible and was installed outside of the pool at a lower elevation to keep a flooded suction. it was not enough flow to make them happy.

        i stacked /bolted, 2 bolt flange to the first one and it actually made a big difference. i was surprised too, but grundfos was the one who suggested it.

        p.s. i was not the water fall installer. i only fixed their screw up.

        not sure if this applies to a closed loop system, but it worked for this open water fall system. could it have been a head issue it was less than a 6' head.

        rick.
        phoebe it is

        Comment


        • #5
          Re: Will two pumps increase output?

          Rick,

          I would suspect a head issue on the waterfall if the pump had the desired flow assuming the pump you added was the same flow rate.

          Its kind of hard to explain pumps to someone who does not deal with them everyday. IF one knows and understands a "pump curve" its pretty easy to get the right pump the first time.

          I all too often see people install pumps that dont work properly. They replace a 50 gpm pump with another 50 gpm pump. Problem is the origional may have had an impeller capable of providing flow at 75 feet of head and the new one would only provide designed flow at 20'. See it more often that one should.

          There are a ton of variables with pumps.

          Comment


          • #6
            Re: Will two pumps increase output?

            Originally posted by biscuit View Post
            Before you get too carried away, you need to look at the pipe size you have and take a hard look at velocity. Changing to a larger pump will increase the flow if the system can handle it.

            Two pumps in parallel (the return line will "tee" off and feed each pump and the reverse on the supply side) will increase the flow. but this can be a dangerous situation if the piping system is not sized to accomodiate that flow rate. Too high of a velocity will quickly erode the pipe.

            Two 25 gpm pumps inline with each other will not increase your flow. You would have a 25 gpm pump feeding a 25 gpm pump. Nothing gained.

            IF the system worked fine before, I would say you have a problem with the new pump (not enough flow/head).

            It sounds to me like you need to verify a few things before you go and add another pump
            I like redundancy

            http://good-times.webshots.com/photo/2897801750102246532msaiIh

            Comment


            • #7
              Re: Will two pumps increase output?

              Pumps in Parallel or Serial Connection
              For pumps in serial - add heads, for pumps in parallel - add flowrates

              Sponsored Links

              Pumps can be arranged in serial or parallel to provide additional head or flowrate capacity.
              Pumps in Serial - Heads Added

              When two (or more) pumps are arranged in serial, their resulting pump performance curve is obtained by adding heads at the same flowrate.
              www.engineeringtoolbox.com/pumps serial-parralel
              pumps in series

              For two identical pumps the head will be twice the head of a single pump at the same flow rate.
              Pumps in Parallel - Flow Rate Added

              When two or more pumps are arranged in parallel, their resulting performance curve is obtained by adding their flowrates at the same head.

              pumps in parallel

              For two identical pumps the flow rate will be twice the flowrate of a single pump at the same head.

              Comment


              • #8
                Re: Will two pumps increase output?

                Originally posted by seanwarde View Post
                Pumps in Parallel or Serial Connection
                For pumps in serial - add heads, for pumps in parallel - add flowrates

                Sponsored Links

                Pumps can be arranged in serial or parallel to provide additional head or flowrate capacity.
                Pumps in Serial - Heads Added

                When two (or more) pumps are arranged in serial, their resulting pump performance curve is obtained by adding heads at the same flowrate.
                www.engineeringtoolbox.com/pumps serial-parralel
                pumps in series

                For two identical pumps the head will be twice the head of a single pump at the same flow rate.
                Pumps in Parallel - Flow Rate Added

                When two or more pumps are arranged in parallel, their resulting performance curve is obtained by adding their flowrates at the same head.

                pumps in parallel

                For two identical pumps the flow rate will be twice the flowrate of a single pump at the same head.

                thanks for the explanation. it makes sence now. the parellel is a no brainer. the series is interesting.

                so in my water fall case the secondseries pump was to overcome the head loss.

                thanks

                rick.
                phoebe it is

                Comment

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