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Twinning injection pumps on single control....Boilerpro

Mark Eatherton1
Mark Eatherton1 Member Posts: 2,542
will double the GPM. Doubling the GPM increase the pressure drop by 3 1/3 times (that's tree-n- a turd for my students...) In most cases you can't simply double the flow in a given system due to the difference in pressure drop. It might end up someplace between 1 and 2 times the flow rate. Now on the other hand, if only one pump were working, it might move more GPM than the twins...

Ever seen one of them Grundfos double breasters.

I saw the power head from one of those that blew off the end of the pump and went through two sheet rock walls and imbedded itself in a cinder block wall...

Seems the chemical salesman who serviced the laundry decided the water wasn't hot enough. Turned it up to 210 degrees F. Low incoming water pressure compounded by pumps starting with less than required NPSH, and KABLOOEYYY. Water flashed to steam and sent the power head flying...

Ya gotsta be careful with them pumps, they'll kill ya. In fact, 100% of the people that handles pumps dies...

Pumps in series will kill ya too...


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  • Boilerpro
    Boilerpro Member Posts: 410
    Twinning injection pumps on single control....Boilerpro

    Anyone ever try this? I usually set up my larger systems with back up throughout.... ie. two boilers each with its own pump, two system pumps, etc. Tekmar has given the idea its blessing as has B&G pump rep. Since check vavles are now considered okay, why not pipe two in parallel and if one goes down the other will continue to supply flow. The two pumps are not for increased flow, but this is also a possibility(2 NRF-33's give about 70 gpm flow. Plan on using this on my next job and wanted to see other experiences.

  • Boilerpro
    Boilerpro Member Posts: 410
    Ohhhhh, Yes I understand that problem, ME, however..

    I take the load, divide it in half, and let each pump carry half the load at design. If one pump fails, the other pump will run out on its curve and often supply nearly 90% of the flow of the two pumps. B&G has a really good manual on using pumps in both parallel and series ( Parallel and SEries Pump Application, Bulletin No. TEH-1065, copyright 1965). Never done series yet, because I never needed that much head pressure on my jobs, but do parrallel pumping all the time. Tekmar makes a control just for this type of application, if your interested, that stages pumps according to load. Eventually I might use a variable speed system pump controller for big jobs, but not doing anything that big yet.

  • j_4
    j_4 Member Posts: 59
    each pump carry half the load

    Boilerpro is right in the money...the single pump will run out & give 70 to 90% of the flow depending how flat the curve is....if the piping is generously sized it'll be closer t0 90%....ever seen one of these, armstrong dual-arm pumps....two pumps & two motors with a built-in check/isolation valve...they can back each other up, operate in parallel, can be isolated to work on one while the other stays on, & you pie up one set of trim
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