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comm. flow switch application issue?

These flow switches aren't making at all or intermittent at best.  There's about 10 total and none of them are making on a regular basis. I'm thinking wrong flow switch, but am looking for ideas.

I have a job where some commercial pumps need to have water cool off the pump seal and they need to have a minimum of 5 gpm.  These Johnson flow switches (F61MG-1) are rated to make at 4.2 gpm.  <a href="http://cgproducts.johnsoncontrols.com/MET_PDF/125225.pdf">[url=http://cgproducts.johnsoncontrols.com/MET_PDF/125225.pdf]http://cgproducts.johnsoncontrols.com/MET_PDF/125225.pdf</a>

Before the pump is activated the solenoid valve opens and the flow switch must verify flow before the pump activates. This is city water pressure and is 35-45 psi.

We have adjusted sensitivity to it's lowest setting and verified the 5 gpm flow by filling bucket and timing.

Any help is greatly appreciated.


  • Alan (California Radiant) Forbes
    Flow Switch

    The only thing that comes to mind is to check that the flow switch paddle moves freely.  They usually give you assorted paddles depending on the size of the line.  With your small line size, the paddle needs to be small.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • bob_46
    bob_46 Member Posts: 813
    Catch 22

    Flow switches tend to be tricky and problematic. I notice you increase pipe size before each switch and then reduce again after the switch. That is part of your problem. When you increase pipe size the water slows down in that section i.e. static pressure goes up and velocity pressure goes down. Velocity pressure is what moves the paddle. However, the mechanical properties of the switch need the larger size so that the paddles have clearance. I think your switches may be too large for the application.

    There was an error rendering this rich post.

  • BobbyG
    BobbyG Member Posts: 79
    thank you

    Bob - that is what, in the back of my mind, I was wondering about.  Thank you for clarifying that for me. 

    Thank you both (Alan F. and Bob)  for your help!
This discussion has been closed.