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Thread: Head preassure from flow monitor

  1. #1
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    Head preassure from flow monitor

    I have a 1/2 inch installed on the water pump (Danner Mag 12) which is the pump for my ATS. The line from the pump to the ATS is about 28" of rise and 3.5 feet of horizontal with 5 90 elbows, two threaded unions and 1 Gate valve. The tubing (PVC) from the pump is 1/2" and increases to 3/4" after the gate valve. With the gate valve fully open I am only getting 310 GPH of flow. I would like to have 350.

    Could I get better flow if I did 3/4" from the pump, down to 1/2" for the monitor and than back to 3/4".

    Second option might be 3/4' to 1" monitor and back to 3/4" after the monitor. That is how my return pump monitor is set up.

  2. #2
    Frequent Contributor zombie's Avatar
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    Depends. How much percentage wise do you think is 1/2" vs 3/4". If it's half and half, keeping the same monitor and upping the half that's 1/2 to 3/4" should give you about 20% more flow. I would guess probably more like 30-40% more flow with a 1" monitor and reducers.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by hkgar View Post
    I have a 1/2 inch installed on the water pump (Danner Mag 12) which is the pump for my ATS. The line from the pump to the ATS is about 28" of rise and 3.5 feet of horizontal with 5 90 elbows, two threaded unions and 1 Gate valve. The tubing (PVC) from the pump is 1/2" and increases to 3/4" after the gate valve. With the gate valve fully open I am only getting 310 GPH of flow. I would like to have 350.

    Could I get better flow if I did 3/4" from the pump, down to 1/2" for the monitor and than back to 3/4".

    Second option might be 3/4' to 1" monitor and back to 3/4" after the monitor. That is how my return pump monitor is set up.
    That's a lot of 90's, all 1/2" from the way I read your description? If so, that is most of your pressure loss there. Mag pumps are particularly sensitive to head loss - the right end of their pump curves gets steep. You are running a Mag 12 at only 25% of its rated capacity, so that is a lot of head pressure for that pump. I would upsize as many of those fittings as you can.

    If those are in fact 1/2" PVC elbows at 310 gph, you have around 10.8-ft of head loss just in those elbows...those elbows by themselves are causing most of the head loss. If you can change them to 3/4, you will drop the losses to about 1/2 the current loss and it looks like your flows may end up somewhere around 650 gph. Now you can use your valve to throttle the flows where you want them precisely.

    Even better and more efficient, change the elbows to 3/4", reduce the head loss and then change the pump to a Mag 7. This will put you around 390 gph and the pump will be better matched for the application.

    The actual loss from the FMM is minimal compare to the elbows.

    I will also add that the 310/350 gph is outside the optimal operating range for the 1/2" sensor. The velocities are around 8.5 ft/s which is pretty high and I recall reading that the ideal range for the 1/2" unit is up to 250 gph. The 1" sensor is a better fit for your application, but this is not the source of your pressure loss.

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    Thank you for your responses. I think I intuitively figured the elbos were crating the head loss. I also wondered about the capcity (effective range) for the 1/2" sensors.

    I have already ordered the 1" sensor, and will be installing that on 3/4 line and then will see if my Mag 9 will handle it. Sounds like it should.

    Here is a video of the current set up. The stubbed off on the right is going to be a line to the GFO & GAC reactors
    https://goo.gl/photos/Tb8ZsoVu44DDn59s7

    When I switch to 1" sensors I will get all the height up from the pump to eliminate two 90 elbos and the stub off will be an inline tee to eliminate another 90.

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    Quote Originally Posted by hkgar View Post
    Thank you for your responses. I think I intuitively figured the elbos were crating the head loss. I also wondered about the capcity (effective range) for the 1/2" sensors.

    I have already ordered the 1" sensor, and will be installing that on 3/4 line and then will see if my Mag 9 will handle it. Sounds like it should.

    Here is a video of the current set up. The stubbed off on the right is going to be a line to the GFO & GAC reactors
    https://goo.gl/photos/Tb8ZsoVu44DDn59s7

    When I switch to 1" sensors I will get all the height up from the pump to eliminate two 90 elbos and the stub off will be an inline tee to eliminate another 90.
    Sounds good, you should see an improvement. Makes me wonder if you were reading 310 gph on the 1/2" meter, how much you were really getting. I'm not sure which way the error will favor. I have not found the official Neptune range limits for the meter, but BRS lists 50 to 250 gph for the 1/2" and 150 to 1500 gph for the 1".

  6. #6
    Master Control Freak RussM's Avatar
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    Usable ranges for flow sensors are available on the main Neptune website https://www.neptunesystems.com/fmm-accessories/
    Please do not send me PMs with technical questions or requesting assistance - use the forums for Apex help. PM me ONLY if the matter is of a private or personal nature. Thanks.

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    Thanks Russ

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    Quote Originally Posted by RussM View Post
    Usable ranges for flow sensors are available on the main Neptune website https://www.neptunesystems.com/fmm-accessories/


    @RussM, do you know any info regarding the meter error once you go outside this range?

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    Now that's an interesting question. My way of thinking is that if there was a known error outside the range, then software could be written to adjust for the error and then there would be no error. Circular logic?

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    Quote Originally Posted by hkgar View Post
    Now that's an interesting question. My way of thinking is that if there was a known error outside the range, then software could be written to adjust for the error and then there would be no error. Circular logic?
    Not always. Within the operating range of a flow sensor, the relationship between the physical value and the voltage/current the FMM reads is mostly linear which makes the conversion very simple in that range. Once you go outside that range, you have to deal with non-linearities, saturation, and peak measurement capabilities that makes the conversion incredibly difficult or even impossible (when the signal is above the measurement range) to accurately show. Outside the normal measuring range, these non-linearities also vary significantly more between individual units.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Quote Originally Posted by zombie View Post
    Not always. Within the operating range of a flow sensor, the relationship between the physical value and the voltage/current the FMM reads is mostly linear which makes the conversion very simple in that range. Once you go outside that range, you have to deal with non-linearities, saturation, and peak measurement capabilities that makes the conversion incredibly difficult or even impossible (when the signal is above the measurement range) to accurately show. Outside the normal measuring range, these non-linearities also vary significantly more between individual units.

    You might be an engineer if...You have no life and can prove it mathematically.
    OH! Got it - not even close , So my reading of 310 with the 1/2" sensors could be just about anything? Glad I have the 1" sensor ordered for this application.

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    Frequent Contributor zombie's Avatar
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    Quote Originally Posted by hkgar View Post
    OH! Got it - not even close , So my reading of 310 with the 1/2" sensors could be just about anything? Glad I have the 1" sensor ordered for this application.
    Could very well be. My calcs earlier suggested you should be sitting closer to the 400-500 range (depending on proportion of 1/2 vs 3/4 and assuming the flow meter was no more loss than a 90) so it's definitely possible that saturation is coming into play here and skewing the measurement vs reality.

    You might be an engineer if...You have no life and can prove it mathematically.

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    Just for kicks. 1/2 inch tube vertical from pump rises 10.5 " to Tee than horizontal 2" to 90 than 3" to union (1/2") than 7.5" to sensor, then 5" to 90, 4" to 3/4" gate valve than 3/4" pipe 12" to a 90 than vertical 8" to 90 than 12" to 3/4' union than to ATS and empties through a 1/4" by 10" slit in 3/4" tube.

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    Quote Originally Posted by hkgar View Post
    Just for kicks. 1/2 inch tube vertical from pump rises 10.5 " to Tee than horizontal 2" to 90 than 3" to union (1/2") than 7.5" to sensor, then 5" to 90, 4" to 3/4" gate valve than 3/4" pipe 12" to a 90 than vertical 8" to 90 than 12" to 3/4' union than to ATS and empties through a 1/4" by 10" slit in 3/4" tube.
    I need a sketch to visualize it, on the verticals, you should clarify up or down so someone could determine net vertical lift. I do agree with Zombie that on a Mag 12 you should be getting more than 310 though, I just dont see 15+ ft of head pressure, even if it were all 1/2".

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    Quote Originally Posted by clsanchez77 View Post
    I need a sketch to visualize it, on the verticals, you should clarify up or down so someone could determine net vertical lift. I do agree with Zombie that on a Mag 12 you should be getting more than 310 though, I just dont see 15+ ft of head pressure, even if it were all 1/2".
    Al verticals are up. Total vertical lift (up) is 18.5". 10.5 through 1/2"pipe 8" through 3/4".
    Total horizontal is 45.5" Not including the slit in the ATS
    See the video I posted in post #4
    Here it is again
    https://goo.gl/photos/Tb8ZsoVu44DDn59s7


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