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  1. #1

    Float Valve Curves

    Why does a Float Valve use a Flow vs Headloss curve? Shouldn't there be a Tank Level vs % Open curve to control a Float Valve?

  2. #2
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    Steve,

    Thank you for posting your question on the Innovyze Forum.

    Float valves in essence are just a general purpose valve (GPV) with controls based on the tank level set on a pipe connected to the valve, except that the pipe controls are hidden and set in the valve attributes. A GPV by default uses a headloss vs flow curve which is why float valves use this setup.

    However, if you wish you can replicate the float valve by using a Throttle control valve (TCV) with the up or downstream pipe connected to the valve set to open or close based on the desired tank water levels. Just make sure NOT to put the controls on the valve as it is difficult to close and activate either a TCV or a GPV during a simulation due to not being able to set a valve to "OPEN" or give it a setting to run with and have them operate as intended. The "Open" value on a valve control will make the valve simply act like an open pipe and should be avoided. But by placing the open and closed controls on a pipe connected to the valve you con make the valve active or closed while letting the valve act as it would.

    The only key for either using the Float valve (GPV type) or the Throttle Control type (TCV) is to make sure the curve used will produce the headloss characteristics desired. The TCV type sets the Minor Loss coefficient for the valve and will calculate headloss as K*V^2/2G, where K is the ML coefficient and V is the velocity in ft/s and G is the gravitation value 32.2 ft^2/s^2. Also note a TCV set to zero is not truly closed in the model either as the high K value at zero will restrict but not eliminate flow.

    Help notes for Float Valves
    Float Valves - Many storage tanks and reservoirs are fitted with float valves (e.g., ball float valves) on the inlet pipe to control rate of flow and prevent overflow. These valves gradually close (increase the resistance of the inlet pipe) as the water level in the controlling tank rises. The headloss across the valve is modeled (via a curve) based on any user specified pairs of headloss vs. flow points. The valve is active if the water level in the controlling tank is below the lower control level or the water level is between the lower and upper levels after the valve opening. Likewise, the valve is closed if the water level in the controlling tank is at or above the upper control level or the water level is between the lower and upper after the valve closes.
    Specify the Valve Type as Float Valve in the Type field of the Modeling Data section of the Model Explorer - Attribute Tab.

    Required Fields:
    Diameter - Diameter of valve, in. (mm)
    Curve - Select the curve ID that represents the Float Valve headloss vs. flow.
    PID - The tank whose levels dictate the behavior of the Float Valve.
    LCL - The low "turn-on" level of the tank.
    UCL - The high "turn-off" level of the tank.
    Note: For float valve's please do not enter any data to the elevation, setting and minor loss fields.

    Help Notes for TCVs
    Throttle Control Valves (TCV) - A TCV may be used to
    simulate a partially opened valve by adjusting the minor loss coefficient. They
    are normally used to increase or decrease flows or to control pressures in the
    system. A TCV can either have a Minor Loss vs.
    %Open
    curve associated with it or not. Whether a curve is associated or not
    depends on what the Setting value means to InfoWater.


    Specify the Valve Type as Throttle Control in the Type field of the Modeling
    Data section of the Model Explorer - Attribute Tab.

    Required Fields:

    Setting - %Open (with curve identified), K value (no
    curve)
    Diameter - Diameter
    of valve, in. (mm)
    Curve
    (Optional)
    - Minor Loss vs. %Open Curve ID

    Note: For TCV's please do not enter any data to the
    PID, UCL and LCL fields.


    We hope this helps. IF you need further explanation please respond to this thread with your additional questions

    Innovyze Support

  3. #3
    Patrick,

    Can you give me a generic example of a headloss vs flow curve for a float valve?

  4. #4
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    The best thing to do is to go the manufacturer site and find the flow vs pressure drop curve, and simply convert the pressure values to ft of headloss using the 2.31 ft = 1 psi conversion. Most manufacturers have these curve on their public sites.

    Here is one - Go to Page 31 and 32: http://stocktonvalve.com/pdfs/Watts/C-CACV.pdf


    Because each manufacturer is different it's best to find or request these curves from your valve supplier.

    Innovyze Support

  5. #5
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    Steve,

    Here is another example of hl vs flow curve for Cla-VAL hyrotol 100-20 valve used in most of its varied control valves: to get a specific flow on a certain size valve one needs a specific difference in pressure drop across the valve to get that flow. For example a 3 inch globe valve (blue lines) would need 10 psi difference between the upper and downstream head to flow 200 gpm. To create a HL vs flow curve when the headloss is in PSI, simply convert the pressure drop to ft or meters.

    Capture from here: http://www.cla-val.com/documents/pdf/E-100-20.pdf

    (click for larger image)
    HLvsFlowCurve-ClaVal.jpg
    Attached Images Attached Images

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