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Thread: Throttle Control Valves - Clarification on their use in InfoWater, H2OMap, and H2ONet

  1. #1
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    Lightbulb Throttle Control Valves - Clarification on their use in InfoWater, H2OMap, and H2ONet

    Throttle control valves are one feature within the software that may or may not get used as much by different modelers as other valve types, but are another tool that in the modeler's toolbox that can be used. Due to some recent support calls we wanted to point out a few things regarding TCV's that may or may not be obvious to all users to help avoid confusion once they are used. These key points are added here to help clarify information that can help users best use this feature in the software.

    First, let's start with a description of the Throttle Control Valve (TCV) from the software help file to describe what they are:

    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.

    In addition here is the help description regarding the type of curve a TCV uses which is a Minor Loss vs % Open (Control Valves - Motorized Throttled)

    For Motorized Throttled Valves (MTVs), a Minor Loss Coefficient Curve consists of a collection of points defining the minor loss coefficient K (Y-axis) as a function of the percentage (degree) opening setting (X-axis). It provides the capability to model valves with unique headloss characteristics such as cone and butterfly valves.

    A sample table and curve are provided below. Either a general (multi-purpose) type of curve or a specific MinorLoss vs % Open curve will work as long as the X values are percent open and the y values are the minor loss K values.(Click for larger image)
    General Curve
    Minor Loss Vs. Percent Open Curve.jpg
    MinorLoss vs. % Open Curve
    ML vs % Open Curve.jpg

    Here are a few key notes regarding Throttle Control Valves that will clarify their use in the model

    1. Throttle Control Valves use a setting which is the percent open for the valve. The TCV setting is expected to range from 0-100. (Note this is different from pump speed which is expressed as a decimal from 0-1).
    2. A percent open of zero as a valve setting will not directly make the valve have zero flow.
      1. This is due to the way TCV's were developed in EPANET. In EPANET the TCV does not have a curve, but simply assigns a minor loss K based on the setting. This means that the percent open is not used in EPANET and that at zero percent open the model will simply assign the K value to the valve. Even with the largest k value you can enter of 9999999999.00 used as the K for 0 percent open, the valve will still generally have a small flow. This is due to the intended purpose of TCV's to be used more as throttling a valve's flow rather than closing a valve off completely.
      2. This means the only way to completely shut off flow in a TCV is to change it's status to "closed". To make it active again the valve would have to be assigned a new setting. Be careful not to set the valve to "Open" though as this will make it act like an open pipe. Note: One could also put open/closed controls on a pipe downstream of the valve as well if you need to completely shut it off and would rather avoid the specifics of closing and making a valve active.
      3. Note: This may be of importance if you use TCV's to model isolation valves, which is something we see periodically in Technical Support. Make sure to close the valve rather than set it to zero percent open if you want to truly "close" the valve in the model.

    3. The key to understanding flow through a TCV is to understand how the headloss is calculated by the software:
      1. The valve setting (which ranges from 0-100) is used to identify the minor loss K to use for the valve. Once the K is known the model will calculate a flow that will induce a headloss through the valve to match the calculated head difference on both sides of the valve.
      2. Key points in how the headloss is calculated and how it impacts model results:
        1. The headloss through the valve is calculated by the following formula: HL = K*(V^2/2g), where HL is headloss in feet, K is the minor loss coefficient, V is the velocity through the valve in ft/s and g is gravity at 32.2 ft/s^2.
        2. Given that 2*32.2 ft/s^2 is 64.4 ft/s^2 is the divisor to the square of the velocity, headloss through the valve would need to be roughly 8 ft/s to get a value close to 1 in the V^2/2g term. Thus, unless the K is large, or the valve is small (increases the velocity) the TCV will potentially do little to throttle the flow (i.e. induce headloss to limit the flow) as the headloss will be small unless the velocity is very high.
        3. In essence, the model will push water through the valve until the headloss equals the head difference up and downstream of the valve. This can potentially lead to large flows if the valve is very large ( i.e. low velocity) or the K is very small, so be aware of this when you use this type of valve and make adjustments as needed to get the valve working as desired. Understanding the headloss and how it is calculated for a TCV is the key to understanding how a TCV controls the flow within the model. For lower flows through the valve either increase the K, lower the valve diameter, or decrease the setting used. If flows are still too large at the desired setting, increasing the K values in the curve or simply reducing the valve diameter may be the only way to reduce the actual flow through the valve as the only way to reduce the flow is to increase the headloss.



    We hope this information will help our users to make better use of TCV's in their models and help clarify a few things that may not have been completely apparent from the current information in the help files for TCV's.

    If you find you need further assistance with TCV's please don't hesitate to contact us at support@innovyze.com.

    Thank you!

    Innovyze Support
    Last edited by Patrick Moore; November 3, 2016 at 12:08 PM.

  2. #2
    H2OMAP
    Say my throttle valve (butterfly) is being modelled fully open (90 degrees). No curve just a K value, does the setting (0-100) take a percentage of the K value? So a setting of 50 would half the K value?
    Cliff Dredge

  3. #3
    OK I see now. If I don't have a curve then my setting is the K value. Sometimes the minor loss field is greyed out (as it should be for a TCV) but sometimes it is not and you can input numbers which was why I was confused there.

  4. #4
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    Cliff,

    You are correct. With a curve the setting represents the % Open on the minor loss vs. %open curve. Without a curve it will use the minor loss K value (in InfoWater and H2ONET) but in H2OMAP Water the K is typically greyed out and the user assigns the K value as the valve setting which is what EPANET uses as the valve setting for a TCV.

    Patrick Moore
    Last edited by Patrick Moore; March 3, 2016 at 01:50 PM.

  5. #5
    There's something wrong with because some of my TCVs use the setting as the K but some of them use the minor loss field. I have been testing it for a while now. As I mentioned when you open the software none of the TCV fields are greyed out, but when you change valves and back to TCV it will grey out the minor loss. But even when it's greyed and has a number applied it will use that as a K value. It seems to be the TCVs that are connected to a tank use the minor loss and a TCV in the reticulation uses the setting for the K?

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    Cliff,

    It looks like in the latest version of H2OMAP Water and InfoWater that the software is greying out the ML coefficient for throttle control valves. I tested several connections in the latest version of H2OMAP Water (version 10.0 Update 7) and found them all to be consistent regardless of how they were connected. Are you using an older version of the software by chance?

    By the way, it is often good practice to separate any valve or pump from a tank or reservoir when using H2OMAP Water as EPANET has specific restrictions that won't allow certain valve types to connect to a Tank/reservoir. Since H2OMAP Water uses valves and pumps as "links" just like EPANET, these rules would also apply. By always keeping a junction and pipe in-between the valve or pump and the tank you don't have to remember which types are restricted. This also seems to help model stability as well somewhat.

    EPANET Help
    Because of the ways in which valves are modeled the following rules apply when
    adding valves to a network:
    • a PRV, PSV or FCV cannot be directly connected to a reservoir or tank (use a length of pipe to separate the two)
    • PRVs cannot share the same downstream node or be linked in series
    • two PSVs cannot share the same upstream node or be linked in series
    • a PSV cannot be connected to the downstream node of a PRV.

  7. #7
    Hi Patrick,

    Thanks for your advice on connecting to tanks, I did connect through a pipe and it made no difference with the TCVs. I was on update 6, updating to 7 now. The minor loss field is generally greyed out, when I installed these valves it wasn't and I used the minor loss field for the K value. And now it's the minor loss field which is the K and the setting does nothing. I can show you if you like? Or maybe the update 7 will change it?

  8. #8
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    Cliff, Let's move further discussion off this thread and into a separate support case to expedite the issue.

    Please email me the screenshots, and let's definitely see if the upgrade resolves the issue as it appears to be consistent in update 7. We can set up a time to meet that fits your schedule.

    The good news and potential short term workaround you may also have is that TCV's are essentially adding headloss only by modifying the valve ML coefficient and if you ever have question regarding a TCV operation an easy workaround is to either "open" the valve and use a ML coefficient on one of the pipes connected to it as a surrogate or simply inactivate the valve and add a bypass around it and use the diameter and ML to regulate the headloss to mimic exactly what the TCV does.

    EDIT: If you want to enter in a ML value for any TCV, another workaround is to change the valve type to a different type to enter in a minor loss value and then change the valve type back to a TCV as well. This appears to work as currently any value entered in the ML field of a TCV (even when greyed out) is still being exported as a ML value in the EPANET file used in the analysis. The EPANET file used for that scenario is the ~INP file you can find in the .OUT folder/scenario/scenario name folder. This ML value however is not often used for TCVs as it only is relevant when the valve status is operating with a status of "OPEN". When the valve is active the valve setting (with no curve) represents the ML value and with a curve the ML value is based on the ML vs. % Open curve using the %Open value in the valve setting.

    Patrick Moore
    Last edited by Patrick Moore; March 8, 2016 at 01:02 PM.

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