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Modelling Hydrants in WaterGEMS as 'discharge to atmosphere'

Hi,

I'm modelling a hydrant on a system as a 'discharge to atmosphere' item and wondering if I am modelling it correctly. I want to know the discharge from the hydrant under normal pressure conditions in the system. The hydrant I am using has a pressure loss of 1.7bar at 42l/s, calculated by using the Kv value at design flow given by the manufacturer. Therefore, the typical pressure drop and flow I am using 1.7bar and 42l/s for the 'orifice' element type. However, I am not seeing the significant pressure drop I would expect to see at the discharge node. Also, if the pressure in the system changes from the typical, should I not expect to see a change in the typical flow as well, how do I model this?

thanks 

  • Exactly what problem are you trying to solve? is this for estimating available fire flow or for getting an idea of how much was will come out during flushing?

    In WaterGEMS, you are usually better off using the Hydrant element with an emitter coefficient. See the help topic on Estimating Hydrant Discharge using Flow Emitters.

  • Hi Tom,

    I just wish to see the available flow at the hydrant, dependent on the pressures in the system. But I want to include the losses in pressure through the hydrant. 

    If an emitter coefficient corresponds to the size of the hydrant opening, and is used to define how much flow you can get from the hydrant. If I have a Kv value of 92. Is this the same as the emitter coefficient to be used in the modelling? 

    Is there a tutorial video of using emitters as hydrants? 

    thanks 

  • Hello Sam,

    I do not know that there is a video specific to model emitters. However, the Help topic Dr. Walski mentioned and this wiki article have some additional information:  Junction vs. Hydrant .

    It is also possible to model the hydrant lateral loss in the hydrant properties. If you set the hydrant property "Include Hydrant Lateral Loss?" to True, additional properties are displayed that will be used to model the headloss in the lateral.

    Regards,

    Scott

  • HI Scott, thanks for responding. 

    I've looked at the page -Calculating available flow at a hydrant - OpenFlows | Water Infrastructure Wiki - OpenFlows | Water Infrastructure - Bentley Communities 

    and found that the estimate emitter coefficient for a 2.5inch outlet is 185 gpm/sqrt(psi) or 14 l/s/bar can be used.  would that then be the same if the hydrant supplier has a Kv of 92 at 2000 l/min?

    thanks 

  • Sam,

    The "Pressure Drop (Typical)" for a Discharge-to-Atmosphere (D2A) element is the difference between pipeline pressure and atmospheric pressure. Meaning, the actual pressure at the node (with the corresponding "typical flow"), not the headloss across it.

    If you just want to know how much water will flow out of the hydrant for example during a hydrant flushing, it is best to use an emitter coefficient per the guidance in the article you found. Also see the WaterGEMS help topic "Estimating Hydrant Discharge Using Flow Emitters" and chapter 5.2 of our AWDM book.

    and found that the estimate emitter coefficient for a 2.5inch outlet is 185 gpm/sqrt(psi) or 14 l/s/bar can be used.  would that then be the same if the hydrant supplier has a Kv of 92 at 2000 l/min?

    By "Kv" do you mean the "K" emitter coefficient, or something else? Can you clarify? See the table at the bottom of the aforementioned help topic.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.