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Hammer-How to run pump for specific flow rate

Dear Bentley Team,

We have a one pumping system, source is storage tank-1 which is open to atmospheric & pump suction is taking from this tank –1 & destination of the pump is connected to another storage tank-2 which is also open to atmospheric, in this case I need to run a pump (Pump is purchased & pump performance curve also available) for specific flow rate, where can I mention flow rate, if i choose junction on destination point & mention the flow rate  then required flow is showing whereas pressure is coming more than the atmospherics pressure on the destination point.  If I select reservoir then required pressure i can get but flow rate is coming different required, request you to help us.

Thank you

Parents
  • Hi Jayakanthan,

    When using the approach of using a junction with demand at the downstream end of the system, the pump is forced to operate at that known flow, and will add the corresponding head from its pump characteristic curve. Head loss in the pipes will reduce that and you will end up with a specific pressure at that junction.

    When using the approach of modeling the downstream end as a tank, the pump will add enough head to "lift" the water from the upstream tank boundary elevation to the downstream tank boundary elevation (considering the friction losses between, as well) and you will end up with a certain flow that corresponds to that head, from the pump curve. 

    If the real system has a tank at the downstream end, then it would be best to use the approach of modeling it as a tank. If the pump does not operate at the desired point (flow) when doing this, then you may need to adjust the physical parameters in order to achieve that desired operating point. For example if the pump flow is lower than what you want, then increasing the pipe diameter is one possible way to reduce the headloss, which reduces the amount of head that the pump needs to add to overcome it, and thus increases the flow as it shifts its operating point. Looking at a system head curve can help with this, if you have access to WaterGEMS or WaterCAD. Please see the following related articles:

    Understanding System Head Curves (see this about HAMMER)

    How are pumps handled in each OpenFlows product?

    If you simply want to force a specific flow rate for a pump, you could keep the tank at the downstream end and replace the upstream tank+pump with a periodic head-flow element, with a flow pattern set to force that inflow. However, this may not be a good reflection of the real system for a transient simulation, as the pump element incorporates a four-quadrant pump curve for accurate modeling during transient conditions.

    If the system is more complex and you are not sure which parameters to adjust (diameter, roughness, demands, valve status), then this may be a calibration exercise to get the model results to match the field measurements.


    Regards,

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

  • Dear Bentley Team,

    Thank you for your reply

    As we know source pressure is atmospheric & destination is also operating at atmospheric pressure & also we have a performance curve then getting desire flow at destination point we used junction & given flow rate,  for adjusting  pressure drop in the system we have used Orifice between pipe, software should calculate orifice drop based on system pressure drop, but Hammer /waterGEMS is asking  to give pressure drop as a manual input, if all i give as a manual input then why we need to use software.   Kindly guide me if i am wrong. 

  • Hello Jayakanthan, 

    Using flow and pressure drop values, Hammer calculates discharge coefficient, which it uses to vary the head loss with flow.

    You could use the formula based user data extension to calculate the pressure drop using orifice equation, by giving diameter and flow values. 

    This is explained in the below wiki, please go through it. 

    Defining Orifice Between Pipes element by diameter - Formula based UDX

    How is an Orifice between Pipes element used in WaterGEMS and WaterCAD?

    Regards,

    Sushma Choure

    Bentley Technical Suppport

  • Dear Bentley Team,

    Thank you for your reply

    Could you please share us one sample file for calculating orifice pressure drop, so that we can understand. 

  • Could you please share us one sample file for calculating orifice pressure drop, so that we can understand. 

    The "Orifice UDX sample" model found at the bottom of the related wiki article has an example of this. The orifice diameter is 6 inches, the orifice coefficient is assumed to be 0.6, and the typical flow is 2 CFS. The equation in the article is solved to determine the head which is then entered as the "pressure drop (typical):

    P = (Q/CA)^2 / 2g

    P = (2 / (0.6*0.196349375) )^2 / 64.34

    P = 4.47ft


    Regards,

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

  • Dear Bentley Team,

    I got the simulation file, i tried but i am getting some error like Field named "Orifice_diameter; feet" not found. I will try to understand this concept. 

    Thank you

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