ref: https://communities.bentley.com/products/hydraulics___hydrology/f/haestad-hydraulics-and-hydrology-forum/208958/watercad-gpm-drop-error/
Hello,
I read the article on the difference between the "Constant Speed - 4 Quadrant Characteristics" pump type and the "Constant Speed Pump Definition," but I am still unclear of what one to use in my model's case. I modeled a build out system with the source being a pump by using the fire flow test results for a standard 3 point pump curve. I assigned the definition, but now do not know what to assign the pump as. I do have negative flows in the system but the "Pump Definition" constant speed pump still works even through it only works within the first quadrant. If I use the "4-Quadrant Characteristics" constant speed pump, do I need to specify a specific speed in the transient tab of the pump definitions?
Just very unclear on the real difference between the two if they both work in the model. I have been running the model using the "Constant Speed - 4 Quadrant Characteristics" but just defined the 3 point pump curve and did not input a specific speed. Is this wrong?
Any advice would be greatly appreciated!
Hi Allison,
Since this is a new topic I have split your reply to this new thread.
Your other posts appeared to be about WaterCAD - are you using WaterCAD still or are you using HAMMER? I assume this is the article you're referring to: Differences between the Constant Speed transient pump types
The field you are describing is the "Pump Type (Transient)" which is only used during the transient simulation, as it dictates the behavior of a constant speed pump during transient conditions, where it is possible to operate in the other three quadrants. HAMMER first uses the pump definition in conjunction with the system head curve (from the system characteristics) to determine the operating point of the pump in the initial conditions (just like WaterCAD and WaterGEMS), but then if the transient pump type is set to "constant speed - 4 quadrant characteristics" (or shut after time delay/variable speed) it takes the operating point along with the Specific Speed (defining the shape of the 4-quadrant pump characteristic) to construct the 4-quadrant pump curve used during the transient simulation. If the transient pump type is set to "constant speed - pump definition", it instead uses the pump definition that you have entered to determine the characteristics used during the transient simulation (which means it can only operate in the first quadrant). So, for HAMMER the choice depends on whether you want the model to closely follow the pump definition you entered during the transient simulation (but without the ability to operate in other quadrants) or whether you anticipate that operation in the other quadrants may be necessary.
In WaterCAD and WaterGEMS, this field is not used though it is exposed so that you can configure transient parameters in case you would like to later perform a transient simulation. If you are using WaterCAD to model a connection to an existing system by using a pump to model the connection point based on hydrant flow test data, you would use the information in the following article to set up the 3-point pump definition and reservoir: Modeling a Connection to an Existing System
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Allison G.
Thank you for splitting this into a new post and for your insight!
I am using WaterCAD and a 3-Point Standard Curve for the pump. WaterCAD still indicates in the pump properties that a "Constant Speed - 4 Quadrant Characteristics" is being used by default (see attached). Is what you are saying that the model doesn't even use this information?
Correct. Notice that it is within the "Transient (Operational)" section, denoting that it is for HAMMER/transient simulations only. As mentioned in my previous reply, HAMMER, WaterCAD and WaterGEMS share the same file format and the transient properties are exposed in WaterCAD and WaterGEMS so that you can configure transient properties for later use in HAMMER. Here are some related articles:
Can WaterCAD or WaterGEMS perform a transient analysis?
Opening WaterCAD and WaterGEMS models in HAMMER