Hi,
In WaterCAD, after validating my network, there occurs two messages for the pump in user notifications:
1- Reference to a deleted or inactive downstream pipe.
2- Directed node has an invalid downstream link.
What do these messages mean and what can I do?
Regards,
Seylan
Great and amazing support from Bentley. Thanks.
Mohamad Azzam,
Yes, Jesse's formula is correct. The 33.4 is atmospheric pressure at sea level in ft and the 0.5 is the vapor pressure of water in ft at 20 deg C. You would use the values appropriate for your situation. The general formula is
HGL(pump suction) + atmospheric pressure - elevation (pump) - vapor pressure of fluid
The procedure he gave is correct.
Mohamad,
You're welcome.
Please see the screenshot in my previous post. From what I understand, NPSH is the upstream pressure head, plus atmospheric pressure, minus absolute vapor pressure. The latter two terms are different depending on your location, and the upstream pressure head can be gotten from the difference between the upstream HGL and pump physical elevation (or suction pressure field, in feet or meters). So, here's another way you might set it up, in SewerCAD:
Our Advanced Water Distribution Modeling and Management book goes into greater detail on NPSH (see pages 324 and 325). It also has tables that show typical atmospheric pressure and vapor pressure values, for various elevations and temperatures.
I hope this helps.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Jesse,
Thank you so much, you are as usual impressing me.
Please may you explain more about the formual and terms of NPSH should be used in the program, as you know the formula has many terms in theory, i.e some are using vabour pressure ans so and so ..... of terms.
what do you think is the best one to work with the product and how to create that.
Thanks,
Mohamad
Hello Mohamad,
With the SELECTseries 2 release of SewerGEMS and SewerCAD V8i, the pump orientation behavior actually matches. Both SewerGEMS and SewerCAD only need the "downstream link" attribute for a pump.
Regarding NPSH - one of the great things about SELECTseries 2 is the introduction of Formula-Based User Data Extensions. With this feature, you can add your own result fields. The value in these fields will automatically update based on a formula that you enter, which can consider other calculated or user-input fields. So, in SewerCAD and SewerGEMS V8i SELECTseries 2, you can create a formula user data extension to compute the NPSH for your pumps. The next release of WaterGEMS and WaterCAD should have this feature as well.