Need help working from home with your Bentley software? We're here to help - click here

Hammer- Hydropneumatic Tank

Hi All,

I'm not sure if this is a question or discussion, and not sure if it is related to Hammer directly, but I hope someone can steer me in the right direction.

In summary, a booster pumping station has been proposed on a dn700mm watermain. Also, together with a booster pumping station a 1m3  air vessel and pump bypass with a check valve have been proposed as a transient protection measures.

Firstly, to me it seems that protection is not required on the watermain as per below screengrab:

However, when we added a 1m3 hydropneumatic tank it seems that the min and max pressure envelope actually got worse(meved further away from the steady state HGL) as per screengrab below:

When I introduced a 6m3 hydropneumatic tank the situation improved and pressure envelope actually moved closer to the steady state HGL.  Is there a chance that a small/undersized hydropneumatic tank can make the situation worse transient wise if it is not required at the first place?

Thank you and Stay safe!


  • Hi Oliver,

    Transient simulations are often complex and interesting. There are certainly situations where adding an air valve can potentially make the transient response (to an event such as a pump shutdown) even worse if the air is expelled too quickly (see this article). For a hydropneumatic tank, you may be encountering a check valve "slam" situation due to the pressure in the hydropneumatic tank (see the "Pump Check Valve" section of this article) Transient results can indeed be sensitive to the tank configuration, but the exact sensitivity can be different for each modeling situation.

    First, be sure to check your user notifications for any problems, and make sure the transient simulation duration is set long enough. Check the inertia in the pump definition as this is often a key factor in the "downsurge" that occurs when the pump shuts down. Be sure to also enable the profile animation option in the transient calculation options, and animate your profile path in the Transient Results Viewer. This is a great way to visualize how things are interacting and responding during the transient event. See: Using Transient Results Viewer animations for visualizing a transient simulation

    From your first screenshot, I see that most of the pipeline is at a lower elevation than what I assume is the upstream and downstream boundary conditions reservoirs or tanks (left and right side of the profile), which is likely why you aren't seeing a problem with low/sub-vapor pressures even without protection.


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

    Answer Verified By: Matija Oliver