How to lower leakage in Simscape valves

I'm building a pneumatic system using Simscape and I'm seeing a lot more leakage than I would expect. I've adjusted the leakage flow fraction from the default (1e-6), but changing this to a smaller value (by orders of magnitude) makes basically no difference to the opening_area_fraction when the valve is closed.

It seems like there's a base level of opening_area_fraction that can't be lowered by adjusting the leakage flow fraction, I can't see where this base level comes from because none of the Simscape valve source code is available that I'm aware of.

In the test model that I setup (shown below), the constant volume chamber is losing around 15% pressure per minute (regardless of starting pressure), this seems way too high for a simple system with 3 closed valves. I'm seeing the same thing regardless of the type of valve used.

Any help on how to lower this leakage would be appreciated.

[Yifeng Tang]

Is it possible for you to share a model to demonstrate the problem? I suspect it's a parameter issue but I could be more certain if a mode lis available.

[Adam]

I ended up getting this resolved with some assistance from MathWorks. It was the smoothing factor on the valves that needed to be lowered. Thanks.

[Yifeng Tang]

Feel free to move your comments into the "Answer" so the question will be marked as answered :)

Answer 1

[Luke Halberstadt]

Summarizing the comments above and my own experience: The smoothing factor used to improve solver robustness can increase very small leakage. Lowering the smoothing factor to the right order of magnitude typically addresses this issue. For more info about Numerical Smoothing, see the corresponding page in our Documentation.

Numerical Smoothing - MATLAB & Simulink (mathworks.com)