Limit tank flow when level <= 0 in Modelica - modelica

Question

I have a model of a tank that I am creating as follows:
model Tank "Simple model of a tank"
parameter Real volume=1 "tank volume (m^3)";
parameter Integer num_ports=1 "Number of ports";
parameter Real static_pressure=1 "Internal Tank Pressure";
parameter Real initial_level = 0;
Stream[num_ports] ports "Stream Connectors";
Real level "Level in % 0-100";
protected
Real vol "Volume of medium in the tank";
Real pressure(start=static_pressure) "Pressure inside the tank";
initial equation
level = initial_level;
/* Pressure */
equation
pressure = vol * 0.01; // Add correct factor here to get from volume to pressure change (based on height and head)
for i in 1:num_ports loop
ports[i].pressure = static_pressure + pressure;
end for;
/* Volume Flow */
equation
der(vol) = sum(ports.m_flow); // Add density factor to get form mass flow to Volume Flow
level = vol * 100 / volume;
end Tank;
How can I make it so that when the level <=0 the tank will not allow any flows with a negative value (no ports can have fluid leaving, but fluid can still enter)? I feel like I am missing something trivial, but can't seem to find a way without having too many equations (over-determined system).
Thanks

Answer 1

You could try with a when equation:
when level < 0 then
reinit(level, 0)
end when;