This partial model is used to model one way flow-elements. It holds the conservation equations and should be extended by definition of one of the following variables:
m_flow = mass flow rate trough the component
or
V_flow = volume flow rate through the component
The flow from A->B is the positive flow.
The resulting equation should be in the extends
statement,
not in the equation section since this model sets both
m_flow = V_flow*rho
and V_flow = m_flow/rho
.