.Annex60.Fluid.Actuators.Valves.TwoWayPressureIndependent

Information

Two way valve with a pressure-independent valve opening characteristic. The mass flow rate is controlled such that it is nearly equal to its set point y*m_flow_nominal, unless the pressure dp is too low, in which case a regular Kv characteristic is used.

Main equations

First the minimum pressure head dp_min required for delivering the requested mass flow rate y*m_flow_nominal is computed. If dp > dp_min then the requested mass flow rate is supplied. If dp < dp_min then m_flow = Kv/sqrt(dp). Transition between these two flow regimes happens in a smooth way.

Typical use and important parameters

This model is configured by setting m_flow_nominal to the mass flow rate that the valve should supply when it is completely open, i.e., y = 1. The pressure drop corresponding to this working point can be set using dpValve_nominal, or using a Kv, Cv or Av value. The parameter dpValve_fixed can be used to add additional pressure drops, although in this valve it is equivalent to add these to dpValve_nominal.

The parameter l2 represents the non-ideal leakage behaviour of this valve for high pressures. It is assumed that the mass flow rate will rise beyond the requested mass flow rate y*m_flow_nominal if dp > dpValve_nominal+dpFixed_nominal. The parameter l2 represents the slope of this rise: d(m_flow)/d(dp) = l2* m_flow_nominal/dp_nominal. In the ideal case l2=0, but this may introduce singularities, for instance when connecting this component with a fixed mass flow source.

Options

Parameter deltax sets the duration of the transition region between the two flow regimes as a fraction of dp_nominal or m_flow_nominal, depending on the value of from_dp.

Implementation

Note that the result in the transition region when using from_dp = true is not identical to the result when using from_dp = false.

Revisions

• March 15, 2016, by Michael Wetter:
  Replaced spliceFunction with regStep. This is for issue 300.
• January 22, 2016, by Michael Wetter:
  Corrected type declaration of pressure difference. This is for #404.
• January 29, 2015, by Filip Jorissen:
  First implementation.