Annex60.Fluid.Actuators.Valves.TwoWayPressureIndependent

# .Annex60.Fluid.Actuators.Valves.TwoWayPressureIndependent

Model of a pressure-independent two way valve

## 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.

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