# ControlValve


## Copyright © EDF 2002 - 2026  
## ThermoSysPro Version 4.2  
This component model is documented in Sect. 13.8 of the ThermoSysPro book.   
# Control valve   
   
Control valves are used to control the fluid flow, pressure or liquid level. They are usually automatically driven by an electrical, hydraulic or pneumatic actuator. A control valve is the critical part of any control loop. For water/steam, the flow regime is single-phase or homogeneous two-phase flow.  

Following assumptions are made in this model:  
- the fluid is subsonic and incompressible.  
- the volume inside the valve is negligible, and so is its inertia.  

If the control valve switches only between fully open and fully closed positions, in negligible time, the [switch valve](ThermoSysPro.WaterSteam.PressureLosses.SwitchValve) can be used instead.  

## Modelica component model  

The equations mentioned below are implemented in the component *ControlValve*, located in the *WaterSteam.PressureLosses* sub-library.   
This component has 3 connectors:  
- C1: fluid inlet,  
- C2: fluid outlet,  
- Ouv: valve opening.  
   
![ThermoSysPro.WaterSteam.PressureLosses.ControlValve.svg](./icons/ThermoSysPro.WaterSteam.PressureLosses.ControlValve.svg)  

## Nomenclature  

| Symbol| Description| Unit| Definition| Modelica name |  
| :----------------------------------------------- | :------------------------------------------------------------------------------------- | :------------------------------- | :-------------------------------- | :----------- |  
| $C_{\mathrm{v}}$| Flow coefficient of the valve| U.S. [USG/min]|| Cvmax |  
| $h$| Fluid specific enthalpy| $\mathrm{J} / \mathrm{kg}$|| h |  
| $m$| Fluid mass flow rate| $\mathrm{kg} / \mathrm{s}$|| Q |  
| $P_{\mathrm{i}}$| Fluid pressure at the valve inlet| $\mathrm{Pa}$|| C1.P |  
| $P_{\mathrm{o}}$| Fluid pressure at the valve outlet| $\mathrm{Pa}$|| C2.P |  
| $\Delta P$| Fluid pressure loss between the inlet and the outlet| $\mathrm{Pa}$| $P_{\mathrm{i}}-P_{\mathrm{o}}$ | deltaP |  
| $\rho$| Fluid density| $\mathrm{kg} / \mathrm{m}^{3}$ || rho |  
| $\rho_{\text {water, } 60^{\circ} \mathrm{F}}$ | Density of water at $60^{\circ} \mathrm{F}\left(15.5556^{\circ} \mathrm{C}\right) .$ | $\mathrm{kg} / \mathrm{m}^{3}$ || rho_15 |  
| $\Omega$| Valve position \(between 0 and 1\)| $-$|| Ouv.signal |  



## Governing equations  

### Static momentum balance equation  


- Validity domain:   
   
$\forall \dot{m}$ and $C_{\mathrm{v}} \geq 0$. For $C_{\mathrm{v}}=0, \Delta P$ must be defined.  

- Mathematical formulation:   
   
 $$\Delta P \cdot C_{\mathrm{v}} \cdot \lvert C_{\mathrm{v}}\rvert =1.732189 \times 10^{12} \cdot \frac{\dot{m} \cdot \lvert \dot{m} \rvert }{\rho \cdot \rho_{\text {water, } 60^{\circ} F}}$$  

- Comments:   
   
 The valve flow coefficient $C_{\mathrm{v}}$ is a function of the position $\Omega$ of the valve: $C_{\mathrm{v}}=f_{v}(\Omega)$. $f_{v}$ is called the valve characteristic. The valve is fully closed for $\Omega=0$ and fully open for $\Omega=1$.  

## References   
   
El Hefni, Baligh and Bouskela, Daniel (2019). [Modeling and Simulation of Thermal Power Plants with ThermoSysPro](https://link.springer.com/book/10.1007/978-3-030-05105-1), sect. 13.8. Springer Nature Switzerland AG.