Pressure-Reducing Valve (IL)
Pressure reducing valve in an isothermal liquid network.
Description
The Pressure-Reducing Valve (IL) unit is a pressure-reducing valve in an isothermal liquid network. The valve remains open when the pressure at port B is less than the set point pressure. When the pressure at port B reaches or exceeds the set point, the valve closes. The unit is controlled by the difference between the set pressure and the pressure at port B. The block contains a check valve part that functions identically to the block Check Valve (IL) when the flow is reversed. For pressure control based on another fluid system component, see block Pressure Compensator Valve (IL).
Pressure Control
The Pressure-Reducing Valve (IL) regulates pressure between the set pressure and the maximum pressure.
The unit supports two control modes:
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When the Controlled set pressure checkbox is selected, the set pressure is set by the signal from the Ps port. The unit regulates pressure when the pressure at port B is above the set pressure and below . The pressure at port B acts as the control pressure for this valve. The value is equal to the sum of and the pressure control range.
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If the Controlled set pressure checkbox is not selected, the set pressure is constant and is set by Set pressure (gauge).
The definition of the pressure control range depends on the value of the Opening parameterization:
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Linear - Area vs. pressure- the pressure regulation range is defined by the parameter Pressure regulation range. -
Tabulated data - Area vs. Pressure- the pressure regulation range is defined as the difference between the last and the first element of the Pressure at port B (gauge) vector parameter. -
Tabulated data - Volumetric flow rate vs. pressure- the pressure regulation range is defined as the difference between the first and last elements of the Reference pressure at port B (gauge) vector.
Parametrization: pressure dependent area
If the Opening parameterization is set to Linear - Area vs. pressure, the valve cross-sectional area is as follows
The normalised pressure is
When the valve is in the nearly open or nearly closed position in linear parameterization, it is possible to maintain numerical stability in the simulation by adjusting the Smoothing factor parameter. If the Smoothing factor is non-zero, a smooth variation of the control pressure and is ensured.
The figure shows the valve opening characteristics when using linear area parameterization. The opening area decreases linearly with increasing outlet pressure . The opening area varies from to , and the operating pressure range starts at and goes up to .
If Opening parameterization is set to Tabulated data - Area vs. Pressure, the block calculates the opening area as
where
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- control pressure;
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;
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- is the value of the parameter Pressure at port B (gauge) vector;
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- internal pressure offset at which the valve starts to close when , ;
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- value of parameter Opening area vector.
The values and are the first and last elements of the Opening area vector respectively.
The figure shows the opening characteristics of the valve using the tabular parameterization.
*Mass conservation
If Opening parameterization is set to Linear - Area vs. pressure or `Tabulated data - Area vs. Pressure', the mass conservation equation for the valve passage is as follows:
The mass flow rate through the valve is calculated as follows:
where
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- flow coefficient, the value of the Discharge coefficient parameter;
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- instantaneous valve opening area;
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- Cross-sectional area at ports A and B;
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- is the average density of the fluid;
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- pressure difference in the valve .
Critical pressure drop, - pressure drop related to the value of critical Reynolds number , given by the parameter Critical Reynolds number, which is the point of regime transition between laminar and turbulent flow regimes. The block calculates the critical pressure drop as:
Pressure loss takes into account the pressure drop in the valve due to the reduced valve area and is calculated as:
Pressure recovery describes the positive change in valve pressure due to an increase in area. To disregard pressure recovery, uncheck the Pressure recovery box. In this case the pressure loss .
The unit calculates , using the valve opening dynamics.
Opening dynamics You can choose to simulate the valve opening dynamics to parameterise any of the areas. If the Opening dynamics check box is selected, the block introduces a delay in the flow response to valve opening and the value becomes the dynamic opening area , otherwise, is the steady-state opening area. The derivative of the dynamic control pressure is calculated from the Opening time constant :
By default, the Opening dynamics checkbox is unchecked.
The steady state dynamics is set by the same parameterization as the valve opening and is based on the signal pressure, .
parameterization: Pressure-dependent volume flow rate
The equations for the parameterization of the volumetric flow rate apply to the following quantities:
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- Reference volumetric flow rate vector parameter.
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and - parameters Reference pressure at port A (gauge) vector and Reference pressure at port B (gauge) vector respectively.
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- is either the Set pressure (gauge) parameter or the port pressure value Ps.
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- is the flow coefficient through the pressure reducing stage that the unit calculates during simulation.
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- is the average density of the liquid in the pressure reducing valve.
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- is the pressure drop of the fluid flow at the valve.
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- critical pressure drop of the liquid.
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- the flow coefficient, which is set within the block.
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- critical Reynolds number, which is set within the block.
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- kinematic viscosity, which is assumed constant for an isothermal liquid network.
If the Opening parameterization is set to Tabulated data - Volumetric flow rate vs. pressure, the block calculates the smoothed mass flow rate of the pressure reducing valve by:
The block calculates the value using the tablelookup function:
The control pressure is calculated as
where is the drainage pressure taken as 1 atm.
The reference control pressure vector is defined as follows
where is the internal pressure offset that causes the valve to start closing when . Thus, . The figure shows how the block controls the pressure using the volumetric flow parameterization.
Ports
Parameters
Controlled set pressure - enable control pressure port
off (by default) | on
If the checkbox is unchecked, the valve closes linearly within the fixed pressure control range or according to the provided tabulated pressure and opening area.
If the checkbox is selected, the valve closes according to the set pressure set at port Ps in the fixed pressure control range.
Opening parameterization - method of calculating the opening or closing of the valve
| `Linear - Area vs. pressure (by default) | `Tabulated data - Area vs. pressure | `Tabulated data - Volumetric flow rate vs. pressure'.
Method for modelling valve opening. Options for selection:
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Linear - Area vs. pressureorTabulated data - Area vs. pressure- area of valve opening from control pressure. -
Tabulated data - Volumetric flow rate vs. pressure - uses a reference curve of flow rate and differential pressure of the pressure reducing valve.
Set pressure (gauge) - overpressure above which the valve is actuated
0.1 MPa (by default) | positive scalar.
The overpressure above which the valve is actuated. When the pressure in port B reaches this value, the valve begins to close. This parameter shifts the reference curve so that the pressure reducing valve starts to close when the pressure at port B is equal to the set pressure.
Dependencies
To use this parameter, clear the Controlled set pressure checkbox.
Pressure regulation range - pressure regulation range
1 MPa (by default) | positive scalar
The operating pressure range of the valve. The pressure regulation range defines the difference between the Set pressure (gauge) parameter and the maximum operating pressure of the valve.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure'.
Maximum opening area - area of the valve fully open
1e-4 m² (by default) | positive scalar
Cross-sectional area of the valve opening in the fully open position.
Dependencies
To use this parameter, set the Opening parameterization to `Linear - Area vs. pressure'.
Leakage area is the clearance area of the valve in the fully closed position
1e-10 m² (by default) | positive scalar.
The sum of all clearances when the valve is in the fully closed position. Any area less than this value is maintained at the specified leakage area. This parameter contributes to the stability of the numerical solution by maintaining flow continuity.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure'.
Pressure at port B (gauge) vector is the gauge pressure vector used for the tabular parameterization
[0.2:0.2:1.2…] MPa (by default) | vector
Vector of gauge pressure values for the tabular parameterization of the valve opening area. The elements of the vector must correspond one-to-one to the elements of the vector from parameter Opening area vector. The elements are listed in ascending order and must be greater than 0. Linear interpolation is used between the tabulated data points.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Tabulated data - Area vs. pressure'.
Opening area vector - vector of valve opening area values for tabulated parameterization
[1e-10, 1e-05, 2e-05, 3e-05, 4e-05, 5e-05, 6e-05, 7.5e-05, 8.5e-05, 0.0001] m² (By default) | `vector'.
Vector of valve opening area values for tabular parameterization. The elements of the vector must correspond to the elements of the parameter Pressure at port B (gauge) vector. The elements are listed in ascending order and must be greater than 0. Linear interpolation is used between the tabular data points.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Tabulated data - Area vs. pressure'.
Cross-sectional area at ports A and B - valve inlet and outlet area
Inf (By default) | positive scalar
The cross-sectional area of ports A and B. This quantity is used in the pressure-flow equation that determines the mass flow rate through the port.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure'.
Discharge coefficient - flow coefficient
0.64 (by default) | ` positive scalar in the range [0,1]`
Correction factor that takes into account discharge losses in theoretical flows.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure'.
Critical Reynolds number - upper limit of the Reynolds number for laminar flow
150 (By default) | `positive scalar'.
The critical Reynolds number value that corresponds to the upper limit of laminar flow through the valve.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure'.
Smoothing factor - smoothing factor
0.01 (by default) | positive scalar
A continuous smoothing factor that specifies the degree of change in flow response when the valve is in the nearly open and nearly closed positions. Set a non-zero value less than one to increase the stability of the simulation in these modes.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure'.
Pressure recovery - whether to take into account the pressure increase when the area expands
Off (By default) | `On
Whether to take into account the pressure rise when fluid flows from a smaller cross-sectional area to a larger cross-sectional area.
Dependencies
To use this parameter, set Opening parameterization to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure'.
Opening dynamics - whether to take into account the flow response to valve opening
off (by default) | on.
Whether to account for transient effects in the fluid system caused by valve opening. Checking the Opening dynamics box approximates the opening conditions by introducing a first order lag in the flow response. The simulated opening dynamics are controlled by the Opening time constant parameter.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure'.
Opening time constant - valve opening time constant
0.1 s (By default) | on.
A constant that defines the time required for the fluid to reach steady state when opening or closing the valve from one position to another. This parameter affects the modelling of the opening dynamics.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Linear - Area vs. pressure' or `Tabulated data - Area vs. pressure' and check the Opening dynamics checkbox.
Reference pressure at port A (gauge) - reference pressure at port A
1.5 MPa (by default) | `positive scalar'.
The constant pressure at port A from which the reference curve is based. This value usually corresponds to the maximum operating pressure of the valve. During simulation, the pressure at port A can be any pressure.
Dependencies
To use this parameter, set the Opening parameterization parameter to Tabulated data - Volumetric flow rate vs. pressure.
Reference pressure at port B (gauge) vector - reference pressure at port B
[1.2, 1.0, 0.8, 0.6, 0.4, 0.2] MPa (by default) | ` vector'.
Vector of monotonically decreasing values of port pressure B on the reference curve as the valve opening area changes. The first element is the reference maximum pressure at which the valve closes completely. The last element is the reference control pressure.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Tabulated data - Volumetric flow rate vs. pressure'.
Volumetric flow rate vector - vector of volumetric flow rate values for tabular parameterization
[1.0e-9, 1.8e-5, 6.6e-5, 1.3e-4, 2.0e-4, 2.8e-4] m3/s (By default) | vector
A vector of monotonically increasing reference flow rates through the valve. The unit uses this curve to calculate the flow coefficient for a varying valve area.
Dependencies
To use this parameter, set the Opening parameterization parameter to `Tabulated data - Volumetric flow rate vs. pressure'.
Check Valve
Enable check valve - check valve enable option
off (by default) | on.
Whether the internal check valve is connected in the unit.
Cracking pressure differential - set pressure for check valve operation
0.1 MPa (by default) | Positive scalar
The differential pressure at which the check valve will operate.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization parameter to Linear - Area vs. pressure.
Maximum opening pressure differential - maximum opening pressure differential across the valve
0.2 MPa (by default) | positive scalar
Pressure drop when the check valve is fully closed.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization parameter to Linear - Area vs. pressure.
Maximum opening area - area of the valve fully open
1e-4 m² (by default) | positive scalar
The cross-sectional area of the valve opening in the fully open position. Internally, the check valve is parallel to the reducing stage.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization to `Linear - Area vs. pressure'.
Pressure differential vector - differential pressure values for check valve operation
[0.1:0.1:1:1…] MPa (by default) | vector
The differential pressure vector for the check valve stage. The unit calculates the check valve differential pressure as the pressure at port B versus the pressure at port A.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization parameter to `Tabulated data - Area vs. pressure' or `Tabulated data - Volumetric flow rate vs. pressure'.
Opening area vector - vector of check valve opening area values
[1e-10, 1e-5, 2e-5, 3e-5, 4e-5, 5e-5, 6e-5, 7.5e-5, 8.5e-5, 1e-4] m² (By default) | `vector'.
Vector of opening area values for the check valve stage. The values in this vector correspond one-to-one to the vector elements from the Pressure differential vector parameter.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization parameter to `Tabulated data - Area vs. pressure' or `Tabulated data - Volumetric flow rate vs. pressure'.
Volumetric flow rate vector is a vector of check valve volumetric flow rate values
[.000358, .045, .11, .191, .284, .39, .505, .63, .764, .905] m3/s (By default) | `vector'.
Vector of volumetric flow rate values for the check valve stage. The vector values must match the elements of the Pressure differential vector.
Dependencies
To use this parameter, select the Enable check valve check box and set the Opening parameterization parameter to `Tabulated data - Volumetric flow rate vs. pressure'.