Pressure Compensator Valve (IL)

Pressure compensator valve in an isothermal liquid network

Since R2020a

• 

Libraries:
Simscape / Fluids / Isothermal Liquid / Valves & Orifices / Pressure Control Valves

Description

The Pressure Compensator Valve (IL) block represents a pressure compensator in an isothermal liquid network, such as a pressure relief valve or pressure-reducing valve. Use this valve to maintain the pressure at the valve based on signals from another part of the system.

The pressure differential between ports X and Y is the control pressure, P_control. When this value meets or exceeds the set pressure, the valve area opens or closes depending on the Valve specification parameter. The pressure regulation range begins at the set pressure, P_set. You can choose between constant and controlled set pressure regulation. A physical signal at port Ps provides a varying set pressure.

Pressure Control

The block regulates pressure when P_control exceeds P_set. The block continues to regulate the pressure up to P_max, the sum of P_set and the pressure regulation range. The block supports two modes of regulation:

• When you set Set pressure control to Controlled and connect a pressure signal to port Ps, the block keeps the pressure regulation range constant. The valve regulates pressure when P_control is greater than the value of the signal at port Ps and less than P_max.

• When you set Set pressure control to Constant, the Set pressure differential parameter defines a constant set pressure.

Conservation of Mass

The block conserves mass such that

$${\dot{m}}_A+{\dot{m}}_B=0.$$

The block calculates the mass flow rate through the valve as

$$\dot{m}=\frac{C_d{A}_{valve}\sqrt{2\overline{\rho }}}{\sqrt{P{R}_{loss}\left(1-{\left(\frac{A_{valve}}{A_{port}}\right)}^2\right)}}\frac{\Delta p}{{\left[\Delta p^2+\Delta p_{crit}^2\right]}^{1/4}},$$

where:

• C_d is the Discharge coefficient parameter.

• A_valve is the instantaneous valve open area.

• A_port is the Cross-sectional area at ports A and B parameter.

• $$\overline{\rho }$$ is the average fluid density.

• Δp is the valve pressure difference p_A – p_B.

The critical pressure difference, Δp_crit, is the pressure differential specified by the Critical Reynolds number parameter, Re_crit. This parameter represents the flow regime transition point between laminar and turbulent flow. The block finds the critical pressure difference as

$$\Delta p_{crit}=\frac{\pi \overline{\rho }}{8A_{valve}}{\left(\frac{\nu {\mathrm{Re}}_{crit}}{C_d}\right)}^2.$$

The pressure loss, PR_loss, describes the reduction of pressure in the valve due to a decrease in area. The block calculates the pressure loss as:

$$P{R}_{loss}=\frac{\sqrt{1-{\left(\frac{A_{valve}}{A_{port}}\right)}^2\left(1-C_d^2\right)}-C_d\frac{A_{valve}}{A_{port}}}{\sqrt{1-{\left(\frac{A_{valve}}{A_{port}}\right)}^2\left(1-C_d^2\right)}+C_d\frac{A_{valve}}{A_{port}}}.$$

The pressure recovery describes the positive pressure change in the valve due to an increase in area. When you set Pressure recovery to Off, the block sets PR_loss to 1.

The block calculates A_valve using the opening parameterization and the valve opening dynamics.

Valve Opening Parameterization

When you set Opening parameterization to Linear, the valve area for normally open valves is

$$A_{valve}=\widehat{p}\left(A_{leak}-A_{max}\right)+A_{max}.$$

This figure demonstrates how the block controls the opening area for a normally open valve using the linear parameterization.

For normally closed valves, the block uses

$$A_{valve}=\widehat{p}\left(A_{max}-A_{leak}\right)+A_{leak}.$$

This figure demonstrates how the block controls the opening area for a normally closed valve using the linear parameterization.

The normalized pressure, $$\widehat{p}$$, is

$$\widehat{p}=\frac{p_{control}-p_{set}}{p_{max}-p_{set}}.$$

When the valve is in a near-open or near-closed position in the linear parameterization, you can maintain numerical robustness in your simulation by adjusting the Smoothing factor parameter. If the Smoothing factor parameter is nonzero, the block smoothly saturates the control pressure between p_set and p_max. For more information, see Numerical Smoothing.

When you set Opening parameterization to Tabulated data, A_leak and A_max are the first and last parameters of the Opening area vector parameter, respectively. The block calculates the opening area as

$$A_{valve}=tablelookup\left(p_{control,TLU,ref},A_{TLU},p_{control},interpolation=linear,extrapolation=nearest\right),$$

where:

• p_control is the control pressure, the pressure differential between ports X and Y.

• p_{control,TLU,ref} = p_TLU + p_offset.

• p_TLU is the Pressure differential vector parameter.

• p_offset is an internal pressure offset that causes the valve to start closing when p_{control,TLU,ref} = p_set.

• A_TLU is the Opening area vector parameter.

This figure demonstrates how the block controls the opening area for a normally open valve using the tabulated parameterization.

This figure demonstrates how the block controls the opening area for a normally closed valve using the tabulated parameterization.

Opening Dynamics

When you select Opening dynamics, the block introduces a control pressure lag where p_control becomes the dynamic control pressure, p_dyn. The block calculates the instantaneous change in dynamic control pressure based on the Opening time constant parameter, τ:

$${\dot{p}}_{dyn}=\frac{p_{control}-p_{dyn}}{\tau }.$$

By default, the block does not model Opening dynamics. For the linear parameterization, a nonzero value for the Smoothing factor parameter provides additional numerical stability when the orifice is in near-closed or near-open position.

The block calculates the steady-state dynamics according to the Opening parameterization parameter, and are based on the control pressure, p_control.

Faults

To model a fault, in the Faults section, click the Add fault hyperlink next to the fault that you want to model. In the Add Fault window, specify the fault properties. For more information about fault modeling, see Introduction to Simscape Faults.

You can set the Opening area when faulted parameter to:

• Closed — The valve area stops at its smallest value, depending on the Opening parameterization parameter setting:

  • Linear — The valve area stops at the value of the Leakage area parameter.

  • Tabulated data — The valve area stops at the smallest element of the Opening area vector parameter.

• Open — The valve stops at its largest value, depending on the Opening parameterization parameter setting:

  • Linear — The valve area stops at the value of the Maximum opening area parameter.

  • Tabulated data — The valve area stops at the largest element of the Opening area vector parameter.

• Maintain last value — The valve area stops at the valve open area when the trigger occurred.

Due to numerical smoothing at the extremes of the valve area, the minimum area the block uses is larger than the leakage area, and the maximum is smaller than the value of the Maximum orifice area parameter. This effect is in proportion to the amount of smoothing you apply.

After the fault triggers, the valve remains at the faulted area for the rest of the simulation.

Examples

Drill-Ream Actuator

An actuator that drives a machine tool working unit performing a sequence of three technological operations: coarse drilling, fine drilling, and reaming. The actuator speed is controlled by one of three pressure-compensated flow control valves metering out return flow from the cylinder. The selection of an appropriate flow control is performed by directional valves that are activated by a control unit.

Open Model

Ports

Conserving

A — Liquid port

isothermal liquid

Isothermal liquid conserving port associated with the A side of the valve.

B — Liquid port

isothermal liquid

Isothermal liquid conserving port associated with the B side of the valve.

X — Pressure reference

isothermal liquid

Isothermal liquid conserving port associated with sensing the pressure at point X, P_x.

Y — Pressure reference

isothermal liquid

Isothermal liquid conserving port associated with sensing the pressure at point Y, P_y.

Input

Ps — Controlled pressure differential, Pa

physical signal

Pressure differential for controlled valve operation, in Pa.

Dependencies

To enable this port, set Set pressure control to Controlled.

Parameters

Parameters

Valve specification — Valve bias

Normally open (default) | Normally closed

Normal operating condition of the pressure compensator valve. For a reducing valve, choose Normally open valve. For a relief valve, choose Normally closed.

Set pressure control — Constant or controlled valve operation

Constant (default) | Controlled

Valve operation method. When you set this parameter to:

• Controlled and connect a pressure signal to port Ps, the block keeps the pressure regulation range constant. The valve regulates pressure when P_control is greater than the value of the signal at port Ps and less than P_max.

• Constant, the Set pressure differential parameter defines a constant set pressure.

Opening parameterization — Opening parameterization

Linear (default) | Tabulated data

Method to parameterize the opening action of the valve.

Set pressure differential — Range outside of which constant valve operation is triggered

0 MPa (default) | scalar

Magnitude of the pressure differential that triggers pressure compensation.

Dependencies

To enable this parameter, set Set pressure control to Constant.

Pressure regulation range — Valve operational pressure range

0.1 MPa (default) | scalar

Operational pressure range of the valve. The pressure regulation range defines the difference between the Set pressure differential parameter and the maximum valve operating pressure.

Dependencies

To enable this parameter, set Opening parameterization to Linear.

Maximum opening area — Area of fully open valve

1e-4 m^2 (default) | positive scalar

Cross-sectional area of the valve in the fully open position.

Dependencies

To enable this parameter, set Opening parameterization to Linear.

Leakage area — Gap area when in fully closed position

1e-10 m^2 (default) | positive scalar

Sum of all gaps when the valve is in the fully closed position. Any area smaller than this value saturates to the specified leakage area. This value contributes to numerical stability by maintaining continuity in the flow.

Dependencies

To enable this parameter, set Opening parameterization to Linear.

Pressure differential vector — Differential pressure values for tabulated parameterization

[0.2 : 0.2 : 1.2] MPa (default) | 1-byn vector

Vector of pressure differential values for the tabulated parameterization of the opening area. The vector elements must correspond one-to-one to the values in the Opening area vector parameter. The pressures must be in ascending order.

Dependencies

To enable this parameter, set Opening parameterization to Tabulated data.

Opening area vector — Valve opening areas for tabulated parameterization

[1e-05, 8e-06, 6e-06, 4e-06, 2e-06, 1e-10] m^2 (default) | 1-byn vector

Vector of opening area values for the tabulated parameterization of the opening area. The vector elements must correspond one-to-one to the values in the Pressure differential vector parameter. For normally open valves, list elements in descending order. For normally closed valves, list elements in ascending order.

The opening area vector must have the same number of elements as the Pressure differential vector. The block uses linear interpolation between table data points.

Dependencies

To enable this parameter, set Opening parameterization to Tabulated data.

Cross-sectional area at ports A and B — Area at valve entry or exit

inf m^2 (default) | positive scalar

Cross-sectional area at the entry and exit ports A and B. The block uses this area in the pressure-flow rate equation that determines mass flow rate through the valve.

Discharge coefficient — Discharge coefficient

0.64 (default) | positive scalar

Correction factor that accounts for discharge losses in theoretical flows.

Critical Reynolds number — Upper Reynolds number limit for laminar flow

150 (default) | positive scalar

Upper Reynolds number limit for laminar flow through the valve.

Pressure recovery — Option to include pressure recovery

Off (default) | On

Whether to account for pressure increase when fluid flows from a region of a smaller cross-sectional area to a region of larger cross-sectional area.

Smoothing factor — Numerical smoothing factor

0.01 (default) | positive scalar in the range of [0,1]

Continuous smoothing factor that introduces a layer of gradual change to the flow response when the valve is in near-open or near-closed positions. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.

Dependencies

To enable this parameter, set Opening parameterization to Linear.

Opening dynamics — Option to simulate flow response to valve transitions

off (default) | on

Whether to account for transient effects to the fluid system due to the valve opening. When you select Opening dynamics, the block approximates the opening conditions by introducing a first-order lag in the flow response.

Opening time constant — Valve opening time constant

0.1 s (default) | positive scalar

Time constant by which to compute the lag in the opening dynamics.

Dependencies

To enable this parameter, select Opening dynamics.

Faults

To modify the faults, create a fault and, in the block dialog, click Open fault properties. In the Property Inspector, click the Fault behavior link to open the faults.

Pressure Compensator Valve Area fault — Option to model valve area fault

Add fault

Option to model a valve area fault in the block. To add a fault, click the Add fault hyperlink. After a fault, the block sets the valve area based on the value specified in the Opening area when faulted parameter.

Opening area when faulted — Faulted valve position

Closed (default) | Open | Maintain last value

Faulted opening area. You can choose for the valve to seize when the valve is opened, closed, or at the area after a fault.

Dependencies

To enable this parameter, enable faults for the block by clicking the Add fault hyperlink.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020a

R2024a: Model faults with the Simscape faults interface

The Pressure Compensator Valve (IL) block now supports the Simscape faults interface. To learn more, see Introduction to Simscape Faults.