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Pressure Reducing Valve

(To be removed) Valve used to reduce pressure to a specified value

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The Hydraulics (Isothermal) library will be removed in a future release. Use the Isothermal Liquid library instead. (since R2020a)

For more information on updating your models, see Upgrading Hydraulic Models to Use Isothermal Liquid Blocks.

  • Pressure Reducing Valve block

Libraries:
Simscape / Fluids / Hydraulics (Isothermal) / Valves / Pressure Control Valves

Description

The Pressure Reducing Valve block models the flow through a valve that constricts so as to maintain a preset gauge pressure at its outlet (port B). The normally open valve contracts when the outlet pressure, measured against atmospheric pressure, exceeds the valve pressure setting. The drop in opening area is a function of the outlet pressure—proportional to it in a linear parameterization (the block default) or a general function of it in a tabulated parameterization. The valve serves its purpose until it hits the limit of its pressure regulation range—a point at which the valve is fully closed and the outlet pressure can again rise unabated.

Valve Opening

The figures show the opening characteristics of the valve. In the default valve parameterization, the opening area (S) drops linearly with the outlet pressure (pB) with its value ranging from a maximum in the fully open position (SMax) to a minimum in the fully closed position (SLeak). The drop occurs over a pressure range stretching from the valve pressure setting (pSet) to a maximum equal to the sum of the valve regulation range (pReg) and the valve pressure setting.

Opening area in the Linear area-opening relationship parameterization

In the optional tabulated parameterization, the opening area is a general function of the outlet pressure, with its value dropping from a maximum (SMax) to a minimum (SMin) contained in the tabulated data. The maximum opening occurs at the minimum pressure (pMin) contained in the data and the minimum opening at the maximum pressure (pMax). Calculations are based on linear interpolation (between the tabulated bounds) and nearest-neighbor extrapolation (outside of those bounds).

Opening area in the Tabulated data - Area vs. pressure parameterization

Composite Diagram

This block is a composite component with a Pressure Compensator block connected as follows: its sensor port X connected to its outlet (port B) and its sensor port Y connected to a hydraulic reference. The hydraulic reference is by definition at atmospheric pressure as defined for the entire hydraulic network. For detailed block calculations see the Pressure Compensator block (noting that quantities at port X are defined at port B and those at port Y are defined at reference conditions).

Composite model of the pressure relief valve

Ports

Conserving

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Opening through which the flow can enter the valve.

Opening through which the flow can exit the valve.

Parameters

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Method by which to calculate the opening area of the valve. The default setting prescribes a linear relationship between the opening area of the valve and the pressure drop between its sensor ports. The alternative setting allows for a general, nonlinear relationship to be specified in tabulated form.

Opening area of the valve in the fully open position. The valve is fully open if the pressure at port B relative to a hydraulic reference at atmospheric pressure is less than the value specified in the Valve pressure setting block parameter.

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Linear area-pressure relationship.

Gauge pressure that the valve is to maintain at port B. The valve closes in proportion to the gauge pressure if it should exceed the value specified here. If the pressure drop is less than this value, the opening area is that specified in the Maximum passage area block parameter.

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Linear area-pressure relationship.

Pressure interval over which the valve is designed to operate. This interval stretches from the largest pressure at which the valve is fully open to the lowest pressure at which the valve is fully closed. Only within this range is the valve capable of maintaining the specified pressure setting.

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Linear area-pressure relationship.

Ratio of the actual flow rate through the valve to the theoretical value that it would have in an ideal valve. This semi-empirical parameter measures the flow allowed through the valve: the greater its value, the greater the flow rate. Refer to the valve data sheet, if available, for this parameter.

Opening area of the valve in the fully closed position, when only internal leakage between its ports remains. This parameter serves primarily to ensure that closure of the valve does not cause portions of the thermal liquid network to become isolated. The exact value specified here is less important than its being a small number greater than zero.

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Linear area-pressure relationship.

Vector of gauge pressures at port B at which to specify the opening area of the valve. The vector elements must increase monotonically from left to right. This order is important when specifying the Opening area vector block parameter.

The block uses this data to construct a lookup table by which to determine from the gauge pressure at port B the valve opening area. Data is handled with linear interpolation (within the tabulated data range) and nearest-neighbor extrapolation (outside of the range).

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Tabulated data - Area vs. pressure.

Vector of opening areas corresponding to the breakpoints defined in the Pressure differential vector block parameter. The vector elements must decrease monotonically from left to right (with increasing pressure). For best results, avoid regions of flattened slope.

The block uses this data to construct a lookup table by which to determine from the gauge pressure at port B the valve opening area. Data is handled with linear interpolation (within the tabulated data range) and nearest-neighbor extrapolation (outside of the range).

Dependencies

This parameter is active when the Opening area parameterization block parameter is set to Tabulated data - Area vs. pressure.

Parameter in terms of which to specify the boundary between the laminar and turbulent flow regimes. The pressure ratio of the default parameterization is defined as the gauge pressure at the outlet divided by the same at the inlet.

Pressure ratio at which the flow is assumed to transition between laminar and turbulent regimes. The pressure ratio is defined as the gauge pressure at the outlet divided by the same at the inlet. The transition is assumed to be smooth and centered on this value.

Dependencies

This parameter is active when the Laminar transition specification block parameter is set to Pressure ratio.

Reynolds number at which the flow is assumed to transition between laminar and turbulent regimes.

Dependencies

This parameter is active when the Laminar transition specification block parameter is set to Reynolds number.

Choice of whether to capture the opening dynamics of the valve. Selecting Include valve opening dynamics causes the valve to open gradually, so as to approach its new steady-state area over a small time span. The characteristic time for such transitions is given in the Opening time constant block parameter.

Setting this parameter to the alternative Do not include valve opening dynamics is equivalent to specifying a value of 0 for the opening time constant. The opening area is in this case assumed to reach its new steady-state value instantaneously.

Include opening dynamics to more accurately capture the behavior of a real valve. For best real-time simulation performance, use with a local solver or disable valve opening dynamics altogether.

Measure of the time taken by the valve to transition from its current opening area to a new steady-state value. The block uses this parameter to calculate the rate at which a valve is opening and from it the instantaneous opening area at the next time step.

Dependencies

This parameter is active when the Opening dynamics block parameter is set to Include valve opening dynamics.

Area normal to the direction of flow within the valve at the start of simulation. The block uses this parameter to calculate the initial rate at which the valve is opening and from it the instantaneous opening area at the next time step.

Dependencies

This parameter is active when the Opening dynamics block parameter is set to Include valve opening dynamics.

Extended Capabilities

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

Version History

Introduced in R2016a

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R2023a: To be removed

The Hydraulics (Isothermal) library will be removed in a future release. Use the Isothermal Liquid library instead.

For more information on updating your models, see Upgrading Hydraulic Models to Use Isothermal Liquid Blocks.

See Also

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