Check Valve (G)

A non-return valve in the gas network.

blockType: EngeeFluids.Gas.Valves.DirectionalControl.Check

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Description

The Check Valve (G) unit is an orifice with a unidirectional opening mechanism that prevents unwanted backflow. The opening mechanism responds to pressure and opens the orifice when the pressure drop decreases from the inlet to orifice A to the outlet to orifice B. Check valves protect upstream components from pressure surges, temperature surges and chemical contamination occurring downstream.

The valve begins to open when pressure reaches the actuation pressure and continues to open until the end of the pressure control range. The actuation pressure is the initial resistance, due to friction or spring force, that the valve must overcome to open. Below this threshold, the valve is closed and can only allow leakage flow. Beyond the pressure control range, the valve is fully open and the maximum flow rate is determined by the instantaneous pressure conditions.

The flow can be laminar or turbulent and can reach sonic velocities. Maximum velocity is reached at the valve seat where the flow is narrowest and fastest. Flow reaches critical mode and maximum velocity when the pressure drop downstream can no longer increase velocity. The flow becomes critical when the ratio of outlet pressure to inlet pressure reaches a critical value specific to the valve. The unit does not calculate supersonic flow.

Control and other pressures

The pressure to which the valve responds is the control pressure. By default, the control pressure is the differential pressure from inlet to outlet. This setting ensures that the valve will close if the flow direction is reversed.

You can also set the control pressure as the inlet overpressure. Use this setting if you know that the inlet will always have a higher pressure than the outlet. For example, if the inlet is connected to a pressure source such as a pump.

You can select the control pressure by setting the parameters Opening pressure specification to a value of Pressure difference of port A relative to port B or Gauge pressure at port A.

Pressure drop from port A to port B

If the parameter Opening pressure specification is set to . `Pressure difference of port A relative to port B`then:

Control pressure:

where and are absolute pressures at ports A and B respectively.
The trigger pressure is the value of the parameter Cracking pressure differential.
The maximum valve pressure , at which the valve is fully open, is the value of the parameter Maximum opening pressure differential.

_ Overpressure at port A_

If the parameters Opening pressure specification are set to `Gauge pressure at port A`then:

Control pressure:

where is the atmospheric pressure specified in the block Gas Properties (G).
The trigger pressure is the value of the parameters Cracking pressure (gauge).
Maximum valve pressure , at which the valve is fully open - value of parameter Maximum opening pressure (gauge).

Valve opening degree

The degree to which the signal pressure exceeds the actuation pressure determines the extent to which the valve opens. The standardised control pressure is:

where

- control pressure;
- actuation pressure;
- maximum valve pressure at which the valve is fully open.

The degree of opening is normalised so that it is 0 when the valve is fully closed and 1 when the valve is fully open. If the calculation returns a value outside these limits, the block equates it to the nearest of the two limits.

Valve opening degree:

where is the value of the parameters Leakage flow fraction.

Numerical smoothing

If the parameter Smoothing factor has a non-zero value, the block applies numerical smoothing to the normalised control pressure, . Enabling smoothing helps maintain the numerical stability of the simulation.

Valve parameterization

The block behaviour depends on the parameters Valve parameterization:

Cv flow coefficient - The flow coefficient determines the dependence of the flow capacity on the differential pressure.
Kv flow coefficient - The flow coefficient determines the dependence of the flow rate on the differential pressure, .
Sonic conductance - steady-state acoustic conductivity determines the flow capacity at critical flow, the condition at which the flow velocity is equal to the local speed of sound. Flow becomes critical when the ratio of outlet pressure to inlet pressure reaches a value called the critical pressure ratio.
Orifice area - the orifice area determines the flow capacity.

The unit scales the specified flow capacity by the valve opening degree. As the valve opening degree increases from 0 to 1, the capacity value increases from the set minimum to the set maximum.

Pulse storage

Parameters Valve parameterization determines which equations will be used to calculate the flow rate. If the parameter Valve parameterization is set to. Cv flow coefficient, the mass flow rate will be defined as:

where

- is the flow coefficient;
- a constant equal to 27.3 for mass flow rate in kg/hour, pressure in bar and density in kg/m³;
- expansion coefficient;
- inlet pressure;
- outlet pressure;
- inlet density.

The expansion coefficient is defined as:

where

- is the ratio of the adiabatic exponent to 1.4;
- is the value of the parameters xT pressure differential ratio factor at choked flow.

When the pressure ratio exceeds the value of the parameters Laminar flow pressure ratio, , there is a smooth transition to usage of the linearised equation:

where

When the pressure ratio falls below , the flow becomes critical and the equation is used:

If the parameter Valve parameterization is set to Kv flow coefficient, the unit uses the same equations, but replaces with using the relationship . For more information on the mass flow equations, when the parameters Valve parameterization are set to Kv flow coefficient or `Cv flow coefficient`is given in [2] and [3].

If the parameter Valve parameterization is set to the value of Sonic conductance, then the mass flow rate of is defined as:

where

- acoustic conductivity;
- critical pressure ratio;
- parameter value Subsonic index;
- parameter value ISO reference temperature;
- parameter value ISO reference density;
- inlet temperature.

When the pressure ratio exceeds the value of the parameters Laminar flow pressure ratio, , there is a smooth transition to usage of the linearised equation:

When the pressure ratio falls below the critical pressure ratio , the flow becomes critical and the equation is used:

The value of Sonic conductance parameter Valve parameterization is for pneumatic systems. If you use this value for gases other than air, you may need to adjust the acoustic conductivity value by the square root of the specific gravity.

For more information on the mass flow equations when the parameter Valve parameterization is set to Sonic conductance, see [1].

If the parameter Valve parameterization is set to the value of Orifice area, the mass flow rate of is defined as:

where

- is the area of the orifice or valve;
- parameter value Cross-sectional area at ports A and B;
- parameter value Discharge coefficient;
- adiabatic value.

When the pressure ratio exceeds the value of the parameters Laminar flow pressure ratio, , there is a smooth transition to usage of the linearised equation:

When the pressure ratio falls below , the flow becomes critical and the equation is used:

For more information on mass flow equations when the parameter Valve parameterization is set to Orifice area, see [4].

Mass conservation

It is assumed that the volume and mass of gas inside the component are very small and these values are not considered, so no gas can accumulate in the valve. According to the principle of conservation of mass, the mass flow rate of gas entering through one port is equal to the gas flow rate leaving through the other port:

where and are the mass flow rate at port A and B respectively.

Energy conservation

The valve is an adiabatic component. There is no heat exchange between the gas and the valve wall. No work is done on the valve as the gas passes through the valve. Under these assumptions, energy can only flow in and out of the valve by convection through ports A and B. According to the principle of conservation of energy, the sum of the energy flows through the ports is always zero:

where and are the energy flow into the valve through ports A and B respectively.

Assumptions and limitations

The equation for the parameterization of the Orifice area has a lower accuracy for gases that are far from ideal.
This block does not model supersonic flow.

Ports

Conserving

# A — valve inlet
gas

Details

Gas port associated with the valve inlet.

Program usage name

inlet

# B — valve outlet
gas

Details

Gas port associated with the valve outlet.

Program usage name

outlet

Parameters

# Opening pressure specification — differential pressure used to control the valve
Pressure difference of port A relative to port B | Gauge pressure at port A

Details

Defines the control opening pressure of the valve.

The value Pressure difference of port A relative to port B defines the signal pressure as the pressure difference between ports A and B.

Value Gauge pressure at port A defines the control pressure as the inlet overpressure.

Values	`Pressure difference of port A relative to port B` \| `Gauge pressure at port A`
Default value	`Pressure difference of port A relative to port B`
Program usage name	`opening_pressure_type`
Evaluatable	No

# Cracking pressure differential — Pressure drop required to open the valve
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

The minimum differential pressure between inlet and outlet required to open the valve. This value marks the beginning of the differential pressure range of the valve, where the valve gradually opens, allowing an increase in flow.

Dependencies

To use this parameter, set the Opening pressure specification parameters to . Pressure difference of port A relative to port B.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.01 MPa`
Program usage name	`delta_p_crack`
Evaluatable	Yes

# Maximum opening pressure differential — differential pressure at which the valve is fully open
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

The differential pressure between inlet and outlet at which the valve is fully open. This value marks the end of the differential pressure range of the valve, where the valve gradually opens, allowing an increase in flow.

Dependencies

To use this parameter, set the Opening pressure specification parameters to . Pressure difference of port A relative to port B.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.1 MPa`
Program usage name	`delta_p_max`
Evaluatable	Yes

# Cracking pressure (gauge) — minimum inlet overpressure required to open the valve
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Minimum inlet overpressure (port A) required to open the valve. This value marks the beginning of the differential pressure range of the valve, where the valve gradually opens, allowing an increase in flow.

Dependencies

To use this parameter, set the Opening pressure specification parameters to . Gauge pressure at port A.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.1 MPa`
Program usage name	`p_crack_gauge`
Evaluatable	Yes

# Maximum opening pressure (gauge) — maximum inlet overpressure
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

The maximum inlet overpressure (port A) at which the valve is fully open. This value marks the end of the valve’s differential pressure range, where the valve gradually opens, allowing the flow rate to increase. If in your model the valve does not open fully as expected, you can try reducing the value of this parameters.

Dependencies

To use this parameter, set the Opening pressure specification parameters to . Gauge pressure at port A.

Units	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`0.2 MPa`
Program usage name	`p_gauge_max`
Evaluatable	Yes

# Valve parameterization — method of specifying the flow characteristic through the orifice
Cv flow coefficient | Kv flow coefficient | Sonic conductance | Orifice area

Details

The method of mass flow calculation is based on:

Cv flow coefficient - flow coefficient .
Kv flow coefficient - flow coefficient , which is defined as .
Sonic conductance - acoustic conductivity in steady-state mode.
Orifice area - orifice area.

Values	`Cv flow coefficient` \| `Kv flow coefficient` \| `Sonic conductance` \| `Orifice area`
Default value	`Cv flow coefficient`
Program usage name	`valve_parameterization`
Evaluatable	No

# Maximum Cv flow coefficient — flow coefficient corresponding to the maximum orifice area

Details

The value of the flow coefficient is , when the orifice area is at its maximum. The flow coefficient determines the dependence of the flow capacity on the pressure drop.

Dependencies

To use this parameter, set the parameter Valve parameterization to the value of Cv flow coefficient .

Default value	`4.0`
Program usage name	`C_v_max`
Evaluatable	Yes

# xT pressure differential ratio factor at choked flow — critical differential pressure ratio

Details

The ratio between the inlet pressure and the outlet pressure , defined as , at which the flow becomes critical. If this value is not known, it can be found in Table 2 in ISA-75.01.01 [3]. By default the value 0.7 is suitable for many valves.

Dependencies

To use this parameter, set the parameter Valve parameterization to the value of Cv flow coefficient.

Default value	`0.7`
Program usage name	`delta_p_ratio_C_v`
Evaluatable	Yes

# Maximum Kv flow coefficient — flow coefficient corresponding to the maximum orifice area

Details

The value of the flow coefficient, , when the orifice area is at its maximum. The flow coefficient determines the dependence of the flow capacity on the pressure drop.

Dependencies

To use this parameter, set the parameters Valve parameterization to Kv flow coefficient.

Default value	`3.6`
Program usage name	`K_v_max`
Evaluatable	Yes

# xT pressure differential ratio factor at choked flow — critical differential pressure ratio

Details

Dependencies

To use this parameter, set the parameter Valve parameterization to the value of Kv flow coefficient.

Default value	`0.7`
Program usage name	`delta_p_ratio_K_v`
Evaluatable	Yes

# Maximum sonic conductance — acoustic conductivity corresponding to the maximum aperture area
l/(bar*s) | gal/(min*psi) | m^3/(Pa*s)

Details

The value of acoustic conductivity when the orifice cross-sectional area is maximised.

Dependencies

To use this parameter, set the parameter Valve parameterization to . Sonic conductance.

Units	`l/(bars)` \| `gal/(minpsi)` \| `m^3/(Pa*s)`
Default value	`12.0 l/(bar*s)`
Program usage name	`C_max`
Evaluatable	Yes

# Critical pressure ratio — critical pressure ratio

Details

The ratio of pressures at which the flow becomes critical and the flow velocity reaches a maximum determined by the local speed of sound. The ratio between the outlet pressure and the inlet pressure : .

Dependencies

To use this parameter, set the parameter Valve parameterization to Sonic conductance.

Default value	`0.3`
Program usage name	`B_critical_linear`
Evaluatable	Yes

# Subsonic index — degree value used to calculate the mass flow rate in subsonic flow regime

Details

An empirical value used to more accurately calculate the mass flow rate in subsonic flow regime.

Dependencies

To use this parameter, set the Valve parameterization parameters to . Sonic conductance.

Default value	`0.5`
Program usage name	`m`
Evaluatable	Yes

Details

The temperature in the standard reference atmosphere in ISO 8778.

The ISO reference parameters need only be adjusted if acoustic conductivity values obtained with different reference values are used.

Dependencies

To use this parameter, set the parameters Valve parameterization to . Sonic conductance.

Units	`K` \| `degC` \| `degF` \| `degR` \| `deltaK` \| `deltadegC` \| `deltadegF` \| `deltadegR`
Default value	`293.15 K`
Program usage name	`T_reference`
Evaluatable	Yes

# ISO reference density — reference density according to ISO 8778
g/cm^3 | kg/m^3 | lbm/gal

Details

Density in a standard reference atmosphere in ISO 8778.

The ISO reference parameters need only be adjusted if acoustic conductivity values obtained with different reference values are used.

Dependencies

To use this parameter, set the parameters Valve parameterization to . Sonic conductance.

Units	`g/cm^3` \| `kg/m^3` \| `lbm/gal`
Default value	`1.185 kg/m^3`
Program usage name	`rho_reference`
Evaluatable	Yes

# Maximum orifice area — flow cross-sectional area corresponding to the maximum orifice area
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

Maximum cross-sectional flow area when the cross-sectional area of the orifice is maximum.

Dependencies

To use this parameter, set the parameter Valve parameterization to . Orifice area.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`1e-4 m^2`
Program usage name	`max_restriction_area`
Evaluatable	Yes

# Discharge coefficient — flow coefficient

Details

The correction factor is the ratio of the actual mass flow rate to the theoretical mass flow rate.

Dependencies

To use this parameter, set the Valve parameterization parameters to . Orifice area.

Default value	`0.64`
Program usage name	`C_d`
Evaluatable	Yes

# Leakage flow fraction — cost ratio

Details

The ratio of the flow rate through a closed orifice to that through an open orifice.

Default value	`1e-6`
Program usage name	`leakage_fraction`
Evaluatable	Yes

# Smoothing factor — numerical smoothing factor

Details

A continuous smoothing factor that ensures smooth opening by correcting the orifice characteristic in the nearly open and nearly closed positions.

Default value	`0.01`
Program usage name	`smoothing_factor`
Evaluatable	Yes

# Laminar flow pressure ratio — pressure ratio at which the flow transitions between laminar and turbulent regimes

Details

The ratio of outlet pressure to inlet pressure at which the flow transitions between laminar and turbulent flow regimes.

Typical values range from 0.995 to 0.999.

Default value	`0.999`
Program usage name	`B_laminar`
Evaluatable	Yes

# Cross-sectional area at ports A and B — area at the inlet or outlet of the valve
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2

Details

This area is used when calculating the mass flow rate through the ports.

The ports are all the same size. The value of this parameter must match the inlet area of the component to which the unit is connected.

Units	`m^2` \| `cm^2` \| `ft^2` \| `in^2` \| `km^2` \| `mi^2` \| `mm^2` \| `um^2` \| `yd^2`
Default value	`0.01 m^2`
Program usage name	`port_area`
Evaluatable	Yes

Literature

ISO 6358-3. "Pneumatic fluid power - Determination of flow-rate characteristics of components using compressible fluids - Part 3: Method for calculating steady-state flow rate characteristics of systems". 2014.
IEC 60534-2-3. "Industrial-process control valves - Part 2-3: Flow capacity - Test procedures". 2015.
ANSI/ISA-75.01.01. "Industrial-Process Control Valves - Part 2-1: Flow capacity - Sizing equations for fluid flow underinstalled conditions". 2012.
P. Beater. "Pneumatic Drives." Springer-Verlag Berlin Heidelberg. 2007.