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Hydraulic continuous 2-way directional valve

Directional Valves

The 2-Way Directional Valve block represents
a continuous, 2-way directional valve, also referred to as a shut-off
valve. It is the device that controls the connection between two lines.
The block has two hydraulic connections, corresponding to inlet port
(A) and outlet port (B), and one physical signal port connection (S),
which controls the spool position. The block is built based on a Variable
Orifice block, where the **Orifice orientation** parameter
is set to `Opens in positive direction`

. This means
that positive signal * x* at port S opens
the orifice, and its instantaneous opening

`h`

$$h={x}_{0}+x$$

where

`h` | Orifice opening |

`x` | Initial opening |

`x` | Control member displacement from initial position |

Because the block is based on a variable orifice, you can choose one of the following model parameterization options:

`By maximum area and opening`

— Use this option if the data sheet provides only the orifice maximum area and the control member maximum stroke.`By area vs. opening table`

— Use this option if the catalog or data sheet provides a table of the orifice passage area based on the control member displacement.`A=A(h)`

`By pressure-flow characteristic`

— Use this option if the catalog or data sheet provides a two-dimensional table of the pressure-flow characteristics.`q=q(p,h)`

In the first case, the passage area is assumed to be linearly
dependent on the control member displacement, that is, the orifice
is assumed to be closed at the initial position of the control member
(zero displacement), and the maximum opening takes place at the maximum
displacement. In the second case, the passage area is determined by
one-dimensional interpolation from the table * A=A(h)*.
Flow rate is determined analytically, which additionally requires
data such as flow discharge coefficient, critical Reynolds number,
and fluid density and viscosity. The computation accounts for the
laminar and turbulent flow regimes by monitoring the Reynolds number
and comparing its value with the critical Reynolds number. See the Variable Orifice block reference page for
details. In both cases, a small leakage area is assumed to exist even
after the orifice is completely closed. Physically, it represents
a possible clearance in the closed valve, but the main purpose of
the parameter is to maintain numerical integrity of the circuit by
preventing a portion of the system from getting isolated after the
valve is completely closed. An isolated or "hanging"
part of the system could affect computational efficiency and even
cause simulation to fail.

In the third case, when an orifice is defined by its pressure-flow characteristics, the flow rate is determined by two-dimensional interpolation. In this case, neither flow regime nor leakage flow rate is taken into account, because these features are assumed to be introduced through the tabulated data. Pressure-flow characteristics are specified with three data sets: array of orifice openings, array of pressure differentials across the orifice, and matrix of flow rate values. Each value of a flow rate corresponds to a specific combination of an opening and pressure differential. In other words, characteristics must be presented as the Cartesian mesh, i.e., the function values must be specified at vertices of a rectangular array. The argument arrays (openings and pressure differentials) must be strictly increasing. The vertices can be nonuniformly spaced. You have a choice of three interpolation methods and two extrapolation methods.

The block positive direction is from port A to port B. This
means that the flow rate is positive if it flows from A to B and the
pressure differential is determined as $$p={p}_{A}-{p}_{B}$$. Positive signal at the physical
signal port `S`

opens the valve.

Fluid inertia is not taken into account.

Spool loading, such as inertia, spring, hydraulic forces, and so on, is not taken into account.

**Model parameterization**Select one of the following methods for specifying the valve:

`By maximum area and opening`

— Provide values for the maximum valve passage area and the maximum valve opening. The passage area is linearly dependent on the control member displacement, that is, the valve is closed at the initial position of the control member (zero displacement), and the maximum opening takes place at the maximum displacement. This is the default method.`By area vs. opening table`

— Provide tabulated data of valve openings and corresponding valve passage areas. The passage area is determined by one-dimensional table lookup. You have a choice of two interpolation methods and two extrapolation methods.`By pressure-flow characteristic`

— Provide tabulated data of valve openings, pressure differentials, and corresponding flow rates. The flow rate is determined by two-dimensional table lookup. You have a choice of two interpolation methods and two extrapolation methods.

**Valve passage maximum area**Specify the area of a fully opened valve. The parameter value must be greater than zero. The default value is

`5e-5`

m^2. This parameter is used if**Model parameterization**is set to`By maximum area and opening`

.**Valve maximum opening**Specify the maximum displacement of the control member. The parameter value must be greater than zero. The default value is

`5e-3`

m. This parameter is used if**Model parameterization**is set to`By maximum area and opening`

.**Tabulated valve openings**Specify the vector of input values for valve openings as a one-dimensional array. The input values vector must be strictly increasing. The values can be nonuniformly spaced. The minimum number of values depends on the interpolation method: you must provide at least two values for linear interpolation, at least three values for smooth interpolation. The default values, in meters, are

`[-0.002 0 0.002 0.005 0.015]`

. If**Model parameterization**is set to`By area vs. opening table`

, the**Tabulated valve openings**values will be used together with**Tabulated valve passage area**values for one-dimensional table lookup. If**Model parameterization**is set to`By pressure-flow characteristic`

, the**Tabulated valve openings**values will be used together with**Tabulated pressure differentials**and**Tabulated flow rates**for two-dimensional table lookup.**Tabulated valve passage area**Specify the vector of output values for valve passage area as a one-dimensional array. The valve passage area vector must be of the same size as the valve openings vector. All the values must be positive. The default values, in m^2, are

`[1e-09 2.0352e-07 4.0736e-05 0.00011438 0.00034356]`

. This parameter is used if**Model parameterization**is set to`By area vs. opening table`

.**Tabulated pressure differentials**Specify the vector of input values for pressure differentials as a one-dimensional array. The vector must be strictly increasing. The values can be nonuniformly spaced. The minimum number of values depends on the interpolation method: you must provide at least two values for linear interpolation, at least three values for smooth interpolation. The default values, in Pa, are

`[-1e+07 -5e+06 -2e+06 2e+06 5e+06 1e+07]`

. This parameter is used if**Model parameterization**is set to`By pressure-flow characteristic`

.**Tabulated flow rates**Specify the flow rates as an

`m`

-by-`n`

matrix, where`m`

is the number of valve openings and`n`

is the number of pressure differentials. Each value in the matrix specifies flow rate taking place at a specific combination of valve opening and pressure differential. The matrix size must match the dimensions defined by the input vectors. The default values, in m^3/s, are:This parameter is used if[-1e-07 -7.0711e-08 -4.4721e-08 4.4721e-08 7.0711e-08 1e-07; -2.0352e-05 -1.4391e-05 -9.1017e-06 9.1017e-06 1.4391e-05 2.0352e-05; -0.0040736 -0.0028805 -0.0018218 0.0018218 0.0028805 0.0040736; -0.011438 -0.0080879 -0.0051152 0.0051152 0.0080879 0.011438; -0.034356 -0.024293 -0.015364 0.015364 0.024293 0.034356;]

**Model parameterization**is set to`By pressure-flow characteristic`

.**Interpolation method**Select one of the following interpolation methods for approximating the output value when the input value is between two consecutive grid points:

`Linear`

— Select this option to get the best performance.`Smooth`

— Select this option to produce a continuous curve (`By area vs. opening table`

) or surface (`By pressure-flow characteristic`

) with continuous first-order derivatives.

For more information on interpolation algorithms, see the PS Lookup Table (1D) and PS Lookup Table (2D) block reference pages.

**Extrapolation method**Select one of the following extrapolation methods for determining the output value when the input value is outside the range specified in the argument list:

`Linear`

— Select this option to produce a curve or surface with continuous first-order derivatives in the extrapolation region and at the boundary with the interpolation region.`Nearest`

— Select this option to produce an extrapolation that does not go above the highest point in the data or below the lowest point in the data.

For more information on extrapolation algorithms, see the PS Lookup Table (1D) and PS Lookup Table (2D) block reference pages.

**Flow discharge coefficient**Semi-empirical parameter for valve capacity characterization. Its value depends on the geometrical properties of the valve, and usually is provided in textbooks or manufacturer data sheets. The default value is

`0.7`

.**Initial opening**Orifice initial opening. The parameter can be positive (underlapped orifice), negative (overlapped orifice), or equal to zero for zero lap configuration. The default value is

`0`

.**Laminar transition specification**Select how the block transitions between the laminar and turbulent regimes:

`Pressure ratio`

— The transition from laminar to turbulent regime is smooth and depends on the value of the**Laminar flow pressure ratio**parameter. This method provides better simulation robustness.`Reynolds number`

— The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches the value specified by the**Critical Reynolds number**parameter.

**Laminar flow pressure ratio**Pressure ratio at which the flow transitions between laminar and turbulent regimes. The default value is

`0.999`

. This parameter is visible only if the**Laminar transition specification**parameter is set to`Pressure ratio`

.**Critical Reynolds number**The maximum Reynolds number for laminar flow. The value of the parameter depends on the orifice geometrical profile. You can find recommendations on the parameter value in hydraulics textbooks. The default value is

`12`

, which corresponds to a round orifice in thin material with sharp edges. This parameter is visible only if the**Laminar transition specification**parameter is set to`Reynolds number`

.**Leakage area**The total area of possible leaks in the completely closed valve. The main purpose of the parameter is to maintain numerical integrity of the circuit by preventing a portion of the system from getting isolated after the valve is completely closed. The parameter value must be greater than 0. The default value is

`1e-12`

m^2.

Parameters determined by the type of working fluid:

**Fluid density****Fluid kinematic viscosity**

Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.

The block has the following ports:

`A`

Hydraulic conserving port associated with the valve inlet.

`B`

Hydraulic conserving port associated with the valve outlet.

`S`

Physical signal port to control spool displacement.

In the Closed-Loop Actuator with 2-Way Valve example, the 2-Way Directional Valve block is used to control the position of a double-acting cylinder. At the start of simulation, the valve is open by 0.42 mm to make the circuit initial position as close as possible to its neutral position.

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