3-way flow control valve in an isothermal system
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The 3-Way Directional Valve (IL) block represents a directional control valve with three ports and two positions. For example, this block could provide flow control between a pump, storage tank, and actuator.
Example Valve Configuration
Valve control occurs through the spool, which is connected to a physical signal at port S. In the default configuration, zero displacement indicates a fully closed valve between positions I and II. A negative displacement shifts the spool toward valve position I, and a positive displacement signal shifts the spool toward valve position II.
Fluid can flow between port A and port T (figure I below) or between port P and port A (figure II below). The block uses the same formulation for flow rate and opening area as the Orifice (IL) block. See Orifice (IL) for more details on flow calculation.
Valve Positions
The Orifice parameterization determines the calculations used
for the valve opening area. The calculations are based either on the orifice
parameters or tabulated data sets specified in the Model
Parameterization tab. The block uses the same data for both flow
paths if Area characteristics is set to Identical
for all flow paths
; otherwise, individual equations are applied
for the Different for all flow paths
setting. The orifice
parameterizations are:
Linear - area vs. spool travel
The opening area is a linear function of the spool travel distance, the signal received at port S:
where:
Smin is the control member position when the orifice is fully closed.
ΔS is the Control member travel between closed and open orifice.
Amax is the Maximum orifice area.
Aleak is the Leakage area.
ε is the Opening orientation.
Tabulated data - Area vs. spool travel
Provide spool travel vectors for your system or for individual flow paths between ports P and A and ports A and T. This data will be used to calculate the relationship between the orifice opening area and spool travel distance. Interpolation is used to determine the opening area between given data points. Aleak and Amax are the first and last parameters of the Opening area vector, respectively.
Tabulated data - Volumetric flow rate vs. spool travel and
pressure drop
Provide spool travel and pressure drop vectors. The volumetric flow rate is calculated based on the relationship between pressure change and the spool travel distance. Interpolation is used to determine flow rate between given data points. The mass flow rate is the product of the volumetric flow rate and the local density.
The block is a composite of two Orifice (IL) blocks that are driven by a single physical signal at S. Block Orifice P-A represents the flow path between ports P and A. Block Orifice A-T represents the flow path between ports A and T.
In the diagram below, a positive signal opens Orifice P-A while closing Orifice A-T. A negative signal opens Orifice A-T while closing Orifice P-A.
Valve Structural Diagram
The initial valve position is determined by the opening offset, or the orifice opening at zero spool displacement. An offset can be due to a change in distance between ports or spool lands. It can also be due to a change in the thicknesses of the spool lands. Orifice opening is determined in the same way as for the Orifice (IL) block.
Fluid inertia is ignored.
Spool loading due to inertial, spring, and other forces is ignored.
All valve orifices are assumed to be identical in size unless otherwise specified.
2-Way Directional Valve (IL) | 4-Way Directional Valve (IL) | Orifice (IL) | Pressure-Compensated 3-Way Flow Control Valve (IL) | Pressure-Reducing 3-Way Valve (IL)