Cartridge Valve Actuator (IL)
Actuator that maintains equilibrium between valve and pilot pressures in an isothermal liquid system
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The Cartridge Valve Actuator (IL) block models an actuator that maintains equilibrium between the valve and pilot-line pressures. The valve between ports A and B remains closed until the pilot spring Spring preload force is surpassed, at which point the piston begins to move. The piston position is output as a physical signal at port S. A schematic of a 4-port cqrtridge valve actuator is shown below.
Actuator Force Balance
The actuator piston moves to adjust the pressure in the actuator chamber, which maintains equilibrium between the actuator port pressures and pilot line pressures:
pA and pB are the pressures at ports A and B.
AX is calculated from the Port A to port X area ratio.
AB is the port B area, , when the Number of pressure ports is set to
3. When the Number of pressure ports is set to
4, AB is .
Fpreload is the initial spring force in the system.
Fpilot is if Number of pressure ports is set to
3and if Number of pressure ports is set to
The steady piston displacement is calculated as:
where ε is the Opening orientation, which assigns movement in a positive direction (extension) or negative direction (retraction). The dynamic change in piston displacement is:
where τ is the Actuator time constant. When is less than the Spring preload force, xsteady = 0.
If is greater than the sum of the preload force and kxstroke, xsteady = xstroke.
If opening dynamics are modeled, a lag is introduced to the flow response to the modeled control pressure. pcontrol becomes the dynamic control pressure, pdyn; otherwise, pcontrol is the steady-state pressure. The instantaneous change in dynamic control pressure is calculated based on the Opening time constant, τ:
By default, Opening dynamics is set to
When the actuator is close to full extension or full retraction, you can maintain numerical robustness in your simulation by adjusting the block Smoothing factor. A smoothing function is applied to all calculated forces, but primarily influences the simulation at the extremes of the piston motion.
The normalized force is calculated as:
The Smoothing factor, s, is applied to the normalized force:
Assumptions and Limitations
Internal fluid volumes are not modeled in this block. There is no mass flow rate through ports A, B, X, and Y.
A — Pressure port
Pressure port associated with the valve inlet.
B — Pressure port
Pressure port associated with the valve outlet.
X — Pressure port
Pressure port at poppet end.
Y — Pressure port
Pilot pressure port. To enable this port, set Number of
pressure ports to
S — Poppet position, m
Poppet position in m, specified as a physical signal.
Number of pressure ports — Number of pilot pressure ports
3 (default) |
Number of pilot pressure ports. Port X measures the
pressure at the end of the poppet. Setting this parameter to
4 enables the additional pilot-side port
Port A poppet area — Cross-sectional area of port A
1e-4 m^2 (default) | positive scalar
Cross-sectional area of port A.
Port A poppet to port X pilot area ratio — Ratio of inlet to pilot port area
0.5 (default) | positive scalar
Ratio of the inlet port, A, to the pilot pressure port, X. This value is used to calculate the force at port X.
Port Y pilot area — Cross-sectional area of port Y
1.5e-4 m^2 (default) | positive scalar
Cross-sectional area of port Y.
To enable this parameter, set Number of pressure
Spring preload force — Initial spring force
25 N (default) | positive scalar
Spring force in the valve due to spring preloading. This parameter is a threshold value which, when added to the pilot pressures at ports X and Y, counterbalances the valve opening due to the pressures at ports A and B.
Spring stiffness — Stiffness constant
15e3 N/m (default) | positive scalar
Spring stiffness constant.
Poppet stroke — Maximum poppet extension
5e-3 m (default) | positive scalar
Maximum poppet extension.
Smoothing factor — Numerical smoothing factor
0.01 (default) | positive scalar in the range [0,1]
Continuous smoothing factor that introduces a layer of gradual change to the piston position when it is near full extension or full retraction. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.
Connected valve opening orientation — Direction of poppet displacement
Positive displacement opens
valve (default) |
Negative displacement opens valve
Direction of the poppet displacement that opens a connected valve. Setting
this parameter to
Positive displacement opens
valve indicates poppet extension. Setting the parameter to
Negative displacement opens valve indicates
Actuator dynamics — Whether to account for transients during actuation
Off (default) |
Whether to account for transient effects in the spool position due to
actuation. Setting Actuator dynamics to
On approximates actuator motion by introducing a
first-order lag in the spool position. The Actuator time
constant also impacts the modeled dynamics.
Actuator time constant — Piston displacement time constant
0.1 s (default) | positive scalar
Constant that captures the time required for the piston to reach steady-state when moving from one position to another. This parameter impacts the modeled actuator dynamics.
To enable this parameter, set Actuator dynamics