Pilot Valve Actuator (IL)
Single-acting or double-acting, pressure-controlled actuator in an isothermal liquid network.
Description
The Pilot Valve Actuator (IL) unit simulates a single-acting or double-acting actuator controlled by a control pressure to control a connected valve or orifice in an isothermal liquid network.
For a single-acting actuator, when the control pressure, , exceeds the Spring preload force at port X, the piston starts to move in the direction set by the Mechanical orientation parameter.
For a double-acting actuator, the control pressure, , is the difference between and . The piston moves in the direction of the larger differential pressure, counteracting the spring force on the opposite port. When the piston movement is reversed, this spring does not extend and has no counterbalancing effect on the piston position.
The pistons in ports X and Y are mounted on the same spool. Both springs return the spool to the neutral position when falls below the preload force of the opposite spring. For single-acting actuators, the neutral position is at port X. For double-acting actuators, the neutral position is in the centre of the actuator.
Single-acting actuator
The force on the piston is generated by the differential pressure between port X and atmospheric pressure:
where is the piston area at port X, the value of the parameter Piston area at port X. The piston starts to move when is greater than the value of Spring preload force at port X.
Single-acting actuator diagram
The figure shows a schematic diagram of a single-acting motor axis.
Piston position
The instantaneous change in piston position is:
where the stable piston position is the piston position at the current differential pressure, proportional to the spring force at maximum piston stroke:
where
-
- is the value of parameter Spring preload force at port X;
-
- maximum spring force acting on the piston position, , where is the value of parameter Spring stiffness at port X;
-
- value of parameter Piston stroke from port X;
-
- the value of the Mechanical orientation parameter, which specifies the movement in positive (extension) or negative (retraction) direction.
If the force acting on the piston is less than the value of the Spring preload force at X parameter, the piston stays in the neutral position or moves to the neutral position. If the force on the piston meets or exceeds the maximum spring force, the piston remains in the stroke position until the applied pressure changes.
Double-acting actuator
The difference between the forces on the X and Y ports determines the movement of the piston:
The pressure applied to port X moves the spool away from chamber X and opposes the spring at port Y. Similarly, the pressure applied to port Y moves the spool away from chamber Y and counteracts the spring in port X. When the spool reverses direction, the previously stretched spring compresses, exerting a force on the spool. The previously compressed spring, located in the port in the direction of travel, is not stretched and does not affect the position of the spool.
Directional actuator diagram
The figure shows a diagram of a double-acting actuator.
Piston position
The change in piston position is calculated as:
where the stable piston position is the piston position at the current differential pressure proportional to the spring force at maximum piston stroke:
where
-
and - value of parameters Spring preload force at port X and Spring preload force at port Y, respectively;
-
and are the maximum spring forces acting against piston displacement at ports X and Y, respectively, , where is the spring stiffness for each port;
-
- is the stroke of the piston on the port;
-
- the value of the Mechanical orientation parameter, which specifies movement in the positive (extend) or negative (retract) direction.
Numerical smoothing of the force value
When the actuator is almost fully extended or retracted, it is possible to maintain numerical stability in the simulation by adjusting the Smoothing factor parameter. With a non-zero smoothing factor, the smoothing function is applied to all calculated forces, but primarily affects the modelling at the extremes of piston motion.
If Actuator configuration is set to `Single-acting', the normalised force on the piston is calculated as:
If the Actuator configuration is set to `Double-acting', the normalised force on the piston at X is calculated as:
The normalised force on the piston at Y is calculated as:
If the Smoothing factor parameter is non-zero, the block smoothly changes the value of the normalised force between 0 and 1.
Ports
Conserving
#
X
—
pressure port pX
isothermal liquid
Details
The pressure at port X. There is no mass flow through this port.
| Program usage name |
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#
Y
—
pressure port pY
isothermal liquid
Details
The pressure at port Y. There is no mass flow through this port.
Dependencies
To use this port, set the Actuator type parameter to Double-acting.
| Program usage name |
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Output
#
S
—
piston displacement, m
scalar
Details
Piston displacement as a scalar signal. The sign of the displacement corresponds to the direction specified in the Mechanical orientation parameter.
| Data types |
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| Complex numbers support |
No |
Parameters
Parameters
#
Actuator configuration —
type of drive to be modelled
Single-acting | Double-acting
Details
Type of drive to be modelled.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
No |
#
Piston area at port X —
cross-sectional area of the stem in the port X
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Details
Cross-sectional area of the piston rod at port X.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Piston area at port Y —
cross-sectional area of the stem in the port Y
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Details
Cross-sectional area of the piston rod at port Y.
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Spring preload force —
neutral force
N | kN | lb | mN | dyn | lbf
Details
Force acting on the piston in the neutral position.
Dependencies
To use this parameter, set Actuator type to Single-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Spring preload force at port X —
force on the X port in neutral position
N | kN | lb | mN | dyn | lbf
Details
Force on the X port in the neutral position.
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Spring preload force at port Y —
force on port Y in neutral position
N | kN | lb | mN | dyn | lbf
Details
Force on the Y port in the neutral position.
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Spring stiffness —
stiffness factor
N/m | lbf/ft | lbf/in
Details
Spring stiffness coefficient. The maximum spring force is determined from the stiffness of and the value of Spring preload force:
.
Dependencies
To use this parameter, set the Actuator type parameter to Single-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Spring stiffness at port X —
port stiffness coefficient X
N/m | lbf/ft | lbf/in
Details
The spring stiffness of the port X. The maximum spring force is determined from the stiffness of and the value of Spring preload force at port X:
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
|
| Program usage name |
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| Evaluatable |
Yes |
#
Spring stiffness at port Y —
port stiffness coefficient Y
N/m | lbf/ft | lbf/in
Details
The spring stiffness of the port Y. The maximum spring force is determined from the stiffness of and the value of Spring preload force at port Y:
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Piston stroke —
piston stroke
m | cm | ft | in | km | mi | mm | um | yd
Details
Maximum possible piston travel.
Dependencies
To use this parameter, set Actuator type to Single-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Piston stroke at port X —
piston stroke in port X
m | cm | ft | in | km | mi | mm | um | yd
Details
Maximum possible piston travel in port X.
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Piston stroke at port Y —
port stroke Y
m | cm | ft | in | km | mi | mm | um | yd
Details
Maximum possible piston travel in port Y.
Dependencies
To use this parameter, set the Actuator type parameter to Double-acting.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Smoothing factor — numerical smoothing factor
Details
A continuous smoothing factor that introduces a level of gradual change based on the flow characteristic when the valve is in the nearly open and nearly closed positions. Set a non-zero value less than one to increase the stability of the simulation in these modes.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Actuator dynamics — whether to take into account transients during tripping
Details
Option to take into account transient effects in the spool position during actuation. Checking the Actuator dynamics box approximates the actuator motion by introducing a first order delay in the spool position. The Actuator time constant value also affects the modelled dynamics.
| Default value |
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| Program usage name |
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| Evaluatable |
No |
#
Actuator time constant —
piston displacement time constant
d | s | hr | ms | ns | us | min
Details
A constant that determines the time required for the piston to reach steady state when moving from one position to another. This parameter affects the modelled actuator dynamics.
Dependencies
To enable this parameter, select the Actuator dynamics checkbox.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Mechanical orientation —
piston displacement direction
Pilot pressure at port X causes positive piston displacement | Pilot pressure at port X causes negative piston displacement
Details
The direction of piston displacement depending on the X port configuration. If Actuator configuration is set to Double-acting, the displacement force at port Y acts in the opposite direction to the direction of the force at port X.
The `Pilot pressure at port X causes positive piston displacement' corresponds to positive displacement when the pressure at port X pushes the piston in the direction of port Y. The `Pilot pressure at port X causes negative piston displacement' corresponds to negative displacement when the pressure at port X pushes the piston towards port Y.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
No |