Pilot-Operated Check Valve (IL)
Check valve with pilot pressure control in an isothermal liquid system
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The Pilot-Operated Check Valve (IL) block models a flow-control valve with variable flow directionality based on the pilot-line pressure. Flow is normally restricted to travel from port A to port B in either a connected or disconnected spool-poppet configuration, according to the Pilot configuration parameter.
Pilot-Operated Check Valve Schematic
The control pressure, pcontrol is:
ppilot is the control pilot pressure differential.
kp is the Pilot ratio, the ratio of the area at port X to the area at port A:
pA – pB is the pressure differential over the valve.
When the control pressure exceeds the Cracking pressure differential, the poppet moves to allow flow from port B to port A.
There is no mass flow between port X and ports A and B.
Valve Pressure Control with a Pilot Port
The pilot pressure differential for valve control can be configured in two ways:
When the Opening pilot pressure specification parameter is set to
Pressure at port X relative to port A, the pilot pressure is the pressure differential between port X and port A.
When Opening pilot pressure specification is set to
Pressure at port X relative to atmospheric pressure, the pilot pressure is the pressure difference between port X and atmospheric pressure.
When Pilot configuration is set to
Disconnected pilot spool and poppet, the relative
pressure at port X must be positive. If the measured pilot
pressure is negative, the control pressure is only based on the pressure
differential between ports A and B. In the
Rigidly connected pilot spool and poppet setting, the
pilot pressure is the measured pressure differential according to the opening
Mass Flow Rate Equation
Mass is conserved through the valve:
The mass flow rate through the valve is calculated as:
Cd is the Discharge coefficient.
Avalve is the instantaneous valve open area.
Aport is the Cross-sectional area at ports A and B.
is the average fluid density.
Δp is the valve pressure difference, pA – pB.
The critical pressure difference, Δpcrit, is the pressure differential associated with the Critical Reynolds number, Recrit, the flow regime transition point between laminar and turbulent flow:
Pressure loss describes the reduction of pressure in the valve due to a decrease in area. PRloss is calculated as:
Pressure recovery describes the positive pressure change in the valve due to an increase in area. If you do not wish to capture this increase in pressure, clear the Pressure recovery check box. In this case, PRloss is 1.
The opening area, Avalve, is also impacted by the valve opening dynamics.
The linear parameterization of the valve area is
where the normalized pressure, , is
When the valve is in a near-open or near-closed position, you can maintain numerical robustness in your simulation by adjusting the Smoothing factor parameter. If the Smoothing factor parameter is nonzero, the block smoothly saturates the control pressure between pmax and pcracking. For more information, see Numerical Smoothing.
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, the Opening dynamics check box is cleared.
A — Liquid port
Liquid entry point to the valve. When the control pressure exceeds the cracking pressure, liquid is able to exit from this port.
B — Liquid port
Liquid exit point from the valve. When the control pressure exceeds the cracking pressure, liquid is able to enter the valve from this port.
X — Pressure port
Pressure port that contributes to the flow control through the valve.
Pilot configuration — Valve geometry
Rigidly connected pilot spool and
poppet (default) |
Disconnected pilot spool and poppet
Valve geometry. The valve can either have an opening mechanism that is
connected to the valve poppet, in the case of the
connected pilot spool and poppet setting, or an opening
mechanism that is aligned with, but moves freely away from, the valve
poppet, in the case of the
Disconnected pilot spool and
poppet setting. The configuration choice determines the
pilot pressure calculation.
Opening pilot pressure specification — Reference pressure differential for valve control
Pressure at port X relative to port
A (default) |
Pressure at port X relative to atmospheric
Reference pressure differential used for valve control. This differential defines the pilot pressure differential, which is added to the pressure differential between ports A and B and compared against the valve threshold Cracking pressure differential.
Cracking pressure differential — Pressure threshold
0.01 MPa (default) | positive scalar
Set pressure for the valve operation.
Maximum opening pressure differential — Maximum pressure differential in opened valve
0.02 MPa (default) | positive scalar
Maximum pressure differential in an opened valve. This value provides an upper limit to simulation pressures so that results remain physical.
Pilot ratio — Pilot port area ratio
1 (default) | positive scalar in the range of (0,1]
Ratio of port area X to port area A.
Maximum opening area — Maximum valve area
1e-4 m^2 (default) | positive scalar
Maximum valve area. This value is used to determine the normalized valve pressure and the valve opening area during operation.
Leakage area — Gap area when in fully closed position
1e-10 m^2 (default) | positive scalar
Sum of all gaps when the valve is in the fully closed position. Any area smaller than this value is saturated to the specified leakage area. This contributes to numerical stability by maintaining continuity in the flow.
Cross-sectional area at ports A and B — Area at conserving ports
inf m^2 (default) | positive scalar
Areas at the entry and exit ports A and B, which are used in the pressure-flow rate equation that determines the mass flow rate through the valve.
Discharge coefficient — Discharge coefficient
0.64 (default) | positive scalar
Correction factor accounting for discharge losses in theoretical flows.
Critical Reynolds number — Upper Reynolds number limit for laminar flow
12 (default) | positive scalar
Upper Reynolds number limit for laminar flow through the orifice.
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 flow response when the valve is in near-open or near-closed positions. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.
Pressure recovery — Whether to account for pressure increase in area expansions
off (default) |
Whether to account for pressure increase when fluid flows from a region of smaller cross-sectional area to a region of larger cross-sectional area.
Opening dynamics — Whether to introduce flow lag due to valve opening
off (default) |
Whether to account for transient effects to the fluid system due to opening the valve. Selecting Opening dynamics approximates the opening conditions by introducing a first-order lag in the pressure response. The Opening time constant also impacts the modeled opening dynamics.
Opening time constant — Valve opening time constant
0.1 s (default) | positive scalar
Constant that captures the time required for the fluid to reach steady-state conditions when opening or closing the valve from one position to another. This parameter impacts the modeled opening dynamics.
To enable this parameter, select Opening dynamics.
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