Pressure-maintaining valve for external component in an isothermal system
Simscape / Fluids / Isothermal Liquid / Valves & Orifices / Pressure Control Valves
The Pressure Compensator Valve (IL) block represents an isothermal liquid pressure compensator, such as a pressure relief valve or pressure-reducing valve. Use this valve when you would like to maintain the pressure at the valve based on signals from another part of the system.
When the pressure differential between ports X and
Y (the control pressure) meets or exceeds the set pressure, the valve
area opens (for normally closed valves) or closes (for normally open valves) in order to
maintain the pressure in the valve. The pressure regulation range begins at the set
pressure. Pset is constant in the case of a
Constant
valve, or varying in the case of a
Controlled
valve. A physical sign at port
Ps provides a varying set pressure.
Pressure regulation occurs when the sensed pressure, Px – PY, or Pcontrol, exceeds a specified pressure, Pset. The Pressure Compensator Valve (IL) block supports two modes of regulation:
When Set pressure control is set to
Controlled
, connect a pressure signal to
port Ps and set the constant Pressure
regulation range. pressure regulation is triggered when
Pcontrol is greater than
Pset, the Set
pressure differential, and below
Pmax, the sum of the set
pressure and the user-defined Pressure regulation
range.
When Set pressure control is set to
Constant
, the valve opening is
continuously regulated between
Pset and
Pmax by either a linear or
tabular parametrization. When Opening
parametrization is set to Tabular
data
, Pset
and Pmax are the first and
last parameters of the Pressure differential
vector, respectively.
Momentum is conserved through the valve:
The mass flow rate through the valve is calculated as:
where:
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 Pressure recovery is
set to Off
,
PRloss is 1.
The opening area, Avalve, is determined
by the opening parametrization (for Constant
valves only)
and the valve opening dynamics.
The linear parametrization of the valve area for Normally
open
valves is:
and for Normally closed
valves is:
The normalized pressure, , is:
For tabular parametrization of the valve area in its operating range, Aleak and Amax are the first and last parameters of the Opening area vector, respectively.
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
Off
.
Steady-state dynamics are set by the same parametrization as the valve opening, and are based on the control pressure, pcontrol.
Pressure Relief Valve (IL) | Pressure-Compensated Flow Control Valve (IL) | Pressure-Reducing 3-Way Valve (IL) | Pressure-Reducing Valve (IL)