Normally closed or normally open hydraulically operated remote control valve
The Hydraulically Operated Remote Control Valve block represents a hydraulically operated remote control valve as a data-sheet-based model, meaning that most of the model parameters are generally available in catalogs or manufacturer data sheets. Hydraulically operated remote control valves are widely used in hydraulic systems as hydraulic switches, unloading and sequencing valves. You can also use them as pressure-relief and pressure-reducing valves. The block covers both the normally closed and normally open configurations, shown in the following figure.
The valve opens (closes) by the pilot pressure. The valve control member remains in its initial position as long as the pilot pressure is lower than the cracking pressure. When cracking pressure is reached, the valve control member (spool, ball, poppet, and so on) is forced off its seat and starts opening the normally closed valve, or closing the normally open valve. The control member displacement is directly proportional to pilot pressure. The member reaches its maximum displacement after the pilot pressure becomes equal or greater than the preset maximum value. The valve maximum area, cracking pressure, and maximum pressure are the key parameters of the block. These three parameters are usually provided in catalogs or data sheets.
In addition to the maximum area, the leakage area is also required to characterize the valve. The main purpose of the parameter is not to account for possible leakage, even though this is also important, but to maintain numerical integrity of the circuit by preventing a portion of the system from getting isolated after the valve is completely closed. An isolated or "hanging" part of the system could affect computational efficiency and even cause failure of computation. Theoretically, the parameter can be set to zero, but it is not recommended.
Schematic fragments in the next illustration show some typical valve applications: remote control valve (a), pressure-relief valve (b), and pressure-reducing valve (c).
The flow rate through the orifice is proportional to the orifice opening and the pressure differential across the orifice. The flow rate is determined according to the following equations:
For the normally closed valve, the instantaneous orifice passage area A(p) is computed with the equations:
For the normally open valve, the equations are similar:
The rest of the equations apply to both valve configurations:
|q||Flow rate through the valve|
|p||Pressure differential across the valve|
|pA, pB||Gauge pressures at the block terminals|
|pp||Gage pressure at the pilot terminal|
|CD||Flow discharge coefficient|
|A(p)||Instantaneous orifice passage area|
|Amax||Fully open valve passage area|
|Aleak||Closed valve leakage area|
|pcrack||Valve cracking pressure|
|pmax||Pilot pressure to shift the control member to its maximum|
|pcr||Minimum pressure for turbulent flow|
|Recr||Critical Reynolds number|
|DH||Instantaneous orifice hydraulic diameter|
|ν||Fluid kinematic viscosity|
Connections A and B are hydraulic conserving ports associated with the inlet and the outlet of the valve. Connection X is the pilot port, which is a hydraulic conserving port that provides the pilot pressure. The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B, and the pressure differential is determined as .
Control member displacement is linearly proportional to pilot pressure.
No flow consumption is associated with the pilot chamber.
No loading on the valve, such as inertia, friction, spring, and so on, is considered.
The transition between laminar and turbulent regimes is assumed to be sharp and taking place exactly at Re=Recr.
Select the valve configuration: Normally closed valve or Normally open valve. The default is Normally closed valve.
Valve passage maximum cross-sectional area. The default value is 1e-4 m^2.
Pressure level at which the valve control member is forced off its seat and starts to either open or close the valve, depending on the valve type. The default value is 3e4 Pa.
Pilot pressure at which the valve control member shifts to its maximum displacement and remains there until the pressure falls below this level. Its value must be higher than the cracking pressure. The default value is 1.2e5 Pa.
Semi-empirical parameter for valve capacity characterization. Its value depends on the geometrical properties of the orifice, and usually is provided in textbooks or manufacturer data sheets. The default value is 0.7.
The maximum Reynolds number for laminar flow. The transition from laminar to turbulent regime is assumed to take place when the Reynolds number reaches this value. The value of the parameter depends on the orifice geometrical profile. You can find recommendations on the parameter value in hydraulics textbooks. The default value is 12.
The total area of possible leaks in the completely closed valve. The main purpose of the parameter is to maintain numerical integrity of the circuit by preventing a portion of the system from getting isolated after the valve is completely closed. An isolated or "hanging" part of the system could affect computational efficiency and even cause simulation to fail. Therefore, MathWorks recommends that you do not set this parameter to 0. The default value is 1e-12 m^2.
Parameters determined by the type of working fluid:
Fluid kinematic viscosity
The block has the following ports: