Hydraulic needle valve
Flow Control Valves
The Needle Valve block models a variable orifice created by a conical needle and a round sharp-edged orifice in thin material.
The flow rate through the valve is proportional to the valve opening and to the pressure differential across the valve. The flow rate is determined according to the following equations:
|pA, pB||Gauge pressures at the block terminals|
|CD||Flow discharge coefficient|
|A(h)||Instantaneous orifice passage area|
|x||Needle displacement from initial position|
|hmax||Maximum needle stroke|
|ν||Fluid kinematic viscosity|
|pcr||Minimum pressure for turbulent flow|
|Recr||Critical Reynolds number|
|DH||Valve instantaneous hydraulic diameter|
|Aleak||Closed valve leakage area|
|Amax||Maximum valve open area|
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 . Positive signal at the physical
S opens the valve.
Fluid inertia is not taken into account.
The flow passage area is assumed to be equal to the frustum side surface area.
The diameter of the orifice of the valve. The default value
The angle of the valve conical needle. The parameter value must
be in the range between 0 and 180 degrees. The default value is
The initial opening of the valve. You can specify both positive
and negative values. The default value is
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
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
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
Parameters determined by the type of working fluid:
Fluid kinematic viscosity
The block has the following ports:
Hydraulic conserving port associated with the valve inlet.
Hydraulic conserving port associated with the valve outlet.
Physical signal port to control spool displacement.