Iconic Diagrams\Hydraulics\Valves\Basic Valves
Domains: Continuous. Size: 1-D. Kind: Iconic Diagrams (Hydraulics).
This model describes a 2/2-way directional control valve with second order spool dynamics. The flow through the valve is described as laminar/turbulent flow through an orifice:
dp = pa.p - pb.p
phi = sign(dp) * Cd * A(sp) * sqrt( (2/rho) * abs(dp) ) + GLeak * dp;
Here Cd is the discharge coefficient which normally has a value between 0.55 and 0.7. A(sp) is the area of the orifice opening. A(sp) depends linearly on the spool position sp and varies between 0 (sp = 0) and the maximum area Amax (sp = 1). Gleak is the conductance of laminar leakage flow when the valve is closed. The relative opening of the spool valve is indicated by sp. For a closed valve the spool position (sp) is equal to zero and for an open valve the spool position (sp) is equal to 1.
In the neutral spool position (sp = 0) the valve is just closed. A positive overlap indicates that the spool must travel a certain distance before the valve opens.
A negative overlap indicates that the valve is already open in the neutral position.
The overlap is indicated by the parameter overlap, which is given as a fraction of the spool position.
The spool position sp is a function of the input signal spoolpos:
sp = SO(f,d,discrete(spoolpos))
where SO is a second order transfer function to model the spool dynamics. The function is characterized by the bandwidth (f) and damping (d). The model acts as a directional valve (a valve which is either open or closed) because the input signal spoolpos is rounded to 0 or 1:
spoolpos < 0.5 => 0
spoolpos >= 0.5 => 1
The pressure at both ports has a lower limit which is equal to the vapour pressure. Therefore the actual equations used in this component are:
pa_lim = if pa.p < p_vapour then p_vapour else pa.p end;
pb_lim = if pb.p < p_vapour then p_vapour else pb.p end;
Ports |
Description |
pa, pb |
Both terminals of the valve. |
Causality |
|
fixed volume flow out pa fixed volume flow out pb |
|
Inputs |
|
spoolpos |
position of the spool valve spoolpos < 0.5 => valve is closed spoolpos >= 0.5 => valve is open |
Parameters |
|
Q_nom
|
Nominal flow at nominal pressure per edge, spool in the open position [m3/s], Q_nom > 0 |
Q_leak p_nom overlap f |
Leakage flow at nominal pressure per edge [m3/s], Q_leak > 0 Nominal pressure per edge [Pa], p_nom > 0 Valve overlap as percentage of full stroke, -1 < overlap < 1. Natural frequency, f > 0. |