This is a model of a hydraulic spool with two additional pilot ports. It has four input pressure signals and y is the current spool opening.


Normalization of the characteristic curve

The opening of the valve depends on the pressure difference, dP, which depends on the pressures according to the equation below:



where

		:	Pressure difference used for computing the spool position
		:	Pressure at port a
		:	Pressure at port b
		:	Pressure at pilot port a
		:	Pressure at pilot port b
		:	Pilot ratio for pilot port a
		:	Pilot ratio for pilot port b

The parameter pOpen defines the pressure difference when the valve starts to open and the parameter pSwitch defines the pressure at which the valve is fully open. The dynamics of the spool are a first-order system with the time constant t1.

pOpen	Value: 10000.0 Type: Pressure (Pa) Description: Opening pressure
pSwitch	Value: 500000.0 Type: Pressure (Pa) Description: Switching pressure
t1	Value: 0.1 Type: Time (s) Description: Time constant for first-order system
kpa	Value: 1 Type: Real Description: Pilot ratio for pilot port a; a positive value helps port_a
kpb	Value: 1 Type: Real Description: Pilot ratio for pilot port b; a positive value helps port_b
yMax	Value: 1 Type: Real Description: Upper limit for output value
yMin	Value: -1 Type: Real Description: Lower limit for output value