Needle Valve control: What is the physical port S meaning?

I have a Needle Valve with the following parameters:

Orifice diameter: 1 inch

Needle cone angle: 179 deg

Initial opening: 0 m

Flow discharge: 0.1425

Other parameters as default.

Connected to the Physical port S i have a Physical constant, i set up to control the flow through the valve.

I don't understand, and i couldn't find any evidence on the official help, how does this Physical signal works: apparently the valve is full open (no flow cut) for S:0.00635. Where does this number come from?

I found this value simply reducing S until the flow rate started to decrease. How is S connected to the opening?

Thank you very much in advance.

Answer 1

[Andrew Schenk]

The port S represents the variable x in the equations listed on:

http://www.mathworks.com/help/physmod/hydro/ref/needlevalve.html

Since the PS constant block does not have a unit, the value should be entered in meters. Finally, double check the cone angle you have specified since 179 deg is very near flat.

[Paolo]

Thank you. Actually I put 179 deg because from the sketch provided in its datasheet (attached) the cone angle seems to be very flat. Is it a mistake? Should I use another valve block?