input voltage flow rate properties of a servo valve

[alanled9999]

Hi I want to carryout an inspection of input voltage vs flow rate properties of a hydraulic servo valve Im impressing a triangular wave (frequency 0.01Hz amplitude +-10v) and plotting voltage and flow on an X Y graph. I have to set the main pressure so that the valve pressure fall at the flow rate when the input voltage is 10v (rated flow rate)is 2Bar.
Valve pressure fall=Ps-(Pa-Pb)-Pt
Ps:Main pressure
Pa:A port pressure
Pb:B port pressure
Pt:T port pressure
Im having trouble understanding this, why should I need to subtract Pa from Pb as this is only measuring the pressure drop accross the external system. Any Servo orintated engineers please!!! many thanks.

A Ledson.CSWP (when it was hard!)

 

[gerhardl]

Could you please draw a diagram or symbol showing the different port placing, being no servo engineer I dont directly take the diagram connection a-b and t.

I have an inkling though about your question.

How do you (plan to?) measure the pressure in your system, or is it all theoretical?

 

[alanled9999]

Ive drawn a quick diagram of what Im doing, any help would be great.

A Ledson.CSWP (when it was hard!)