How It Works
What is a Servo Valve?
A servo valve (or servovalve) is a high-performance electrohydraulic valve that precisely controls flow and pressure in response to an electrical input signal. Unlike proportional valves, servo valves offer higher frequency response, better null characteristics, and tighter tolerances for motion control applications.
Key Sizing Parameters
- Rated Flow (Qr): Flow at rated pressure drop, typically at 70 bar (1000 psi) total valve dP
- Flow Gain (Kq): Change in flow per unit change in input signal (LPM/mA or GPM/mA)
- Pressure Gain (Kp): Change in load pressure per unit change in input
- Frequency Response: -3dB bandwidth, typically 50-200 Hz for industrial valves
Servo Valve Flow Equation
The flow through a servo valve follows the orifice equation:
Q = Qrated x (u/100) x sqrt(dP_load / dP_rated)
Where u is the spool position (command signal) as percentage of full stroke.
Sizing for Cylinder Applications
For a hydraulic cylinder controlled by a servo valve:
Q_required = A_piston x V_max
Account for the valve pressure drop (typically 1/3 of supply pressure for best control):
dP_valve = P_supply / 3
Frequency Response Requirement
The valve bandwidth should be at least 3-5 times the closed-loop system bandwidth:
f_valve > 5 x f_system
Servo Valve Sizing Calculator
Size electrohydraulic servo valves for cylinder motion control applications. Calculate required rated flow based on actuator and system requirements.
Results
Standard Servo Valve Sizes
| Size | Rated Flow | Bandwidth | Application |
|---|---|---|---|
| 5 LPM | 5 LPM @ 70 bar | 200+ Hz | Small axes, test rigs |
| 10 LPM | 10 LPM @ 70 bar | 150 Hz | General purpose |
| 20 LPM | 20 LPM @ 70 bar | 100 Hz | Medium cylinders |
| 40 LPM | 40 LPM @ 70 bar | 80 Hz | Large cylinders |
| 80 LPM | 80 LPM @ 70 bar | 50 Hz | Heavy duty |