Testing electro hydraulic servo valves and proportional valves

Testing control valves

Used to control the flow or pressure of fluid to a hydraulic actuator or hydraulic motor for motion control, servo-valves are found in Aircraft and Aerospace Flight Controls and Engine Controls. They are also used for numerous industrial and heavy equipment applications.

Electro hydraulic servo and proportional valves provide an output flow rate or output pressure that is linear and proportional to the input voltage or current level. Servo Valves are differentiated from Proportional Valves in that they exhibit a zero-crossing dead band of less than 3% of the spool’s travel.  For critical applications, servo valves are specified for their greater accuracy, and faster response times.

A variety of tests are performed during the design and manufacturing of these valves. Tests may include: no-load flow, linearity, hysteresis, internal leakage, null leakage, dynamic response and several others.  Likewise, flow measurement is often used during the assembly process to set internal spacing and stops that define the valve’s performance specification. 

All high end valves are tested and most likely shipped with a hysteresis graph that documents its flow output over the full range of inputs.  Bidirectional valves are especially complex devices, requiring a high degree of precision during testing.  To fully describe the valve’s performance during the middle 3% of its spool’s travel a Max meter with a matching zero crossing capability is essential.

Max Piston Series flow meters have a small displacement per revolution and when combined with a fast reacting, non-dithering analog transmitter will create repeatable hysteresis and zero-crossing graphs.  When combined with a 1000 pulse per cc transmitter, the Max flow meters can provide near instantaneous registration of a leak, greatly speeding up testing time. If you would like a quote for a similar project, please let us know.

Products Specified for this Application

High resolution, low flow meter Model P001
0.005 to 200 cc/min (0 to 0.053 gpm)...Combined with our highest, 500 bar (7250 psi) pressure rating
Precision low flow meter Model P213
0.5 to 1800 cc/min (0 to 0.48 gpm) with a 210 bar (3000 psi) pressure rating