Flow Testing of Servo and Proportional Valves
Product Announcement from Max Machinery, Inc.
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 ml transmitter, the Max flow meters can provide near instantaneous registration of a leak, greatly speeding up testing time.