Here at HydraForce our Technical Services department typically receives multiple question daily regarding our Proportional Valves. Common questions include, "What is the proper dither frequency for a particular proportional valve?' and "What coil should I use with this type of system?". Following these five simple rules when applying proportional valves will prevent field failures, reduce valve instability, and ensure that your system performs as desired without having to reach out to a tech service representative.
1. Applying dither to a valve reduces actuator friction and reduces hysteresis. A good rule of thumb is to use 70 -250 Hz dither frequency on all SP, ZL, and PV valves (flow and directional control valves), and 200-300 Hz dither frequency on TS Valves (proportional pressure control valves). Otherwise, at lower frequencies the actuator will follow the dither signal and the valve output will appear unstable.
You generally want to tune your dither frequency as low as possible, however, when you have system excitation, you will need to set the dither higher until the excitation goes away.
Higher frequencies have little effect on the valve, although at high frequencies, there is a slight increase in hysteresis. When tuning the dither for a poppet style valve, in the case of frequency matching, you would not want to use a dither frequency in the range of 15-50 Hz as it will cause instability and chattering of the poppet. For more information on Dither click here.
2. When applying 4-way valves in cylinder circuits use port 2 for the cylinder's blind or cylinder end connection. There will be lower overall pressure drop since the magnified return flow from the cylinder will not have to go through the center of the spool.
3. HydraForce test data is generated using 12 volt D-coils. All SP valves work with the E coil with an approximate 2% shift upward of the current levels for I-Min and I-Max when compared to the 12 volt D-Coil performance data provided on our catalog pages.
4. Valve position is directly related to the applied current, not the applied voltage. This is because coil resistance is not constant, but rather it increases with temperature. Therefore, you should limit I-Max current to 1.0 amp on 08 size and 1.2 amps on 10 size valves in high ambient temperature/continuous duty applications. In high temp conditions you may run out of votage and will not be able to use the full resolution of the catalog page performance graph. Remember to size the valve with these current limits in mind.
5. Match the valve to the job. Over sizing a metering valve usually gives extremely poor resolution, as only a small portion of the metering curve is useful. In other words, if the valve is over-sized, it will have a negative effect on metering capabilities of the valve. Everyone likes to keep the number of parts in their systems and inventories to a minimum, but trying to apply the same valve across several machine platforms, especially at significantly different flowrates, should be avoided.
For more information on Solenoid Proportional Valves and Coil Operating Parameters, click here.
About the author:
Fred Biederman is a Valve Project and Design Engineer at HydraForce with over 25 years of hydraulic experience, 11 of it served at HydraForce.