E-spool: All ports blocked – Overlap 10% to 20% on each side – Differential cylinder may creep, due to leakage in cylinder and spool –…
All direct operated proportional valves have Power Limits ( Qvalve · ?pvalve ) Bernoulli forces try to center spool at high ?pv Power Limit decreases…
Yes, valve ?p over 50% system pressure is high Avoid over-flowing valve! curve 5 High flow forces try to center spool on direct operated proportional…
Estimate ?p required across valve in both flow paths, System pressure – Load pressure Each housing size may have several spool flow options Find a…
Required Flow is normally given, Qreq Nominal valve drop ?p = 10 bar (145 psi) You must estimate pressure drops, To find a spool, solve…
“Nominal Flow” for proportional spools is rated at ?p = 10 bar (145 psi) total, 5 bar per land Example 4WRA “Nominal Flow” is 7…
Proportional spools slide in cast body – No sleeve, in main stage (unlike a servo valve) – Robust construction similar to on/off directional valves –…
LVDT position feedback improves performance – Increased flow capacity – Higher Power Limit – Better Response Sensitivity – Better Hysteresis < 0.3%
Adding LVDT position feedback greatly improves resolution 0.2% Hysteresis