|Someone recently joked with me that I’ve never created a circuit that didn’t have at least one Logic Valve in it. HydraForce model numbers for these valves begin with the prefixes EP, EPFR and EV. Typically, these valves are piloted-closed, vented-open, or used as pressure compensators or regulators. I use them often because they are versatile, and they have low pressure-rise and pressure-drop characteristics.|
On our catalog pages for these valves, we describe them as: “hydraulic directional element, with multifunction potential when used with other directional, pressure, or flow control devices.” Talk about a vague (albeit true) statement. So, to demystify this situation a little, I started to think about all the different ways spool-type logic valves can be used in integrated circuits. I’ve sketched up some generic circuits that show different ways in which we use spool type logic valves:
L.S. (Load Sense) Pump Spike Clipper
An EP valve can be used to reduce the overshoot spike in a closed-center L.S. system
by popping opne momentarily, allowing the pump time to de-stroke when needed.
As long as the spring value in the EP valve is slightly higher than the low-pressure
stand-by setting of the pump, the valve will stay closed until cylinder "bottoming-out,"
or similar functions are accomplished. Since load-sense pressure is not maintained
during this condition, the EP valve pops open while the pump de-strokes,
thus greatly reducing the pressure spike.
EP valves make great pressure regulators
due to their flat pressure-rise. EP valves
have a true vent port, so they are virtually
un-affected by down-stream pressures
(as long as the downstream pressure
is lower than the EP spring value).
There are many potential circut applications,
like maintaining smooth charge pressure,
holding a constant back pressure,
or as a pressure build-up valve for
circuits that require pilot pressure.
Large EP/EV valves used with small
EP valves can be used as post compensators
Do you have another Vented Spool-Type Logic Element Application?
Scott Parker is a Senior Application Engineer at HydraForce.