HydraForce Insider Blog

5 More Ways to Apply Spool Type Logic Valves

Posted by David Price on Wed, Mar 09, 2011 @ 16:03 PM

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

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.

Pressure Regulator

Pressure Regulator

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.

High-Flow Selector
or Directional Valve

High Flow selector or directional valve, vented open

High Flow selector or directional valve, piloted closed

Large EP/EV valves used with small
solenoid valves can create a cost-effective
high-flow selector or directional valve circuit.


Post Compensator

Post compensator

EP valves can be used as post compensators
to sense the highest load in the circuit.
Flow is either split evenly or all functions
can be slowed down equally if the pump
flow drops below the demand
(depending on the circuitry).

Do you have another Vented Spool-Type Logic Element Application?
Do you have any questions about any of the circuits I describe here?
Shoot me an email if you’d like to share your application or ask a question.

About the Author:

Scott Parker is a Senior Application Engineer at HydraForce.
He’s been developing Hydraulic Systems for 20 years. Contact Scott


Tags: cartridge valves, pressure control valve, logic valves, pressure compensators, Bypass Pressure Compensator, Sequence Valve, Accumulator Charging Circuit, cartridge