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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:
Bypass Compensator
Maintains a constant pressure drop
(EP spring value) across a fixed or variable
orifice, thus maintaining proper flow rate
regardless of changing load pressures. |
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Bypass Compensator
with Pressure-Compensated
Bleed-Off
Built-in flow regulator bleeds-off trapped
pressure in sense line. Bleed-off is
pressure-compensated, making a
proportional circuit more accurate and controllable. |
Bypass Compensator
with Boost Circuit
Allows for a low unloading-pressure drop
while boosting the compensator value
only when needed to perform the work. |
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High-Flow Sequence Valve
Most sequence valves have limited
flow capabilities. However, a high-flow
circuit can be accomplished by using
a
large EV valve along with a small RV valve. |
Accumulator Charging Circuit
Works with a UP10-31 valve to unload
a fixed-displacement pump at a low
unloading-pressure drop. The EV valve
can be sized to handle any flow while
cycling to keep a predetermined
range
of pressure in the accumulator. |
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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
Large EP/EV valves used with small
solenoid valves can create a cost-effective
high-flow selector or directional valve circuit. |
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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). |
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. |
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
Send your Comments about HydraForce Insider to: HydraForce.Online@hydraforce.com
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Disclaimer: Nothing in this document constitutes an implied warranty of merchantability or of fitness for a particular purpose. The information contained in this document is provided for technical illustration purposes only and may not be used as a statement of suitability for use in any particular application. Each application is unique and prospective purchasers should conduct their own tests and studies to determine the fitness of HydraForce’s products for their particular purposes and specific applications. |
