3Parker Hannifin Corporation
Open-Center Directional Control Valve
VO40
Catalog HY17-8505/UK
General Description
The VO40 is an open-center directional control valve
with the flexibility of sectional construction. Consis-
tent with this technology, it is simple in its application,
reliable, easy to troubleshoot, and cost effective. The
global design reflects the performance and quality ex-
pected by today’s machine designers. Spools have me-
tering notches in the three critical areas – open- center,
parallel path and tank, which optimizes simultaneous
metering. Contemporary honing technology is used to
deliver low work port to tank leakage. Additionally, each
work section has a transition check to ensure that a
load does not “dip” during simultaneous operation. All
of these features, plus those listed below, were intend-
ed to take machine controllability to the next level.
Operation
The VO40 incorporates traditional open-center technol-
ogy. It is usually interfaced with a constant flow pump,
whose flow is routed directly to tank when the spools
are in neutral. When one or more spools are selected,
flow is directed to the actuators. The throttling of that
flow depends upon the spool position and the design of
the metering notches. Spool notches can be designed
to accommodate resistive loads (meter-in) and nega-
tive loads (meter-out). To accommodate multiple pump
circuits, split flow and combined flow mid inlets are
available.
Benefits
•Enhanced metering – especially during simultaneous
operation, this is accomplished by having notches in the
three critical areas of the spool: open center, parallel path
and tank.
•Improved simultaneous metering – having a transition
check in each work section ensures that a load does not
“dip” downward when metering two or more work-sections.
•Repeatability – consistent metering from valve to valve
is achieved by flycutting all of the critical cast lands. This
means that the notch position relative to the spool stroke
is controlled and predictable. The result is consistent
machine control.
•Reduced operator fatigue – the open-center core is
a split wing or “Y” core design, which provides for a
consistent lever force when selecting the spool from
neutral to both power positions.
•Reduced function drift – low internal leakage
accomplished thru the use of contemporary honing
technology. Also, for those functions requiring near zero
drift, pilot-operated checks are available.
•Small footprint – port accessories are installed vertical
to the spool, allowing the handle to be positioned closer to
the valve body.
•Ease of service – the bottom two stud assemblies are
slotted, enabling a work section to be replaced without
completely disassembling the valve assembly. This is
accomplished by loosening the top tie bolt and then lifting
the section out of the assembly. Downtime is minimized.
•Easy conversion from a left-handed to a right-handed
section – the work section housing and spool are
symmetrical, which enables the spool to be inserted in
either end of the housing.
•Improved spool seal life – the enclosed handle assembly
protects the spool and spool seal area from contamination
and the potential corrosion.
Technical Information
