8
Section V
–
Special Features
The normally open spool type, used with a special counter-
balance or decompression control requires a needle valve or
orifice installed between the primary port and the secondary
port to accomplish the decompression feature.
Operation of this valve when used with a gravity returned
single acting ram is such that pump fluid passes free flow
into secondary chamber B, then through the check valve and
chamber A into the ram. Pressure buildup in the ram closes
the spool.
When the work stroke is completed, fluid flow is diverted from
the secondary port by directing the pump delivery to tank.
On the return stroke, trapped fluid under pressure in the
primary port holds the valve spool and check valve closed
until a small amount of fluid bleeding off through the needle
valve or orifice reduces the trapped pressure.
When pressure drops below the valve setting, the spring
forces the valve spool to open directing the discharge flow
through the secondary port to tank.
DECOMPRESSION FEATURE
OPTIONAL INSTALLATIONS:
Figure 3. 11.
Secondary Port
Inlet Flow
1. A Needle Valve installed
between the Gage Ports
Primary Port
outlet to ram
or control
return flow
Normally open Spool Type
“
O
”
Auxiliary Control Type
“
P
”
Control
Pressure
Port
2. Orifice of size required
drilled in Check Valve
Poppet to control the
rate of decompression
B
A
B
A
C
C
D
Valves with the
“
P
”
feature, auxiliary remote control are
available in both the R* and the RC* series.
These valves may be used to stop the movement of a
hydraulic cylinder or motor by providing hydraulic braking
when the driving force is removed.
Because of the difference in effective areas between the
bottom of the spool and the bottom of the pilot piston, the
external pilot pressure needed to open the valve to resume
movement is only one-eighth of the internal pilot pressure
required for the A, B or D rated valves and one-sixteenth of
the internal pressure required by the F rated valves.
Operation is such that the cylinder or motor is maintained in
a fixed position when force is removed until pilot pressure
applied to the large area of the spool, overcomes the spring
force. This permits the discharge fluid to pass through the
primary port into the secondary port and back to tank.
The integral check valve permits free flow from the
secondary port to the primary for reversing action of the
cylinder or motor.
