7
Section III
–
Principles of Operation
A. General
Figure 2 is a schematic illustration of a four section valve,
showing the cylinder ports and the by-pass pressure and
tank passages. The pressure passage is used to carry fluid
to the cylinder ports when the spools are shifted. The by-
pass passage permits flow directly to the outlet when the
spools are not being operated. The tank passages carry fluid
to the tank port by return flow from the cylinder ports or fluid
diverted past the flow control and relief valve.
The spools are shown in the centered or neutral position.
Under these conditions, fluid in the pressure passage is
blocked from the cylinder ports by the spool lands. Flow
through the valve is through the by-pass and tank passage
to the tank port.
B. Operating Sections
1.
Inlet Section
- The CM2 and CM3 series valve banks
may be obtained with operating, R*, F*, or K*, inlet sections.
These sections are available with B, C, D, or T, type spools.
These sections are individually described below.
a.
R* Section
- The R* section is equipped with an
integral relief valve for overload protection. It is built to accept
a check valve to prevent return flow through the valve.
The integral relief valve, with an orifice plug, also
acts as a partial flow control valve. This feature lowers the
pressure drop between the inlet and outlet ports. (See para-
graph 4 for relief valve and flow control operation.)
The relief valve cracking pressure is pre-set at the
factory. The pre-set cracking pressures range up to 2500 psi
maximum. (See Table 2 Model Code for pressure settings.)
b.
F* Section
- The F* section has two pressure
connections. One connection is made to the pump source
and the second connection is made with a preceding valve
assembly to accept the by-pass flow for tandem operation.
The F* section like the R* section is built to accept
a check valve to prevent return flow when this feature is
required. However, F* sections do not employ relief valve or
partial flow by-pass.
c.
K* Section
- The K* section is essentially the same
as the R* section except it has a full flow by-pass feature.
2.
Outlet Sections
a.
*L Section
- When two or more spools are required
in a valve bank, the last section will be an *L section. The
“
*
”
denotes the spool type. This section contains the exhaust oil
port and also is built to accept a check valve to prevent back
flow when this feature is required.
b.
*E Section
- This section is used for tandem
operation by providing an outlet connection through which
the by-pass feature for pump unloading is extended on to a
subsequent valve bank. It is used in conjunction with an
“
F*
”
type inlet section in the next valve bank. Like the *L section it
contains an operating spool and is built to accept a check
valve to prevent back flow when this feature is required.
3.
Spool Operation
General
- Four standard spool designs are available
(
“
B,
”
“
C,
”
“
D,
”
or
“
T,
”
). Any combination of spools may be
used with a valve bank to perform a variety of operations. All
operating spools are equipped with centering springs which
return the spools to neutral.
Figure 2.
Check Valve
Flow Control &
Relief Valve
Cylinder Ports
“
B
”
Spool
Control Valve
Sensing Orifice
Out
Neutral
In
Out
Neutral
In
Out
Neutral
In
Out
Neutral
In
“
C
”
Spool
“
D
”
Spool
“
T
”
Spool
Float
Relief Valve
Tank Passage
Tank Passage
Tank
Port
By-Pass
Carry over Port
Cap
A
B
A
B
Pressure
Tank Passage
Pressure
Port
By-Pass
Flow Control
Orifice
A
B
