Operation and maintenance manual

Section 250-0090
SM 2254 11-03
3
2. Make sure all control valves to supply lines are closed.
3. Turn on hydraulic power supplies and make sure
hydraulic oil is at normal operating temperature.
4. Open control valve for port 'P' supply and adjust to
give a supply reading of 185 bar (2 682 lbf/in²). Reading
on pressure gauge at port 'B' should be zero.
Note: The directional control valve starts to de-energise
(close) when transmission pilot pressure falls below
7 bar (100 lbf/in²) and is fully de-energised (closed)
when transmission pilot pressure falls to 5.5 bar
(80 lbf/in²).
5. Open control valve for port 'a' supply and slowly
increase this supply pressure from 0 - 21 bar
(0 - 300 lbf/in²) thus energising (opening) directional
control valve. Pressure reading at port 'B' should now
read 185 ± 7 bar (2 682 ± 100 lbf/in²). Reading on
pressure gauge at port 'B' should begin to fall when
supply pressure at port 'a' drops to 7 bar (100 lbf/in²).
This rate of fall should reach a maximum rate when
supply pressure at port 'a' drops to 5.5 bar (80 lbf/in²) or
below. With supply pressure at port 'a' at 5.5 bar (80
lbf/in²) or less, pressure on gauge at port 'B' should
quickly drop to almost zero, by exhausting to tank via
port 'T'.
6. Slowly energise (open) control valve for port 'a'
supply. Pressure reading at port 'B' should start to
rise when pressure at port 'a' reaches 5.5 bar
(80 lbf/in²). Rate of pressure increase at port 'B',
should reach a maximum level, when supply
pressure at port 'a' reaches 7 bar (100 lbf/in²) or
above.
7. Close all control valves and turn off hydraulic
supply pressures. Bleed off hydraulic supply lines
and remove directional control valve from test bed for
installation.
INSTALLATION
Note: Tighten all fasteners to torques listed in
Section 300-0080, STANDARD BOLT AND NUT
TORQUE SPECIFICATIONS.
Note: Tighten all hydraulic lines fitted with ORFS
connections, as described in Section 250-0000,
BRAKING SYSTEM SCHEMATIC. Renew all 'O' rings
where used.
1. Position directional control valve assembly on the
vehicle and secure with mounting hardware removed
at removal.
Braking System - Directional Control Valve
5. Release and remove mounting hardware and remove
directional control valve from the vehicle. Move
directional control valve to a clean area for
disassembly.
DISASSEMBLY/ASSEMBLY
Numbers in parentheses refer to Fig. 1.
Note: Tighten all fasteners to standard torques listed
in Section 300-0080, STANDARD BOLT AND NUT
TORQUE SPECIFICATIONS.
Note: With the exception of replacing 'O' rings (11 & 12),
the directional control valve is a non serviceable item
and should be replaced as a complete assembly. The
'O' rings can be replaced as follows:
1. Note orientation of valve body (1) to sub plate (13)
to facilitate assembly.
2. Clamp sub plate (13) lightly in a soft jawed vice and
remove allen bolts (9) and spacers (8).
3. Separate valve body (1) from sub plate (13) and
discard 'O' rings (12).
4. Install new 'O' rings (12) in valve body (1) and fit
valve body (1) to sub plate (13) as noted prior to
disassembly. Install spacers (8) in valve body (1)
and secure valve body (1) to sub plate (13) with allen
bolts (9).
5. Remove allen bolts (10) and end covers (2) from
valve body (1) and discard 'O' rings (11).
6. Install new 'O' rings (11) in end covers (2) and
secure to valve body (1) with allen bolts (10).
BENCH TEST
Letters in parentheses refer to Fig. 1.
1. Install directional control valve on a test bench and
connect as follows:
a. Install hydraulic supply capable of 0 - 159 bar
(0 - 2 300 lbf/in²) to port 'P'.
b. Install hydraulic supply capable of 0 - 21 bar
(0 - 300 lbf/in²) to port 'a'.
c. Install a suitable return line to port 'T'.
d. Install a pressure gauge suitable for 0 - 207 bar
(0 - 3 000 lbf/in²) to port 'D'.