Tilt Control (for A238 and B238 until
Mid-2017)
A 14 MPa (2031 psi) relief valve is installed in the
connection with the rod side of the tilt cylinders to
improve tilt movement control. When tilting
backward, a check valve opens the connection to the
rod side. Tilt cylinder movement is stopped by
moving the tilt cylinder spool in the hydraulic
control valve to the neutral position
A. TILT FORWARD
B. TILT BACKWARD
1. TILT MANIFOLD
2. RELIEF VALVE
3. TILT CYLINDER
Figure 2. Tilt Lock Valve Schematic for A238/B238
until Mid-2017
Tilt Control (for B238 after Mid-2017)
Latest B238 trucks have a tilt lock valve for
dynamic tilt control. Different check valves in the
tilt lock valve prevent the mast from falling forward
in case one of the hoses at the rod side of the
cylinders would fail.
When tilting forward, oil supply enters through port
A and transfers directly to the piston side of the tilt
cylinders. Pressure at the piston side is limited by
the 19 MPa (2756 psi) relief valve at port A.
Extruded oil from the rod side has to pass the pilot
operated check valve that opens if oil pressure at
the piston side is at least 22% of the oil pressure at
the rod side of the tilt cylinders. Extruded oil from
the rod side of the tilt cylinders returns to tank
through the tilt control spool in the main control
valve.
When tilting backward, oil supply enters through
port B and transfers directly to the rod side of the
tilt cylinders. Admitted pressure to the rod side is
limited by the 19 MPa (2756 psi) relief valve at port
B. Extruded oil from the piston side of the tilt
cylinders returns to tank through the tilt control
spool in the main control valve.
Without supply pressure, the mast forward tilt
movement is restricted by the 30 MPa (4351 psi)
pilot operated check valve and mast backward tilt
movement is restricted by the 19 MPa (2756 psi)
relief valve at port A.
1. TILT LOCK VALVE
2. TILT CYLINDER
3. PILOT OPERATED CHECK VALVE
4. RELIEF VALVE
Figure 3. Tilt Lock Valve Schematic for B238 after
Mid-2017
Description And Operation
4000 SRM 1664
2
