The boom telescope circuit consists of a
Foreign material is prevented from entering the
telescope/clamshell foot pedal actuated remote
cylinder by a wiper seal during rod retraction. O-ring
control valve, telescope/clamshell directional control
seals prevent internal an external leakage. Refer to
valve, holding valve, and the telescope cylinder.
CYLINDERS in Section 8 for a complete description
of the telescope cylinder.
The telescope/clamshell directional control valve is
described under VALVES in Section 8.
The holding valve is threaded into the rod end of the
telescope cylinder. The holding valve functions
Refer to VALVES in Section 8 for a complete
during the retraction, extension, or holding operation.
description of the telescope/clamshell remote control
When holding the boom section at a given length, oil
valve. The boom telescope cylinder has a 5.5 in.
is trapped in the cylinder by the holding valve. Refer
(13.9 cm) bore.
to VALVES in Section 8 for a complete description of
the holding valve.
THEORY OF OPERATION
The valve bank housing the telescope directional
the poppet (check) valve in the holding valve when
control valve is supplied by flow from the 39 gpm
pressure is 6 4 psi (41.4 27.6 kPa). This oil is
(147.6 lpm) middle pump section. Flow from the
routed to the piston side of the cylinder which forces
pump travels through port 13 of the swivel to the
the rod out of the cylinder, causing the boom section
telescope directional control valve. When the foot
pedal for telescope functions is moved from neutral,
it sends a pilot pressure signal to the directional
During retraction, oil enters the retract port and flows
control valve, which shifts the spool in the directional
to the rod side of the cylinder. When pilot pressure
control valve. This shift aligns the appropriate
reaches a pre-determined value, the main poppet
passages in the control valve to route oil to the
unseats, and oil flows from the piston side of the
telescope cylinder holding valve. The holding valve,
cylinder to the reservoir causing the boom section to
with its' internal makeup of valves and springs,
retract. All return flow from the directional control
passes oil to and from the telescope cylinder. During
valve goes through the swivel to the reservoir.
extension, oil unseats
REMOVAL AND INSTALLATION.
DISASSEMBLY AND ASSEMBLY.
Removal and installation of the telescope cylinder
Disassembly and assembly procedures of the
from the boom is described under disassembly and
telescope cylinder and control valve are provided in
assembly of the boom.
Refer to BOOM
Section 8 under CYLINDERS and VALVES
MAINTENANCE in this Section.