Published 08-25-09, Control # 077-04 4-23
RT9130E SERVICE MANUAL BOOM
TELESCOPE CIRCUIT
Description
The boom telescope circuit consists of the telescope
hydraulic remote controller, telescope directional control
valve, holding valve, hose reel, and the upper and lower
telescope cylinders.
The telescope control valve is the closed spool type and is
described under VALVES in Section 2.
Refer to VALVES in Section 2 for a complete description of
the hydraulic remote controller.
The boom telescope system has a lower and an upper
telescope cylinder. The lower telescope cylinder is a two
stage cylinder. The first stage is 7.50 inch bore and the
second stage is a 9.25 inch bore. The upper telescope
cylinder has a 7.50 inch bore. Foreign material is prevented
from entering the cylinder by a wiper seal during rod
retraction. O-ring seals prevent internal and external
leakage. Refer to CYLINDERS in Section 2 - HYDRAULIC
SYSTEM for a complete description of the telescope
cylinder.
A holding valve is threaded into a port block on the rod end of
the upper telescope cylinder and the first stage rod end on
the lower telescope cylinder. The holding valve for the
second stage of the lower telescope cylinder is mounted into
the port block on the barrel end of the second stage barrel.
The holding valves function during the retraction, extension,
or holding operation. When holding the boom section at a
given length, oil is trapped in the cylinder by the holding
valve. Refer to VALVES in Section 2 for a complete
description of the holding valve.
Theory Of Operation
Flow from the pump travels to the telescope directional
control valve. Movement of the foot pedal for telescope
functions from neutral sends a pilot pressure signal to the
directional control valve to shift the spool in the directional
control valve. This aligns the appropriate passages in the
control valve to route oil to the telescope cylinders.
For more information, refer to BOOM - THEORY OF
OPERATION in this Section.
Maintenance
Table 4-2
Troubleshooting
SYMPTOM PROBABLE CAUSE SOLUTION
1. Erratic operation of
extending
telescoping
cylinder.
a. Low hydraulic oil level. a. Check system for leaks. Make repairs
as needed. Fill reservoir.
b. Damaged relief valves. b. Repair or replace relief valves.
c. Air in telescope cylinder. c. Bleed by lowering telescope cylinder
below horizontal.
d. Low engine rpm. d. Increase engine rpm to recommended
setting.
e. Lack of lubrication on boom sections. e. Properly lubricate all boom sections.
f. Extremely tight boom extension
sheaves.
f. Inspect and properly lubricate boom
extension sheaves.
g. Improper boom alignment caused from
side loading.
g. Reduce and properly hoist load.
h. Worn boom wear pads. h. Replace wear pads and properly
lubricate.
i. Distorted boom section. i. Replace distorted section.
j. Damaged telescope cylinder. j. Repair or replace cylinder.
k. Clogged, broken, or loose hydraulic
lines or fittings.
k. Clean, tighten, or replace lines or
fittings.
l. Damaged control valve. l. Repair or replace control valve.
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