SkyTrak 6036 Service Manual - Manual (Page 161)

Section 9 Hydraulic System
Model 6036/6036T S/N 9B0500 thru 14833 9-11
Fig. 9.7 Inlet Section - Sectional View
either of the two pulsar solenoids, one for each
function. The pulsar solenoids are energized 33
times per second by PWM signals from the
controller to generate control pressure which is
proportional to the PWM on-off cycle, Fig. 9.8.
The pulsar solenoids are fitted with matched
orifice plates and seals at the return. Oil leaving a
pulsar solenoid is restricted by the orifice plate to
result in proportional back pressure which is
applied to either end of the main spool in the
corresponding control chamber.
The position of the main spool is determined by
the centering spring and the differential pressure
between the two chambers at either end of the
spool. In the static condition there is no differential
pressure, the main spool is centered, there is no
flow at the cylinder ports, and the reservoir and
cylinder pressure passages are at reservoir
pressure. If no PWM signals are sent to the pulsar
solenoids, both valve sections are static, load
sensing pressures are vented back to the reser-
voir, and the inlet compensator valve flow is
bypassed to the reservoir at approximately 200 psi
(13,8 bar).
When one of the pulsar solenoids is energized by
PWM signals, control pressure is applied to one of
the control chambers. The differential pressure
between the chambers shifts the main spool to
allow oil flow across the spool lands to the corre-
sponding cylinder port. Initial metered oil flow
occurs at 60 psi
(4,1 bar) differential pressure with
full flow at 132 psi (9,1 bar). Unused oil is by-
passed to the reservoir at approximately 200 psi
(13,8 bar) over load pressure.
c. Working Sections - Main Spool Control
Pilot pressure is supplied to two pulsar solenoids,
Fig, 9.8, in the pilot stage of each working section.
The main spool in the main stage is actuated by
b. Inlet Unloading Pressure Compensation
and Relief
The inlet section bypass spool, Fig. 9.7, is bal-
anced between the system pressure and the load
plus spring force pressures. Under static condi-
tions the valve remains closed until the supply oil
pressure in the supply passage reaches approxi-
mately 200 psi
(13,8 bar) and overcomes the
compensator spring force. This shifts the spool to
open the valve and bypass the oil to return. When
a working section is actuated, the combined
compensator spring force and load pressure in the
load sense cavity shift the bypass spool to close
the valve. The spool will shift to open the valve
and bypass excess oil to the reservoir once the
working sections are supplied with the selected
flow rate at the required pressure. Pressure
supplied to the working sections is 200 psi
(13,8
bar) over load pressure. The bypass pressure can
be adjusted with the adjustment plug and seat.
The pilot-operated relief valve maintains load
pressure at a preset maximum allowable value.
Whenever the load pressure exceeds the poppet
spring force, the poppet cone, Fig. 9.7, will unseat
causing the bypass spool to relieve flow to the
reservoir. The relief valve setting can be adjusted
with the setscrew. Refer to paragraph 9.6.2.m for
control valve adjustments.
BYPASS
ADJUSTMENT
PLUG AND SEAT
COMPENSATOR
SPRING
RETURN
PASSAGE
RELIEF
VALVE
SETSCREW
POPPET
SPRING
POPPET
CONE
LOAD
SENSE
CAVITY
BYPASS
SPOOL
SUPPLY
PASSAGE
MK0050