REED B50HPG, Technical Manual, Page: 27 / 235

OPERATION and MAINTENANCE
Rev 1.2 26 of 80
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S-TUBE CIRCUIT OPERATIONAL SEQUENCE
In the operational sequence of the shift circuit with the engine at full RPM, the tandem
pump is producing its rated displacement. The flow is going through the system and is
being dumped or directed back to the tank thru the solenoid cartridges of the s-tube
circuit manifold.
When the HORN/RESET switch is placed to RESET, an electrical signal closes the
solenoid cartridges. When this occurs, the hydraulic fluid is now directed to the
accumulator where it starts compressing the bladder and building up pressure. When
the pressure in the shift circuit reaches a setting of the unloader valve, the unloader
valve activates causing the relief cartridge to open. The open relief valve now directs
the oil flow from the pump back to the tank instead of continuing to pressurize the
accumulator. A check valve retains the pressure in the swing circuit and prevents the
fluid from going back into the pump line.
In the main pump circuit description, it was described how an electrical signal was
generated by the proximity sensor which was sent to the logic controller and used to
control the alternating action of the hydraulic drive cylinders. This same signal is also
used to shift the s-tube so that its movement is synchronized with that of the hydraulic
drive cylinder, shifting the s-tube to the material cylinder which is ready to extend
(normal forward operation).
The electrical signal activates the solenoid coil of the directional valve, shifting the spool
to the appropriate side. The accumulator then releases, exhausting the fluid which flows
through the directional valve and is directed to the appropriate side of the shift cylinder.
As soon as the shift is made the accumulator is refilled immediately and the sequence
starts all over again.