REED 00 MODEL: C50SS
TRAILER CONCRETE PUMP
MAINT
PAGE 22
ACCUMULATOR
The accumulator is incorporated into the shift circuit to provide instant pressure and volume
for the shifting of the swing tube, which cannot be obtained under normal circumstances.
An accumulator is a hydraulic reservoir that retains the hydraulic fluid under high pressure.
To accomplish this, the accumulator contains a rubber bladder on the inside of the
reservoir. This bladder prior to the installation of the accumulator on the machine must be
pre-charged to a certain pressure using a dry nitrogen gas. In this pre-charge operation,
the bladder is expanded much like a balloon and is retained in that state. In the application
of the shift circuit, the hydraulic fluid is pumped into the accumulator at a higher pressure
than that inside the bladder. This compresses the bladder building up high pressure within
the accumulator that is retained until released.
CIRCUIT OPERATIONAL SEQUENCE
In the operational sequence of the shift circuit with the engine at full RPM, the tandem
pump is operating, producing its rated displacement. The flow is going through the system
and is being dumped or directed back to the tank by the solenoid cartridge of the unloader
manifold.
When the “E-STOP” switch is placed to ON and the horn sounds, an electrical signal,
closes the solenoid cartridge. When this occurs the hydraulic fluid is now directed to the
accumulator where it starts compressing the bladder building up pressure. When the
pressure in the shift circuit reaches the setting of the relief cartridge, which in this
application is 2300 PSI (160 Bar), the relief opens and activates the unloader valve. The
valve then shifts and directs the flow from the pump back to the tank through the relief in
lieu of continuing to pressurize the accumulator. The check valve then prevents the fluid in
the accumulator from going back to 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 black box and used to control the
alternating action of the hydraulic drive cylinders. This same signal is also used to shift the
swing tube so that its movement is synchronized with that of the hydraulic drive cylinder,
shifting the swing 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 is then
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.
REVISION:
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