St-70 — operation (how it works) – Multiquip ST70 User Manual
Page 19
ST-70 — PARTS & OPERATION MANUAL — REV. #4 (05/29/07) — PAGE 19
ST-70 — OPERATION (How it Works)
The following is a brief explanation of
how the concrete cylinders, hydraulic
cylinders, shuttle tube, valves and
hopper work in sequence to pump
concrete.
The hydraulic pressure is generated by
a variable volume, pressure
compensated, axial piston pump that is
driven by a diesel engine. The hydraulic
pressure is applied to one of the two
hydraulic cylinders causing the
hydraulic piston, which is connected to
the concrete piston, to discharge
concrete into the delivery line. The rod
sides of the drive cylinders are
hydraulically connected together
creating a “slave circuit.” As one cylinder
is discharging concrete, the hydraulic oil
from the rod side of the drive cylinders
is being transferred through the slave
circuit causing the opposite cylinder to
move back on the suction stroke filling
the cylinder with concrete. This
operation is made possible by the
shuttle tube located in the hopper and
is sequenced to operate in conjunction
with the cycling of the drive cylinders.
The ST-70 cycling sequence is initiated
by an electrical signal generated by two
proximity switches located in the drive
cylinder. The proximity switches are
normally open, magnetically sensing the
movement of the main drive cylinder. As
the drive cylinder piston head passes
the proximity switch, an electrical signal
is sent to the solenoid operated pilot
valve which in turn directs pilot oil to the
four valves controlling the drive cylinder
and the shuttle cylinder.
A one-gallon accumulator assists the
movement of the shuttle tube. This circuit
assures that the shuttle tube will throw
with the same intensity of each stroke
regardless of how fast the main drive
cylinders are cycling.
TO TANK
HIGH PRESSURE
OIL FROM PUMP
TO TANK
HYDRAULIC
CYLINDERS
PISTON
CUP
CONCRETE
CYLINDERS
SLAVE
OIL
SLAVE
OIL
A
A
B
B
Figure 1
CYLINDER A — INTAKE STROKE
CYLINDER B — DISCHARGE STROKE
CYLINDER A — DISCHARGE STROKE
CYLINDER B — INTAKE STROKE
Figure 2
PROXIMITY SWITCH
PROXIMITY
SWITCH
SHUTTLE TUBE