SDS Meters
4
Part 1009912E
E
2005 Nordson Corporation
Theory of Operation
The metering cylinder is filled by positive pressure from a
Rhino unloader. As the servo motor retracts the ball
screw assembly, hydraulic pressure pushes the metering
cylinder piston out to its starting position. The proximity
switches provide positioning information to the servo
motor and the system controller.
Heated Versions—The system controller either enables
or disables the SDS meter heat circuit to maintain the
material temperature setpoint.
Operation consists of 3 phases: the refill phase, the
ready/idle phase, and the dispense/purge phase. Table 2
lists the inlet and outlet valve positions during operation.
Table 2 Inlet/Outlet Valve Positions
Operation
Inlet Valve
Outlet Valve
Refill
Open
Closed
Ready/Idle
Closed
Open
Dispense/Purge
Closed
Open
Refill Phase
See Figure 2. During the refill phase, the drive assembly
retracts. The material inlet valve opens. Material flows
from the unloader and fills the metering cylinder.
When the cylinder is full, the plunger is fully retracted and
is registered by the proximity switch. The inlet valve
closes. The metering cylinder is full of material and the
unit is ready to dispense.
Ready/Idle Phase
See Figure 2. During the ready/idle phase, the material
inlet and outlet valves remain closed until the dispense
sequence begins.
Dispense/Purge Phase
See Figure 2. During the dispense phase, the material is
pre-pressurized to a set value. When triggered, the drive
assembly forces the metering cylinder piston into the
metering cylinder. The material outlet valve opens at the
same time and material extrudes proportionally to the
given input signal.
DISPENSE/PURGE
READY/IDLE
REFILL
TO
OUTLET
VALVE
FROM
INLET
VALVE
Figure 2
Metering Cylinder
