Technical Description: Ink System
Issue 2
85
Part No. 306-0430-102
At the bottom of the VMS chamber is a restrictor orifice (R2), which provides a controlled flow of ink out of the
chamber. For operation
(
see
V3 VMS Diverter Valve (located on the FMS ink system)
, page
81).
Venturi (Jet Pump) (located inside the FMS top box)
The Venturi jet pump provides a partial vacuum (typically – 0.6 bar) but more importantly a forced flow of air
through the gutter return line.
The velocity of the air flow inside the gutter tube draws the non printed ink along the tube and returns it through
the Venturi jet pump and into the FMS mixer tank for re-use.
The vacuum derived from the Venturi jet pump is created by the flow of high-pressure ink through a small
diameter tube (inlet tube) into a slightly larger diameter tube (outlet tube).
The jet of ink is directed out of the inlet tube and into the outlet tube. The inlet and outlet tubes are directly in
line with each other and a suction port or third tube is located at the point between the inlet and outlet tubes.
The gutter return tube is connected to this suction port.
The high velocity of the jet of ink as it enters the outlet tube causes air to be drawn from the suction port and
into the jet. The higher the jet velocity the higher the flow rate generated at the suction port.
Pressure Transducer (located on the FMS connect manifold)
The pressure transducer (Figure 32 (
8
)) monitors the ink system pressure, providing continuous electrical
feedback to the system electronics and pump control system to maintain (within limits) a constant printing
pressure.
Ink System Pump (located in the base of the machine)
The ink system pump (Figure 32 (
10
)) is a positive displacement gear pump driven by a 24 V dc brushless
motor.
The pump provides stable ink pressure to the nozzle during printing and also provides a flow of ink to the VMS
and Venturi jet pump for drawing unused ink from the printhead and returning it to the FMS ink system for
recirculation.
Flush Pump (located close to the FMS)
The flush pump (Figure 32 (
11
)) is a simple diaphragm type pump consisting of two injection moulded pump
housings, a flexible diaphragm, two check valves and housings.
A flange of the diaphragm (the diaphragm is located in a cavity in one the two housings) acts as a sealing
gasket when the two housings are bolted together. The housing containing the diaphragm cavity also has an ink
connection which allows either ink under pressure or vacuum to move the diaphragm backwards and forwards.
The other housing contains the two check valves:
•
The input check valve only allows flow into the pump and is connected to a pipe, which draws flushing
solvent from the top-up reservoir.
•
The output check valve only allows flow out of the pump and is connected to a pipe that feeds the flush
solvent to the manifold in the printhead.
During operation, the diaphragm is controlled by V7.
When vacuum (generated by the suction of the main system pump) is applied to the diaphragm, flush solvent is
drawn from the top-up reservoir and into the pump cavity to prime the pump.
During ‘clean start’ and ‘stop’ cycles, pressure is applied to the diaphragm through the switching of V7. The
input check valve seals close, forcing flushing solvent through the output check valve to the printhead and
through V11.
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