DESCRIPTION
2-14 20509 Issue 7 Jan 2018
INK SYSTEM
The ink system is shown schematically in the diagram opposite. Fresh ink
is contained in a 5 litre disposable ink container, which consists of a flexible
bag protected by a robust cardboard box. The ink container is connected
using a special quick QCD connector.
A gear pump draws ink into the system through a 20 micron filter and spring
Non-Return Valve (NRV) and pumps it into the bleed reservoir. Residual air
collects in the reservoir and opening the bleed valve allows this air to
escape through the vent in the cabinet floor. A by-pass loop, containing a
choke to reduce the flow rate, is connected from the bleed reservoir to the
inlet side of the gear pump. This ensures that the pump remains primed if
air is drawn in through the ink feed pipe.
Ink from the bleed reservoir is forced through a plain NRV into the
accumulator which holds the working reservoir of ink for the print heads.
The accumulator has a flexible diaphragm clamped between the
accumulator body and the mounting flange on the steel frame. The
diaphragm is shaped to contain a volume of air. The mounting flange is
sealed and the only access into the diaphragm is an air valve provided for
maintenance purposes.
As ink is pumped into the accumulator it compresses the air sealed inside
the diaphragm. When the ink is pressurised to 7psi (0.48 Bar) the pressure
switch trips and switches the pump off. The plain NRV closes to maintain
the pressure in the accumulator and re-opens only when the pump next
runs. As ink from the accumulator is used up in printing, the pressure
drops. At approximately 5psi (0.35 Bar) the pressure switch resets,
switching on the pump. The accumulator has a capacity of approximately
70ml, provided by compressing the air behind the diaphragm.
Pressurised ink is fed from the accumulator, through the print head hand
valve and the conduit feed pipe, to the print head manifold behind the
nozzle plate.
When the pump is running and the ink supply container becomes empty, a
vacuum is generated in the feed line. At 8 - 10 inches of mercury (2.76 -
3.45 kilogrammes per sq cm) the vacuum switch trips, switching off the
pump and lighting the Ink Container Empty indicator. The spring NRV shuts
off, and maintains the vacuum.
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