A drop in operating amps can be an indicator that a purging condition has begun. An
ammeter circuit can be installed to alarm or trip the system when a reduction in motor amps
occurs. This is rarely done.
The fact that the screw shaft extends beyond the cake discharge results in the formation of a
donut of cake, rather than a plug. Donuts break up easier than plugs.
Bridging
Bridging (sometimes called rat holing) occurs in the inlet hopper when an arch or bridge
forms over the screw and material doesn't fall. Bridging often occurs in a feed hopper
attached above the press inlet hopper. Feed hoppers of this type should have at least two
adjacent vertical sides to prevent bridging.
The best way to prevent bridging is to control the feed rate into the press so that the screw is
never completely covered over. If bridging is still occurring in the press inlet hopper, here
are some possible solutions:
1. Cover the inlet hopper walls with Teflon sheets
2. Polish the inside of the inlet hopper to make it smoother
3. Install a vibrator on the inlet hopper (preferably pneumatic)
4. Add a water sluice above the inlet hopper
5. Auto-reverse the screw with the VFD
Fluid Injection
Resistor teeth can be drilled to permit injection of steam, caustic solution, solvent or water
while the press is in operation. Also, these modified resistor teeth can be used for cleaning,
without the need of removing the screen from the press.
Commonly alcohol injection is used to achieve in-line washing to remove sugars. Hot water
injection is used to recover dissolved solids in juice production. Steam injection is used in
dewatering raw organic materials.
The moisture reduction that results from steam injection is related to a chemical change that
comes with blanching, or parboiling, a material. Steam injection works well on pineapple
skin, citrus waste, and raw fish. Tests run with steam injection in a Vincent press at
Anheuser-Busch showed little benefit. The material being pressed, spent grain, had already
been "cooked" before steam was added.
Injection is achieved by drilling holes through the resistor teeth and piping these holes to a
manifold outside of the screen. Photos and drawings are available from the factory. Vincent
does not charge for providing a drilled resistor bar.
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