Jamming / Plugging
Definitions: Vincent speaks of jamming when a press stops and the motor trips out, typically
when the material inside the press is getting very, very dry. Plugging is used to describe
when the press continues to run, but solids stop moving through the press.
Should a press trip out on overload because it has become jammed, a series of steps can be
taken to un-jam the press. Do them in the order below, until the press is running again.
1. Open the cone.
2. Reverse the leads on the motor. This will cause the screw to feed material backward
into the inlet hopper. Of course, if a VFD is used, this is just a matter of hitting
reverse. When a press is operated in the reverse direction it is possible that solids in
the press will be forced against the A-plate. This can damage the shaft seal. For this
reason, run the press in reverse only for short periods of time.
3. Check for tramp material in the inlet hopper.
4. Try going forward again.
5. Use high pressure water to clean out the discharge end of the press and thoroughly
wet the material in the press by spraying the screen extensively.
If these steps don't work, remove the screen and check for damage. Sometimes when a press
is jammed, a flight on the shaft of the screw will fold backwards, toward the gearbox. This
can happen if tramp metal is caught between a flight and a resistor tooth. The weld at the
shaft may tear. When this happens flow through the press is greatly impeded.
Folded Flights
Screen Blinding
A common problem is for the screen of the press to become blinded when solids form a mat
on the inside of the screen. When this happens, the flow of press liquor coming through the
screen diminishes. The level in the inlet hopper will fill up to where it overflows.
In some cases, the screen can be cleared by periodically reversing the direction of rotation of
the screw. This can be programmed with many VFDs, so that the press runs forward for a
given period and then reverses direction briefly for three or four revolutions of the screw
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