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In the case of sloppy materials like manure and DAF sludge, it may be advisable to
start off by first packing the discharge of the press with any available fibrous
material.
Alternatively, the press can be turned on and the feed pump allowed to run just
long enough to fill the feed line and the press. Then shut off the pump, leaving the
press running, and wait until no more liquid drains from the screen of the press.
Repeat this process until a plug of cake starts to open the cone.
PRE-THICKENING
Almost always, the thicker a flow going into a press, the better it will work.
If the flow into a screw press is too dilute, the high volume of liquid going through
the press screen can cause either of two problems. The flow may either flush most
of the solids through the screen, or it may plaster solids against the screen, thus
blinding (covering over) the screen.
To prevent these things from occurring, it may be necessary to pre-thicken the flow
ahead of the screw press. This is commonly done with a static screen (sidehill) or
a rotary drum screen (RDS). In the case of very dilute feed to the press, a Vincent
Fiber Filter can be used.
AIR CYLINDER REGULATOR
To regulate the air pressure of the discharge air cylinder, presses are supplied with
an air pressure regulator along with a Parker four-way reversing valve. These
should be installed near the cone end of the press. (Until recently FRL (Filter,
Regulator, Lubricator) sets were provided to regulate air pressure. Most air
cylinder manufacturers now recommend against the use of lubricators.)
The Parker valve allows manual selection of the shut, open, or "neutral" position.
This valve connects air supply from the regulator to one end of the air cylinder,
while simultaneously opening the other end to atmosphere. The vent line on the
4-way valve allows air to escape when pressure is switched from one end of the air
cylinder to the other.
Continuous air flow from the Parker vent line indicates a leak inside the air cylinder,
or possibly a faulty 4-way valve.
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