tailings (solids) from the screen can be funneled into the press. This arrangement is desirable
when the feed to the press is dilute. We're often asked what the optimal feed consistency is.
It's different in just about every application, but with fibrous material, we've had success with
consistency as low as 1% solids. Generally, thicker is better, but that's not an iron cast rule.
Building a Plug
For the press to work, a plug of cake must form between the cake discharge spout and the
pressure cone. The press will almost always do this on its own accord as material is fed into
the press.
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.
Additional Hints
Vacuum Effect
In some applications, typically slimy materials, increased screw press capacity can be
obtained if the area outside of the screen is under a vacuum. This can be achieved by
mounting the press at a high elevation, with the press liquor drain line dropping below the
surface of a drain tank or pit.
That is, the drain line from the press should go below the surface of the pit or pond into
which it drains. If this line is relatively small in diameter and has a steady downward slope, a
vacuum will be induced around the screen of the screw press. The mass and velocity of press
liquor flowing through the drain line create this vacuum. To draw air bubbles downwards
with the press liquor, the velocity of the fluid must be greater than five feet per second.
The cover over the screen of the press will have to be sealed, usually with Silicone.
The amount of vacuum is a function of the elevation between the press and the drain pond.
For good results, the press should be mounted on a stand that is 20' tall or higher.
Instruments
The most useful instrument to have when testing a press is an ammeter. The load drawn by
the drive motor of the press is indicative of how much work the press is doing. The higher
the amps, the better the dewatering. Also, the higher the amps, the closer the press is to
jamming, and the greater is the abrasive wear. Very low amps indicate little dewatering is
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