May 9, 2001,
Revised April 2003

ISSUE #M16

There are a number of details relating to the installation of screw presses as manure separators that should be noted:

Unless a piston pump is used, it is necessary to have a line that allows manure to recirculate from the press inlet back to the manure pit. This will prevent pressurizing the inlet of the press, which can be a cause for purging.

It is best to have a vent line at the inlet to the press. A 1″ line, 5′ tall, is adequate for breaking a suction in the recirculation line. Such a suction can lead to reduced press capacity.

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. This will increase press capacity.

The amount of vacuum is a function of the elevation between the press and the drain pond. Where convenient presses should be mounted on 20′ or higher stands.

The control panel for the manure pump and the press should have a timer. This timer should be set to have the press run for two minutes after the pump shuts off. This will partially clear the press so that it will not trip out on overload when it is re-started.

Minimize the time that the press is run with no material being fed into it. Running dry will allow abrasive rubbing. The last manure admitted to the press will dry to an abrasive powder.

When bolting the frame of a manure separator to its platform, look into the cake discharge end. Note if the screw is being pulled into the screen. This is an indication that the frame is racking. If this occurs, shims should be used so that the mounting bolts tighten evenly. The screw must be kept centered in the screen.

Elevate the discharge end of the press a few inches to minimize any tendency for the press to purge. This has been found to be particularly effective when the pit is low and the flow of solids to the press is reduced. At this time the cake discharge becomes so slow that water wicks (soaks) into the cake on the lower side of the screw, allowing part of the plug to become soft and to blow out. Without sufficient solids being fed into the press, the plug does not re-form. A 5º incline to the press can make a world of difference, and it can cause no harm.

Where the manure is very thin, it may be necessary to pre-thicken the flow to the screw press. This is best done with a sidehill (inclined) screen. Without pre-thickening, some dilute flows will flush the solids through the screen. This makes it difficult to form a plug, and the capture rate is reduced excessively.