In the space between the opposed output window and rotating disk of a light valve, loose particulate material in the fluid which becomes charged and held on the nonconductive surface of the disk or the inside surface of the output window is repelled from one surface to the opposing surface by applying a high voltage between the disk and exterior conductive shell. By periodically reversing polarity of the applied voltage, with an interval of zero voltage interposed between opposite polarity intervals, the particles are moved back and forth between the disk and output window. When the particles adhere to the disk, they are transported toward the fluid reservoir where they are repelled from the disk into the bulk of the fluid and are subsequently pulled through the fluid filter.
A flushing system is provided for a light valve of the Schlieren dark field type. A small amount of filtered fluid is injected into the space between the rotating disc and the output window of the light valve. This is done by injecting the fluid through the center disc bearing, thereby providing a uniform radial flow outwardly from the center and flushing out any particles in the space and preventing any particles in the surrounding fluid from moving into the raster area. By properly regulating the flow of the center flush fluid, the disc can be floated off the support during rotation. This reduces wear generated particles which contribute to substrate buildup and subsequent loss of light throughput. In addition, erratic disc motion caused by a stick and slip frictional effect is reduced.
A neutralizing electrode is provided in a light valve of the Schlieren dark field type. The purpose of this neutralizing electrode is to neutralize the large electrostatic forces which develop between the transparent conductive electrode on the rotating disc and the face plate of the light valve causing erratic rotational motion of the disk. The neutralizing electrode is connected to a source of potential which is of the same polarity and substantially the same the potential as that of the rotating disk electrode.
An electrostatic precipitator is provided in a light valve of the Schlieren dark field type. The electrostatic precipitator comprises two conductive surfaces within the fluid reservoir of the light valve. One of these surfaces may be the filter housing (81), and the other may be a metal coating (105) which is applied to the inner glass surface of the rear housing (53) of the light valve. By applying a constant d.c. potential across these two conductive surfaces, a resinous or lacquer build-up occurs which is composed of the fine colloidal particulate wear material and a fluid related component which are produced as a result of the normal operation of the light valve. Both the wear material and the fluid related component are too fine to be filtered by mechanical means. Because the wear material and the fluid related component form an adherent resinous material which bonds to the negative electrode, these particulates are permanently removed from the fluid.
