In order to wash the lower run of a horizontal belt filter more effectively, and simultaneously provide for tensioning of the lower run, as required when progressing the belt intermittently, a dead weight roller is supported in a bight of the lower run of the filter belt and reciprocates up and down in a wash liquor vessel as a drive roller is alternately extended, so as to advance the upper run of the belt, and retracted. A one way device is located upstream of the dead weight roller to prevent backward movement of lower run. As the bight decreases and increases, rolling action of the dead weight roller rubs the belt and forces wash liquor therethrough. A plurality of dead weight rollers in one or more wash liquor vessels may be provided and they may be guided at their ends in vertical or oblique guide tracks.

In horizontal belt filter apparatus wherein the belt is progressed by alternate incremental motion of the upper run and the lower run, wash liquor used for washing the belt in the lower run, e.g. by spraying into a wash box, is recycled and used for washing filter cake on the upper run at several spaced apart locations. Also, in the upper run, a respective compression device is arranged subsequent to each supply of wash liquor in the direction of travel of the upper run, and during compression gas is blown into the filter cake through the pressure plate of each device so as to maximise extraction of liquid. Trays mounted below the belt are connected to vacuum during stationary periods of the upper run and are arranged to ensure separate collection of liquid for successive sections of the upper run, which liquid may optionally be recycled to upstream locations.

Batch filtration is carried out within a rockable/rotatable housing, suspension to be filtered being fed in via ports in the upper region onto a curved filter fixed within the housing, and filtrate draining from below, via outlets to which vacuum may be applied. The housing is preferably cylindrical and may be mounted upon rollers or wheels so that rocking or rotating can be effected by belts or chains attached between the housing and a linearly reciprocable member, or by a rotary gear or friction drive wheel acting on the housing circumference, or by rack and pinion means, or a variety of other means. Washing of filter cake, reslurrying, drying by hot gases, and pressurization can all take place "in situ" whilst rocking continues, and discharge of cake is effected via the same ports as for inlet by turning the housing over.

The invention provides an improved web guidance mechanism in which the location of a web is detected and any deviation from a desired path is corrected without causing damage to the web material, for example a filter cloth. The improved mechanism includes two tracker units 10 having a pair of rollers 12, 14 defining a nip for an edge margin of a web. The lower roller 14 is acted on by an inflatable actuator 28 in the form of bellows and operative to raise or lower the roller 14 with respect to the upper roller 12. This is achieved by pivotally mounting a bracket 16, which carries the roller 14, and attaching thereto a bar 24 which rests via a contact plate 26 on the actuator 28. The actuator 28 is controlled by a sensor positioned adjacent to an edge of the web and operative to detect the presence or absence of the edge of the web on its desired path. In a preferred embodiment the sensor controls a pneumatic valve operable to inflate or deflate the actuator 28.