We cannot name another industrial product that goes by so many different names. Static Screens are known as Sidehill Screens in the pulp and paper industry. The same devises are commonly referred to as Gravity Screens, Hydrasieves, DSM's, and Hydradensers. Sometimes they are called Catenary Screens, after the shape that a chain takes when it is hung from two points (although the screens generally have either a flat or a circular profile).

The device we are referring to consists of a liquid reservoir at the top, a weir over which liquid flows, and a sloped screen which allows filtered liquid to flow through while suspended solids are being separated. The solids, known as tailings, fall off the lower end of the screen.

Vincent Corporation has an interest in static screens because they can be used to thicken a dilute flow ahead of our screw presses. For example, if a client has a dilute flow with only 0.5 to 1% solids, it may take a large press to handle the volume of liquid involved. If instead the client thickens the flow to 3% or 4% solids by running it across a static screen, a press one or two sizes smaller than otherwise required will be able to handle the job. The combination of the static screen along with the smaller press will cost less than the single larger press.

Vincent currently has two paper mill jobs where we are supplying static screens along with our presses. The screens are an old Vincent design that has some unique premium features. The screen surface is made of woven wavy wedgewire which performs better and is more durable than the straight wedgewire. The screen surface is curved, which makes the screen far more effective than a flat surface screen.

In addition, the weir box at the top of the screen has adjustment jack bolts and it is mounted independently from the frame of the screen. This allows leveling and cocking the weir after the unit has been mounted and placed in operation.

Another premium feature is that the slope of the screen can be adjusted while the screen is in operation. The screen is hinged at the top and jack bolts are on the sides for this purpose.

Static screens are sold in standard widths: 2', 3', 4', 5' and 6'. We generally think of them as having capacities of 50 to 150 gpm per foot of width. This figure works on press liquor flows found in juice processing plants. In paper mill applications, figures of 300 to 600 gpm per foot are used with certain "high freeness" flows.

Another option available in static screens is the slot width of the wedgewire. The most common specifications are 0.020" and 0.030". The finer the slot, the finer the filtration. This is offset by capacity reduction and a propensity to blind with the finer slot width.

When the solids in the liquid flow have a tendency to blind the screen, a spray bar accessory can be supplied. The spray bar is a network of pipes and nozzles. It is used to periodically spray the face of the screen with water. Sometimes a timer is used to automate the process.