ViST is Vacuum Shaker Screen Technology which is developed and designed by GN Solids Control. The shaker screen vacuum unit is to work with shale shaker to reduce drilling waste and recycle drilling fluids. At some jobsites, clients use screen vacuum unit to replace drilling waste high G drying shaker.
There are insert type screen vacuum unit and external mounting type screen vacuum unit. For GN own design shale shaker and some other shaker model which use frame screens, if there is space to insert the catch pan (tray) under the outside discharge end shaker screen, we call it insert type screen vacuum unit. It is relative small modification on job site shale shaker. If for GN brand shale shaker, all shaker models reserve the design to add screen vacuum unit directly.
For insert type vacuum screen unit, the catch pan is fixed directly under the discharge side shaker screen. The screen API size depends on the shale shaker API screen, or the high G drying shaker API screen.
But for the external type screen vacuum unit, the client will use a small screen after the shale shaker or high G drying shaker.
Some clients want to use very fine screens, like API-230,270 and 325 while they add the external screen vacuum units to the shale shakers on offshore drilling rig mud system.
GN Solids Control does not recommend clients to choose such fine screens for external screen vacuum unit after solids control shale shaker. As solids control shale shaker does not use very fine screens. The high G drying shale shaker may use fine screens. But API 230, API 270 and API 325 are not used by solids control shale shaker. The small screen API size should be similar to the shale shaker screen. It cannot be too fine. Otherwise, it may cause block.
In other job site while clients use the screen vacuum unit for GN shale shakers, the max. shaker screen API size they use is API 120 and API 140. Hardly over API 140.