Контекст такой например: Orientation of the filter unit is not critical unless a filter aid precoat or bodyfeed is used, in which case it is best to position the unit upright.

Посмотрите здесь: http://www.gusmerenterprises.com/Gusmer/techsupport/FaqList.asp?deptId=6

Question: What is a precoat?
Answer: A precoat is a layer of DE and/or fiber, used to coat a screen that acts as a filtration barrier. Precoat addition rates vary. For fiber, the typical addition level is 5- 10 pounds per 100 sq. ft of filter surface area. For DE, the typical addition level is 15- 25 pounds per 100sq. ft.

Question: What is a bodyfeed?
Answer: A bodyfeed is an addition of DE and/or fiber to the contaminated product to help improve clarification and extend filtration cycles. The bodyfeed materials must be homogeneously distributed throughout the product for optimum performance. Addition rates vary depending on the amount of contaminant in the product.