So you have a table containing downtime information indexed by EquipmentId, and you want to filter the contents of this table using a combobox populated with equipment?
Combobox Databinding:
SELECT EquipmentId, EquipmentName FROM tbl_Downtime;
Table Databinding:
SELECT * FROM tbl_Downtime WHERE EquipmentId={SomePath.ToThe.Combobox.selectedValue};