XUD9TE engine has a higher flow oil pump than it’s little sibling XUD7TE. Don’t yet know why, but at least to my knowledge, extra oil flow and consecutively pressure will not harm. Actually, higher oil flow helps lubricating and cooling.
XUD7TE and XUD9TE oil pumps. Pressure regulating valve above left sprockets and below right
The one on the right has larger diameter and height sprockets and slightly different external dimensions but otherwise completely interchangeable. To install it on an engine only sump has to be removed.
When replacing BX pump, inspect gap between sprockets sides and pump body (0,064 mm) and their end float (0,12 mm) as well as pump’s condition in general: it should not have any damage marks or be excessively loose though oil pumps are not prone to failure, as far as I know.
Such oil pump used in most road cars. It is a positive displacement pump. This means it can produce constant flow per revolution. Only internal and external leaks limits pressure. Thus a pressure regulating valve is a part of it. It consists of a spring and a a piston which are placed in the thee . When pressure increases to a set limit, it pushes piston against spring and oil returns to pump intake side. As long as pump feeds enough oil to feed engine’s lubrication system, pressure stays constant. Some BXs have 5 bar springs and some have 6 bar ones. Both XUD7TE (1.8TD) and XUD9TE (1.9TD) engines have 6 bar springs in their pumps.