Why 2 oil filters on non Quattro 200 Turbo?

[quk@sievers.com (Phil Payne)]

In message <1.5.4.32.19970324214417.00680e88@sundial.net> Dave Head writes:

> Audi being users of supply parts to the end, some cars got the dual filter
> setup long after it should have gone away. The dual filter setup was
> originally for the non watercooled turbos. After changing to the watercooled
> model in 86, there was some carryover. The aftermarket oil filter books show
> dual filter setups through 87, and don't show the single for t and tq...!

Actually the 200T/5000T seems to have been the "takeup car" on this change.
 
On the ur-quattro (which was non-US at this point) the tie-up of non water 
cooled turbo with dual filter (WR engine) and water cooled turbo with single 
filter seems perfect - I've not yet heard of a cross-match.  We do seem to have 
late 200Ts here with the dual filter, though.
 
What I don't understand is the function of the "spring loaded valve" in the 
dual filter holder ... any ideas?

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club