The piston has to be raised from the bottom, no o rings. Have you ever seen a piston in an engine with o rings?
They are sealed by the piston being tight seal and operated against the spring under pressure.
The valve wouldnt work with the pressure to the side it just wouldnt move.
I think you either installed it incorrectly or just didnt turn the valve spring up enough.
Eh?
Have you ever seen a DV007P ?
Or even the original Bosch one, for that matter ??
Try to understand how they work, and you know what I mean.
In a DV the pressure should come from the side.
That is : sideways to the piston, so pressure can not move it.
( the DV007P has 2 O-rings to guarantee a tight seal ).
Only the vacuum-hose on top (!) should pull up the piston,
so pressure can escape from the side (input) to the bottom (output).
In a Split-R, the boost pressure alone moves the piston up and
leaks it away. Because it's coming from below...
Even if it wouldn't, it would leak past the sides of the piston.
It doesn't seal at all.