We discuss a generalized form of IIA/IIB supergravity depending on all R-R potentials C^(p) (p=0,1,...,9) as the effective field theory of Type IIA/IIB superstring theory. For the IIA case we explicitly break this R-R democracy to either p<=3 or p>=5 which allows us to write a new bulk action that can be coupled to N=1 supersymmetric brane actions. The case of 8-branes is studied in detail using the new bulk & brane action. The supersymmetric negative tension branes without matter excitations can be viewed as orientifolds in the effective action. These D8-branes and O8-planes are fundamental in Type I string theory. A BPS 8-brane solution is given which satisfies the jump conditions on the wall. It implies a quantization of the mass parameter in string units. Also we find a maximal distance between the two walls, depending on the string coupling and the mass parameter. We derive the same results via supersymmetric flow equations.
Download