I‘m a learner，Why are the inlet and outlet pressure of the fluidized bed set to the same value?

MFiX
#1

Why are the inlet and outlet pressure of the fluidized bed set to the same value?
e.g.
BC_P_g(1)=1.0e5, BC_P_g(2)=1.0e5

#2

These are depends on your design parameters.