  In this paper, we have designed and employed a suspended-wall silo to remove
Janssen effect in order to explore directly the local pressure dependence of
Granular Orifice Flow (GOF) systematically. We find that as Janssen effect is
removed, the flow rate Q changes linearly with the external pressure. The slope
{\alpha} of the linear change decays exponentially with the ratio of the silo
size and the size of the orifice {\Phi}/D, which suggests the existence of a
characteristic ratio {\lambda} (~2.4). When {\Phi}/D > {\lambda}, {\alpha}
gradually decays to zero, and the effect of external pressure on the GOF
becomes negligible, where the Beverloo law retrieves. Our results show that
Janssen effect is not a determining factor of the constant rate of GOF,
although it may contribute to shield the top load. The key parameter in GOF is
{\Phi}/D. In small {\Phi}/D, the flow rate of GOF can be directly adjusted by
the external pressure via our suspended-wall setup, which may be useful to the
transportation of granules in microgravity environment where the gravity-driven
Beverloo law is disabled.
