  We report results of a new spectral analysis of two BeppoSAX observations of
the Z source GX 17+2. In one of the two observations the source exhibits a
powerlaw-like hard (> 30 keV) X-ray tail which was described in a previous work
by a hybrid Comptonization model. Recent high-energy observations with INTEGRAL
of a sample of Low Mass X-Ray Binaries including both Z and atoll classes have
shown that bulk (dynamical) Comptonization of soft photons can be a possible
alternative mechanism for producing hard X-ray tails in such systems. We start
from the INTEGRAL results and we exploit the broad-band capability of BeppoSAX
to better investigate the physical processes at work. We use GX 17+2 as a
representative case. Moreover, we suggest that weakening (or disappearance) of
the hard X-ray tail can be explained by increasing radiation pressure
originated at the surface of the neutron star (NS). As a result the high
radiation pressure stops the bulk inflow and consequently this radiation
feedback of the NS surface leads to quenching the bulk Comptonization.
