  We test the operation of two methods for selective application of Artificial
Viscosity (AV) in SPH simulations of Keplerian Accretion Disks, using a ring
spreading test to quantify effective viscosity, and a correlation coefficient
technique to measure the formation of unwanted prograde alignments of
particles. Neither the Balsara Switch nor Time Dependent Viscosity work
effectively, as they leave AV active in areas of smooth shearing flow, and do
not eliminate the accumulation of alignments of particles in the prograde
direction. The effect of both switches is periodic, the periodicity dependent
on radius and unaffected by the density of particles. We demonstrate that a
very simple algorithm activates AV only when truly convergent flow is detected
and reduces the unwanted formation of prograde alignments. The new switch works
by testing whether all the neighbours of a particle are in Keplerian orbit
around the same point, rather than calculating the divergence of the velocity
field, which is very strongly affected by Poisson noise in the positions of the
SPH particles.
