  We present and compare different versions of a simple particle pump-model
that describes average directed current of repulsively interacting particles in
a narrow channel, due to time-varying local potentials. We analyze the model on
discrete lattice with particle exclusion, using three choices of
potential-dependent hopping rates that obey microscopic reversibility. Treating
the strength of the external potential as a small parameter with respect to
thermal energy, we present a perturbative calculation to obtain the expression
for average directed current. This depends on driving frequency, phase, and
particle density. The directed current vanishes as density goes to zero or
close packing. For two choices of hopping rates, it reaches maximum at
intermediate densities, while for a third choice, it shows a curious current
reversal with increasing density. This can be interpreted in terms of a
particle-hole symmetry. Stochastic simulations of the model show good agreement
with our analytic predictions.
