We utilize a time-periodic ratchetlike potential modulation imposed onto a two-dimensional electron system inside a GaAs/AlxGa1-xAs heterostructure to evoke a net pumped direct current. The modulation is induced by two sets of interdigitated gates, interlacing off center, which can be independently addressed. When the transducers are driven by two identical but phase-shifted periodic signals, a lateral pumped direct current I(φ) results, which strongly depends on both, the phase shift φ and the wave form V(t) of the imposed gate voltages. We find that for different periodic signals, the phase dependence I(φ) closely resembles V(t). A simple linear model of pumping in two-dimensional electron systems is presented, which reproduces well our experimental findings.