Here, we report the design of a microchip based hydraulic pump that can generate pressure-gradients within a microchannel network via electrokinetic means allowing very precise dynamic control over the flow rates. The pump consists of 3 channel segments in a tee geometry one of which has a depth of about 100 nanometers. By applying appropriate electric fields across this design, a mismatch in electroosmotic transport rate is introduced at the micro-nanochannel junction. This occurs due to suppression of electroosmotic flow within the nanometer sized duct as the Debye layers around its inner walls overlap. The pressure-driven flow thus generated is then preferentially guided to the third channel in the tee geometry by making it deeper which reduces its hydraulic flow resistance. The third channel also connects the hydraulic pumping unit to a separation section in this device that was used for performing reverse phase liquid chromatography. Further, a solvent programming capability was realized on the device by introducing an additional channel within the network to deliver buffer at high organic solvent strength to the separation column.