are chute control lift rotate fold etc as well as tag axle pressure control but other functions may be incorporated fig2 depicts a schematic diagram of a combination open loop and closed loop pump system 200 for a transit mixer the pump system 200 depicted in fig2 includes an open loop charge circuit a variable displacement closed loop pump system to drive the drum motor and a variable displacement open loop pump system to drive the auxiliary components of the transit mixer a control circuit 280 includes a number of components used to connect and disconnect the open and closed loop circuits the charge circuit includes provide a charge pump 202 to charge and control pressure for the closed loop hydrostatic drive circuit depicted in part by side a and side b the charge pump 202 draws hydraulic fluid from a unit reservoir 204 via a main suction line a suction screen or filter 206 prevents debris from the reservoir 204 from being drawn into the system the charge pump 202 is driven by a power source or motor 208 typically an internal combustion engine or an electric motor in the depicted system a common motor 208 provides power via a through drive to all of the charge pump 202 an open loop pump 210 and a closed loop pump 212 in such an.