A control system for controlling a drive motor operating a discharge valve installed in a conduit on a firefighting vehicle. The system includes a pressure sensor configured to measure a pressure of liquids flowing through the conduit, a flow sensor configured to measure a flow rate of liquids flowing through the conduit, a variable control switch operable to generate a variable control signal in response to manual activation, and a microcontroller operable to receive the pressure and flow rate, and generate a variable non-linear control signal operable to cause the drive motor to change the position of the discharge valve at a variable non-linear speed directly proportional to a distance of a current setting from a desired setting.