A spray system comprising: a first fluid source (22a, 24a) configured to provide a first fluid; a second fluid source (22b, 24b) configured to provide a second fluid; a sprayer (28, 30) configured to combine and spray the first and second fluids; a first pump configured to pump the first fluid at a variable first pumping speed from the first fluid source (22a, 24a) to the sprayer (28, 30); a second pump configured to pump the second fluid at a variable second pumping speed from the second fluid source (22b, 24b) to the sprayer (28, 30); a first pressure sensor disposed to sense a first output pressure of the first pump; a second pressure sensor disposed to sense a second output pressure of the second pump; and a controller configured to control the first and second pumps (12a, 12b) based on the first output pressure, wherein the controller is configured to control the second pump to follow the first pump at a target primary-to-secondary spray component flow ratio, characterized in that: the controller is configured to identify a pump failure condition if the second output pressure differs from a target spray pressure by more than a material-specific pressure factor margin for more than a threshold duration, and the spray system further comprises a local operator interface configured to accept inputs of the target spray pressure, the material-specific pressure factor margin, and the threshold duration from a user. a first fluid source (22a, 24a) configured to provide a first fluid; a second fluid source (22b, 24b) configured to provide a second fluid; a sprayer (28, 30) configured to combine and spray the first and second fluids; a first pump configured to pump the first fluid at a variable first pumping speed from the first fluid source (22a, 24a) to the sprayer (28, 30); a second pump configured to pump the second fluid at a variable second pumping speed from the second fluid source (22b, 24b) to the sprayer (28, 30); a first pressure sensor disposed to sense a first output pressure of the first pump; a second pressure sensor disposed to sense a second output pressure of the second pump; and a controller configured to control the first and second pumps (12a, 12b) based on the first output pressure, wherein the controller is configured to control the second pump to follow the first pump at a target primary-to-secondary spray component flow ratio, characterized in that: the controller is configured to identify a pump failure condition if the second output pressure differs from a target spray pressure by more than a material-specific pressure factor margin for more than a threshold duration, and the spray system further comprises a local operator interface configured to accept inputs of the target spray pressure, the material-specific pressure factor margin, and the threshold duration from a user. the controller is configured to identify a pump failure condition if the second output pressure differs from a target spray pressure by more than a material-specific pressure factor margin for more than a threshold duration, and the spray system further comprises a local operator interface configured to accept inputs of the target spray pressure, the material-specific pressure factor margin, and the threshold duration from a user.