Agricultural machines such as sprayers can be improved by providing a pressure relief system in the operator cab to allow the operator cab to be pressurized while avoiding over-pressurization. The pressure relief system can be arranged to allow air to freely escape from the operator cab during what would otherwise be an over-pressurization event, such as a door or window being closed. In one aspect, the pressure relief system can include a spring-loaded pressure relief valve configured to passively allow air to escape from the cab in order to maintain a cab pressure at or below a predetermined threshold, such as 100 Pascals. In addition, interior and exterior pressures can be monitored for implementing a closed loop control for the pressurization system to enable a more comfortable experience for the operator.