Every bus, truck, or truck tractor with air operated brakes shall be equipped with at least one reservoir sufficient to ensure that, when fully charged to the maximum pressure as regulated by the air compressor governor cut-out setting, a full service brake application may be made without lowering such reservoir pressure by more than twenty percent. Each reservoir shall be provided with means for readily draining accumulated oil or water. A violation of this section is a Class 2 misdemeanor.
SDCL 32-18-19