61-9-310. Reservoir capacity and check valve. (1) A bus, truck, or truck tractor with air operated brakes must 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 cutout setting, a full service brake application is made without lowering the reservoir pressure by more than 20%. Each reservoir must be provided with means for readily draining accumulated oil or water.

(2) A truck with three or more axles equipped with vacuum assistor type brakes or a truck tractor and truck used for towing a vehicle equipped with vacuum brakes must be equipped with a reserve capacity or a vacuum reservoir sufficient to ensure that, with the reserve capacity or reservoir fully charged and with the engine stopped, a full service brake application is made without depleting the vacuum supply by more than 40%.

(3) A motor vehicle, trailer, semitrailer, or pole trailer, when equipped with air or vacuum reservoirs or reserve capacity as required by this section, must have reservoirs or reserve capacity safeguarded by a check valve or equivalent device that, in the event of failure or leakage in its connection to the source of compressed air or vacuum, prevents the stored air or vacuum from being depleted by the leak or failure.