[Code of Federal Regulations]
[Title 49, Volume 4]
[Revised as of October 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR393.50]

[Page 1068-1069]
 
                        TITLE 49--TRANSPORTATION
 
        CHAPTER III--FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION,
                      DEPARTMENT OF TRANSPORTATION
 
PART 393--PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATION--Table of Contents
 
                            Subpart C--Brakes
 
Sec. 393.50  Reservoirs required.

    (a) General. Every commercial motor vehicle using air or vacuum for 
breaking shall be equipped with reserve capacity or a reservoir 
sufficient to ensure a full service brake application with the engine 
stopped without depleting the air pressure or vacuum below 70 percent of 
that pressure or degree of vacuum indicated by the gauge immediately 
before the brake application is made. For purposes of this section, a 
full service brake application is considered to be made when the service 
brake pedal is pushed to the limit of its travel.
    (b) Safeguarding of air and vacuum. (1) Every bus, truck, and truck 
tractor, when equipped with air or vacuum reservoirs and regardless of 
date of manufacture, shall have such reservoirs so 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 the air or 
vacuum supply in the reservoir shall not be depleted by the leak or 
failure.
    (2) Means shall be provided to establish the check valve to be in 
working order. On and after May 1, 1966, means other than loosening or 
disconnection of any connection between the source of compressed air or 
vacuum and the check valve, and necessary tools for operation of such 
means, shall be provided to prove that the check valve is in working 
order. The means shall be readily accessible either from the front, 
side, or rear of the vehicle, or from the driver's compartment.
    (i) In air brake systems with one reservoir, the means shall be a 
cock, valve, plug, or equivalent device arranged to vent a cavity having 
free communication with the connection between the check valve and the 
source of compressed air or vacuum.
    (ii) Where air is delivered by a compressor into one tank or 
compartment (wet tank), and air for braking is taken directly from 
another tank or compartment (dry tank) only, with the required check 
valve between the tanks or compartments, a manually operated drain cock 
on the first (wet) tank or compartment will serve as a means herein 
required if it conforms to the requirements herein.

[[Page 1069]]

    (iii) In vacuum systems stopping the engine will serve as the 
required means, the system remaining evacuated as indicated by the 
vacuum gauge.

[33 FR 19735, Dec. 25, 1968, as amended at 53 FR 49400, Dec. 7, 1988]