[Code of Federal Regulations]
[Title 49, Volume 5]
[Revised as of October 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR393.50]

[Page 406]
 
                        TITLE 49--TRANSPORTATION
 
                      DEPARTMENT OF TRANSPORTATION
 
PART 393_PARTS AND ACCESSORIES NECESSARY FOR SAFE OPERATION--Table of 
Contents
 
                            Subpart C_Brakes
 
Sec.  393.50  Reservoirs required.

    (a) Reservoir capacity for air-braked power units manufactured on or 
after March 1, 1975, and air-braked trailers manufactured on or after 
January 1, 1975. Buses, trucks, and truck-tractors manufactured on or 
after March 1, 1975, and air-braked trailers manufactured on or after 
January 1, 1975, must meet the reservoir requirements of FMVSS No. 121, 
S5.1.2, in effect on the date of manufacture.
    (b) Reservoir capacity for air-braked vehicles not subject to FMVSS 
No. 121 on the date of manufacture and all vacuum braked vehicles. Each 
motor vehicle using air or vacuum braking must have either reserve 
capacity, or a reservoir, that would enable the driver to make a full 
service brake application with the engine stopped without depleting the 
air pressure or vacuum below 70 percent of that indicated by the air or 
vacuum gauge immediately before the brake application is made. For the 
purposes of this paragraph, a full service brake application means 
depressing the brake pedal or treadle valve to the limit of its travel.
    (c) Safeguarding of air and vacuum. Each service reservoir system on 
a motor vehicle shall be protected against a loss of air pressure or 
vacuum due to a failure or leakage in the system between the service 
reservoir and the source of air pressure or vacuum, by check valves or 
equivalent devices whose proper functioning can be checked without 
disconnecting any air or vacuum line, or fitting.
    (d) Drain valves for air braked vehicles. Each reservoir must have a 
condensate drain valve that can be manually operated. Automatic 
condensate drain valves may be used provided (1) they may be operated 
manually, or (2) a manual means of draining the reservoirs is retained.

[70 FR 48052, Aug. 15, 2005]