Historical textIn force on Oct. 1, 2000Source: annual CFR editions 1996–2004

§ 393.50 Reservoirs required.

Wording first on file in the 1996 annual edition, superseded by the 2005 annual edition.

govinfo, 2000 edition ↗

Compare with

Before Jan. 1, 2017 the record is one snapshot per annual CFR edition, revised as of October 1. This is the 2000 edition's wording. An amendment that took effect between Oct. 1, 2000 and Oct. 1, 2000 would not appear until the next edition, so check the citations below and the Federal Register for exact effective dates.

49 CFR § 393.50 — Reservoirs required.. Text in force on October 1, 2000. This wording effective October 1, 1996 to October 1, 2005. Source: govinfo, 2000 edition, https://www.govinfo.gov/app/details/CFR-2000-title49-vol4/CFR-2000-title49-vol4-sec393-50. Retrieved from FMCSR.com, https://fmcsr.com/reg/393.50?asof=2000-10-01, on October 26, 2026. Unofficial compilation; verify against the official source.

(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.

(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]

Amendment history

2 distinct wordings on file since Oct. 1, 1996

Oct. 1, 2005 → presentannual editions 2005–2016diff vs. previous
[70 FR 48052, Aug. 15, 2005]
Oct. 1, 1996 → Oct. 1, 2005annual editions 1996–2004viewing
[33 FR 19735, Dec. 25, 1968, as amended at 53 FR 49400, Dec. 7, 1988]

A new entry appears whenever the regulatory words change between government snapshots. Day-precise from the eCFR (2017 onward); before that, one snapshot per annual CFR edition (revised as of October 1). Bracketed citations are the Federal Register history printed with the section.